Main Engine PREP/OPERATION Flashcards

Question

With reference to medium Speed Diesel Engine, Sketch and label a typical arrangement for the Piston and connecting rod.

Answer 1

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Answer 2

a.) On 2 stroke engines, the connecting rod is attached to the piston rod via the crosshead bearings, which transfer much of the engine thrust to the crosshead guides in the engine frames. Four stroke engines connect the piston to connecting rod directly using a gudgeon pin. As a result the cylinder liners on four strokes are considerably shorter to allow transverse movement of connecting rod. Piston skirts on 4 stroke engines are comparably longer to absorb the side loading against the cylinder liner created by the rotating crankshaft The cylinder liners on two stroke engines have scavenge ports to allow entry of fresh combustion air, whereas four stroke cylinders do not. b.) Stuffing box separates the scavenge space from the crankcase, preventing cross contamination of oil and keeping the scavenge air out of crankcase, via scraper and sealing rings the diaphragm is positioned between the crankcase and cylinder of a 2 stroke engine, to segregate the 2 areas. Its purpose is to prevent crankcase oil being carried into the scavenge space, and to prevent scavenge air, used cylinder oil and the products of combustion all from contaminating the crankcase oil.

Answer 3

a.) SEE EOOW ORAL/IAMI Sketch Pack for Drawing b.) the total are of the diagram is divided by the length of the diagram to obtain the mean height. mean height can then be multiplied by the spring scale of the indicator mechanism giving indicated mean effective pressure for the cylinder. W^.i= Pi x l x A x n W^.i= indicated power (for one cylinder only) Pi = indicated mean effective pressure l = stroke or length of the cylinder A = area of the cylinder A = TTD^2/4 n = number of power strokes per second (rev/sec) D = diameter of cylinder (m) power calculated from the diagram is called indicated power of the engine. its the power developed inside the cylinder of the engine. mean effective pressure can be found by dividing the area of the diagram by the length. the result is multiplied by the spring rate of the indicator spring, giving an average cylinder pressure. its used in the expression for indicated power and used as a value for comparison between engines. 4 stroke = n is divided by 2 because for one power there is revs for crankshaft. The area within the diagram represents the work done within the measured cylinder in one cycle. The area can be measured by an instrument known as a 'planimeter* or by the use of the mid-ordinate rule. The area is then divided by the length of the diagram in order to obtain a mean height. This mean height, when multiplied by the spring scale of the indicator mechanism, gives the indicated mean effective pressure for the cylinder. The mean effective or 'average' pressure can now be used to determine the work done in the cylinder. To obtain a measure of power it is necessary to determine the rate of doing work, i.e. multiply by the number of power strokes in one second. For a four-stroke-cycle engine this will be rev/sec -r 2 and for a two-stroke-cycle engine simply rev/sec.

Answer 4

a.) chocks, are used to restrict sideways and forward motion of the engine, both against the static weight of engine but also the dynamic loads created by running machinery. b.) The bedplate forms the base of the engine. It supports the crankshaft during rotation and is strong to avoid deflections of the shaft. c.) The Tie Rods are hydraulically tightened bolts that compress the crankcase sections together. They are used to resist the forces of combustion that are pulling the engine apart. d.) The entablature is mounted on top of the A frame. The cylinder liners are supported within the entablature. e.) Holding down bolts are used to connect the bedplate of the engine to the ship. They will keep the engine in position avoiding crankshaft deflection and vertical movement. f.) Crankshaft is used to convert the reciprocating motion of the pistons to rotational motion used to drive the ship via a propeller. It can also be used to transmit LO to different components via drillings.

Answer 5

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Answer 6

a.) * Check LO, FO, cooling water level and activate the starting handle. * Compressor must be unloaded and drain valve opened. * Check gear lever is in neutral. * Set the decompression lever to the decompression position in order keep the air inlet valve open to gain momentum for the flywheel, swing round the starting handle building up speed until maximum speed, then push over decompression lever whilst continuing to maintain speed with the starting handle. then when there is enough momentum deactivate the lever handle. When cranking ensure to control the fuel supply. b.) when engine is in cold climate engine cranking will be more difficult because the LO viscosity would have increased. partially blocked fuel injector nozzle no fuel in tank insufficient cranking because of air lock due to engaged load from the compressor ( need to drain compressor) insufficient compression due to cold climate temperature malfunction of decompression lever meaning air inlet valve is kept open leaky inlet and exhaust valve or cylinder cover gaskets too high viscosity of fuel due to cold climate

Answer 7

a.) SEE EOOW ORAL/IAMI Sketch Pack for Drawing b.) Air starting distributor Cylinder lubricators

Answer 8

a) Each engine cylinder will have a set of Cams, which govern and drive the fuel pumps and control exhaust valve timing. b) cam gears - allow the rotation of the camshaft to be in time with, the rotation of the crank shaft and thereby allows the valve opening, valve closing, and injection of fuel to occur at precise moments in the piston's travel. cam chain drive - The Cam shaft can be driven with a chain connected from the crank shaft. A chain drive is used to transmit motion from the crankshaft of the engine to the camshaft. This drive is known as timing chain and it is responsible for rotation of the camshaft. c.) The speed of the camshaft on a four stroke engine is half the speed of the crankshaft The speed of the camshaft on a 2 stroke engine is the same speed as the crankshaft d.) SEE EOOW ORAL/IAMI Sketch Pack for Drawing

Answer 9

a.) one method of reversing which is done by MAN BMW is to change the position of the cam follower. The Cam is symmetrical which means that the rise, peak and dwell will be the same regardless of the direction of rotation. when the order for astern is given the compressed air from air starting system is used to actuate the pneumatic valve which displaces each cam follower unit. if position isn't properly locked fuel delivery is stopped. this is carried out by a sensor fitted on each pump once the cam follower has shifted fuel timing changes and the firing order changes. air supplied to each cylinder will now be carried out according to the new reverse firing order. The simplest method for reversing is through utilising two sets of cams per cylinder and moving the camshaft axially to align the cams in the ahead or astern position. These are used in Mitsubishi engines the camshaft contains one for ahead and one for astern direction for each unit. Entire camshaft is axially moved to change the cam and thereby changing the firing order. one method of reversing cam is Sulzer reversible engines utilise a servo motor to rotate only the fuel cam. When the astern signal is given the hydraulic oil is supplied into the servo motor and acting against the rotating vane will rotate the cam to the desired position . b.) lost motion is the angular period between the top dead centre points for ahead and astern running. The lost-motion clutch uses a rotating vane which is attached to the camshaft and moves in relation to the camshaft drive from the crankshaft. The vane is shown held in the ahead operating position by oil pressure. When oil is supplied under pressure through the drain, the vane will rotate through the lost-motion angular distance to change the fuel timing for astern operation. The starting air system is retimed, either by camshaft movement or by a directional air supply being admitted to the starting air distributor, to reposition the cams.

Answer 10

TDC = Top dead centre - The point at which pistons direction of travel, changes from an upward to a downward stroke. BDC = Bottom dead centre - The point at which pistons direction of travel, changes from a downward to an upward stroke.

Answer 11

A total-loss oiling system is an engine lubrication system whereby oil is introduced into the engine, and then burned. the cylinder oi sued for this system is specially formulated to combat the acids that are found in an engine burning high sulphur fuel oil. when ship has to change over to low sulphur fuel a different set of circumstances will exist and there is different requirement for the oil. engineers must change the cylinder oil at the same time as fuel is changed from high to low sulphur fuel.

Answer 12

The diesel engine is a type of internal combustion engine which ignites the fuel by injecting it into hot, high-pressure air in a combustion chamber. In common with all internal combustion engines the diesel engine operates with a fixed sequence of events, which may be achieved either in four strokes or two, a stroke being the travel of the piston between its extreme points.

Answer 13

The engine is made up of a piston which moves up and down in a cylinder which is covered at the top by a cylinder head. The fuel injector, through which fuel enters the cylinder, is located in the cylinder head. The inlet and exhaust valves are also housed in the cylinder head and held shut by springs. The piston is joined to the connecting rod by a gudgeon pin. The bottom end or big end of the connecting rod is joined to the crankpin which forms part of the crankshaft. With this assembly the linear up-and-down movement of the piston is converted into rotary movement of the crankshaft. The crankshaft is arranged to drive through gears the camshaft, which either directly or through pushrods operates rocker arms which open the inlet and exhaust valves. The camshaft is 'timed' to open the valves at the correct point in the cycle. The crankshaft is surrounded by the crankcase and the engine framework which supports the cylinders and houses the crankshaft bearings. The cylinder and cylinder head are arranged with water-cooling passages around them.

Answer 14

The piston is solidly connected to a piston rod which is attached to a crosshead bearing at the other end. The top end of the connecting rod is also joined to the crosshead bearing. Ports are arranged in the cylinder liner for air inlet and a valve in the cylinder head enables the release of exhaust gases. The incoming air is pressurised by a turbo-blower which is driven by the outgoing exhaust gases. The crankshaft is supported within the engine bedplate by the main bearings. A-frames are mounted on the bedplate and house guides in which the crosshead travels up and down. The entablature is mounted above the frames and is made up of the cylinders, cylinder heads and the scavenge trunking.

Answer 15

The main difference between the two cycles is the power developed. The two-stroke cycle engine, with one working or power stroke every revolution, will, theoretically, develop twice the power of a four-stroke engine of the same swept volume. Inefficient scavenging however and other losses, reduce the power advantage to about 1.8. For a particular engine power the two-stroke engine will be considerably lighter—an important consideration for ships. Nor does the two-stroke engine require the complicated valve operating mechanism of the four-stroke. The four-stroke engine however can operate efficiently at high speeds which offsets its power disadvantage; it also consumes less lubricating oil. Each type of engine has its applications which on board ship have resulted in the slow speed (i.e. 80— 100 rev/min) main propulsion diesel operating on the two-stroke cycle. At this low speed the engine requires no reduction gearbox between it and the propeller. The four-stroke engine (usually rotating at medium speed, between 250 and 750 rev/ min) is used for auxiliaries such as alternators and sometimes for main propulsion with a gearbox to provide a propeller speed of between 80 and 100 rev/min.

Answer 16

There are two possible measurements of engine power: the indicated power and the shaft power. The indicated power is the power developed within the engine cylinder and can be measured by an engine indicator. The shaft power is the power available at the output shaft of the engine and can be measured using a torsion meter or with a brake.

Answer 17

It is made up of a small piston of known size which operates in a cylinder against a specially calibrated spring. A magnifying linkage transfers the piston movement to a drum on which is mounted a piece of paper or card. The drum oscillates (moves backwards and forwards) under the pull of the cord. The cord is moved by a reciprocating (up and down) mechanism which is proportional to the engine piston movement in the cylinder. The stylus draws out an indicator diagram which represents the gas pressure on the engine piston at different points of the stroke, and the area of the indicator diagram produced represents the power developed in the particular cylinder. The cylinder power can be measured if the scaling factors, spring calibration and some basic engine details are known. The procedure is described in the Appendix. The cylinder power values are compared, and for balanced loading should all be the same. Adjustments may then be made to the fuel supply in order to balance the cylinder loads.

Answer 18

A marine shaft power (torsion) meter measures the real time torque (torsion), speed, and power output on a propeller shaft, this way power can be adjusted and engine efficiency. If the torque transmitted by a shaft is known, together with the angular velocity, then the power can be measured, i.e. shaft power = torque x angular velocity The torque on a shaft can be found by measuring the shear stress or angle of twist with a torsion meter.

Answer 19

A basic part of the cycle of an internal combustion engine is the supply of fresh air and removal of exhaust gases. This is the gas exchange process. Scavenging is the removal of exhaust gases by blowing in fresh air. Charging is the filling of the engine cylinder with a supply or charge of fresh air ready for compression. With supercharging a large mass of air is supplied to the cylinder by blowing it in under pressure. Older engines were 'naturally aspirated'—taking fresh air only at atmospheric pressure. Modern engines make use of exhaust gas driven turbo chargers to supply pressurised fresh air for scavenging and supercharging. Both four-stroke and two-stroke cycle engines may be pressure charged. On two-stroke diesels an electrically driven auxiliary blower is usually provided because the exhaust gas driven turbo blower (turbocharger) cannot provide enough air at low engine speeds, and the pressurised air is usually cooled to increase the charge air density. At high enough engine speed the turbocharger is used, it consist of a single shaft. The single shaft has an exhaust gas turbine on one end and the air compressor on the other. Suitable casing design and shaft seals ensure that the two gases do not mix. Air is drawn from the machinery space through a filter and then compressed before passing to the scavenge space. The exhaust gas may enter the turbine directly from the engine or from a constant-pressure chamber. Each of the shaft bearings has its own independent lubrication system, and the exhaust gas end of the casing is usually water-cooled.

Answer 20

Efficient scavenging is essential to ensure a sufficient supply of fresh air for combustion. In the four-stroke cycle engine there is an adequate overlap between the air inlet valve opening and the exhaust valve closing. With two-stroke cycle engines this overlap is limited and some slight mixing of exhaust gases and incoming air does occur. A number of different scavenging methods are in use in slow-speed two-stroke engines. In each the fresh air enters as the inlet port is opened by the downward movement of the piston and continues until the port is closed by the upward moving piston. The flow path of the scavenge air is decided by the engine port shape and design and the exhaust arrangements. Three basic systems are in use: the cross flow, the loop and the uniflow. All modern slow-speed diesel engines now use the uniflow scavenging system with a cylinder-head exhaust valve. In a Four Stroke Cycle IC Engine Separate exhaust stroke pushes burnt gases through Exhaust Valve so in this case scavenging is achieved by valve overlapping.

Answer 21

In cross scavenging the incoming air is directed upwards, pushing the exhaust gases before it. The exhaust gases then travel down and out of the exhaust ports. Figure 2.10(a) illustrates the process. In loop scavenging the incoming air passes over the piston crown then rises towards the cylinder head. The exhaust gases are forced before the air passing down and out of exhaust ports located just above the inlet ports. The process is shown in Figure 2.10(b). Loop scavenge arrangements have low temperature air and high temperature exhaust gas passing through adjacent ports, causing temperature differential problems for the liner material. Uniflow is the most efficient scavenging system but requires either an opposed piston arrangement or an exhaust valve in the cylinder head. All three systems have the ports angled to swirl the incoming air and direct it in the appropriate path. With uniflow scavenging the incoming air enters at the lower end of the cylinder and leaves at the top. The outlet at the top of the cylinder may be ports or a large valve. The process is shown in Figure 2.10(c). Each of the systems has various advantages and disadvantages. Cross scavenging requires the fitting of a piston skirt to prevent air or exhaust gas escape when the piston is at the top of the stroke. With uniflow scavenging the two-stroke engine is designed to have the exhaust at one end of the cylinder (top) and scavenge air entry at the other end of the cylinder (bottom) so that there is a clear flow traversing the full length of the cylinder. This design means that the scavenge air does not have to travel up the cylinder and down again, as with the other designs, to purge the exhaust gas from the previous cycle, hence the name UNI-flow.

Answer 22

Cylinder oil can collect in the scavenge space of an engine. Unburned fuel and carbon may also be blown into the scavenge space as a result of defective piston rings, faulty timing, a defective injector, etc. A build-up of this flammable mixture presents a danger as a blow past of hot gases from the cylinder may ignite the mixture, and cause a scavenge fire. A loss of engine power will result, with high exhaust temperatures at the affected cylinders. The affected turbo-chargers may surge and sparks will be seen at the scavenge drains. Once a fire is detected the engine should be slowed down, fuel shut off from the affected cylinders and cylinder lubrication increased. All the scavenge drains should be closed. A small fire will quickly burn out, but where the fire persists the engine must be stopped. A fire extinguishing medium should then be injected through the fittings provided in the scavenge trunking. On no account should the trunking be opened up. To avoid scavenge fires occurring the engine timing and equipment maintenance should be correctly carried out. The scavenge trunking should be regularly inspected and cleaned if necessary. Where carbon or oil build up is found in the scavenge, its source should be detected and the fault remedied. Scavenge drains should be regularly blown and any oil discharges investigated at the first opportunity.

Answer 23

A flyweight assembly is used to detect engine speed. Two flyweights are fitted to a plate which rotates about a vertical axis driven by a gear wheel (Figure 2.22). The action of centrifugal force throws the weights outwards; this lifts the vertical spindle and compresses the spring until an equilibrium situation is reached. The equilibrium position or set speed may be changed by the speed selector which alters the spring compression. As the engine speed increases the weights move outwards and raise the spindle; a speed decrease will lower the spindle. The hydraulic unit is connected to this vertical spindle and acts as a power source to move the engine fuel controls. A piston valve connected to the vertical spindle supplies or drains oil from the power piston which moves the fuel controls depending upon the flyweight movement. If the engine speed increases the vertical spindle rises, the piston valve rises and oil is drained from the power piston which results in a fuel control movement. This reduces fuel supply to the engine and slows it down. It is, in effect, a proportional controller. The actual arrangement of mechanical engine governors will vary considerably but most will operate as described above.

Answer 24

The principal control device on any engine is the governor. It governs or controls the engine speed at some fixed value while power output changes to meet demand. This is achieved by the governor automatically adjusting the engine fuel pump settings to meet the desired load at the set speed. Governors for diesel engines are usually made up of two systems: a speed sensing arrangement and a hydraulic unit which operates on the fuel pumps to change the engine power output.

Answer 25

The electric governor uses a combination of electrical and mechanical components in its operation. The speed sensing device is a small magnetic pick-up coil. The rectified, or d.c., voltage signal is used in conjunction with a desired or set speed signal to operate a hydraulic unit. This unit will then move the fuel controls in the appropriate direction to control the engine speed

Answer 26

The cylinder relief valve is designed to relieve pressures in excess of 10% to 20% above normal. A spring holds the valve closed and its lifting pressure is set by an appropriate thickness of packing piece. Only a small amount of lift is permitted and the escaping gases are directed to a safe outlet. The valve and spindle are separate to enable the valve to correctly seat itself after opening. The operation of this device indicates a fault in the engine which should be discovered and corrected. The valve itself should then be examined at the earliest opportunity.

Answer 27

The presence of an oil mist in the crankcase is the result of oil vaporisation caused by a hot spot. Explosive conditions can result if a build up of oil mist is allowed. The oil mist detector uses photoelectric cells to measure small increases in oil mist density. A motor driven fan continuously draws samples of crankcase oil mist through a measuring tube. An increased meter reading and alarm will result if any crankcase sample contains excessive mist when compared to either clean air or the other crankcase compartments. The rotary valve which draws the sample then stops to indicate the suspect crankcase. The comparator model tests one crankcase mist sample against all the others and once a cycle against clean air. The level model tests each crankcase in turn against a reference tube sealed with clean air. The comparator model is used for crosshead type engines and the level model for trunk piston engines

Answer 28

As a practical safeguard against explosions which occur in a crankcase, explosion relief valves or doors are fitted. These valves serve to relieve excessive crankcase pressures and stop flames being emitted from the crankcase. They must also be self closing to stop the return of atmospheric air to the crankcase. Various designs and arrangements of these valves exist where, on large slow-speed diesels, two door type valves may be fitted to each crankcase or, on a medium-speed diesel, one valve may be used. A light spring holds the valve closed against its seat and a seal ring completes the joint. A deflector is fitted on the outside of the engine to safeguard personnel from the out flowing gases, and inside the engine, over the valve opening, an oil wetted gauze acts as a flame trap to stop any flames leaving the crankcase. After operation the valve will close automatically under the action of the spring.

Answer 29

The turning gear or turning engine is a reversible electric motor which drives a worm gear which can be connected with the toothed flywheel to turn a large diesel. A slow-speed drive is thus provided to enable positioning of the engine parts for overhaul purposes. The turning gear is also used to turn the engine one or two revolutions prior to starting. This is a safety check to ensure that the engine is free to turn and that no water has collected in the cylinders. The indicator cocks must always be open when the turning gear is operated

Answer 30

Engine reversing When running at manoeuvring speeds: 1.Where manually operated auxiliary blowers are Fitted they should be started. 2.The fuel supply is shut off and the engine will quickly slow down, 3.The direction handle is positioned astern. 4.Compressed air is admitted to the engine to turn it in the astern direction. 5. When turning astern under the action of compressed air, fuel will be admitted. The combustion process will take over and air admission cease. When running at full speed: 1.The auxiliary blowers, where manually operated, should be started. 2.Fuel is shut off from the engine. 3.Blasts of compressed air may be used to slow the engine down. 4.When the engine is stopped the direction handle is positioned astern. 5.Compressed air is admitted to turn the engine astern and fuel is admitted to accelerate the engine. The compressed air supply will then cease

Answer 31

Starting Air Overlap There must be some overlap between the operation of starting air valves to the different cylinders of an engine, so that as one cylinder valve is closing another one is opening just at the correct moment to ensure a continued rotation of the engine before the fuel is introduced. This is essential to ensure a positive angular motion of the engine crankshaft with sufficient momentum to give a positive start. The usual minimum amount of overlap provided in practice is 15°. Starting air is admitted on the working stroke and the period of opening is governed by practical considerations with three main factors to consider: 1.The firing interval of the engine.for example, with a four-cylinder two-stroke engine the firing interval is 90°, that is, 360/4 and if each cylinder valve covered 90° of the cycle then the engine would not start if it had come to rest in the critical position with one valve fractionally off closure and another valve just about to start opening. 2.The valve must close before the exhaust commences. It is rather pointless blowing high pressure air straight to exhaust and it could be dangerous. 3.The cylinder starting air valve should allow the air to enter the cylinder after its associated piston has passed TDC to give a positive turning moment in the correct direction. In fact some valves are arranged to start to open as much as 10° before TDC because the engine is past this position before the valve is effectively open and the compressed air is having an effect. Any reverse turning effect is negligible as the turning moment exerted on a crank very near dead centre is small indeed.Consider figure 5.1a for a four-stroke engine. With the timings as shown the air starting valve opens 15° after dead centre and closes 10° before exhaust begins. The air start period is then 125°. The firing interval for a six-cylinder four-stroke engine is 720/6 = 120°. The period of overlap is 5° which is insufficient. Although this example could easily be modified so as to give sufficient (say 15°) overlap by reducing the 15° after dead centre and the 10° before exhaust opening, it can become very difficult to arrange with very early exhaust opening on turbo-charged engines. A seven-cylinder four-stroke engine is much easier to arrange. Consider figure 5.1b which represents a two-stroke engine. This has an air start period of 115°. Firing interval for a three-cylinder two-stroke engine = 360/3 = 120°. This means no overlap. Modification can arrange to give satisfactory starting with this example but for modern turbo-charged two-stroke engines having exhaust opening as early as 75° before BDC (outer) it becomes virtually impossible. A four-cylinder two-stroke engine is much easier to arrange and would be adopted. Consider figure 5.1c which is a cam diagram for a two-stroke engine with four cylinders. The air open period is 15° after dead centre to 130° after dead centre, that is, a period of 115°. This gives 25° of overlap (115 – 360/4) which is most satisfactory. Take care to note the direction of rotation and this is a cam diagram so that for example, No. 1 crank is 15° after dead centre when the cam would arrange to directly or indirectly open the air start valve. The firing sequence for this engine is 1 4 3 2. This is very much related to engine balancing and no hard and fast rules can be laid down about crank firing sequences as each case must be treated on its merits. It may be useful to note that for six-cylinder, two-stroke engines a very common firing sequence is 1 5 3 6 2 4 and similarly for seven and eight cylinders 1 7 2 5 4 3 6 and 1 6 4 2 8 3 5 7 respectively are often used. The cam on No. 1 cylinder is shown for illustration as it would probably be for operating say cam operated valves, obviously the other profiles could be shown for the remaining three cylinders in a similar way. The air period for cylinder numbers 1, 4, 3 and 2 are shown respectively in full, chain dotted, short dotted and long dotted lines and the overlap is shown shaded

Answer 32

Each cylinder is fitted with a starting air valve which is operated pneumatically by one of the starting air distributor control valves. These are arranged radially around the starting air distributor cam. At the correct engine position an air signal from the control valve is directed to the cylinder starting air valve upper chamber and acts on the piston to open the valve. As this is happening the air from the lower chamber is vented to atmosphere through the control valve. At the end of the starting air admission period control air is redirected to the lower chamber to close the valve while the upper chamber is vented to atmosphere through the control valve. The valve opens and closes quickly with air cushioning at the end of the closing motion to reduce shock on the valve seat. If the pressure in the cylinder is substantially higher than the starting air pressure, the valve will not open. This prevents hot gases entering the starting air manifold. During engine operation the air inlet to the starting valve should be regularly checked. A hot inlet would indicate a leaking starting air valve allowing hot combustion gases to enter the air manifold which may lead to an explosion if starting air is admitted

Answer 33

There are many designs of air distributor all with the same basic principles, that is, to admit air to the pistons of cylinder relay valves in the correct sequence for engine starting. Valves not being supplied with air would be vented to the atmosphere via the distributor. Some overlap of timing would obviously be required. The starting control valves are arranged radially around the starting air distributor cam, which is driven via a vertical shaft from the camshaft. When the engine starting lever is operated air is admitted to the distributor forcing all control valves, against the return spring, onto the cam. The control valve of a cylinder which is in the correct position for starting, will be pushed into the depression in the cam and assume the position shown in figure 5.3b. In this position air from the starting system will be directed to the upper part of the cylinder starting air valve causing the valve to open. At the same time air from the lower chamber of the cylinder starting air valve will be vented to atmosphere. At the end of the cylinder starting air period the distributor cam moves the control valve to the position. In this position air from the starting air system is directed to the lower chamber of starting air valve causing the valve to close. Air from the upper chamber is vented through the control valve to atmosphere. The starting control valves are held off the distributor cam by springs when starting air is shut off the engine

Answer 34

The general trend in four-stroke practice is to utilise a unidirectional engine, coupled, via a reduction gearbox, to a controllable pitch propeller. The need for reversing mechanisms on the four-stroke engines is, therefore, no longer required.

Answer 35

Refer now to figure 5.5. The design in this figure which is based on older Wartsila Sulzer engine practice has a lost motion on the fuel pump camshaft of about 30°. When reversal is required oil pressure and drain connections are reversed. Oil flowing laterally along the housing moves the centre section to the new position, that is, anti-clockwise as shown in figure 5.5. The oil pressure is maintained on the clutch during running so that the mating clutch faces are kept firmly in contact with no chatter. Figure 5.5 Lost motion clutch There are a number of variations on this design but the principle of operation is similar although not all types rotate the clutch to its new position before starting and merely allow the camshaft to ‘catch on’ with the crankshaft rotation when lost motion is completed. It is worth pausing for a moment and reflecting upon the limitations of the mechanical designs. For example, think how difficult it would be to arrange a fuel cam with a profile that gave a pre-ignition and post-ignition phase to the injection process

Answer 36

One of the easiest ways of changing the settings on a two-stroke engine is to reposition the fuel, exhaust valve and starting air cams on the camshaft, with their associated equipment, so that the engine operating in reverse can utilise one cam. This avoids the complication of moving the camshaft axially but it also means that it is necessary to provide a ‘lost motion clutch’ on the camshaft.

Answer 37

Exhaust gases from engines and boilers contain atmospheric pollutants which are principally nitrogen oxides (NOX), sulphur oxides (SOX), carbon oxides and unburnt hydrocarbon particulates. These various pollutants contribute to smog and acid rain, and carbon oxides contribute to the greenhouse effect, which is increasing global temperatures. The IMO Marine Environment Protection Committee is considering ways to reduce the pollutants in exhaust emissions. IMO is to add a new Annex to MARPOL 73/78 to deal with atmospheric pollution. The SOX content of emission may be reduced by either a reduction of the sulphur content in fuels or an exhaust gas treatment system. New engine technology may reduce NOX formation and thus emissions, while carbon oxides can be reduced by good plant maintenance. Selective Catalytic Reduction Systems are in use on some vessels, which are said to reduce NOX emissions by 90 per cent and carbon oxides by 80 per cent.

Answer 38

The term medium speed refers to diesels that operate within the approximate speed range of 300–800 rev/min. High speed is usually 1,000 rev/min and above.

Answer 39

1.Compact and space saving. The vessel can have reduced height and broader beam – useful in some ports where shallow draught is of importance. The considerable reduction in engine height compared to direct drive engines and the reduced weight of components means that lifting tackle, such as the engine room crane, is reduced in size as it will have lighter loads to lift through smaller distances. More cargo space is made available and because of the higher power to weight ratio of the engine a greater weight of cargo can be carried. 2.Through using a reduction gear a useful relationship between ideal engine speed and ideal propeller speed can be achieved. For optimum propeller speed hull form and rudder have to be considered, the result is usually a slow turning propeller (for large vessels this can be as low as 50–60 rev/min). Gearing enables the naval architect to design the best possible propeller for the vessels without having to consider any dictates of the engine. Engine designers can ignore completely propeller speed and concentrate solely upon producing an engine that will give the best possible power weight ratio. 3.Modern tendency is to utilise unidirectional medium-speed geared diesels coupled to either a reverse reduction gear, controllable pitch propeller (CPP) or electric generator. The second two of these methods are the ones primarily used and the advantages to be gained are considerable. They include: a.Less starting torque required, clutch disengaged or CPP in neutral. b.Reduced number of engine starts, hence starting air capacity can be greatly reduced and compressor running time minimised. Classification society requirements are six consecutive starts without air replenishment for non-reversible engines and twelve for reversible engines. Cylinder liner wear rate increases during starting. c. Engines can be tested at full speed with the vessel alongside a quay without having to take any special precautions. d. With the mechanical drive arrangement and the engine or engines running continuously, power can be taken off via a clutch or clutch/gear drive for the operation of electric generators or cargo pumps, etc. Hence the main engine has become a multi-purpose ‘power pack’. e. Improved manoeuvrability, vessel can be brought to rest within a shorter distance by intelligent use of the engines and CPP. f. Staff work load during ‘stand-by’ periods is reduced and the system lends itself ideally to simple bridge control. 4.With two engines coupled via gearing one may be disengaged, while the other supplies the motive power, and overhauled. This reduces off hire time as the voyage is continued at slightly reduced speed with a fuel saving. 5.Spare parts are easier to store and manhandle, therefore unit overhaul time will be greatly reduced.

Answer 40

Reverse reduction gear These gear systems are mainly restricted, at present, to powers of up to about 4800 kW for twin-engined single-screw installations. Their obvious advantages are as follows: 1.Uni-directional engine. 2.No c.p. propeller required. 3.Ability to engage or disengage either engine of a twin-engine installation from the bridge by a relatively simple remote control. 4.Improved manoeuvrability, etc. When dealing with higher powers the friction clutches used in the system can become excessively large, great heat generation during engagement may require a cooling system, the overall arrangement becomes more expensive and it may be cheaper to use direct reversing engines – however it would also, for reasons previously outlined, be prudent to use a c.p. propeller. Two systems of reverse reduction gear are shown in figures 8.3 and 8.4. In figure 8.3, the engine drives a steel drum which has two inflatable synthetic rubber tubes bonded to its inner surface. These tubes have friction material, like brake lining, on their inner surface. Air is supplied through the centrally arranged tube, or the annulus formed by the tube and shaft hole to one or the other of the inflatable tubes. Two flanged wheels are connected via hollow shafts and gears to the main gear wheel and shaft. For operation ahead, air would be supplied to inflatable tube A. which would then by friction on flanged wheel B bring gears 1 and 2 up to speed; gears 3, 4 and 5 together with flanged wheel D would be idling. For astern operation, air would be supplied to inflatable tube C (A evacuated) and by friction on flanged wheel D gears 3, 4, 5 and 2 would be brought up to speed, gear 1 and drum B would be idling. For single reduction, gears 3 and 4 would be the same size and so would be gears 1 and 5.An alternative system, either single or double reduction but probably the latter, is shown in figure 8.4. Friction clutches A and B are pneumatically controlled from some remote position. Gears 1, 2, 3 and 4 would have to be the same size if the gear were to be single reduction – but this is most unlikely.

Answer 41

These are completely self-contained, apart from a cooling water supply, they require no external auxiliary pump or oil feed tank. A scoop tube when lowered picks up oil from the rotating casing reservoir and supplies it to the vanes for coupling and power transmission; withdrawal of the scoop tube from the oil stops the flow of oil to the vane which then drains to the reservoir. During power transmission a flow of oil takes place continuously through the cooler and clutch. fluid clutches operate smoothly and effectively. They use a fine mineral lubricating oil and have no contact and hence no wear between driving and driven members. Torsional vibrations are dampened out to some extent by the clutch and transmitted speeds can be considerably less than engine speed if required by suitable adjustment of the scoop tube. It is possible to have a dual entry scoop tube for reversible engines, this obviates the use of c.p. propellers or reversible reduction gears but the control problem is considerably more complex with reversible engines, they have to be stopped and started and if four-stroke engines are used camshafts have to be moved, etc. (figure 8.2).

Answer 42

These are used between engine and gearbox to dampen down torque fluctuations, reduce the effects of shock loading on the gears and engine, cater for slight misalignments. They are also used in conjunction with clutches for power take-off when required. In construction they may be similar to the well-known multi-tooth type to be found in turbine installations or employ diaphragms or rubber blocks. Those types that use rubber or synthetic rubber, such as Nitrile, give electrical insulation between driving and driven members, but all types will minimise vibration and reduce noise level.

Answer 43

The main function of a Geislinger coupling is to assist in the damping out of torsional vibrations. This is accomplished by connecting the engine crankshaft to the load via flexible steel leaf springs arranged radially in the coupling, which is also filled with oil. As torsional fluctuations occur they are absorbed by the leaf springs which deflect and displace oil to adjacent chambers, slowing down the relative movement between the inner and outer components of the coupling. The makers claim that this effective damping is achieved without problems of wear because of the absence of friction. Damping oil is supplied from the engine oil system through the centre of the coupling. It is returned to the engine through hollow coupling bolts. Maintenance is limited to cleaning, inspection and the replacement of ‘O’ rings.

Answer 44

Gear boxes are very interesting and need a great deal of care in both manufacture and on-going care. They have to transmit sometimes large forces through relatively small areas of contact. The metal obviously transmits that power but metal-to-metal contact would mean that the component parts would not last for long. This means that the quality of the oil and the oil supply is vital to the on-going success of the gearbox. Although the gears are said to be meshing they are actually sliding over one another and the oil needs to be in the right place to ensure that the gear teeth perform correctly. Another major consideration for the ship’s engineering staff is to ensure that no metal, tools or other foreign bodies are allowed to enter the casing of the gearbox. The effect is catastrophic if metal gets between the teeth on the gearwheel due to the small clearance between the gears. Gearboxes transmit power through a drive train. The gears can be arranged to increase or decrease the speed of rotation of input and output shafts or they can be used to transmit power through an angle so that the output shaft is pointing in a different direction to the original shaft. The basic arrangement is to have straight gears around the outside of a wheel, fixed to the end of an input shaft, linking with a second wheel, of a different diameter, fixed to the start of an output shaft. The dimensions of the gear wheels will determine the different input and output speeds to and from the gearbox. Any combination of speeds can be chosen to suit the designer’s needs. Straight cut gears present a problem in so much as they have the minimum surface-to-surface contact area through which to transmit the power. Therefore they have to be sized accordingly. If the teeth are set at an angle across the end of the wheel to form a helical gear then the area for transmitting power in increased and the gear wheel can be more compact than a gear transmitting the same power using straight teeth. The problem here is that because the teeth are set at an angle there will be forces transmitted at different angles. One component of the force will be transmitted through the gear as required and another will be transmitted along the shaft as a vector component of the total force from the input shaft. This will result in a lateral thrust being transmitted along the shaft. The value of the thrust will depend upon the angle of the teeth and the total power from the input shaft. This means that with a single helical gearwheel a thrust block of some sort will be needed to counteract the thrust from the gearwheel. Another answer to this problem is to arrange for half the width of the gearwheel to have helical teeth set in one direction and the other half of the wheel to have teeth set in the opposite direction. This means that the thrust from one set of teeth is offset by the thrust from the other set of teeth and the need of a thrust block has been overcome. The profile of the teeth is very important to the smooth operation of the gearbox because for the teeth at the end of the input shaft to mesh and transmit power they have to slide into the space in-between the gears on the output shaft. It is also important for the tip of the gear not to make any contact with the root of the opposing gear wheel as this will also impose forces on the gears resulting in gearbox failure. Smaller gearboxes and low-power gearboxes might be lubricated by relying on the oil splashing onto the gears as they operate. However this means that at start-up the gears are not so well protected and wear can occur during this time. Larger or more powerful arrangements will have the oil pumped into the gearbox where it is arranged to spray directly onto the meshing gears ensuring the even at the start-up stage the gear teeth are well lubricated. Gearboxes do need to be checked and looked after. Any unusual noises must be investigated and routine inspections must be made at the appropriate intervals. It is not a good idea to make frequent visual inspections because there is more chance of introducing foreign materials inside the casing. When an inspection is made the engineer should be looking out for the following: * Broken teeth on the gearwheels * Discolouration anywhere on the gearwheel of teeth (indicating overheating) * Excessive wear on the faces of the gear teeth (indicating a lack of lubrication) * Condition of the oil. A sample of oil can be sent away for further analysis. This will be checked for any metal or water content and from this analysis a picture of the condition of the gearbox can be formed. This process obviously takes some time therefore some companies such as Kittywake International are now supplying analysis kits that can be used on-board. The next step is to offer online real-time testing of lubricating oil. This will then start to move the industry towards a CBM approach.

Answer 45

These are: 1.Separately caged exhaust valves are preferred even though they increase the initial cost. If they are made integral with the cylinder head and used with poor quality fuel then there will be an increased frequency of valve replacement and overhaul. Cylinder head removal each time becomes a tedious time-consuming operation and the caged valves save a lot of time. However part load or short trip operation can be a problem as the exhaust valves could be running at a temperature where the dew point of the gasses is reached. Some cross-channel operators have in the past had problems with acid erosion of exhaust valves spindles on uprated Pielstick PC 2.5 because they had water-cooled exhaust valve cages. The previous version of the engine running on the short voyages did not have the same problem. 2.All connections to the valves, cooling, exhaust, etc. should be capable of easy disconnection and re-assembly. 3.Materials that have to operate at elevated temperatures must be capable of withstanding the erosive and corrosive effects of the exhaust gas. When burning oils of high viscosity which contain sodium and vanadium deposits can form on the valve seats which, at high temperatures (in excess of 530°C at the valve seat), become strongly corrosive sticky compounds which lead to burnt valves. Hence, the need for materials that can withstand the corrosion and for intense cooling arrangements for valve seats. 4.Stellite valve seats have started the quest for improved durability of exhaust valves. Stellite is a mixture of cobalt, chromium and tungsten extremely hard and corrosion resistant that is fused on to the operating surfaces. Low temperature corrosion due to sulphur compounds can occur during prolonged periods of running under low load conditions. The valve spindle and guide, which would be at a relatively low temperature, are the principal places of attack due to the effective cooling in this region. Ideally, valve cooling should be a function of engine load with the valve being maintained at a uniform temperature at all times, as stated this could prove complicated and expensive to arrange for part load and low load conditions.Further to the use of Stellite, a nickel-chromium alloy, strengthened by additions of titanium, aluminium and carbon called Nimonic 80A, has gained favour for use in exhaust valve construction. Recently MAN have found that welding a high-temperature resilient Ni-Cr alloy onto a stainless steel spindle would dramatically improve the hardness and ductility of the valve seat as well as its resistance to cracking when compared to chromium- and nickel-based hard facings including Nimonic 80A.In the first stage of the process, the stainless steel DuraSpindle is placed through a new robotic welding procedure where Inconel, an alloy traditionally used in gas turbines, is welded into the groove of an exhaust spindle valve seat.Once the alloy has been welded in place, the DuraSpindle is then machined after which more than 10 tonnes of force is used during the special rolling process to work harden the Inconel weld to 500 HV. While the spindle is being rolled and rotated three or four concentric grooves, depending on the spindle size, are etched into the seat at a depth of several millimetres. This further hardens a relatively ductile material.The rolling process provides compressive stresses into the component, as opposed to tensile stresses which may cause cracking in the seat area. Compressive stressing significantly reduces the probability of cracking even in the advent of welding defects. The hard facing on the spindle seat is further hardened by heating the material up to 600–700°C. The metallurgical reaction, called precipitation hardening, further hardens the seat to 600 HV.Compared with an Alloy 50-type hard facing material DuraSpindle is 20% harder and 50% harder if compared to a spindle with Stellite hard facing or Nimonic 80A. 5. Effective lubrication of the valve spindle is necessary to avoid risk of seizure and possible mechanical damage due to a valve ‘hanging up’. In order to minimise lubricating oil usage the lubrication system for the valves would be similar to that used for cylinder lubrication and since the amount of oil used would therefore be in small quantities, any contamination of the oil by combustion products and water, etc. would be minimal, and this would also increase the life of crankcase lubricating oil.

Answer 46

Methane (CH4) slip is where some of the methane from the fuel moves through the engine and out of the exhaust without being burnt. Some manufacturers are keen to point out that this occurs more on the engines that operate on the Otto cycle rather than the Diesel cycle. However, the industry is confident that as the mechanics of the methane slip become better understood, so changes in combustion design will reduce the problem. Some suggestions for how methane can by-pass the combustion process include being injected early or late in the combustion cycle and the gas is therefore caught in the scavenge port and gets sucked though during the overlap period. Another possibility is that the air/gas mix in the Otto cycle can be caught just above the piston ring where it remains unburnt and escapes with the exhaust. It then follows that older, fuel oil, combustion space designs could be more prone to these imperfections than would new engines that are designed with methane slip in mind. It also follows that any reduction in fuel injection performance could make the situation worse. Methane slip occurs when there is a small amount of LNG that is unburned due to incomplete combustion cycle. Without any action being taken to reduce methane slip, methane can escape into the atmosphere. Methane which escapes combustion and is released by the engine exhaust or through the crankcase ventilation is referred to as methane slip. Methane is a Green House Gas that has a greater negative impact on the environment than CO2. For the methane slip for my dual fuel engine, i must keep it as low as possible, as well as for any bunkering operations that will be carried out, otherwise the benefit from reduction in CO2 due to the use of LNG will be non-beneficial. The dual fuel 4 stroke engine i am using in this project operates in an Otto cycle, with gas supply pressure being low. In this cycle fuel is mixed with air and introduced into the cylinder before the compression process starts. The Otto cycle combustion is started by injection of pilot oil. The pilot oil for this dual fuel engine is LNG. Since this engine operates in an Otto cycle, which uses premixed air to fuel ratio, the issue that can occur is methane slip. This wouldn’t occur in a 4-stroke engine because this type of engine doesn’t work in an Otto cycle.

Answer 47

The principal design parameters for medium-speed diesel engines are: 1.High power/weight ratio. 2.Simple, strong, compact and space saving. 3.High reliability. 4.Able to burn a wide range of fuels. 5.Easy to maintain, the fact that components are smaller and lighter than those for slow-speed diesels makes for easier handling, but accessibility and simple to understand arrangements are inherent features of good design 6.Easily capable of adaption to unmanned operation. 7.Low fuel and lubricating oil consumption. 8.High thermal efficiency. 9.Low cost and simple to install. 10. Four-stroke design leads to electronic control and use of advanced environmental techniques such as the Miller cycle

Answer 48

Comparison of coolants Fresh water Inexpensive, high specific heat, low viscosity. Contains salts which can deposit, obstruct flow and cause corrosion. Requires treatment. Leakages could contaminate lubricating oil system leading to loss of lubrication, possible overheating of bearings and bearing corrosion. Requires a separate pumping system. It is important that water should not be changed very often as this can lead to increased deposits. Leakages from the system must be kept to an absolute minimum, so a regular check on the replenishing-expansion tank contents level is necessary. If the engine has to stand inoperative for a long period and there is a danger of frost, (a)drain the coolant out of the system, (b)heat up the engine room or (c)circulate the system with heating on. It may become necessary to remove scale from the cooling spaces and the following method could be used. Circulate, with a pump, a dilute hydrochloric acid solution. A hose should be attached to the cooling water outlet pipe to remove gases. Gas emission can be checked by immersing the open end of the hose occasionally into a bucket of water. Keep compartment well ventilated as the gases given off can be dangerous. Acid solution strength in the system can be tested from time to time by putting some onto a piece of lime. When the acid solution still has some strength and no more gas is being given off then the system is scale free. The system should now be drained and flushed out with fresh water, then neutralised with a soda solution and pressure tested to see that the seals do not leak. Distilled water More expensive than fresh water, high specific heat, low viscosity. If produced from evaporated salt water it would be acidic. No scale-forming salts. Requires separate pumping system. Leakages could contaminate the lubricating oil system, causing loss of lubrication and possible overheating and failure of bearings, etc. Lubricating oil This is expensive and generally there is no separate pumping system required since the same oil is normally used for lubrication and cooling. Leakages from cooling system to lubrication system are relatively unimportant provided they are not too large; otherwise one piston may be partly deprived of coolant with subsequent overheating. Due to reciprocating action of pistons some relative motion between parts in contact with the coolant supply and return system must occur; oil will lubricate these parts more effectively than water. No chemical treatment required. Lower specific heat than water, hence a greater quantity of oil must be circulated per unit time to give the same cooling effect. If the lubricating oil is subject to a high temperature it can burn leaving carbon deposit as it does so. This deposit on the underside of a piston crown could lead to impairment of heat transfer, overheating and failure of the metal. Generally the only effective method of dealing with the carbon deposit is to dismantle the piston and physically remove it. Since oil can burn in this way a lower mean outlet and inlet temperature of the oil has to be maintained. In order to achieve this more oil must be circulated per unit time.

Answer 49

contact the bridge and chief engineer to inform them the engine is being prepared for sea service. test the steering gear to ensure its operational. prepare the jacket water system by first checking the expansion tank level and replenishing it if required. then check the jacket water temperature use preheater if necessary to warm up the gradually to operating temperature (60-65degrees) to allow for sufficient cooling and not raise the internal temperature which would lead to thermal stress and component failure. start the jacket water pump to begin circulating jacket water through the main engine. prepare the LO system by checking LO sump tank level and fill up if necessary. start the LO purifier to begin removing any impurities in LO. start the main engine LO pump to to circulate LO around the main engine for cooling and lubricating components and for jacket water to warm up the LO to operating temperature. continue to monitor all pressures and temperatures for J/W and LO system. prepare the fuel oil system and steam tracing system, by starting FO purifier and ensuring fuel is heated up by the steam system until fuel oil service operating temperature (90degrees). drain any water from fuel oil service tank and settling tank. prepare the air starting system by checking the air reservoir pressure and having compressors on auto so air reservoirs can be filled up automatically when necessary. drain any oil/ water moisture from air starting system from the air compressors and air bottles and open main air starting valve. contact bridge to inform the engine is going to be turned over. manually activate cylinder lubrication and engage the turning gear. ensure engine is turned for at least 15minmum to allow for 2revs and sufficient lubrication. open indicator cocks, start an additional generator for electrical power. kick the engine on air and observe indicator cocks to ensure cylinder are purged of debris/oil and water moisture. then disengage turning gear and close indicator cocks. test engine on fuel by opening necessary valves and starting fuel pump. switch auxiliary blowers to auto position. once all is confirmed okay contact the bridge to let them know the engine is ready and finally fill up the ER logbook.

Answer 50

The purpose with the lambda controller is to prevent injection of more fuel in the combustion chamber of an auxiliary engine on the ship, than can be burned during a momentary load increase. This is carried out by controlling the relation between the fuel index and the charge air pressure. The Lambda controller is also used as stop cylinder.

Answer 51

The lambda controller has the following advantages: 1.Reduction of visible smoke in case of sudden momentary load increases on auxiliary engines. 2.Improved load ability. 3.Less fouling of the engine’s exhaust gas ways. 4.Limitation of fuel oil index during starting procedure.

Answer 52

see motor sketch pack for drawing Figure above illustrates the controller’s operation mode. In case of a momentary load increase, the regulating device will increase the index on the injection pumps and hereby the regulator arm (1) is turned, the switch (2) will touch the piston arm (3) and be pushed downwards, whereby the electrical circuit will be closed. Thus the solenoid valve (4) opens. This valve is supplied with compressed air and the same is supplied to assist the turbocharger. When this jet system is activated, the turbocharger accelerates and increases the charge air pressure, thereby pressing the piston (3) backwards in the lambda cylinder (5). When the lambda ratio is satisfactory, the jet system will be deactivated. At a 50% load change the system will be activated for about 3-8 seconds. If the system is activated more than 10 seconds, the solenoid valve will be shut off and there will be a remote signal alarm for “jet system failure”.

Answer 53

Causes of Top End Bearing Failure Following are the possible causes of top end bearing failure: 1.Wiping of the bearing due to high bearing loads caused by excessive cylinder pressure being developed 2.Insufficient lubricating oil supply due to supply pump failure, failure of the oil piping linkage, oil filter blockage 3.Impurities within the lubricating oil, causing abrasion of the bearing and pin surface 4.Corrosion of the bearing and pin due to oil contamination with acidic products and/or water 5.Wiping of the bearing due to low viscosity of the oil caused by excessive oil temperatures and/or water 6.Insufficient bearing clearances within the bearing, causing excessive oil temperatures and hence low oil viscosity 7.Excessive bearing clearances within the bearing, causing low oil generated pressures due to excessive bearing end leakage Assessment of Top End Bearing Failure The following information would be useful in assessing the possible causes of the failure: History of all work carried out on the bearings, to try and establish if any possible pattern or links exist. History of bearing clearances, to investigate whether the clearances have been maintained at the correct values. Readings of the power developed by the engine, to establish if the engine has been operating at overload. Readings of the maximum combustion pressures developed by each cylinder, to establish if the load on the top end bearing has been excessive. Readings of the lubricating oil analysis, to determine if the oil condition is acceptable.

Answer 54

Prevention of Top End Bearing Failure 1.Bi- monthly monitoring of all bearing clearances, to ensure these are within normal limits 2.Bi -monthly oil analysis of the oil by the oil manufacturer, to ensure oil quality is ensured 3.Weekly oil tests on-board for water contamination, dirt levels, viscosity and BN levels, to ensure that the oil condition is acceptable. 4.Monthly checks of the lubricating oil low pressure alarm and trip, to ensure that the engine is protected at all times 5.Three times a day recording of the supply oil pressure and temperature, to monitor the supply oil 6.Monthly monitoring of the cylinder pressures using indicator cards, to prevent bearing overload 7.Closely monitor any overhaul and repair work carried out on the bearings to ensure that the correct procedure was being followed, and that the re-assembly was correct 8.Monitor any replacement parts that have been used to ensure they are the correct specification 9.Monthly checks of the general crankcase to ensure all locking devices are still in place

Answer 55

Ignition delay is the time between fuel injection and fuel ignition. During this time the fuel get mixed with hot compressed air and vaporizes. After the ignition delay, spontaneous ignition of the fuel occurs. The longer the ignition delay, more fuel will be injected and vaporizes inside the combustion chamber. This results in a rapid explosion or combustion causing shock waves and high surface temperatures. This may lead to excessive loading of piston crown, breaking piston rings weakening of the material due to erosion by hot gas flow, etc. the higher temperatures inside the combustion space also cause an increased NOx emissions. The ignition quality is a measure of the relative ease by which the fuel will ignite. It is measured by the cetane number for distillate fuels. The higher the number, the more easily will the fuel ignite inside the engine. For residual fuel, the ignition quality is measured by the Calculated Carbon Aromaticity Index (CCAI). It is an empirical equation based on the density and viscosity of the fuel. CCAI is normally in the range of 800-870. The higher the CCAI, the longer fuel takes before it starts ignition in the engine. In other words, ignition delay for a fuel with low CCAI is minimal. Changing to a fuel with a higher ignition quality or lower CCAI index means early ignition of fuel, higher peak pressures, excessive load on the bearings (especially cross head bearings) and loss of engine power. Similarly, using a fuel with higher CCAI index or lower ignition quality will cause late ignition, causing after burning which damage exhaust valve, fouling of turbocharger, burning of piston crown and liner, and loss of engine power. Two stroke slow speed engines and some medium speed engine on ships uses variable injection timing (VIT) or fuel quality setting (FQS) levers to control the starting of injection to take account of the ignition delay. These procedures to be done as per maker’s instructions and calculating the CCAI index of the fuel to be used.

Answer 56

The main wheel would contain two journal bearings for shaft support, as well as a thrust bearing to absorb the propeller thrust. The input shaft would only require simple journal bearing supports. The gearings and bearings would be lubricated by a self contained lube oil system, with the gears being supplied by sprayers.

Answer 57

To minimise gear wear, the gear wheels are made from forged steel with post machining hardening. The gear tooth profile is produced using a horizontal machining process known as “Hobbing”. The profile of the tooth is formed on the hobbing tool, and this tool is rotated and passed over the forged gear wheel to form the tooth shape. As marine gearing generally have a helix angle for multiple gear tooth meshing in service, the gear wheel must be slowly rotated during the hobbing process. Once the gear profile is machined, then the gear wheel is hardened using induction hardening process. Gearing inspections should be carried out with minimal disturbance to the gear system or alignment. Hence the condition of the gear teeth will be used to establish that the gearing system is operating in a satisfactory condition. The following items would be inspected: Remove inspection covers to examine wear on gear teeth. Marks along length of tooth could be due to abrasive particles within the oil, so the oil sample report would be checked. Marks or pitting at the pitch line would indicate either overload or inferior properties of the lube oil, such as low viscosity. The previous operating records of the gearbox and the oil test results would be checked. Marks at one edge of the gear tooth could indicate gearing mis-alignment. The clearance at the journal bearings would be recorded, or dismantled if clearance measurements are difficult. The thrust bearing would be removed for inspection on the running face, and the pivot on the back of the bearing. Any defects could require a bearing replacement. The oil filters would be removed to look for particles, and to check the magnetic plug fitted at the filter core. The oil sprayers would be examined to security, and function testing using the auxiliary oil pump

Answer 58

Properties required of a crankcase oil which is to be used for a trunk piston main engine are the following: Detergency This keeps the crankcase, bearings and piston rings area clean from sludge and carbonaceous deposits. As the trunk piston engine suffers from a higher level of contamination into the lube oil system than a slow speed engine, then higher levels of detergency are important. Dispersency The dirt which is removed by the cleaning function is kept in suspension by the dispersency additives. These prevent the build up of sludge in the cooler regions of the engine. Alkalinity The level of this property is determined by the level of sulphur within the fuel oil. The additive reduces the corrosive effects which result when the products of combustion condense on the cooler surfaces. Anti wear This additive is provided to reduce the wear on the highly loaded areas of the engine, such as the camshaft and gearing areas. Anti-emulsion This property allows the oil to be cleaned in a purifier and allow any water contamination to be removed. Stable Viscosity This is ensured by the use of viscosity stabilisers or improvers which reduce the rate of fall in oil viscosity when the oil temperature increases. Clean burning As the oil is used to lubricate the piston ring pack, the oil should burn without leaving a residue.

Answer 59

Exhaust valve is prone to Vanadium induced metal loss at the base of the valve Cold corrosion of the valve stem due to sulphurous effects Impact damage at the valve sealing face causing eventual valve burn out Hot corrosion induced metal loss at the sealing face causing valve burn out Stellite is used as the seating material of exhaust valves to resist the corrosion effects of vanadium and sodium. At high temperatures these elements form highly corrosive compounds that attack the metal oxide layer, causing metal loss and eventual valve sealing loss. This can lead to reduced compression pressure, and eventually total loss of engine power on that cylinder. Stellite will reduce these corrosive effects by 50% over conventional steel valves.

Answer 60

The corrosive areas must be identified if any during exhaust valve overhaul since these could indicate a possible cause of failure. To investigate the corrosion, change in operational factors of the engine such as speed and load, operational parameters such as turbocharger speeds, boost air pressure, or cylinder exhaust gas temperatures to be analysed. Fuel oil samples should be forwarded to the Fuel Testing Lab asking for a full analysis, especially the fuel vanadium and sodium levels. Others possible factors such as incorrect valve clearances and valve carbon build up to be checked while periodic overhauling. If the level of contaminants in the fuel is higher, overhaul period of the valves to be maintained at the low level. The corrosive effects on the exhaust valve are accelerated at higher operating temperatures. To reduce corrosion and hence the possibility of valve burn out, contact temperatures must be controlled. This is achieved by localised cooling of the valve seat (using cooling passages within the seat on the larger valves, and cooling of the cylinder head on the smaller valves). The valve is cooled by the seat when valve is closed.

Answer 61

Thermal stress is caused when the free expansion of the surface metal is prevented by the relative cool metal of the main structure. This is caused when the piston surface is exposed to the hot temperatures of combustion and the outer skin of the piston expands. However this expansion is prevented by the main piston body, which leads to compressive thermal stress in the piston skin, and tensile thermal stress in the piston body. Persistent burning of the piston crown is due to localised excess temperatures in that region. This could be due to either excessive external skin temperatures due to fuel impingement (fuel injector defect or incorrect fuel viscosity), or excessive internal skin temperatures due to fouling/scaling of the coolant surfaces.

Answer 62

The operational stresses present within the crankshaft is influenced by the bending stresses present. If the crankshaft alignment is completely straight then the bending stresses are minimal, but should uneven main bearing wear down occur, then these bending stresses will greatly increase. When the main bearings wear down, the alignment of the crankshaft to the propeller shaft will change. This wear down will increase the bending stress on the propeller shaft, and the external moment at the engine / shaft interface, increasing the crankshaft stresses. When the crankshaft is subjected to these high stresses, the small defects present within the shaft could develop and propagate into cracks that could lead to shaft failure.

Answer 63

Frictional grip is the usual method of crankshaft construction for built-up crankshaft. This grip is subjected to the full torque of the engine output, and hence subjected to high torsional stresses. If there are any defects at this joint, then the resulting stress concentration would trigger a crack and possible shaft failure. To minimise the possibility of such defects, then only a frictional grip is permitted under Classification Rules for crankshaft construction, hence pins, keys, etc are not allowed.

Answer 64

Defect growth from a small surface defect into a crack that propagates through the shaft material require high levels of stress. Such levels of stress are possible when the stress is concentrated at section changes. The oil hole will inherently increase the local stress levels, and thus to minimise these increases, the oil hole will have a significant radius at the surface. The size of this radius will significantly influence the local stress levels, and should be closely monitored during crankshaft construction, and possible crankpin surface repairs by grinding.

Answer 65

Torsional vibrations are inherent within diesel engines, due to the varying torque produced by the piston and crank arrangement from each cylinder. This torque variation is further compounded by the arrangement of the firing order of the crankshaft. The effects of such vibrations is to increase the shear stress and hence total stress levels carried by the crankshaft in service, when other stresses such as bending and combustion loads are present.

Answer 66

The critical speed of a shaft occurs when the shaft rotational speed is at or close to resonant conditions. In this condition the torsional vibration of the shaft increases greatly, and will impose very high shear stress on the crankshaft. These levels of stress could even cause crankshaft failure.

Answer 67

Fatigue cracking occurs when the primary cause of crack propagation is due to the fluctuating nature of the stress applied to the component. The following factors could produce fatigue cracking: High combustion pressures, increasing the bending stress applied to each crankshaft throw Excessive crankshaft bending due to a main bearing failure, which increases the crankshaft bending stresses.

Answer 68

The fitting of either a detuner or vibration damper will reduce the vibration levels of the crankshaft when operating in areas of high torsional vibration, such as close or within a critical speed range. The detuner will change the stiffness of the shaft and hence the natural frequency, thus separating the excitation frequency from the component’s natural frequency, whereas the damper will absorb the vibration within the shaft, reducing the effects of the torsional vibration.

Answer 69

Fatigue failure is identified as starting at a stress raiser or defect, then the crack generates through the material before causing sudden failure. The crack progress is shown as smooth, rippled formation known as striations or beach marks, whilst the sudden failure is a classic brittle fracture with rough appearance.

Answer 70

The initiation site will be where the local stress is high enough to increase the minute cracks which occur on the metal surface. The stress can be increased locally by a surface defect, or even an extreme stress concentration caused by high applied stress. The main causes of fatigue cracks are: Stress raisers These can be reduced by ensuring a smooth surface finish to all area where high stress is applied especially in the web/pin radii area Oil holes These should be minimised whenever possible, and the oil hole opening have wide and smooth radii Tensile stresses Fatigue strength is reduced when tensile stress are present, so the radii areas are often cold rolled to ensure that the fatigue strength in these areas are increased. Stress applied on hardened materials Fatigue cracks can grow faster when the material is harder, as the dislocations in the metal concentrate the stress on a smaller area of the material structure, hence any hardening of the crank pins must not be applied to the highly stressed radii areas.

Answer 71

The atmosphere inside a crankcase is stable and will not allow combustion or an explosion to occur as there is no ignition or fuel source. Hence the first event is the production of an explosive mixture. This will occur when the lube oil in the crankcase is heated by a “hot spot” and lube oil coming into contact with this will be evaporated. The evaporated oil then rises within the crankcase, and then condenses in a cooler part of the crankcase. The resultant white mist is within the explosive range, and is thus flammable. The second event is the ignition of this white mist by either the same or another hot spot within the crankcase. When the oil mist is ignited, a crankcase explosion will occur, which will raise the pressure within the crankcase.

Answer 72

One of the common areas of overheating is the various bearings within the crankcase. Hence bearing temperature monitors could be used to indicate that a bearing is overheating and could be oil mist generation site.

Answer 73

If the engine fails to reverse the following points would be investigated, and remedial action taken. Air start distributor not reversing. The engine controls would be moved ahead and astern whilst observing the movement of the air start distributor. If the distributor is not moving, then the air servo cylinder would be checked to ensure that it is free to move, and that air is being admitted and vented as required to achieve the movement required. Air start valve not opening. It is possible that the air distributor does reverse as expected, but that the required air start valve would not open to rotate the engine in the new direction. This would be investigated by turning the engine in the ahead direction so that it stops in a new position. The engine would again be tested in the astern direction to test if a starting air valve has failed to open. Any valve found faulty would be removed, freed and refitted.

Answer 74

If the engine fails to fire on fuel the following points would be investigated, and remedial action taken. Check for any shut-downs still active. The shut down panel would be examined, and if a trip is active the cause would be investigated and system made operational. Following this the trip reset button would be pressed. Low fuel pressure at the engine manifold. The fuel system would be investigated, and all valves checked to be opened, and all booster and supply pumps checked for running. Sticking fuel linkage. The action of the fuel linkage would be checked during the start sequence. The fuel linkage should admit a “starting level” of fuel after the engine start sequence has been completed. The physical movement of the fuel linkage would be checked, and any mechanical friction reduced by lubrication.

Answer 75

If the engine fails to start on air the following points would be investigated, and remedial action taken. No air pressure at engine manifold. The valves from the air receiver would be checked, and opened if found shut. Low air pressure at engine manifold. This could indicate that the air compressors are either not working or excess air is being used. All air compressors would be started, and air usage restricted to engine manoeuvring only. Turning gear engaged. The turning gear position and the interlock switch would be visually checked. The gear would be removed if found engaged.

Answer 76

For large propulsion engines the Bridge Control is achieved by using the telegraph to select the desired speed and direction. When the bridge telegraph is placed in Stop, the fuel is prevented from injecting as the fuel pump puncture valves are energised. When the bridge telegraph is moved to an ahead command, the air start and fuel cams are placed in the required direction, and the start command is given. This will admit starting air to the engine. Once the engine is turning above the starting speed, the air is closed and fuel is admitted. The quantity of fuel admitted will depend on the position of the telegraph handle, i.e. slow ahead, full ahead, etc. When the bridge telegraph is moved to an astern direction, the air start and fuel cams are reversed. Once the air start is reversed, the engine will start as detailed for the ahead start.

Answer 77

The cylinder oil will require: Ample viscosity to separate the surfaces under high loading conditions Sufficient alkaline reserve to neutralise the acids formed by combustion of residual fuel oil High levels of detergent to maintain piston ring cleanliness and free ring movement A level of anti wear properties to minimise micro seizure The ability to burn without residue

Answer 78

Cloverleafing will be caused when the supply of lube oil is not uniform around the radial bore of the liner. The normal effect is for the oil to reduce in alkalinity away from the injection point, thus if the oil becomes acidic then high corrosive wear rates will result. This will cause uneven bore wear rates, with heavy wear in the areas furthest away from the oil injection points. Microseizure is caused when the liner and piston ring material is pressed together causing localised welding of the material in the absence of sufficient lube oil. The causes are insufficient oil and/or excessive cylinder pressures causes heavy ring/liner contact forces. The appearance is heavy scratching/tearing in the vertical direction, together with a localised hardening of the ring and liner material.

Answer 79

The effective lubrication of the cylinder liner and piston assembly requires a constant lubricant feed over the whole liner surface, and that piston movement will generate the oil pressures required to separate the surfaces. However in the real situation the following problems occur: The oil is injected at defined points which can lead to an oversupply at the feed points, and an under supply away from these points The residual fuel normally used contains acids and abrasives that will reduce the lubrication properties of the oil The normal operation of the piston will cause the piston movement to stop at top dead centre, causing any oil pressure developed between the ring and liner to collapse The high temperatures present at top dead centre reduce the effectiveness of the lubricant The feed rate of the lubricant is regulated usually by the speed of the engine, which will cause a mismatch between actual lube oil requirements over a wide range of engine operation, with usually too little an amount of oil injected at low loads and during engine load changes.

Answer 80

As the explosion is an uncontrolled event, then great care must be taken to ensure the safety of the engineers within the engine room. MAN B&W recommend that: 1.Move away from the crankcase doors immediately 2.Reduce speed to slow, and ask the bridge to stop 3.When the engine has stopped, close the fuel supply 4.Stop the auxiliary blowers 5.Open the skylight and/or stores hatch 6.Leave the engine room 7.Lock engine room entry doors and keep away from them 8.Prepare the fire fighting equipment. 9.Do not open the crankcase for at least 20 minutes after stopping the engine, and ensure that the oil mist detector alarm (or bearing temperature monitor) has reset 10.Stop the LO circulating pump. Shut the starting air, and engage the turning gear. 11.Locate the “hot spot” (source of the oil overheating) 12.Make a permanent repair to the fault

Answer 81

The rapid pressure rise within the crankcase can cause the engine structure to be blown apart, causing physical damage, and the resultant flame travelling across the engine room space causing personnel injury. This pressure rise is limited by the statutory use of relief doors fitted to the crankcase. These doors will open when the pressure rises above 0.02 – 0.1 bar, and prevent the over-pressure of the engine structure. The doors also perform the added function of preventing fresh air ingress into the crankcase where hot burning gases are present, by the quick closing action of the relief door.

Answer 82

1.The power developed by the engine would be measured using power cards. This should conform to that expected at the normal service speed, referring to the power/speed relationship that has been shown over voyages when the service speed was normal. 2.The fuel consumption of the engine would be measured over an extended period of four, eight and twelve hours. This would be converted to specific fuel consumption in g/kWh identify if the engine is efficiently converting the fuel input. 3.A number of fuel injectors would be removed to ensure they are correctly operating by testing them. 4.For a slow speed engine, a scavenge inspection would be carried out to ensure the piston rings are still functioning as expected, and that the scavenge ports are clear and free from carbon residue. 5.The range of engine operating parameters would be measured, and compared to normal operating conditions. This would attempt to identify any system problems, such as air cooler fouling, turbocharger revolution change, etc. 6.The fuel presently being burnt would be analysed to identify if there are any high contaminants levels that could affect engine performance. 7.The slip of the vessel through the water would be calculated from engine revolutions, and actual vessel speed from the GPS system. This could indicate if the propeller is fouled as this problem would cause high propeller slip. The following remedies would be carried out should a defect be identified: 1.If the fuel injectors were found to be defective, then all injectors would be removed and tested. Injector nozzles would be changed, and all internal components inspected by wear, and changed if suspect. 2.Any broken and severely worn piston rings would be changed. The liners would be calibrated during the piston overhaul, and changed if worn 0.5% of the nominal bore. 3.Any coolers that exhibit higher than normal differential pressures would be cleaned. 4.If the turbochargers were operating at a different speed that indicated by the power developed, then these would be dismantled and cleaned, with special attention on the nozzle ring and diffuser condition. 5.If the propeller slip exceeds 10% then the propeller would be inspected and cleaned at the first opportunity.

Answer 83

Reasons for Cylinder Cover Cracking Cylinder covers are exposed to high levels of working stress resulting from the thermal and pressure stresses of combustion, which are imposed on the stress resulting from initial head tensioning. These stresses could be increased by: 1.Excess cylinder combustion pressures. This would increase the mechanical or pressure stress on the head. 2.Excess cylinder thermal stress produced by excess cylinder temperatures, incorrect cylinder cooling or insufficient cooling water treatment. These would lead to larger temperature differences across the cylinder head material leading to larger thermal stresses. 3.Incorrect i.e. over-tensioning of the cylinder cover on assembly. The increase in initial tension would increase the total stress on the cylinder cover, possibly enough to produce cracks in the highly stressed areas of the cylinder cover. How to Prevent Possibility of Cylinder Cover Cracking The possibility of cracking would be reduced if all of the above causes were eliminated by correct operation and maintenance of the engine. 1.The cylinder combustion pressure would be monitored by indicator cards or peak pressure readings. Engine load could also be measured on-line by exhaust temperatures and turbocharger revolutions, and relating these to the engine model curves or test bed readings. The engine room staff would be told to monitor these readings and ensure the maximum levels given were not exceeded. 2.The temperature of the cylinder cooling would be closely monitored to ensure that the temperatures were not excessive (leading to overheating of the liner), or too cold (leading to higher temperature gradients across the liner wall, and hence higher thermal stress). Temperature monitoring would be via control room gauges, and alarm settings. 3.Initial tensioning of the cylinder head should be carried out to the recommended hydraulic tension or torque settings. Thus the gauges that are used to determine these levels must be calibrated regularly. 4.The reserve of cooling water nitrates must be maintained to reduce scaling or fouling of the cylinder cover heat transfer surfaces, and to maintain the fatigue life of the covers.

Answer 84

Torsional vibrations in this installation may be caused by: 1.Power imbalance of the engine producing a greater variance of torsion produced by the crankshaft 2.Operation of the engine at different speeds than normal, which may be closer to the engine critical speeds than normal 3.Rotary imbalance of the main engine due to loss of a balance weight 4.Damage in the gearing being transmitted to the shafting 5.Propeller damage causing rotary imbalance

Answer 85

Effects of Torsional Vibrations The increase in torsional vibrations would produce an increase in torsional stress. This stress would be imposed on the existing stress levels resulting from torque transmission (torsional shear stress), axial stress resulting from the propeller thrust, and the bending stresses resulting of the shaft alignment. Hence this increase in stress levels could result in the generation and growth of cracks in the high stress areas of the transmission shaft and propeller. If left in this condition, the cracks could lead to failure of the transmission and hence loss of propulsive power. The torsional vibrations would also increase wear on the contact faces of the gear teeth, as the contact forces would be varying affecting the lubrication of the gearing. Torsional vibrations will also distort the crankshaft and shafting, which could result in an increase in bearing loads. How to Reduce Effects of Torsional Vibrations The effects of torsional vibrations can be reduced by the following: 1.Detuning of the engine. This is carried out by modifying the stiffness of the shaft when the output shaft starts to vibrate. When the shaft starts to torsionally vibrate the springs in the detuner will be compressed, which increases the stiffness of the coupling. 2.Dampening. Once the shaft starts to vibrate the energy of vibration is reduced by the free mass moving within the fluid inside the dampener. 3.Isolation. The engine can be partly isolated from the gearbox by the use of flexible couplings, whose natural dampening properties will reduce the transmitted level of torsional vibration. 4.Operation of the propeller at a different pitch setting, and the propeller pitch change will change the torsional stiffness of the transmission shaft unit.

Answer 86

How to Find Which is Correct Reading Comparisons would be made between the control room display and the local display. The simplest way of providing an accurate reading would be to exchange the local thermometer for a new unit. This new and correct reading would be used as the datum to check the control room display. Reasons for Difference in Local and Remote Reading The local thermometer could be defective due to: 1.Vibrations 2.Physical damage to the mercury in glass unit 3.The control room display could be defective due to cable damage 4.Physical damage to the probe 5.Incorrect power supply to the display unit. 6.Defective display gauge Preventive Maintenance All remote engine instrumentation should be calibrated, usually within a six month period. The measuring probe would be removed and placed in a test unit that would either change the temperature or pressure depending on the probe classification. For temperature probes, the test unit temperature would be varied in stages over the expected range of the unit and the display readings examined for errors. The display unit should have zero and span adjustments, and if required these would be adjusted to ensure that accurate readings are displayed. Following the calibration and adjustment, the process would be recorded in the appropriate records. Physical damage to the probe or thermometer would be inspected for by visual observation. Vibration of the mercury in glass units could be identified by the mercury column being detached internally. Cable damage would be inspected for by measuring the resistance of the cable to test for continuity and then an insulation test to check for insulation breakdown. Power supply would be checked using a multi-meter. To check for a defective gauge, exchange the gauge for a new spare and test by calibration test.

Answer 87

Precautions Before Cutting off Cylinder Unit If immediate repair is not possible, the engine can be operated with one or more cylinders or turbochargers out of operation, but with reduced speed owing to the following: As, in such cases, the air supply is no longer optimal, the thermal load will be higher. Therefore, depending upon the actual circumstances, the engine will have to be operated according to the restrictions mentioned in operating manual of the engine. Pressure pulsations may occur in the scavenge and exhaust receivers, which can give a reduced air supply to any one of the cylinders, and as a result cause the respective exhaust temperatures to increase. The fuel pump index for these cylinders must therefore be reduced to keep the exhaust temperatures (after valves) within prescribed limits. Since the turbochargers will be working outside their normal range, surging may occur. This can generally be remedied by “blowing off” from the scavenge air receiver. If more than one cylinder must be cut out of operation, and the engine has two or more turbochargers, it may be advantageous to cut out one of the turbochargers. When cylinders are out of operation, governor hunting may occur. When this happens, the fuel pump index must be limited by operating the electric governor on “index control”. With one or more cylinders out of operation, torsional vibrations, as well as other mechanical vibrations, may occur at certain engine speeds. Should unusual noise or extreme vibrations occur at the chosen speed, the speed must be further reduced. If the engine is to be run for a prolonged period with cylinders out of operation, the engine builder should always be contacted in order to obtain advice concerning possible recommended barred speed ranges. Procedure for Cutting off Cylinder Unit The following sequence would be carried out for ships which use the MAN B&W slow speed engine: 1.Stop engine, isolate systems and allow to cool 2.Ensure a procedure is written that minimises the risk to personnel during the operation. 3.Discuss the task and written procedure with the engine room personnel to ensure they are familiar with the risks, and the methods to be used to minimise these risks. 4.Ensure the fuel pump is de-activated by lifting roller and locking. 5.Lift exhaust valve actuators so exhaust valve remains closed during running. (Note: the air spring supply to be left open) 6.Dismantle air start supply line, and blank with suitable steel plates, the main and control air pipes 7.Dismantle bottom end bearing, and turn engine to suspend piston, crosshead and connecting rod from supplied crosshead supports. 8.Secure big end of connecting rod in crankcase. 9.Blank off main lube oil inlet to crosshead within the crankcase with a blanking plate. 10.Isolate the cylinder lubricator for that cylinder by placing all lubricators on no stroke. Difficulties During Manoeuvring When one engine cylinder is isolated, then one problem that may occur is a “dead spot” during manoeuvring. This is due to the air start valve being isolated for that unit, and is more likely when a smaller number of cylinders are present. The Master must be informed that this could occur, and the remedy would be to kick the engine in the opposite direction, and then restart in the required direction.

Answer 88

1.Excess load on the transverse girder from high combustion loads due to excessive power output from that cylinder or misalignment of the bedplate. 2.Incorrect tension of the tie bolts for a slow speed engine 3.Manufacturing defect Limiting Crack Growth Due to the position of the crack in a highly stressed area of the engine structure, investigation into the extent of the damage caused by the crack on diesel engine bedplate would be required and prevention measures implemented to limit crack growth. Checks would be made of the crankshaft deflections and tie rod tension to ensure that these are correct/acceptable. To investigate the crack, the area around it would be exposed, which could include light grinding to remove the protective paint covering. The best non destructive test (NDT) method on-board would be used to find the extent of the crack, and methods such as dye penetrant or magnetic particle investigation (MPI) could be used. Once the extent of the crack is established, then advise would be sought from the engine makers to ensure that the engine is safe to operate. To reduce the loads present in the bedplate, the engine power for those cylinders would be removed by lifting the two fuel pumps. This would be a prudent course of action until the extent of the crack had been fully identified. Class would be informed, especially if repairs are to be performed, to ensure that any proposed method of repair would be acceptable to them. Preventing Crack Formation Future incidents of crack on diesel engine bedplate would be minimised by preventing the causes stated before. Regular checks would be made on the cylinder powers developed by taking indicator cards, and on the crankshaft alignment by taking deflections. Tie bolt tension would be checked every 12 months. Also crankcase inspections would ensure that visual inspections beneath the bedplate are carried out at every inspection.

Answer 89

Complete inspection of cylinder liner and piston assembly will require all components to be removed from the engine and fully dismantled. The initial inspection should be carried out before the components are cleaned to monitor fouling rates, areas of concern such as very dirty liner wall. Once the components have been cleaned, gauging and measurements can be carried out before the final inspection is done. Specific areas of inspection are: Liner wall Coolant side of liner Lubricator quills Piston crown Coolant side of piston Piston ring area Piston rod Piston internals Possible Faults and Causes Excess wear on liner due to insufficient lube oil, abrasives in the fuel, liner too cool Cracks on liner wall due to fuel impingement (fuel injector fault or fuel oil too cold) Deposits on liner coolant side due to insufficient water treatment or oil in water Lubricator quills condition such as poor or nil operation due to supply system defect Burning and cracking of piston crown due to fuel impingement or insufficient coolant Deposits on piston coolant side due to fresh water treatment insufficient or LO additive depletion Wear of piston rings and grooves due to insufficient lube oil, abrasives in the fuel, poor combustion (causes excessive carbon build-up) Scoring of piston rod due to heavy dirt in scavenge space, excess spring tension Cracking of the piston mating surfaces caused by incorrect tensioning procedures Preventive Measures Ensure adequate LO supply, clean fuel using separator at low through-puts, operate FW coolant at 80 degrees Regular inspection and testing of fuel injector, correct setting of FO viscosity control to 12cSt Weekly checks of FW condition for nitrate reserve and low level of chlorides Regular check of flow rate from cylinder LO unit, plus daily consumption Check piston coolant flow alarms Use LO analysis to ensure LO condition maintained correctly Regular checks of combustion efficiency by maintained fuel injection equipment Regular cleaning of scavenge space. and monitor condition of stuffing box drain Check the internals of the piston and correctly tension piston studs and apply fastening devices

Answer 90

Governor is a device which controls the speed of engine automatically in the prescribed limits. The governor does its job in two steps. By measuring the speed and By controlling the a amount of fuel supply to the engine.

Answer 91

To adjust the rate of fuel supply in such a way as to keep the engine running at a steady speed regardless of the load. To control the engine running at a steady speed under all conditions of load.

Answer 92

When considering the engine and governor combination, the difference between the no load speed and full load speed is called governor droop. Small droop results in rapid swing. Large drop results in slower response to change in speed.

Answer 93

1.Mechanical governor. 2.Hydraulic governor. 3.Inertia governor [fitted on older slow speed engine] 4.Electronic governor.

Answer 94

The use of temporary speed droop to prevent over correction of the fuel supply is called compensation. It require two actions: 1.Droop application – as the fuel supply is changed 2.Droop removal – as the engine response to the fuel change and returns to original speed .

Answer 95

G/E governor is a droop speed governor with over speed trip. M/E governor is a constant speed governor with over speed trip.

Answer 96

It is fitted to control the sudden load change and sudden increase in speed. e.g. severe load change when loss of propeller in heavy sea . Thus, to prevent engine parts damage, over speed trip is provided. Set the speed 15% more than MCR. It is attached at camshaft through gearing. If engine speed rise more than 10 to 15% above the rated speed, It shut of fuel & stops the engine. The mechanism has to be manually reset before engine start again.

Answer 97

It is a fluctuation of engine speed due to the over correction of the fuel supply. (too much increase or decrease fuel supply)

Answer 98

It is unavoidable time lag between the movement of the governor act and the movement of engine response.

Answer 99

It is a constant speed governor. It is able to maintain exactly constant speed without hunting. This type of governor that has proportional and reset is called isochronous governor.

Answer 100

It is fitted to get load sharing ability since isochronous governor gives constant speed, thus cannot share the load. AVR is fitted at alternator.

Answer 101

Governor only control the engine speed in prescribed limits. When accidental sudden load change from full load to no load happens, engine speed become too high above 15% of rated speed. Due to time delay of governor control, engine parts may become damage. Thus to prevent this effect over speed trip must be provided to shut down the engine by cutting fuel. Note: It need to reset before restart the engine.

Answer 102

Operation of Hydraulic Jacks In principle, a screw can be tightened when nut is screwed in during tensioning of stud by hydraulic force and then release the hydraulic force. This hydraulic tightening method provides easier working and more reliable result than manual tightening in general. Therefore, most of the important or big screws are tightened hydraulically on ships such as cylinder head nuts, exhaust valve nuts, for crank pin bearing, cross head bearing, main bearing, tie bolts, etc. A hydraulic tightened screw always consists of a set of stud and nut which are designed properly for a hydraulic tool set. The nut has pin holes for turning through the hole of support for jack. The hydraulic tool set consists of a hydraulic pump, hoses and a distributing piece, which are for common use regardless of screw size. Most of the hydraulic screws are tightened in pair, which need distributing piece for same tightening pressure. There are two kinds of distributing piece with different number of ports. Screws on cylinder head need four ports and the others which need two ports use the corresponding distributing piece. Each screw needs own set of hydraulic jack and support for the corresponding screw size. Depending on the working condition, extension screw should be added for the jack.

Answer 103

Hydraulic Jack Tightening Procedure 1.Check pre-tightening of the stud and tighten by wrench, if loosened. 2.Clean studs, nuts and around seats. 3.Screw the nut manually until the nut contacting the seat closely. 4.Check condition of the hydraulic tool set and make them ready to use. 5.Mount support (extension screw) and screw the jack by hand. 6.Connect hoses from the pump to the jacks via the distributing piece. 7.Close the release valve of the hydraulic pump. 8.Open air venting plug of the jack and check air venting by pumping. 9.Close the venting plug and pressurize up to the specified pressure for tightening the nut. 10.Turn the nut to be screwed firmly by a pin manually through the hole of the support. 11.Release the hydraulic pressure by opening the release valve of the hydraulic pump. 12.Repeat pressurizing and check the nut loosened. 13.Retighten the nut, if loosened. 14.If the stud or nut has been replaced by new ones, repeat the tightening three times for the first tightening. This repeat is necessary for the settlement of the threads. 15.Release the hydraulic pressure and dismount the tool set.

Answer 104

Hydraulic Jack Loosening Procedure 1.Clean seat and threads. 2.Check condition of the hydraulic tool set and make them ready to use. 3.Mount support (extension screw) and jack. 4.Connect hoses from the pump to the jacks via the distributing piece. 5.Turn the piston of jack until contacting the nut and then unscrew the piston by about half turn. This is important to provide space for loosening the nut. 6.Close the release valve of the hydraulic pump. 7.Open air venting plug of the jack and check air venting by pumping. 8.Close the venting plug and pressurize up to the specified pressure for loosening the nut. 9.Unscrew the nut by half turn manually by means of a pin through the hole of the support. 10.Be sure to check that loosened nut moves freely without contacting the piston of the jack. Otherwise, jack and the nut may be stuck each other after releasing hydraulic pressure. If stuck, increase hydraulic pressure slightly and turn the nut about 1/4 turn clockwise for loosening from the piston of the jack. 11.Release the hydraulic pressure and dismount the tool set.

Answer 105

1.Crack 2.Fatigue failure of white metal 3.Squeezing of white metal, so oil grooves are partially blocked. 4.Wiping 5.Faulty casting and faulty machining. 6.Tin oxide Corrosion 7.Acid Corrosion 8.Thermal Ratcheting 9.Electrical Potential 10.Fretting 11.Cavitation Erosion

Answer 106

Happens in dynamic loaded bearings / pivoted pad bearing i.e. thrust pads of thrust bearing. Fretting occurs on the back of support surface where the interference fit / nip is insufficient for dynamic forces involved. Caused by the housing, which is insufficiently rigid for the load cycle involved.

Answer 107

Bearings carrying high dynamic loads are liable to fatigue damage Caused by a concentration of load due to mechanical imperfection i.e. poor geometric form, misalignment and distortion. White metal bearings are particularly prone to fatigue since any high loading not only increases the stress in the lining, but the associated temperature rise reduces the strength. Causes of fatigue cracking is due to poor bonding of white metal to its steel shell.

Answer 108

Tin oxide is extremely hard & brittle and corrosion takes place at tin phase of white metal This breaks off rapidly, causing wear of the surfaces & breakdown of oil film Appearance – Grey at initial stage, becomes darker as its thickness increases & particle become detached. With high loads when the oxide layer becomes thick, the bearing temperature may rise sufficiently to melt the underlying metal & failure occurs by wiping. Cause – Water mixes with LO promoting electro-chemical reaction. Prevention – Regular & continuous removal of water from lubricating oil prevent tin oxide formation.

Answer 109

Takes place in high temperature condition Bearing alloy is attacked by acid (condensation of SO2) from high sulphur content fuel. Steel working parts corrode more than bearing alloy Solution – Add rust & corrosion inhibitor in lubricating oil and select proper material.

Answer 110

Caused by alternate cooling & heating of bearing Results in bearing deformation Indication is high bearing temperature Occurs mainly in thrust pad bearing surface

Answer 111

This type of damage occurs frequently in electrical machinery due to stray currents. The damage consists of uniformly distributed pitting, the pits being generally hemispherical with the intensity increasing to a maximum in the zone of thinnest oil film. Caused by incorrect earthlings system which cause spark erosion damage. Prevention – Insulate the non-drying end bearing (pedestal bearing) of electrical machines and sometimes in both bearings.

Answer 112

Severe damage to complete bearing area. Cavities are usually around at low pressure areas i.e. oil groove or oil holes. Caused by an implosion of gas or air bubbles released from a lubricating oil film under particular conditions The pressure set up locally during theses implosions are very high , possibly 220 bar & may cause a pitting / cavitation Prevention – May be reduced by viscous oil because of damping effect high viscous oil & viscosity must be in limit.

Answer 113

Combustion in diesel engines takes place in three distinct phases. First Phase of Combustion Ignition delay period is the time span between commencement of fuel injection and the start of fuel ignition. The fuel emerges into the cylinder as small liquid particles, which are surrounded by hot compressed air. They receive heat from the air and more volatile constituents of the fuel vaporize. During the ignition delay period a large part of the fuel charge is prepared for combustion. During the ignition delay, the injector continued to inject the fuel and, if this has built up a sufficient quantity, the rapid combustion and pressure rise will be quite violent, causing detonation and shock loading creating a noise termed diesel knock. After ignition commences flame propagation proceeds very quickly in the fuel vapour or air mixture, accompanied by rapid temperature and pressure rise. Towards the end of the rapid pressure rise a point is reached where the rate of pressure rise falls away quickly, and the curve flattens out towards the maximum pressure point. The point where the rate of pressure rise changes near and approaching the maximum pressure point is the end of the second phase of combustion. This shows only a small pressure rise, as the rate is decreased due to downward movement of the piston. The end of injection occurs approximately at or slightly beyond the maximum pressure point. Combustion in diesel engines can be termed as a ‘controlled explosion’. Second Phase of Combustion Rapid or uncontrolled combustion usually occur just after the ignition of the fuel vapours. Third Phase of Combustion Controlled combustion is regulated by the rate at which fuel continues to be delivered. After Burning After burning occurs when the third phase of combustion extends over a long period. It may be caused by incorrect fuel grade, bad atomization, poor or excess penetration, incorrect fuel temperature, incorrect injection timing, insufficient air supply, or any combination of these. Slow burning, high viscosity, high density, high carbon content fuels may also cause after burning of a serious nature leading to engine damage. Effect of After Burning After burning creates high exhaust temperatures and may cause overheating of the engine in severe cases. Some drop in the maximum firing pressure usually accompanies this. There is a loss of thermal efficiency when after burning occurs, due to greater loss of heat to exhaust gases and the transfer of large amount of heat to the cooling water. There is a risk of damage to exhaust valves and scavenge fires.

Answer 114

Bearing Defects 1.Abrasive damage: Fine scratches caused by particles in the lub oil. Very common on HFO burning engines. 2.Erosion damage : Removal of the overlay in strips caused when the oil supply pressure is low orrapid journal movements occur. More usual on medium speed engines. 3.Fatigue damage: The overlay becomes detached from the lining when the bearing load becomes too high. The bearing surface loads cracked paving. 4.Corrosion: Discoloration and roughening of the bearing surface indicates that the oil has become acidic. 5.Wiping: This is overlay removal by melting wiping can be re-alignment of the bearing to journal, but if too much metal has been removed then clearances may be affected.

Answer 115

Journal Defects 1.Cracks: These will appear at the high stress points of the fillet radii and oil holes. These cracks may be removed by light grinding, but engine de-rating would be required if deep / numerous cracks are found. 2.Scoring: Similar problem to the abrasive damage. 3.Overheating: As the bearing is weaker than the shaft, the bearing should fail first. However if the engine is run on a failed bearing then shaft overheating will occur. This ‘bluing’ of the shaft increases the hardness of shaft and hence the shaft is less able to resist crack growth. Classification states a maximum hardness for crankshaft journal.

Answer 116

Factors Affecting Bearing Clearance Desired operating temperature – extremely critical Engine speed Oil flow Oil film thickness Working viscosity of lubricant Load carrying capacity Operating temperature Engine ambient temperature.

Answer 117

1.Low LO pressure 2.Reduce load carrying capacity 3.Pounding will case and bearing will damage. 4.High impact load on crankshaft.

Answer 118

Support crankshaft and keep it aligned. To remove heat produced by friction

Answer 119

Cross head Engines: Transmit load from cross head pin to connecting rod Allows relative movement of con rod & cross head pin Trunk Piston Engines: Transmit load from gudgeon pin to connecting rod Allows relative movement of con rod & gudgeon pin

Answer 120

Transmit load from con rod to crankshaft Allows relative movement of con rod & journal

Answer 121

1.Operating temperature of bearing 2.Working temperature of bearing 3.Minimum oil film thickness 4.Rate of oil flow 5.Rate of heat production 6.Power loss of bearing.

Answer 122

1.Fatigue & compressive strength to carry load depends upon thickness of the bearing. 2.0.3 mm white metal can withstand 141 bar pressure and 0.08 mm white metal can withstand 211 bar pressure. 3.Thin lining has poor conformability and too soft material tends to flatten under heavy loads 4.Too hard material withstands high loads, posses high frictional characteristics & may be brittle with poor fatigue characteristics. 5.Softness & modulus of elasticity of bearing alloy should be as low as possible but hard enough to withstand heaviest continuous loading or chock loading without plastic deformation. 6.Soft metal flows locally without damaging the harder steel called conformability. 7.Soft metal allows abrasive particles to embed to prevent damage to journal. 8.Corrosion resistance is required to withstand corrosive attack from lube oil. 9.Compatibility between bearing & journal under boundary condition 10.Anti-weld & anti-score property between shaft & journal during start up & stop and by using turning gear. 11.Antifriction & wear properties –depends upon type of oxide film that material forms on reaction without lube additives.

Answer 123

White Metal White Metal = Tin (Sn) + Antimony (Sb) + Copper (Cu) Thin walled bearings, stiff cross head assembly (88% Sn + 8% Sb + 4% Cu) Thick walled bearing, flexible crosshead & Bottom end bearing ( 87% Sn + 9% Sb + 4% Cu) Tin forms soft matrix to accommodate misalignment Antimony forms hard cubes to withstand load of journal. Tends to float and segregate during casting Copper holds antimony in evenly dispersed pattern, solidifies first. Copper Lead & Lead Bronze Copper Lead & Lead Bronze = Brass (Cu + Zn) & Bronze (Cu + Sn) Can withstand 3 times higher load than white metal Copper / Bronze matrix supplies the strength Lead remains in free state, provides bearing properties and steel strips provides backing Overlay of 0.024 -0.04 mm thickness of lead –tin, lead –tin –copper. Running in prevents acid attack against lead but poor embeddability & conformability Aluminium Tin Aluminium Tin = Al Matrix + Si (minor) + Overlay7 (Pb+Sn) + Steel Backing Soft Aluminum forms the matrix and provides embedability & conformability Tin held in suspension provides bearing properties Lead Tin Overlay of 0.02 mm for initial running in 3 times load carrying capacity than white metal but requires hardened journal Resistant to acid attack and fatigue strength same as Cu & Pb

Answer 124

For thin shell bearing, wall thickness to diameter ratio varies 0.05 mm for 40 mm shaft diameter and 0.02 mm for 400 mm shaft diameter. Have interference fit or bearing crush Interference fit resists relative movement, prevents fretting. For correct axial location of shell but not intended to resist motion Recessed below bearing joint face. Free spread – Bearing shell in snapped into bearing housing Bearing can be held in place when inverted during assembling.

Answer 125

High load carrying capacity; approximately 5 time > conventional bearing Uniform wall thickness permits better metallurgical control of white metal casting process. High Bond Strength and ultrasonic method of bond testing between layers is accurate. Reduced thickness & absence of keying grooves results in higher fatigue strength Blistering on bearing surface due to Hydrogen emission form is less.

Answer 126

Oil Grooves to avoid at pressure areas as oil tend to escape high to low pressure zones Circumferential grooves to compensate with increase length of the shell Longitudinal groove is not extended to ends to avoid excessive side leakage.

Answer 127

Conventional bearing 1.It is made of forged steel and running face is lined with white metal. 2.Vertical clearance is adjusted by shims. 3.Not easy to replace and must be done remodeling. 4.Not easy to handle, transport and store. 5.Suitable oil grooves design is required. 6.Lower load carrying capacity. 7.More cost in manufacturing. Thin shell bearing 1.It is made of tri-metal, they are steel shell, copper or lead alloy and thin layer of soft metal surface. 2.Easy replacement in case of bearing worn out. ( Re-metalling method no longer required) 3.No need to adjust by shim ( can not be adjusted by shims.) 4.Easy handling, transport and storage as spare. 5.Higher bearing load carrying capacity. 6.More economy in manufacturing. 7.No need to take lead reading.

Answer 128

1.Defective tag 2.Insufficient nip clearance 3.Suddenly applied extreme load.( pounding) 4.Improper fitting 5.Incorrect size of bearing use 6.Due to over tightening bolts 7.Frictional force from the back of the shell and keep.

Answer 129

1.Thin shell bearings are used and bearing on either end of crosshead pin. 2.No shim used with thin shell bearing 3.Oil grooves or gutter used on bottom half to distribute oil. 4.Grooves do not extend to end and grooves are small because of loaded half. 5.Grooves to be limited otherwise reduce bearing surface. 6.Lubricating oil is directly supplied to crosshead bearing 7.Bearing material usually Sn-Al with Pb-Sn overlay.

Answer 130

Checking by open scavenging drain (little coming out O.K) at sea. In port: Check the liner is wet or not (thin layer wet O.K) Oil has to not collect at the scavenge space.

Answer 131

1.Promote wear of liner and rings 2.Overheating of local area resulting micro seizure due to lack of boundary lubrication. 3.Consequently major damage to piston and cylinder liner.

Answer 132

1.Fouling of ring grooves and resulting ring zone deposits. 2.Consequently, loss of gas sealing effect and blow by follows. 3.Fouling of scavenge space and scavenge fire follows. 4.Also affecting combustion process. 5.Leading to breakage of piston rings 6.Fouling of exhaust system and turbocharger. 7.Increased cylinder oil consumption.

Answer 133

1.It must reduce sliding friction between piston rings and cylinder liner to a minimum. 2.It must process adequate viscosity at high working temperature and still be sufficiently fluid to spread rapidly over the entire working surfaces to form a good adsorbed oil film. 3.It must form an effective seal in conjunction with the piston rings, preventing gas blow by, burning away of the oil film and lack of compression. 4.It must burn cleanly, leaving as little and as soft a deposit as possible. 5.It must effectively prevent the build up of deposits in the piston ring zones and exhaust ports. 6.It must effectively neutralize the corrosive effects on the mineral acids formed during combustion of the fuel.

Answer 134

1.Remove nut on lubricator quill (L.O connector) 2.Take out lubricator quill fitted directly to the cylinder without passing through the jacket cooling space. 3.Remove lubricator quill (L.O outlet side) 4.Take out spring and non return ball valve. 5.Clean all parts in diesel oil. 6.Check non return valve for occur. 7.Check spring tension. 8.Place the non return valve and spring into the lubricator quill then tighten out. 9.Fit the lubricator quill to the cylinder tighten the nut. 10.After fitting the lubricator quill, It is operated by hand at the same time check the cylinder liner wall for sufficient oil come out and effective cylinder liner lubrication is taking place.

Answer 135

1.Must be capable of delivering regularly every stroke a quantity of oil against moderate pressure 2.Must have a wide range of adjustment 3.The quantity of discharged oil per strike should be clearly visible 4.Can be operated by hand

Answer 136

Lubricator quills are arranged around the periphery of the cylinder liners and connect cylinder lubricators with oil feed points in the cylinder liners.

Answer 137

1.It requires very rapid injection of oil at correct time, with correct amount, and pressure 2.It is discharging through very small bore; with long pipes to various oil feed points 3.Having a non-return valve at the top of lubricator, hence it complicates the timed injection 4.The hot combustion gases tend to carbonize the oil, and block the orifices.

Answer 138

1.Lubricators of each cylinder are synchronized with engine to provide timed cylinder liner lubrication. 2.Cylinder oil is fed; at the time when top two piston rings pass the oil feed points, in the cylinder during piston upstroke [4/S and 2/S Uniflow engines]

Answer 139

Working Modes of Dual Fuel Engines There are basically 3 modes of operation for dual fuel marine engines used on-board ships. 1.When engine is well supplied with natural gas, amount of pilot fuel injected is corresponding to 6% of the total engine load. In other words major contributor to the engine load is natural gas. 2.When gas supply to the engine is constant and limited, then engine is said to be in “Specified Gas Mode”. Here gas supply is constant, but fuel oil quantity injected varies to meet changing engine load demand. 3.In “Fuel Oil Only” mode, gas supply will not be available, and engine runs only on fuel oil. This mode is used when engine is unstable, such as during restricted waters, heavy weather, manoeuvring, etc.

Answer 140

Features of Dual Fuel Engines Natural gas is compressed to about 250-300 bar using a number of compressors, working in series. Compressed gas is then cooled and led to valve blocks of each cylinder unit. Each valve block is fitted with an accumulator (it has a capacity to store about 20 times of the amount of gas injected to the unit at full load) for minimizing pressure drop during injection and to monitor pressure drop in case of any abnormality in the system (such as gas injection valve stuck open). The gas supply pipe lines are double walled. Compressed air is passed between the two walls (air seal), which is continuously monitored for any gas detection (gas is detected means leakage of gas). Outer wall of the gas pipe is made of stainless steel to withstand very low temperatures, in case of a leakage from inner pipe. Whenever the flow of compressed air between the gas supply pipe walls fail, the gas supply shut down and the line is purged with inert gas. For lubrication of parts and sealing of gas, gas injectors are supplied with sealing oil. (Sealing oil is pressurized to about 25-30 bar above gas injection pressure, and the sealing oil is injected and burnt along with the gas). Consumption of the sealing oil is very low, in the order of 0.13 g/kWh. The sealing oil system consist of two pumps for redundancy and a spring loaded accumulator to maintain the sealing oil pressure, since standby pump takes time to build up pressure when one pump fails. When a gas injection valve is stuck open (jammed), then gas pressure drops at the accumulator in the valve block, resulting in gas system shut down and pipe lines are purged with inert gas. If the pressure drop is not detected in the above case, then more gas burn, exhaust temperature rises. This results in gas supply shut down. In the case of late ignition while burning gas, there will be rapid pressure rise in the exhaust system. hence exhaust gas receiver is designed to withstand 15 bar pressure. Failure of pilot fuel oil system result in combustion failure of gas, then gas supply shut down and lines are purged with inert gas.

Answer 141

IACS (International Association of Classification Societies) Require Following Safeties in Dual Fuel Engines Use oil fuel only while starting the engine. Use oil fuel only during unstable engine conditions, such as manoeuvring, restricted waters, etc. Engine should continue to run on fuel oil even when gas supply stops. Crankcase relief valves to be fitted in way of each crank throw. Construction and operation of pressure relief valve of engine units should consider gas leak inside the engine and subsequent pressure rise. Exhaust gas system of the engine to be independent and not to be mixed with any other systems. Starting air line to each unit to be fitted with flame arresters. Flame arrester to be fitted at the inlet of the gas supply valve to the units. Apart from automatic shut down system, gas supply must be able to shut manually from engine starting platform or other control stations.

Answer 142

Maintenance of Chain Drive The chain drive is to be checked at the prescribed intervals given in the manual. At overhauls, the chain must be examined for signs of damage, such as cracks in the wheels or side bars, jamming links, pitted wheels, traces of blows on the outer parts on account of catching, or scoring on the insides of the side bars, due to poorly aligned sprocket wheels. The causes of these defects must be put right immediately. Damaged or broken chains must be replaced as soon as possible. During operation, the teeth of the sprocket wheels acquire a polished or slightly worn band above the root circle. A slight polish is often produced on the inner side bars, in-spite of correctly aligned wheels. If there are signs of marked wear, however, its cause is to be investigated and chain closely inspected. Burrs on the edges of the teeth point to vibration of the chain. Sprocket wheels cause teeth sustained major deformation should be replaced as soon as possible. The bearings and bearing pins, there fastenings and their true and even running are to be checked at overhauls. Special attention to be paid to the securing of the lubricating oil pipes and spray nozzles. The spray nozzles must be directed so that the oil jets correctly hit the side bars. During operation, the functioning of the spray nozzles must be periodically checked and the nozzles cleaned if necessary.

Answer 143

Chain drives are used by manufacturers, to give more flexibility in location of the camshaft, as well as ease of repair / replacement of parts at a lower cost. the chain tension needs to be checked at intervals given in the maintenance schedule, or earlier if any doubt exists. To carry out the checking, turn the engine to slacken the longest free length. At the middle of the longest free length, grasp the chain and try to pull it away from the guide bar, by a distance of approximately half a chain link. if it is possible to pull more, the chain is slack and needs to be re-tensioned. Loosen the screw of chain tightener, and by turning the ‘loose’ plate of the chain tightener, adjust the tension of the chain

Answer 144

Large two stroke marine diesel engine camshafts are driven either by gears or chains. In the case of gear drive, a train of gear wheels is fitted, which transmits the drive from the crankshaft to the camshaft. Appropriate speed and direction is achieved, by suitably arranging the intermediate gears in different positions and sizes. Unlike a chain, the gear does not lose tension; however, gears are subject to damage and difficult / expensive to replace. Large super long stroke engines have Moment Compensators fitted to the gears. the balance weights rotate at the full engine speed or twice the engine speed, in synchronization with the crankshaft to take care of the primary and secondary vibration.

Answer 145

The cylinder entablature, ‘A’ frames and the bed plate are bound firmly together, by long steel tie rods, passing through hollow columns. The tie rods are of ordinary milled steel, and screwed at each end to take the nuts. The lower nut is squared and fits into an opening of similar shape cast in the bed plate, so as to prevent the nut from turning, when the bolt is screwed into it, and the upper nut is tightened. For a 9 meter height engine, the cast iron parts of the engine would be compressed from 0.5 – 0.75 mm by tightening the tie bolts. The tie rods are pre-stressed at assembly, so that the engine structure is under compression at all times. Two tie rods are fitted to each transverse member, and passed through tubes. In large super long stroke low speed marine propulsion engines, the tie rods may be in two parts, two facilitate ease of the removal. To prevent any lateral movement which could cause vibration problems, ‘pinch’ bolts are fitted.

Answer 146

The Tie rods need to be checked for proper tension at intervals laid down in the maintenance schedule, and also after any scavenge fire. This is done hydraulically for modern engines. Large tie bolts are tightened with a hydraulic jack which loads the tie-bolt in tension. The tie bolt nut is usually drilled to take a toggle bar or, slotted to take a hook spanner, and when the correct pull is on the tie bolt, the tie nut is pulled up hand tight; the pressure in the jack is then released leaving the tie bolt tight. The load placed on the tie bolt by hydraulic jack is controlled by the hand pump pressure, which is indicated on the pump pressure gauge. Tie rod tensioning is done by the following procedure: 1.Connect two pre-tensioning jacks to two adjacent tie bolts. 2.Obtain the required hydraulic pressure and maintain this. 3.Check the clearance between the nut and the intermediate ring and adjust if required. 4.Release the pressure and remove jacks. By tensioning the Tie rods, a pre-determined tensile load is induced in the Tie rod, and a pre-determined compressive load is induced in the Entablature, ‘A’ Frame and Bedplate. During the firing stroke, the tensile load on the Tie rod increases. The compressive stresses on the entablature, ‘A’ frame and bedplate are reduced, thereby keeping the components at very low fatigue levels. In other words, if the Tie rods were not pre-tensioned properly, the fluctuation of the stresses in the components between the firing and non firing periods could be higher, leading to fatigue failure of components. To minimize bending, Tie rods are placed as close to the crankshaft axis as possible. This reduces the bending stress on girders and prevents unbalanced loads from being transmitted to the welds.

Answer 147

The classification societies requirement is that holding down bolts be checked by a surveyor, within each survey circle. this interval of time may be too long and the bolts should preferably be checked at six monthly intervals, unless there is a case history of the bolts going slack more frequently. Checking holding down bolts can be carried out on board the ship itself. In new vessels, the bolts should be checked within one month of the commencement of the maiden voyage, or earlier if possible. The interval may then be gradually increased if all is found in order. After a vessel has been through bad weather, the bolts should be checked as soon as possible. A rough method of checking holding bolts is the hammer test. Hold the tip of the thumb on one side of the nut face and strike the nut on the opposite side. If the nut is slack, the nut and stud spring against the thumb and then retract. the movement can be felt against the thumb. If a holding down bolt is of the fitted type, this test cannot be used, and a hydraulic jack must be used. Due to the presence of bilge water on the tank top at various times, the holding down bolt nuts may rust and seize on the studs. In this case, the seized condition makes it seam as if the nut is tight. The hammer testing method, however, can be used in finding slack nuts, even when they are seized on a stud.

Answer 148

The functions of piston rings are: 1.Provide a seal to the combustion chamber to prevent gases and combustion products passing the piston. 2.Control the lubricating oil. 3.Conduct heat away from the piston to the liner.

Answer 149

Types of Piston Rings 1.Compression ring – Provides a gas seal. 2.Scraper or Oil Control ring – Distributes oil on the cylinder liner preventing the oil passing upwards into the combustion chamber. These rings are normally found on trunk piston engines. The piston ring sits in a machined groove, located such that the ring operates at an acceptable temperature. If the rings where fitted too high, the high temperatures would rapidly burn off the oil and the rings would seize in their grooves.

Answer 150

Before starting the engine, the following checks and procedures must be followed: All components that have been overhauled should have been correctly reassembled and fitted and their function checked. All devices and tools which were used, have been removed from the engine and that no cleaning rags or other items have been left behind. Then follow this prcoedure; a) Check the fluid levels of all the tanks in the engine systems including the leakage drain tanks. b) Check that all the shut-offs for the engine cooling water and lubricating oil systems are in the correct position. c) Open the air supply to the shipboard system and from the starting air receivers to the control air supply. d) Prepare the fuel system e) Start up the pumps for cylinder cooling water, crankcase bearing and crosshead bearing lubricating oil and set the pressures to their normal values. Preheat the cooling water to 60°C. f) Check to ensure that all systems have been correctly vented and that there is a positive flow of cooling water and lubricating oil. g) Open the indicator cock on each cylinder cover. Using the turning gear, turn the engine through a minimum of one full revolution to check that all the running gear is in order. Check if any water, oil or fuel has collected on the piston crown. Operate the cylinder pre-lubrication system. Shut the indicator cocks. h) Check to ensure that all the crankcase doors are closed with all the latches tight. i) Check to ensure that cut-out devices for all the fuel injection pumps are correctly positioned for normal fuel pump operation and that the exhaust valve actuator pumps are also ready for operation, i.e. the cut-out devices are removed. j) Check that the fuel regulating linkage moves freely. At the auxiliary manoeuvring stand disengage the fuel control lever from the position REMOTE CONTROL and engage it into the regulating linkage lever. Loosen the fuel control lever lock, pull the hand-grip upwards and move the fuel control lever backwards and forwards between the range 0 and 10. After carrying out this check, put the fuel control lever back to the position REMOTE CONTROL and lock it by tightening the wing nuts of the hand wheel. k) Check the pressure in the starting air receivers and open the receiver drains until any condensate has been completely drained. l) Open the drain and test valve 2.06 on the shut-off valve for starting air until all water has been drained. m) Close venting valve 2.21 at the shut-off valve for starting air and open the main shut-off valves on the starting air receivers. n) Turn the hand wheel on the shut-off valve for starting air until the pointer is at the AUTOMATIC position. The pressure gauges on the pressure gauge panel should now indicate the following pressures: * Safety control air and standby supply for air spring air on the pressure reducing valve 23HA – 6.0kg/cm2 * Air spring air supply on the pressure reducing valve 19HA – 7.5kg/cm2 * Control air standby supply on the pressure reducing valve 19HB – 7.0kg/cm2 o) Set the switch at the control panel for the auxiliary blowers to AUTOMATIC. p) Bring the safety cut-out to operating position. q) Press the EMERGENCY STOP button on the control panel and observe if the safety cut-out on the fuel injection pumps reacts, i.e. their suction valves are lifted. After this check, press the EMERGENCY STOP RESET button. r) Check whether the pressure gauge on the supply unit for cylinder lubrication indicates 40kg/cm2. s) Take out the turning gear and secure the lever. t) Open the test valve 2.06 of the main automatic starting air shut-off valve 2.03 for a short time and listen for the valve opening which can be heard distinctly. Close the valve again. u) Check the hydraulic system of the exhaust valve drive for tightness. v) The levers on the local maneuvering stand must be put into the position from which the engine will be started, i.e., the bridge, the control room or the auxiliary local stand. The changeover buttons of the remote control must be activated. w) Check again to ensure that no personnel are near the flywheel. x) Inform the bridge.

Answer 151

The main engine exhaust valve is a vital component of a marine diesel engine that controls the timing and duration of the exhaust gas flow from the cylinder to the turbocharger. The exhaust valve consists of several parts, such as the spindle, the housing, the seat, the hydraulic cylinder, and the air cylinder. The air cylinder is a device that uses compressed air to close the exhaust valve against the hydraulic pressure that opens it. The air cylinder has a piston that moves up and down along with the spindle, creating an air spring effect that ensures a smooth and reliable operation of the exhaust valve.

Answer 152

Reduced Efficiency: Gas leakage results in a loss of engine efficiency, as the engine must work harder to compensate for the escaping exhaust gases. Environmental Impact: Incomplete combustion due to gas leakage can lead to increased emissions, contributing to air pollution and environmental degradation. Increased Fuel Consumption: Gas leakage forces the engine to burn more fuel to maintain power output, leading to higher operational costs.

Answer 153

To address the issue of gas leakage, various types of air seals are used, each with its own unique characteristics and applications. The air seal is a device that prevents air leakage from the air cylinder to the exhaust valve housing. It is made of a metallic outer ring and a rubber seal that contacts the spindle. The seal can have different shapes depending on the type of valve. The air seal is important for maintaining the proper air pressure and spring force in the air cylinder, as well as for protecting the spindle from corrosion and fouling by the exhaust gas. A faulty or worn-out air seal can cause air loss, reduced performance, increased fuel consumption, and higher emissions. It is essential to inspect and replace the air seal regularly as per the maker’s recommendations.

Answer 154

Floating Ring Seals: Floating ring seals consist of two concentric rings, with the outer ring rotating along with the valve. This design helps create a dynamic seal, minimizing gas leakage. Poppet Valve Seals: Poppet valves are commonly used in internal combustion engines. They employ a cylindrical plug to control gas flow. Air seals in poppet valves help ensure a tight fit between the valve and the valve seat, preventing gas leakage. Rotary Valve Seals: Rotary valves, found in some engines like rotary engines and two-stroke engines, use rotary seals to maintain a seal as the valve rotates. These seals play a crucial role in preventing gas leakage. Labyrinth Seals: Labyrinth seals consist of intricate channels and ridges that create a tortuous path for gas to escape. This design effectively reduces gas leakage by increasing the distance exhaust gases must travel before exiting.

Answer 155

Gas Tightness: The primary function of air seals is to maintain gas tightness within the combustion chamber. This ensures that exhaust gases exit through the designated path, optimizing engine efficiency. Reduced Emissions: By minimizing gas leakage, air seals contribute to lower emissions. This is especially critical in modern engines to meet stringent environmental regulations. Improved Fuel Efficiency: A well-sealed exhaust valve reduces the engine’s workload, leading to improved fuel efficiency and reduced operational costs. Enhanced Engine Longevity: Air seals help protect the engine from excessive wear and tear, prolonging its operational life.

Answer 156

Regular Inspections: Marine engineers should conduct regular inspections to identify and address potential issues that may lead to hydrolock. This includes inspecting intake systems, seals, and valves. Maintenance: They are responsible for the routine maintenance of the engine, ensuring that air filters are changed, seals are in good condition, and the engine is functioning optimally. Emergency Response: In the event of flooding or water intrusion, marine engineers must act swiftly to prevent or mitigate hydrolock. This may involve sealing off the affected area, pumping out water, and assessing and repairing any damage. They use their knowledge and skills to troubleshoot and resolve any issues related to hydrostatic locking or other engine malfunctions. Training: Owners must ensure that the vessel’s engineering crew is trained to follow proper shutdown procedures and respond effectively in emergency situations. Marine engineers also educate and train other crew members on how to operate and maintain marine engines properly. They provide guidance and instructions on how to prevent hydrostatic locking and what to do in case it happens. They also follow emergency procedures and protocols to minimize damage and ensure safety in case of hydrostatic locking or other engine failures.

Answer 157

Regular Maintenance: The most crucial step in preventing engine hydrolock is regular maintenance. This includes: Checking and changing air filters, inspecting seals and valves for leaks, and ensuring that the engine is in optimal working condition. Check and maintain the exhaust system regularly. Install anti-siphon devices or water traps to prevent water from flowing back into the engine. Check and maintain the air intake system regularly. Make sure that the air filter is clean and dry and that there are no obstructions or leaks in the ducts or hoses. Avoid operating the engine in areas with high humidity or spray. Check and maintain the fuel system regularly. Make sure that the fuel tank is vented properly and that there are no leaks or contamination in the lines or injectors. Use fuel additives to prevent water from accumulating in the fuel. Check and maintain the cooling system regularly. Make sure that the coolant level is adequate and that there are no leaks or corrosion in the radiator, hoses, or pump. Use antifreeze to prevent freezing and boiling of the coolant. Proper Ventilation: Adequate ventilation in the engine room can help reduce condensation and the risk of hydrolock. Proper ventilation systems can also help keep the engine room dry. Water-Tight Integrity: Ensuring that the vessel is properly sealed and that water cannot enter the engine room in the event of flooding is essential. Make sure that the exhaust outlet is above the waterline and that there are no leaks or cracks in the pipes or valves. Regular inspections for potential breaches are crucial. Avoid operating the engine in extreme weather conditions or rough seas. Reduce speed and load when encountering waves or wakes. Monitor the engine temperature and pressure gauges and listen for any unusual sounds or vibrations. Proper Shutdown Procedures: When shutting down the engine, it’s important to follow the manufacturer’s recommended procedures. This may include turning off the fuel supply before stopping the engine, preventing the intake of water during the cooling down process.

Answer 158

The most common cause of hydro locking in marine engines is water ingress through the exhaust system. This can happen if the exhaust outlet is submerged due to waves, trim, or loading conditions. Water can also enter the engine through the air intake, fuel system, or cooling system due to leaks, flooding, or condensation. Depending on how much water is in the cylinders and how fast the engine is running, hydro locking can have different effects on the engine. If the engine is stopped or idling, hydro locking may cause the engine to stall or refuse to start. If the engine is running at high speed, hydro locking may cause a loud noise and a sudden stop of the engine. The sudden expansion of gases can also cause gaskets to blow or cylinders to crack. The most common damage caused by hydro locking is bent or broken connecting rods, which connect the pistons to the crankshaft. Apart from water, when the engine is off, and there’s an intake leak, other fluids (oil, fuel) can easily enter the cylinders.

Answer 159

Engine hydrostatic locking, also known as hydrolock, occurs when a liquid, usually water, enters the combustion chamber or cylinders of an engine, preventing the engine from turning over. This unwanted intrusion of liquid disrupts the engine’s internal workings, and in the case of a marine engine, it can spell disaster for the entire vessel. For example, hydrolock happens when a volume of liquid greater than the volume of the cylinder at its minimum (end of the piston’s stroke) enters the cylinder. Since liquids are incompressible, the piston cannot complete its travel; either the engine must stop rotating or a mechanical failure must occur.

Answer 160

The Sulzer RT-flex engine is essentially a standard Sulzer RTA slow-speed two-stroke marine diesel engine except that, instead of the usual camshaft and its gear drive, fuel injection pumps, exhaust valve actuator pumps, reversing servomotors, and all related mechanical control gear, the engine is equipped with a common-rail system for fuel injection and exhaust valve actuation and full electronic (computer) control of engine functions. Two control oil pumps are provided near the engine local control stand, and one of these must always be operational to ensure that the common rail fuel and exhaust valve operation systems can function. The control pump starts automatically once one of the crosshead lubricating oil pumps is started. The engine is monitored and controlled by a WECS (Wartsila Engine Control System) unit. This is a modular electronic system with separate microprocessor control units for each cylinder. Overall control and supervision is by means of separate, duplicate microprocessor control units. The cylinder microprocessor control units are mounted on the front of the engine at the common rail in the hot-box, which is located below the top engine platform. The engine is a single-acting, two-stroke, reversible, diesel engine of crosshead design with exhaust gas turbocharging and uniflow scavenging. Tie rods bind the bedplate, columns and cylinder jacket together. Crankcase and cylinder jackets are separated from each other by a partition, which incorporates the sealing gland boxes for the piston rods. The cylinders and cylinder heads are fresh water cooled. The exhaust gases flow from the cylinders through the hydraulically operated exhaust valves into a manifold and then on to the exhaust gas turbochargers which work on the constant pressure charging principle. The charge air delivered by each turbocharger flows through an air cooler and water separator into the common air receiver. Air enters the cylinders through the scavenge ports, via valve groups, when the pistons are nearly at their bottom dead centre (BDC) positions. At low loads two electrically-driven auxiliary blowers supply additional air to the scavenging air space. The pistons are cooled by bearing lubricating oil supplied to the crossheads by means of articulated lever pipes. The thrust bearing and turning gear are situated at the engine driving end. The fuel and servo oil pumps for the common rail fuel system and exhaust valve actuation are driven by gearwheels from the crankshaft. The engine is started by compressed air, which is controlled by the electronic starting air system. In case of failure of the engine remote control system (from the bridge or the engine room telegraph) the engine can be controlled from a local (emergency) control stand located on the port side of the engine on the middle platform. There is an ECR back-up control system which is linked with the local (emergency) control system. The engine lubrication system, with the exception of turbocharger and cylinder lubrication, is supplied by one of two main pumps, which take suction from the main engine lubricating oil sump tank and supply the main bearings. The engine main bearings and thrust block are supplied with lubricating oil by the duty main lubricating oil circulation pump. There are two pumps fitted and these are located at the aft end of the engine with one working and the other switched to automatic standby. The oil is cooled before supply to the engine. Oil from the main bearing system is also supplied, via articulated lever pipes, to cool the working piston crowns. The main bearing and crosshead oil systems are interconnected as the crosshead pumps take their suction from the main bearing LO supply line to the engine. Two crosshead LO pumps, one working and one on standby, take their suction from the main LO supply to the engine, after the automatic backflush filter and supplies oil at increased pressure to the crosshead bearings and to the servo oil pumps. The bottom end bearings are also supplied with LO from the associated crosshead with the oil flowing down a bore in the connecting rod. The lubrication of crossheads and connecting rod bottom end bearings is made through articulated lever pipes. The turbochargers are supplied with lubricating oil from the turbocharger LO system. There are, usually two or three turbocharger LO pumps (depending of the engine size and design), one/two operating and one on automatic standby. These pumps supply oil to the turbocharger bearings from the turbocharger LO sump tank via a cooler. The pumps have suction filters and there is also an automatic backflushing filter unit with a back-up bypass filter. The fuel oil is supplied to a common rail by the fuel supply pumps which are driven from the crankshaft by a gear system. The fuel pumps are arranged in a V form with four pumps in each bank. The pumps deliver pressurised fuel oil to a collector which then supplies the common fuel rail which is maintained at a pressure of about 1,000 bar at full load (the actual pressure varies with engine load). Recently, for safety and operational reasons the pressure has been reduced to 600 bars. All parts of the high pressure fuel system are sheathed to prevent high pressure fuel leakage from entering the engine room spaces. The fuel supply pumps are driven by a camshaft via three-lobed cams. The lobed cams and the speed of the camshaft means that each pump makes several strokes during a crankshaft revolution. There are six or eight fuel supply pumps (depending on the engine size) and the output of the pumps is such that seven pumps have the capacity to meet the full load requirements of the engine. With only six pumps operational, the engine load must be reduced below maximum. The common fuel rail is divided into two equal sections, one serving the forward six cylinders and the other serving the six aft cylinders. The common rail volume is such that the fuel pressure is constant throughout the operation of the engine. There are three fuel injectors fitted in each cylinder cover and high pressure fuel oil is supplied to these from the common rail. Each cylinder has its own injection control unit which controls the fuel supply to the injectors from the common fuel rail. Each injection control unit has three rail valves and three injection control valves, one of each for each injector. The rail valve is an electrically operated spool valve which can be moved to each end of its casing by electrical signals from the WECS. The spool valve acts as an open or closed valve and when in the open position it directs control oil to the injection control valve. The injection control valve opens and allows high pressure fuel from the common rail to pass to the fuel injector so beginning fuel injection at that injector. When the WECS signals the spool valve to close, the injection control valve is closed and hence fuel injection stops. Control oil is supplied by the servo and control oil manifold at a pressure of 200 bar. The rail valves are bi-stable solenoid valves with a fast actuation time; the valve is not energised for more than 4ms at any time. The WECS controls the fuel injection system via the Flex Control Module (FCM-20) which not only regulates the start and end of injection but also monitors the quantity of fuel injected. The fuel quantity sensor measures the actual amount of fuel injected and this information is relayed to the control system. The control system then calculates any change in fuel timing required from the engine operating conditions and the actual fuel quantity injected. The functioning of the fuel injection system is monitored at each cycle and changes are made for the next cycle if necessary. Operation of the rail valves is under the control of the WECS, which can adjust the timing and quantity of fuel injection to suit operating conditions. Normally all three cylinder fuel injectors, which are of the hydraulically actuated type, operate together but as they are independently controlled it is possible for them to be programmed to operate separately. In the event of one of the fuel injectors or its actuation system failing, the engine may continue to operate with the remaining two injectors. At low engine speeds one or two of the fuel injectors can be cut out for each cylinder to minimise exhaust smoke. The remaining operational fuel injector(s) operate at longer injection periods with the high fuel pressure maintained by the common rail. With injector(s) cut out the operating injector(s) are changed over every 20 minutes to prevent overheating of the cut out injector(s) and to ensure that all of the injectors have equal running. The fuel quantity delivered to the engine by the fuel preparation unit is considerably greater than is actually required by the engine with the excess flowing back to the mixing unit of the main fuel preparation unit. The mixing unit is located at the FO circulating pump suction and also takes a FO feed from the low pressure FO supply pump which draws HFO from the duty HFO service tank. From the circulating pumps the HFO flows through the steam heaters and then to the supply manifold for the high pressure common rail supply pumps. A pressure regulating valve, set at 10kg/cm² is fitted between the engine FO inlet and outlet lines and this allows the correct fuel oil supply pressure to be maintained at the engine inlet. The main engine is designed to operate on HFO during manoeuvring. All pipes are provided with trace heating and are insulated. For reasons of safety, all high-pressure pipes are encased by a metallic hose. Any leakage is contained and led to an alarmed fuel oil leakage tank. The engine may be operated on MDO if necessary. The starting air system of the RT-flex engine is similar to that of a standard RTA engine except for the control of the cylinder starting air valves which is incorporated in the WECS rather than a starting air distributor. Starting air is supplied to the engine starting air manifold from the starting air receivers via the starting air shut-off valve. The individual cylinders are then supplied with starting air via branch pipes which have flame arresters fitted. The cylinder starting valve is operated by pilot air and the pilot air valve is controlled electrically by the cylinder control module. The starting pilot air valve is opened and closed directly by the Flex control module (FCM-20) once every revolution at defined crank angles during the starting period. When the engine has started the starting system is shut down. Each cylinder has a single exhaust valve centrally located in the cylinder cover which is hydraulically opened, but closed by air pressure acting on the piston located below the hydraulic actuating cylinder. When hydraulic pressure is applied to the actuating piston to open the exhaust valve, the air trapped below the air piston is compressed. When the hydraulic opening pressure is removed the air pressure acts on the piston to close the exhaust valve and this is known as the ‘air spring’. The space above the air piston is vented and make-up air is supplied to the space below the piston from the control air system via a non-return valve to replace any leakage that may have occurred. The exhaust valve is fitted with a series of vanes on the stem known as a spinner. When the exhaust valve is opened, exhaust gas escaping from the cylinder acts on the spinner and causes the valve to rotate. Rotation of the valve evens out the temperature of the valve, and as the valve is still rotating when it reseats it creates a light grinding effect which removes deposits from the valve seat and valve face. The FCM-20 controls the exhaust valve opening and closing. Hydraulic pressure for opening the valve comes from the servo oil common rail. This is pressurised to 200 bar by the servo oil pumps which are driven by the same gear drive system as the fuel common rail pumps. The FCM-20 controls an exhaust rail valve which then activates the exhaust hydraulic control slide valve and this directs hydraulic oil to and from the exhaust valve actuator unit. The servo oil acts on the lower face of the free-moving exhaust valve actuator piston and as the piston moves upwards, when servo oil pressure is applied, it exerts an hydraulic force on the exhaust valve piston and opens the exhaust valve. The hydraulic system connecting the upper face of the exhaust valve actuator piston with the exhaust valve piston (the hydraulic pushrod) is filled with engine bearing oil and a connection with the bearing circulation system ensures that the space is always fully charged. This arrangement provides a complete separation of servo hydraulic system and valve actuation/bearing lubricating oil systems, and enables the exhaust valves to be serviced without disturbing the servo oil system. The RT-flex engine control is shared between the WECS internal engine control and the external propulsion control systems which comprise the remote control system, the safety system, the electronic governor and the alarm monitoring system. The WECS is the core engine control. It processes all actuation, regulation and control systems directly linked to the engine: Common rail monitoring and pressure regulation Fuel injection, exhaust valve and starting air valve control and monitoring Interfacing with the external systems via the CAN-open or MOD-bus Engine performance tuning, IMO setting and monitoring The WECS modules are mounted directly on the engine and communicate via an internal CAN-bus. Operator access to the WECS-9520 is integrated in the user interface of the propulsion control system. The manual control panels and the flex View system allow for additional communication with the WECS. The flex View software allows the operator to communicate with the WECS and enables the operator to see operating parameters as required. Each engine cylinder has its own module for all cylinder related functions; all common functions are shared between the cylinder modules.

Answer 161

Safety Protocols: The utmost priority when cutting out a main engine unit is ensuring the safety of the vessel, crew, and engineers involved. Marine engineers must follow established safety protocols, wear appropriate personal protective equipment (PPE), and coordinate with the ship’s personnel to minimize risks during the procedure. Communication and Coordination: Effective communication between the marine engineer, engine room crew, and bridge team is crucial. The bridge team must be aware of any changes in engine configuration to adjust vessel operations accordingly and maintain situational awareness. Monitoring and Alarms: While cutting out combustion, continuous monitoring of engine parameters, alarms, and performance indicators is essential. Any unusual readings or abnormalities should be promptly reported and addressed to prevent further complications. Documentation: It is vital to maintain comprehensive documentation throughout the process, including detailed reports of the engine condition, actions taken, and any observations made during the combustion cut-out. This information assists in analyzing the cause of the malfunction and aids in future maintenance planning.

Answer 162

Technical Malfunctions: In the event of a malfunction or breakdown in one of the main engine units, cutting out the combustion allows the crew to isolate the faulty unit and prevent further damage. This ensures the vessel can continue its operations with the remaining functional engines. The technical malfunctions can be, for instance but not reduced to: blow-by at piston rings or exhaust valve bearing failures which necessitate reduction of bearing load faults in the injection system. Maintenance and Repairs: Routine maintenance and repair activities may require cutting out the combustion on a main engine unit. This allows the marine engineer to safely conduct necessary maintenance procedures, such as inspections, replacements, or repairs, without endangering the crew or vessel. Fuel Economy and Efficiency: During periods of reduced power demand, such as when sailing at lower speeds or in calm waters, cutting out the combustion on one or more engine units can optimize fuel consumption and increase overall efficiency. This strategy helps minimize operating costs and extend the lifespan of the engines.

Answer 163

Initial Assessment: The marine engineer must conduct a thorough assessment of the engine to identify the specific unit requiring combustion cut-out. This includes analyzing performance data, monitoring alarm systems, and conducting visual inspections. Preparing the Engine: Prior to cutting out combustion, the engineer needs to ensure the vessel is at a safe operating condition. This involves reducing the load on the affected unit and synchronizing the remaining engines, if required, for optimal performance. Shutting Down Injection: Once the engine is prepared, the marine engineer can proceed with cutting out the injection on the designated unit. This is typically achieved by isolating the fuel supply, closing relevant valves, and activating the engine control system to cease fuel injection. In case of camshaft type engine the injection can be cut out by lifting and securing the fuel pump roller guide. The entire procedure for cutting out the injection on one of the units is fully described in the engine manual. Should the engine be kept running with the injection cut out for an extended period, the lubricating oil feed rate for the respective cylinder must be reduced to the minimum. If the piston and exhaust valve gear are still operational, do not shut down the piston cooling oil and cylinder cooling water on that particular unit. In case of electronic controlled engines, cutting out the injection is more simpler as everything is done from the Engine Control Panel Unit. You must be aware that with an injection pump cut out the engine can no longer be run at its full power.

Answer 164

The procedure is as follow: Cut out the fuel pump by lifting and securing the roller guide. Put the exhaust valve out of action and lock it in open position. Shut-off the air supply to the exhaust valve, and stop the lube oil pumps. Dismantle and block the actuator oil pipe. Restart the lube oil pumps. Close the cooling water inlet and outlet valves for the cylinder. If necessary, drain the cooling water spaces completely. Dismantle the starting air pipe, and blank off the main pipe and the control air pipe for the pertaining cylinder. When operating in this manner, the speed should not exceed 55% of MCR speed. Note: The joints in the crosshead and crankpin bearings have a strength that, for a short time, will accept the loads at full speed without compression in the cylinder. However, to avoid unnecessary wear and pitting at the joint faces, it is recommended that, when running a unit continuously with the compression cut-out, the engine speed is reduced to 55% of MCR speed, which is normally sufficient to manoeuvre the vessel. During manoeuvres, if found necessary, the engine speed can be raised to 80% of MCR speed for a short period, for example 15 minutes. Under these circumstances, in order to ensure that the engine speed is kept within a safe upper limit, the overspeed level of the engine must be lowered to 83 % of MCR speed.

Answer 165

Cut out the fuel pump by lifting and securing the roller guide. Put the exhaust valve out of action so that the valve remains closed (lift the guide or stop the oil supply and remove the hydraulic pipe).  the cylinder cooling water and piston cooling oil must not be cut out.

Answer 166

Cut out the fuel pump by lifting and fixing the roller guide. Put the exhaust valve out of action so that the valve remains closed. Dismantle the starting air pipe. Blank off the main pipe and the control air pipe for the pertaining cylinder. Suspend the piston, piston rod and crosshead, and take the connecting rod out of the crankcase. Blank off the oil inlet to the crosshead. Set the cylinder lubricator for the pertaining cylinder, to ‘ ‘zero’’ delivery. The blanking-off of the starting air supply is particularly important, as otherwise the supply of starting air will blow down the suspended engine components.

Answer 167

fuel pressure too low – this can be due defective fuel injection pump or pump fuel starvation (fuel inlet line blockage, leaking inlet pipe, cone connection over-tightening etc). leaking suction/exhaust valve on four stroke engines or exhaust valve on two stroke engines – It is very important to check and compare the compression pressure Pcomp between cylinders in order to eliminate eliminate this cause and make further assumptions (the Pcomp must be nearly the same with small variations between cylinders). On the four stroke engines if there is a leaking suction valve, you can check it by comparing the inlet air temperature among units (the hotter the inlet the highest probability of a leaking valve). If there is an exhaust valve leaking (for both four and second stroke engines), this can be seen through very high exhaust temperature and low Pcomp and Pmax as the combustion takes place into the exhaust. faulty fuel valve/s – as specified at the beginning this is the most common fault. In this case, the fuel injector valve need to be removed, checked, pressure tested and replaced as found necessary. wrong fuel injection timing – timing need to be checked and re-adjusted as found necessary in accordance with the engine shop trial adjustments. On the four stroke engines, usually there is a shim inserted between plunger and roller tappet of a certain thickness who’s initial dimension can be found into the engine technical file. Several times it happens that the shim found to be of a totally wrong dimension due unavailability or engineer’s in charge lack of knowledge who tries to compensate the wrong timing through fuel pump’s rack adjustment. fuel pump rack adjustment – as I mentioned above this is the most common mistake found on the engines when engineers are trying to compensate the Pmax differences between cylinders without further investigations. This is done due either lack of knowledge or laziness. defective fuel pump suction valve – need to be opened and inspected. Usually the spring found to be broken, thus stopping or restricting the valve stroke. very poor fuel with bad ignition quality – this usually affects all cylinders. piston rings blow-by – as mentioned at the beginning this can be observed if you check the Pcomp and compare it with all other units. Another sign will be high scavenge (under piston) temperature on two stroke engines or an increased sump tank pressure on the four stroke engines. leaking fuel injection pump safety valve – Usually the opening pressure of fuel pump safety valve is 1100 bar and if opening at 300 bar, thus leading to fuel starvation and low Pmax. leaking fuel injection pump spill valve – because of this pump is not able to deliver the fuel at the required pressure for proper fuel valve functioning and spray pattern. wrong valve clearance rail valves malfunction on common rail electronic controlled engines.

Answer 168

The turbocharger uses the exhaust gas from the engine to compress new air and charge the engine with a positive pressure higher than ambient conditions. Exhaust gas temperature convection and compression raises the temperature of the air and this cannot be delivered directly into the engine due to operational limitations exceeding. As a result, the engine is equipped with a cooler that returns the air temperature to ambient relatively close levels. Because hot air has a lower density, the mass of air charged into the engine is smaller than when the air is cold. Thus, the charge air cooler increases the density and lowers the temperature of the charge air. The compressed charged air exiting the charge air cooler will have a temperature of around 40 to 50 degrees Celsius, down from approximately 150 degrees Celsius. At cold temperatures, the lower temperature of the air increases the density of the charge air. Increased charge air density increases scavenging efficiency and allows for more air to be compressed inside the engine cylinder, allowing for more fuel to be burnt inside the combustion chamber, resulting in increased power. Additionally, the engine is kept at a safe operating temperature. Compression temperature reduction alleviates stress on the piston, piston rings, cylinder liner, and cylinder head. Additionally, the charge air cooler lowers the exhaust gas temperature. It has been demonstrated that a one-degree Celsius decrease in scavenging air temperature results in a five- to ten-degree Celsius decrease in exhaust temperature. This does not mean that cryogenic temperatures may be used to charge the air. If very cold air reaches the cylinder liner, a severe thermal stress occurs, resulting in cylinder liner failure. Charge air coolers are installed between the turbocharger compressor outlet and the engine intake or scavenging manifold.

Answer 169

When the air cooler become fouled, the heat transfer between air and cooling agent, which is normally fresh water, is decreasing and this is indicated by the raise in air temperature after cooler and a raise in the pressure drop across the cooler (U-tube manometer). Fouling of the air passages in air cooler, which is part of the engine turbocharging system, is usually due to oil film and oily-water films collected on the sides of the tubes and tube fins. Lint and similar material adheres to these films of oil or emulsion. The presence of oil may be caused by faulty air filters which allow the air to pass by the side of the filter element. Sometimes the oil is drawn from bearing at the blower end. The presence of moisture is usually the result of high humidity, when the engine is operating in warm air temperatures in conjunction with low sea water temperature.

Answer 170

higher pressure drop across the cooler, higher air temperature after the cooler, higher cooling water outlet temperature, higher underpiston scavenging air temperature, higher exhaust temperature on all cylinders and in worst case scenario turbocharger surging.

Answer 171

higher air temperature after the cooler, higher cooling water outlet temperature, higher underpiston scavenging air temperature and higher exhaust temperature on all cylinders.

Answer 172

fouling can be prevented through proper plan maintenance by cleaning the coolers at regular intervals. The air side of the cooler can be water washed and/or chemically cleaned. On most of the 2 stroke main engines there is a possibility of periodically cleaning the air coolers even during engine operation at low load. On some of the vessel there is designated tank available where a mixture of water and Air Cooler Cleaner chemical are mixed and recirculated through the air cooler for a certain period of time. It is very important to rinse with fresh water the air cooler very well after cleaning and blow with air if possible in order to prevent chemical corrosion of the cooler parts. For the water side a soft brush can be used to clean inside tubes and in case of hard deposits a long drill bit can be used, but with caution in order not to damage the tubes. However, if there is no improvement after cleaning then the cooler needs to be removed from the engine and dipped into a chemical bath for several hours. Usually this procedure, especially for main engines are performed during every vessel special survey (dry docking), when the coolers are dismantled and taken into yard facilities for proper cleaning into chemical ultrasonic bath.

Answer 173

When the engine is running, the air in the crankcase has the same types and amounts of gases as the air around it. However, there is a heavy shower of coarse oil droplets that are thrown all over the crankcase when the engine is running. If there is too much friction between the surfaces that slide against each other or if heat is transferred to the crankcase in some other way (like from a scavenge air fire through the piston rod/stuffing box or through the intermediate bottom), “hot spots” can form on the heated surfaces, which makes the oil droplets that land on them evaporate. When the vapour condenses again, it forms many tiny droplets that float in the air. This creates a “milky-white oil mist” that can feed and spread a flame if it gets started. The same “hot spot” that caused the oil mist can also start the fire. Oil mists are formed at temperatures of approximately 350°C and ignition can start at a temperature <500°C. If there was a lot of oil mist before the spark, the burning can cause a huge increase in pressure in the crankcase (an explosion), which forces the relief valves to open for a short time. In rare cases, when the whole crankcase has probably been filled with oil mist, the resulting explosion blows off the crankcase doors and starts fires in the engine room. The chain case and the scavenge air box can also explode in the same way. So, it’s important to have a way to find out early on if oil mist is building up, hence the need of the oil mist detector device (OMD). The oil mist detector is a device which constantly checks the amount of oil mist in the main engine crankcase. It does this with a high-sensitivity light scatter optical sensing system. This makes sure that an alarm goes off before the amount of oil mist gets to the lower explosion limit. Each sensor on the engine sends an electrical signal to a control unit, which checks each sensor in turn to see what its oil mist density value is.. As part of the detector readings, the system also checks itself to see if there are any problems inside. On the ECR console is the control unit. These units scan the signals from the detector heads one at a time, and they do this every 1.2 seconds for all of the engine detector heads. The average density of the oil mist is worked out and saved. Then, each detector signal is put up against the average that has been saved. Then, a positive difference or deviation is compared to a set value. If the set value is higher, an alarm will go off. The stored average is also compared to a pre-set reference. If the reference value is exceeded, an average alarm is set off. The system has a priority for alarms, so that when an alarm goes off at any detector head, it is dealt with right away. all of the detectors work on their own, so if one breaks or needs to be cleaned, it doesn’t affect how the rest of the system works. Some sensors can be taken out of the system for maintenance while the rest are still working. Because the system is made up of separate parts, a broken detector can be changed in just a few minutes. It is very important that the oil mist detector system is kept in good working condition and that any alarms are dealt with right away, as this instrument is an important safety measure against a crankcase explosion. When the oil mist detector goes off, the engine slows down. Every day, the duty engineer should check and test, if possible, how well the oil mist detector works. The unit is tested at the control panel, but each detector head has an LED indicator that must be checked every day to make sure it is working. If a detector head stops working or sends a strange signal, an alarm goes off.

Answer 174

The cylinder liner temperature monitoring system is comprised of temperature sensors that are installed within the cylinder liners. These temperature sensors monitor the temperature of the liner and are interfaced to the alarm system of the ship. In the event that the liner temperature goes over the predetermined thresholds, an alert will be triggered. The system’s objective is to identify instances of thermal instability on the running surfaces of the cylinder liners, which can be caused by: Oil film break down between liner and piston rings and subsequent seizure. Early action can stabilize the situation and prevent scuffing. Loss of cooling. This will affect both fuel pumps and exhaust side sensors simultaneously on the affected units. Broken or collapsed piston rings. The temperature level will increase over time. Piston ring failure can be detected during scavenge port inspection. Two temperature sensors are installed in each cylinder liner, one on the fuel pump side and one on the exhaust side. These sensors are part of the cylinder liner temperature monitoring system. The alarm set points need to be continuously optimized in the manner that will be detailed in the following paragraphs in order to ensure the quickest possible reaction time in the event of temperature instability and to avoid false alerts.: If the parameters are set too low, false alarms will be triggered during any regular service load, such as 75% of MCR, hence it is imperative that Tmax and Tmaxdev are not allowed to do so. False alarms will occur if the values are not high enough. Whenever there is a variation in the level of engine load, Tmax needs to be recalibrated so that it corresponds to the new level. It is imperative that Tmax and Tmaxdev be modified and set to values that are both as low and as close to the temperature band of each sensor as is technically possible in order to guarantee an adequate level of sensitivity. In the event that there is an abnormal temperature variation while the machine is operating at part load, this will ensure the quickest possible reaction time. If many excessive temperature warnings are being raised by single cylinder units, it is of the utmost importance to inspect the condition of the cylinders on the units in question. Scavenge port inspection is performed at the next available opportunity in order to accomplish this objective. The purpose of this is to guarantee that the piston rings and cylinder liners remain in satisfactory working condition at all times. Units that have just undergone maintenance will invariably exhibit temperature instability for the first few days of operation. In light of the fact that the overhauled unit is anticipated to stand out from the rest, the engineers should become accustomed with the typical temperature differences that occur after overhauls. The same goes for when the load is increased after prolonged periods of steady (low) load operation; you should anticipate some light instability as a result of the abrupt change in ring geometry. This is quite natural, although the severity and pattern of it cannot be predicted. Therefore, one must have patience and provide enough time for the geometry to adapt. In the event of scuffing, the temperatures of the liner will oscillate dramatically, and the peak temperatures will be higher than the average temperature measured by all sensors. However, when the load is lower, it may be essential to monitor more closely since the maximum temperature deviation from the average will be lower than when the load is higher; hence, the value of Tmaxdev must be adjusted downwards accordingly. Above one unit is indicating scuffing, detected by AMS by a ΔTmaxdev set to 30°C or lower and a Tmax set to 170°C. In the event of scuffing, increase cylinder lubrication and reduce the load and the Pmax on the cylinder unit in question. Above two units are indicating scuffing, detected by AMS by a ΔTmaxdev set to 25°C or lower and a Tmax set to 150°C.

Answer 175

VIT or Variable Injection Timing is a form of fuel pump control, enabling an engine to operate with the designated maximum cylinder firing or combustion pressure from approximately 75% power output to maximum power. This improves thermal efficiency and lowers fuel consumption. The fuel consumption for an engine at any load will be related to the expansion ratio of the combustion gases from their maximum pressure to the pressure at the commencement of exhaust blowdown. The maximum cylinder pressure is a factor used in the design of the crankshaft and other important engine parts. In a normal engine the maximum cylinder pressure is reached only at full power operation, whereas with VIT the maximum cylinder pressure is reached at about 75% of the full load. The expansion ratio is therefore increased when the engine is operating under light loads right up to full load. When the engine is equipped with a VIT+FQS system (Variable Injection Timing + Fuel Quality Setting) which permits an alteration of injection begin during operation, the system produces a maximum firing pressure over a wide power range close to the value for the Contracted Maximum Continuous Rating (CMCR) and thereby reduces the fuel consumption. It is also possible to tune the VIT+FQS system following NOx emission. In this case the VIT angle is reduced and thereby the injection is retarded over a wide load range in order to reduce NOx emission. Generally is used the indication VIT+FQS because VIT and FQS always act together, unless the data is specified only for VIT or only for FQS. The VIT+FQS control is integrated in the engine remote control and under normal operating conditions the VIT function is always on, but it can be switched off whereupon the actuator moves to the position corresponding to the FQS setting. In its normal operating mode the VIT+FQS system produces earlier injection in the partial power range and therefore raises the maximum firing pressure. The standard VIT program calculates the necessary VIT angle for increased part load using scavenge air pressure and engine speed as input signals and therefore, a reduction of the fuel consumption is effected over the entire load range. The standard VIT program is individually adjusted during the shop trial of the engine. A typical curve can be seen on below diagram. Electronic VIT and FQS unit With the aid of a pneumatic cylinder and a mechanical linkage the suction valve and spill valve regulating are simultaneously altered. For example, the moving out of the pneumatic cylinder gives higher VIT angles, i.e. an earlier injection and therefore a higher maximum firing pressure. MAN Diesel fuel injection timing adjustment Sulzer RTA fuel injection timing adjustment In the electronically controlled engines, the control of fuel injection is based upon volumetric injection control. Each cylinder electronic unit calculates the necessary injection timing for its own cylinder by processing the crank angle signal and the fuel command delivered by the master control module (MCM). In these cases there is no need for adjustment as the VIT angle calculation depends on speed (RPM), charge air pressure and the fuel rail pressure. The (new) fuel rail pressure compensates for the differences in injection timing resulting from different fuel injection pressures in the fuel rail. Higher fuel pressure causes advanced injection and higher maximum pressure (Pmax). Thus the injection start angle is retarded by a small amount with increasing fuel rail pressure.

Answer 176

Carefully remove the fuel injectors from the engine, following the manufacturer’s instructions. Examine the injectors for any signs of damage, such as cracked or broken components. Check the injector tips for carbon build-up or clogging, which can impede fuel flow. Utilize a specialized injector cleaning kit or professional cleaning service to remove deposits, varnish, and carbon build-up. Follow the specific instructions provided with the cleaning kit or consult manufacturer or a professional technician. Replace worn or damaged injector components, such as O-rings, seals, and nozzles, to ensure a proper seal and prevent leaks. Use high-quality replacement parts recommended by the manufacturer. After cleaning, perform a comprehensive fuel injector test to evaluate their performance. This test may include flow rate measurement, spray pattern examination, and leak detection. Replace any injectors that fail the test or show significant performance deviations. Carefully reinstall the fuel injectors, ensuring proper alignment and connection. Follow torque specifications provided by the manufacturer to avoid overtightening or under tightening.

Answer 177

Fuel injectors must deliver fuel in a precise spray pattern and at the right pressure for efficient combustion. Over time, fuel injectors can develop leaks or clogs that disrupt this delicate balance, leading to suboptimal combustion. By conducting regular leak and pressure tests, marine engineers can identify and rectify any issues promptly. Maintaining the integrity of fuel injectors ensures that the engine receives the right amount of fuel, enhancing combustion efficiency, power output, and reducing fuel consumption. Leaking fuel injectors can result in serious consequences for marine engines. When fuel leaks occur, excess fuel can infiltrate the engine’s oil system, diluting the lubricating properties of the oil and causing accelerated wear and tear on internal components. In extreme cases, uncontrolled fuel leaks can even lead to engine fires, posing a significant risk to the vessel and its crew. By performing regular leak tests, potential issues can be detected early, preventing costly engine damage and ensuring safe operation on the water. When fuel injectors leak or malfunction, the combustion process is compromised, leading to incomplete fuel burn and increased emissions of pollutants such as hydrocarbons and nitrogen oxides. Regular leak and pressure tests help maintain optimal injector performance, ensuring cleaner combustion, and reducing the vessel’s environmental footprint. Fuel injectors that are functioning optimally contribute to overall engine performance and reliability. A leak or malfunctioning injector can result in reduced engine power, rough idling, decreased throttle response, and even engine misfires. Through leak and pressure testing, any injector-related issues can be promptly identified and resolved, allowing the engine to operate at its full potential. A well-maintained fuel injection system ensures smooth operation, enhances engine reliability, and minimizes the risk of unexpected breakdowns.

Answer 178

reduced engine power and acceleration, rough idling or stalling, increased fuel consumption, smoke emissions from the exhaust, difficulty starting the engine

Answer 179

Crankshaft is the main element of the motor mechanism and it sums up the rotational motion of all cylinders and transmits it to the consumers, which in the case of marine engine systems can be a propeller or a generator. For this reason, from a mechanical point of view, it has the higher load and stress factor of mobile parts of the engine. The defects of the crankshafts are quite rare but very dangerous because in case of a failure, it will take the engine out of service and the repairing process is very expensive and time consuming. The most frequent defects are: cracks which can lead to crankshaft breakage with disastrous consequences for the engine. The cracks appears usually on the web and pin connection due to the phenomenon of fatigue that is favored by the existence of tension concentrators and the faulty bearing’s alignment. crankshaft deformation by bending or torsion caused by various accidents like: connecting rod studs failure, high Pmax on some of the cylinders, engine overload etc. crankshaft breakage bearing’s failure Due to bearings number their alignment, coaxiallity and load uniformity are very important and must be continuously kept. Coaxiallity deviation is mainly caused by bearing’s weariness, assembling errors or vessel load. This deviation, if exceeds allowable limits, produces crankshaft deformation and leads to additional stress which sum up to already existing stress during engine operation. Bearings wear and alignment are interconnected and a wrong alignment caused by excessive bearing’s wear will cause crankshaft bending and will affect its lubrication. Thus causing and increasing, most of the time, uneven bearing’s wear which will negatively affect the shaft alignment. Excessive clearance in one main bearing can shift the majority of the load to another main bearing and flexing the crankshaft under load may result in crank journal fatigue and ultimately breakage. The change in distance between crank webs, measured during one rotation of the crankshaft is known as crankshaft deflection and is an indirect indication of the crankshaft loading condition. Distance between crank webs There is a good maintenance need of periodically measuring the crankshaft deflections to ensure that the shaft alignment remains within allowed limits. Normally the crankshaft deflection is to be checked into the following situations: Under normal running circumstances, once or twice a year. In case the ship grounded or touched bottom After replacing main bearing shell and again after approximatively 100 hrs. Before and after engine overhaul in case of auxiliary engines. If there is any signs of damaged main bearings Before commencing the measurements the following conditions must be met: The vessel must be afloat and even keel, as much as possible into the water. The crankshaft must rest on all main bearings Indicator valves must be open The measurements can be affected by: the engine temperature (so it might be stated if the engine is cold or at working temperature) vessel load condition ambient air and water temperature The measurement is done by a dial indicator placed at a predefined location between crank webs. The crankshaft is then rotated in one direction and readings are taken at the defined angular locations. Normally, deflection should be measured at four points on the crank, namely the top, bottom, and two sides. However, in practice, the bottom reading is omitted due to the possibility of fouling by the connecting rod, and instead readings are taken on either side of the bottom position, yielding a total of five readings from each crank web at the positions specified. To determine the crank deflection, the crankshaft must always be rotated in such a way that, regardless of the engine’s normal rotation direction, the flywheel 1 and pinion 2 of the turning gear rotate in the direction indicated by the arrow. With the running gear in place, the crank to be measured has to be turned towards (before or after) B.D.C. until the dial gauge can be fitted next to the connecting rod at the position indicated and then pretension the dial gauge slightly and set it to zero. After the dial gauge is set turn the crankshaft with the turning gear, reading the dial gauge in the crank positions which are indicated and noting down the values at B.D.C. – FUEL SIDE – T.D.C. – EXHAUST SIDE – B.D.C. The last value at B.D.C. is for checking and if everything has been carried out correctly it should be nearly zero.

Answer 180

Crankshaft deflection refers to the measurement of the deviation or displacement in the centreline of the engine’s crankshaft from its ideal position during operation. It is a critical parameter that reflects the mechanical health and alignment of the engine components, particularly in large marine engines. Excessive crankshaft deflection can lead to fatigue, fracture, wear, and damage of the crankshaft and other engine components. Accurate interpretation of crankshaft deflection measurements helps prevent catastrophic failures and costly repairs, ultimately ensuring vessel safety.

Answer 181

Crankshaft deflection measurements are usually expressed as a table or a graph showing the values of deflection at different angular positions of the crankshaft for each unit. The values are compared with the manufacturer’s specifications and limits to assess the condition of the crankshaft. Interpreting crankshaft deflection measurements requires a combination of technical knowledge and practical experience. Follow these steps to ensure accurate interpretation: Understand the Measurement Units: Crankshaft deflection measurements are typically expressed in micrometres (µm) or millimetres (mm). Familiarize yourself with these units and their conversion to ensure precision in your interpretations. Moreover, the dial indicator should be calibrated and checked regularly for any errors or defects. A faulty dial indicator can give false readings and lead to incorrect interpretation of deflection measurements. Establish Baseline Measurements: Before interpreting any measurements, it’s essential to establish baseline readings for the engine when it’s in perfect condition. These baseline measurements act as a reference for identifying deviations and can be found in the engine Technical File, under Shop Trial Measurements. Examine Measurement Patterns: Crankshaft deflection measurements are usually taken at multiple points along the crankshaft’s length. Analyse these measurements to identify any recurring patterns or trends. Irregularities may indicate misalignments or mechanical issues. Uniformity: This is when all units show similar values of deflection within acceptable limits. This indicates that the crankshaft is in good condition and aligned properly. Sagging: This is when one or more units show higher values of deflection at either top or bottom positions, indicating that the crankshaft is bending downwards due to gravity or load. Hogging: This is when one or more units show higher values of deflection at either top or bottom positions, indicating that the crankshaft is bending upwards due to gravity or load. Twisting: This is when one or more units show higher values of deflection at either fuel pump side or exhaust side positions, indicating that the crankshaft is twisting along its axis due to torsional forces. Ovality: This is when one or more units show higher values of deflection at all positions, indicating that the crankpin or journal has become oval-shaped due to excessive wear or damage. Consider Operational Conditions: It’s vital to take into account the engine’s operational conditions during measurements. Factors like load, temperature, and RPM can influence deflection readings. Comparing measurements under different conditions can provide valuable insights. For example, the crankshaft expands and contracts with changes in temperature, which can affect the deflection values. Therefore, it is recommended to measure the deflection at a consistent temperature, preferably when the engine is cold or after a short warm-up period. Moreover, the draught of the vessel can cause bending or twisting of the hull, which can affect the alignment of the engine and the crankshaft. Therefore, it is recommended to measure the deflection at a consistent draught, preferably when the vessel is fully loaded or unloaded. Regularly Monitor and Document: Maintain a comprehensive record of all deflection measurements and their interpretations. Regular monitoring allows you to track the engine’s health over time and detect any changes or deterioration. Identify the possible causes and solutions for the crankshaft deflection problems, based on the shape and pattern of the graph and the manufacturer’s recommendations. If the graph shows sagging or hogging, it could be caused by uneven wear of main bearings, misalignment of engine foundation, or distortion of hull structure. The possible solutions are adjusting or replacing main bearings, aligning engine foundation, or correcting hull deformation. If the graph shows twisting, it could be caused by uneven firing pressures, faulty fuel injection system, or misalignment of driven unit. The possible solutions are repairing fuel injection system, adjusting firing pressures, or aligning driven unit. If the graph shows ovality, it could be caused by improper lubrication, journal bearing failure, overspeeding or overloading of engine, excessive crankshaft deflection and misalignment of parts. The possible solutions are replacing crankpin or journal, improving lubrication system, reducing engine speed or load, or correcting crankshaft deflection and alignment.