Fuel Injection and Fuel Pumps Flashcards

Question

what is the sulphur content in ECA zones and outside ECA zones?

Answer 1

ships now trading in ECA areas must use fuel with no more than 0.01 % sulphur content and the maximum sulphur limit outside ECA’s is 0.5 % unless the vessel is fitted with an approved Exhaust Gas Cleaning System, therefore checking the quality of bunkered fuel has become even more crucial, due to the fact that Port State Control inspectors may check fuel inventory records to ensure the ship utilized the correct fuel within an ECA or an EU Community port and complied with other national sulphur standards. Most ships have bunkering check-lists and procedures in place to mitigate fuel spills and follow shipping regulations. ECAs are sea areas that limit SOx and NOx emissions ECAs are designated in the following locations: Baltic Sea area. North Sea area. United States Caribbean Sea area (near Puerto Rico and the United States Virgin Islands) North American area (covering designated Pacific and Atlantic coastal areas of the United States and Canada, including Hawaii)

Answer 2

Prior bunkering operation, the Chief Engineer should create a bunkering plan that specifies which tanks would be used for bunkering and to achieve an efficient and safe operation, all staff must be fully aware of this before the operation begins. There should also be enough known-quality fuel on hand to use until the newly bunkered fuel is tested by a certified laboratory. As part of pre-bunkering preparation you must check the following: All tank lids are closed and locked, and that all bunker tank air vents are open and clear. Overflow tanks must be empty All level gauges, high-level alarms, and remote-controlled valves on bunker tanks must be operational. Check that manual sounding tapes are available and that the soundings pipes are not clogged or obstructed. Check that all valves to the receiving bunker tanks are properly aligned and that all other valves are closed. Check the filters and safety valves on the bunker lines, if installed. All bunker lines and transfer hoses should be pressure tested, and safe operating pressures should not be exceeded. Check that the bunkering hose is properly and securely connected to the ship manifold. Check ahead of time that you have the proper equipment to take a sample before bunkering: a continuous drip feed sampler (which must be a MARPOL Annex VI compliant line sampling device)

Answer 3

During bunkering operations, the hose connection must remain intact and leak-free, and this must be checked regularly during the operation, especially when the barge switches tanks and pressure is dropped for a brief period of time. If the fuel is not homogeneous, the bunker line pressure may also fluctuate. To sample properly, we must employ adequate equipment to collect representative samples that are acceptable to all parties involved. The dependability of test results from fuel quality analysis and the fuel density used in quantity measurement calculations is based on proper sample methods being followed. The sampling device is installed at the point of Custody Transfer, which is typically at the ship bunker manifold, which is the preferred location for joint sampling in agreement with the fuel supplier (this is very important in case to any future quality disputes). The Chief Engineer must examine the quality of the fuel given by the bunker barge supplier when the barge first arrives. They accomplish this by validating the quality and quantity of fuel mentioned on the Bunker Delivery Note (B.D.N).“Details of fuel oil for combustion purposes delivered to and utilized on board shall be recorded by means of a Bunker Delivery Note,” according to MARPOL standards. As a result, a BDN should be presented for each delivery and fuel grade delivered, and it should be stored on board and easily accessible for inspection at all times. The ship and the provider are both required to keep it for three years after the fuel oil has been delivered. The BDN must include information such as the receiving ship’s name and IMO number, the bunkering port, the date the bunkering began, the name, address, and phone number of the marine fuel oil supplier, the product name and grade, the quantity in metric tones, the density at 15 0C in kg/m3, and the sulphur content in percentage by mass. The IMO further suggests to include the seal number of the MARPOL Annex VI fuel sample on the BDN for cross-referencing reasons, as well as a declaration signed and validated by the supplier’s representative declaring that the fuel complies with MARPOL Annex VI. The BDN may be prepared prior to delivery in some situations, but this will not reflect the realities of the delivery. It is very important to note that you should NEVER sign the BDN, sample labels, or any other document until the bunkering operation is complete. The Chief Engineer will decide which tanks will receive the fuel before the barge arrives, and the contents of each receiving tank should then be measured and documented. These should ideally be empty, as different types of fuel may not be compatible. Blending fuels should be avoided unless absolutely necessary, as it can cause operational issues. Because some vessels lack a remote level measuring technology, you may need to use a sounding tape. Bunker Check that the barge’s documentation show the correct grade and quantity of fuel, and agree on sample protocols when it arrives. Careful measurements of the barge tank contents must be taken before connecting the bunker hose. Use your own sounding tape or ensure that the equipment on-board the barge is in good working order and has not been tampered with. Some barges will feature calibration tables for ullages and others for tank content soundings. Check that the right reference point on deck is being utilized for taking ullages as this information should be available in the barge calibration tables. Always accompany the Barge Master while taking ullages or soundings of any barge tanks. It is critical that all of the tanks on board barge are dipped and their levels recorded and this includes tanks that have been reported empty as well as those that may contain fuel for another vessel. After taking each measurement, make a note of it and double-check that the barge operator agrees with your reading as these are critical measurements in determining the amount discharged by the barge, and both parties should sign the opening measurement records. Temperature readings of each tank are also critical, because the volume of bunkers rises with temperature. Temperature changes can create considerable mistakes in calculations, hence thermometers should be checked on a regular basis. Typically, the terms and conditions of the sale indicate that the quantity of fuel delivered will be determined by shore meters or barge outturn measurement. The Chief Engineer or a representative from the ship should be present at the bunkering barge to observe the opening and closing meter readings, barge soundings, and temperature readings. Fuel sampling should be carried out by continuous drip method for the entire duration of the bunkering process. The sample is first collected in a cubitainer which is screwed onto the drip sampler and secured with a seal in order to prevent any unauthorized changes in the adjustment of the drip rate during sampling. Barge Master and the Chief Engineer should be invited to witness the adjusted drip-rate and sealing process and security seal number should be recorded. To ensure that the sample represents all of the fuel bunkered, the sample needle valve should be adjusted to collect enough of each fuel type for all of the required fuel samples without overfilling the cubitainer, which needs to be able to hold enough oil for all of the samples that you may need: a MARPOL sample a retained sample for the ship to keep a retained sample for the barge to keep a retained sample for the testing laboratory if the vessel is utilizing a bunker surveyor, an extra sample may be required. The ship should also be given a retained sample from the bunker supplier, which should be taken properly on the bunker barge. If the sample cannot be obtained from the ship manifold for any reason (vacuum in the line, extreme weather, etc.), the cause should be recorded in the ship’s log book and the sample taken elsewhere. Throughout the bunkering operation, specific crew members should be appointed to ensure that there is always one vessel representative overseeing the activity (monitoring the bunker manifold and the sampling equipment, continuously checking for leakages etc.). Record any start and stop times as well. All of the above responsibilities can be overseen by an experienced and certified bunker quantity surveyor, who can assist the Chief Engineer in ensuring proper bunkering and sampling procedures are followed. When the delivery is complete, the vessel representative should witness the closing soundings on the barge in order to determine and validate the actual volume provided. To accurately calculate how much fuel has been received the following steps should apply: check the volume received and the observed temperature of the fuel. take soundings or ullages of all tanks that have received fuel and correct the soundings or ullage according with the vessel’s trim and list. after correction the observed volume you have received can then be calculated. It should be noted that vessel calibration tables for fuel storage tanks are rarely approved by recognized bodies, but bunker barge calibration tables are routinely reviewed and certified by local authorities. after determining the observed volume, you must correct it to the standard of 15 0C. to determine the correct Volume Correction Factor (VCF), you must first check the density of the fuel at 15 0C, which will be provided by the supplier. the observed volume is then multiplied by the temperature correction factor contained in tables such as ASTM 54B to determine the standard volume at 15 0C. because density in a vacuum is an absolute relationship between mass and volume, it will not be the same as weight to volume in air. To calculate the right density in air, multiply the supplied density by a Weight Correction Factor, which may be found in ASTM 56 table. after that, we can multiply the standard volume at 15 0C by the corrected density to determine the number of tons of fuel received. Many fuel testing laboratories discover that the density on the BDN is frequently exaggerated, implying that the supplied weight was less than it seemed. If the density cannot be found from a representative sample, the BDN should only be signed for volume at the observed temperature, but if the supplier insists on a signature for weight, add “For volume only – weight to be determined after density testing of a representative sample” to the Remarks section in the BDN. When the delivery is finished, the surveyor should concur with the Chief Engineer and Cargo Officer that the bunker delivery is completed. When the bunkering is finished and the cubitainer is full of fuel, close it and shake it for a few minutes to completely mix the sample. Because we will frequently be preparing at least four samples, fill all of the sample bottles one-third at a time, making repeated passes to fill each bottle evenly. Close and seal the sampling bottles, and record the seal numbers on the Sample Details Form. Sign the labels on the fuel quality testing samples with the supplier representative. and put a label on each bottle with both signatures. Under no circumstances should you sign any blank labels or accept any samples that have been created or supplied in advance of the bunkering process. It is critical that you keep one sample on board in a secure area since this may be the only sample remaining that accurately represents the fuel delivered to the ship. If the supplier provides a sample but it was not witnessed, apply the mark “Only for receipt. Unknown source” on its label. The fuel supplier is required to give you a representative MARPOL sample, which must be sealed and signed by a representative of the company. This MARPOL sample must be kept under the ship’s control until the fuel oil is considerably depleted but not for less then twelve months after delivery.

Answer 4

By definition, residual fuel oils are the by-products of refinery processes that remain after the distillate or lighter fractions have been removed. These residues are complex mixtures that vary depending on the source of the crude oils processed and the refinery’s complexity.

Answer 5

An oil refinery can be thought of as a factory that transforms crude oil into a variety of useful products. It is designed to meet market demands in the most cost-effective and efficient manner possible. The first step in the manufacture of petroleum products is the atmospheric distillation of crude oil into its major fractions. When crude oil is heated, the lightest, most volatile hydrocarbons evaporate first, followed by the heaviest, least volatile hydrocarbons. After cooling, the vapors are condensed back into liquids. A fractionating column is used to carry out this distillation process. The column is divided into chambers by perforated trays that condense the vapours and allow the liquids to flow into storage tanks at each stage. The crude oil is preheated to a maximum of 350°C to avoid thermal cracking.

Answer 6

purpose of this periodical test is to find if something is wrong with the fuel oil bunkering system and to take all necessary actions to re-mediate the faults and defects within. Chief Engineer is responsible for performing the pressure test of the bunker line on an annual basis when each transfer pipe on-board a vessel must be tested under static liquid pressure, at least 1.5 times the maximum allowable working pressure (MAWP). Special attention should be paid to flange joints, valve gland packing, pump seals etc. The test preformed to pressure test the vessels bunker lines is a hydrostatic test.Hydrostatic test is a test conducted by filling a space with a liquid to a specified head. Unless another liquid is approved, the hydrostatic test consists of filling a space with either fresh or sea-water, whichever is appropriate for the space being tested. This kind of test is usually performed during vessel’s periodical special survey (dry docking) using fresh water, but sometimes needs to be done also on-board. MAWP is considered to be the design relief valve pressure setting of the relief valve on the bunker transfer pump. In the absence of the relief valve the MAWP should be taken to be 5.0 kg/cm2. In order to perform the test on-board the following should be taken into consideration: A “Permit to Work” should be issued and a “Risk Assessment” must be carried out. Before conducting the test, all scuppers should be sealed and adequate oil spill equipment should kept ready on deck. The test should be performed for a period of 10 minutes under a constant hydrostatic load. The pressure rating for pipe line material should not be exceeded. This pressure can be found and verified into the vessel’s bunker plan and/or piping diagram. During testing onboard bunker transfer pump may be employed for the test. If the transfer pump is a positive-displacement type, it may be stopped when the required test pressure is reached as it should not permit backflow, therefore valves before and after pump should be closed after desired pressure has been reached. If a centrifugal pump is used for testing, constant running is required to ensure the necessary pressure is maintained. The test should be conducted while underway at sea at least 200 nm from shore during day light. Similar test procedure applies for fuel oil and lube oil bunker lines. After the test, the date and test pressure should be stenciled on the pipe lines and deck at prominent locations. The stencil should be: ”Hydro Test Date: xx/xx/xxxx Pressure: xx kg/cm2. The actual testing procedure should comprises of the following steps: Minimum pressure test must be 4 kg/cm2. The bunker line relief valve if fitted must be removed and a blank with a drain valve must be fitted. As an alternative, the relief valve set pressure can be increased and test the bunker line pressure to a value at least 1.5 times, the normal operating set pressure of the relief valve. In the absence of the relief valve the MAWP should be taken to be 5.0 kg/cm2. At the bunker station, fit a flange, fitted with pressure gauge and a connection for a suitable hand pump. The connection should be fitted with a gauge/cock for pressure monitoring. You must ensure that the gauge is verified and calibrated. A communication between engine room and deck must be established and personnel must be arranged to monitor for any leaks on deck and engine room. Use the transfer pump to fill bunker lines up to the manifold. Purge the lines via valves/cocks on manifold. After the line is filled with oil, the pump valves and system valves must be closed. A hydraulic hand pump can be connected to the manifold to build up the pressure or same can be done with the transfer pump but caution must be taken in order not to damage the pump. Maintain the pressure for 10 minutes and check the entire system for leaks. After completion of test drain the pressure into the overflow tank through the relief valve connection or by slowly opening the valve to an empty bunker tank. It is very important to remember that you're not allowed to test the system by air and by doing so it will makes the test worthless and void. The Coast Guard recognizes that achieving the test pressure of 1.5 times MAWP for annual bunkering test on vessels is often impractical while vessel are in service or outside shipyards where special equipment may not be available. Therefore, the Coast Guard will accept the following: The vessel operator submits a written request for the alternative at least 30 days before operations under the alternative proposed, unless the Captain of the Port authorizes a shorter time. The alternative provides an equivalent level of safety and protection from pollution by oil or hazardous material, which is documented in the request.

Answer 7

Sulphur oxide (SOx). Most ships use heavy fuel oil (HFO). This has relatively high sulphur content compared with other types of fuel. This sulphur is released into the atmosphere through the ships exhaust gas system in the form of sulphur dioxide, which leads to acid rain and is harmful to the environment. Carbon dioxide (CO2). Nitrogen oxide (NOx) just as the SOx is also harmful to the environment and can be caused by improper combustion or high cylinder pressure and temperatures. Particulate matter (PM), are particulates found in the air which include dust, dirt, soot and smoke.

Answer 8

Substances which are made up of more than one type of element and are chemically bonded together

Answer 9

The temperature below which the water vapour in a volume of air at a constant pressure will condense into liquid water.

Answer 10

alkali chemical compound that neutralise acids

Answer 11

The fuel oil system for a diesel engine can be considered in two parts—the fuel supply and the fuel injection systems. Fuel supply deals with the provision of fuel oil suitable for use by the injection system. the purpose of the whole fuel oil system is to introduce fuel oil into the engine cylinders at the correct time, at correct pressure, at correct quantity and in correctly atomised form

Answer 12

In the system shown in Figure 2.11, the oil is stored in tanks in the double bottom from which it is pumped to a settling tank and heated. After passing through centrifuges the cleaned, heated oil is pumped to a daily service tank. From the daily service tank the oil flows through a three-way valve to a mixing tank. A flow meter is fitted into the system to indicate fuel consumption. Booster pumps are used to pump the oil through heaters and a viscosity regulator to the engine-driven fuel pumps. The fuel pumps will discharge high-pressure fuel to their respective injectors. The viscosity regulator controls the fuel oil temperature in order to provide the correct viscosity for combustion. A pressure regulating valve ensures a constant-pressure supply to the engine-driven pumps, and a pre-warming bypass is used to heat up the fuel before starting the engine. A diesel oil daily service tank may be installed and is connected to the system via a three-way valve. The engine can be started up and manoeuvred on diesel oil or even a blend of diesel and heavy fuel oil. The mixing tank is used to collect recirculated oil and also acts as a buffer or reserve tank as it will supply fuel when the daily service tank is empty. The system includes various safety devices such as low-level alarms and remotely operated tank outlet valves which can be closed in the event of a fire.

Answer 13

The function of the fuel injection system is to provide the right amount of fuel at the right moment and in a suitable condition for the combustion process. There must therefore be some form of measured fuel supply, a means of timing the delivery and the atomisation of the fuel. The injection of the fuel is achieved by the location of cams on a camshaft. This camshaft rotates at engine speed for a two-stroke engine and at half engine speed for a four-stroke. There are two basic systems in use, each of which employs a combination of mechanical and hydraulic operations. The most common system is the jerk pump; the other is the common rail.

Answer 14

In the jerk pump system of fuel injection a separate injector pump exists for each cylinder. The injector pump is usually operated once every cycle by a cam on the camshaft. The barrel and plunger of the injector pump are dimensioned to suit the engine fuel requirements. Ports in the barrel and slots in the plunger or adjustable spill valves serve to regulate the fuel delivery (a more detailed explanation follows). Each injector pump supplies the injector or injectors for one cylinder. The needle valve in the injector will lift at a pre-set pressure which ensures that the fuel will atomise once it enters the cylinder. There are two particular types of fuel pump in use, the valve controlled discharge type and the helix or helical edge pump. Valve-controlled pumps are used on slow-speed two-stroke engines and the helix type for all medium- and high-speed four-stroke engines.

Answer 15

The injector pump is operated by a cam which drives the plunger up and down. The timing of the injection can be altered by raising or lowering the pump plunger in relation to the cam. The pump has a constant stroke and the amount of fuel delivered is regulated by rotating the pump plunger which has a specially arranged helical groove cut into it. The fuel is supplied to the pump through ports or openings at B (Figure 2.12). As the plunger moves down, fuel enters the cylinder. As the plunger moves up, the ports at B are closed and the fuel is pressurised and delivered to the injector nozzle at very high pressure. When the edge of the helix at C uncovers the spill port D pressure is lost and fuel delivery to the injector stops. A non-return valve on the delivery side of the pump closes to stop fuel oil returning from the injector. Fuel will again be drawn in on the plunger down stroke and the process will be repeated. The plunger may be rotated in the cylinder by a rack and pinion arrangement on a sleeve which is keyed to the plunger. This will move the edge C up or down to reduce or increase the amount of fuel pumped into the cylinder. The rack is connected to the throttle control or governor of the engine. This type of pump, with minor variations, is used on many four-stroke diesel engines.

Answer 16

In the variable injection timing (VIT) pump used in MAN B&W engines the governor output shaft is the controlling parameter. Two linkages are actuated by the regulating shaft of the governor. The upper control linkage changes the injection timing by raising or lowering the plunger in relation to the cam. The lower linkage rotates the pump plunger and thus the helix in order to vary the pump output (Figure 2.13). In the Sulzer variable injection timing system the governor output is connected to a suction valve and a spill valve. The closing of the pump suction valve determines the beginning of injection. Operation of the spill valve will control the end of injection by releasing fuel pressure. No helix is therefore present on the pump plunger.

Answer 17

The common rail system has one high-pressure multiple plunger fuel pump (Figure 2.14). The fuel is discharged into a manifold or rail which is maintained at high pressure. From this common rail fuel is supplied to all the injectors in the various cylinders. Between the rail and the injector or injectors for a particular cylinder is a timing valve which determines the timing and extent of fuel delivery. Spill valves are connected to the manifold or rail to release excess pressure and accumulator bottles which dampen out pump pressure pulses. The injectors in a common rail system are often referred to as fuel valves.

Answer 18

A typical fuel injector is shown in Figure 2.16, It can be seen to be two basic parts, the nozzle and the nozzle holder or body. The high-pressure fuel enters and travels down a passage in the body and then into a passage in the nozzle, ending finally in a chamber surrounding the needle valve. The needle valve is held closed on a mitred seat by an intermediate spindle and a spring in the injector body. The spring pressure, and hence the injector opening pressure, can be set by a compression nut which acts on the spring. The nozzle and injector body are manufactured as a matching pair and are accurately ground to give a good oil seal. The two are joined by a nozzle nut. The needle valve will open when the fuel pressure acting on the needle valve tapered face exerts a sufficient force to overcome the spring compression. The fuel then flows into a lower chamber and is forced out through a series of tiny holes. The small holes are sized and arranged to atomise, or break into tiny drops, all of the fuel oil, which will then readily burn. Once the injector pump or timing valve cuts off the high pressure fuel supply the needle valve will shut quickly under the spring compression force. All slow-speed two-stroke engines and many medium-speed four stroke engines are now operated almost continuously on heavy fuel. A fuel circulating system is therefore necessary and this is usually arranged within the fuel injector. During injection the high-pressure fuel will open the circulation valve for injection to take place. When the engine is stopped the fuel booster pump supplies fuel which the circulation valve directs around the injector body. Older engine designs may have fuel injectors which are circulated with cooling water.

Answer 19

The timing valve in the common rail system is operated by a cam and lever. When the timing valve is lifted by the cam and lever the high-pressure fuel flows to the injector. The timing valve operating lever is fixed to a sliding rod which is positioned according to the manoeuvring lever setting to provide the correct fuel quantity to the cylinder.

Answer 20

The breakup of fuel into very small particles to ensure an intimate mixing of air and fuel oil is known as atomisation. The objective of atomisation is to reduce the size of the fuel particles as much as possible. This is achieved by increasing the injection pressure as high as possible. The surface area/volume ratio of fuel-oil in droplets increases as its diameter decreases. The effect of this is that a smaller droplet can present a greater percentage of its molecules in contact with the available air than can a larger droplet. The smaller the fuel-oil droplets can be made, then the more effective is the atomisation, resulting in more rapid and complete combustion and maximum heat release from the fuel.

Answer 21

This is a swirl effect of the air charge in the cylinder as it enters the cylinder, which in combination with atomised fuel spray gives an intimate mixing of the air and fuel which aids in good combustion.

Answer 22

This is the ability of the fuel spray droplets to spread across the cylinder combustion space, allowing maximum utilisation of the available volume for combustion

Answer 23

The process of atomisation is to achieve as small a fuel droplet size as possible. The reason for this is that at the micro level a drop of pure fuel is too dense to burn instantly. There is a time delay while the outer surface of the fuel droplet absorbs heat, evaporates and mixes with the oxygen to form a flammable mixture. The time interval from the start of injection until the start of ignition is called the ignition delay. Ignition delay will be affected by the: * level of atomisation achieved * grade of fuel being burnt * quality of the fuel being burnt. If the ignition delay is prolonged for any reason then un-burnt fuel could build in the cylinder space and when ignition does occur the result could be more violent than the engine was designed for and would result in ‘diesel knock’.

Answer 24

Fuel injection in a direct injection engine can result in liquid fuel reaching the piston surface thereby causing piston wetting. This is referred to as spray fuel impingement on the piston surface. Excess velocity of fuel spray will result in the fuel droplets making contact with metallic engine parts and resulting in flame burning. Engine manufacturers have found that impingement is responsible for a considerable amount of the smoke produced by an engine.

Answer 25

The diesel engine is designed to operate on a continuous cycle with every component playing its part and operating at the exact moment in the cycle. The ‘timing’ of this process is critical with the burning of the fuel at the correct moment probably being the most important of all the processes. When the piston is just into its journey travelling down the cylinder, that is when it needs the energy boost from the pressure built up by the heat released from the combustion process. The piston will then be assisted in its motion. However if the piston is hit by a force, trying to push it down the cylinder, when it is still travelling up the cylinder, then the two will be in opposition and the result will be a ‘knocking’ sound called diesel knock.

Answer 26

This is an arrangement at the fuel valve tip to direct fuel in the proper direction with the correct velocity. If the sprayer holes are too short the direction can be indefinite and if too long impingement can occur. If the hole diameters are too small fuel blockage (and impingement) can take place, alternatively too large diameters would not allow proper atomisation. In practice each manufacturer has a specific design taking into account method of injection, pressure, pumps, etc. Even with a particular engine different nozzles may be specified for different applications. For example, vessels with engines that still have mechanical fuel injection control, and are engaged in slow steaming, for reasons of economy, may be supplied with fuel valve sprayer nozzles with smaller holes of differing geometry than engines at higher powers. This measure improves the atomising and penetration performance of fuel valves at part load due to the restoration of fuel velocity through the nozzle. The ‘slow steaming’ injectors give the engine improved economy at part load operation. The nozzles must be changed to the original size prior to operating at maximum power. As a generalisation the sprayer hole length: diameter ratio will be about 4:1, maximum pressure drop ratio about 12:1 and fuel velocity through the hole about 250 m/s. This system is still not ideal for complete combustion control at part load operation. This is one of the primary reasons for the development of electronic control of the combustion process.

Answer 27

The correct atomization of fuel will depend upon the viscosity at the point of injection. The demands upon modern engines to burn a variety of fuel types is becoming more important. The ability to burn residual fuel in marine diesel engines is still important and therefore to ensure optimum fuel injection it is important that the correct pre-heating is carried out. If the temperature of the fuel is too low then the viscosity will be high resulting in higher injection pressure and reduced atomising performance, resulting in ignition delay, excessive penetration and possible impingement on internal surfaces.If the fuel temperature is too high then the viscosity will be low thus reducing penetration and causing deposits to be left on nozzle tip affecting atomisation. The relationship between viscosity and temperature is shown in figure 3.2. Careful control of fuel temperature is required to ensure that the fuel viscosity at the engine fuel rail is inside the range specified by the engine manufacturers. It is modern practice to utilise viscosity controllers that ensure correct fuel viscosity by the careful control of fuel temperature. Despite the manufacturers of the viscosity controller specifying that it is fitted in close proximity to the engine, builders do not always do so. It is important, therefore, that the viscosity controller is adjusted so that any cooling of the fuel that takes place between the heater and the engine does not allow the fuel to move out of the optimum viscosity range for injection. This effect will be exacerbated when burning high-viscosity fuels such as residual fuel oil which require considerable heating. Effective trace heating and insulation is an important feature of a well-designed fuel system.

Answer 28

The fuel injection system is vitally important to the efficient operation of the engine. It must: * Supply an accurately measured amount of fuel to each cylinder regardless of load. * Supply the fuel at the correct time for all loads with rapid opening and closing of the fuel valve. * Inject the fuel at a controlled rate. * Atomise and distribute the fuel in the cylinder.

Answer 29

* Mechanical fuel injection * Mechanical common rail * Electronically controlled (common rail) fuel injection (EFI).

Answer 30

This is the traditional system employed in modern marine diesel engines. It is the most commonly used one in existing engines but it is very quickly being replaced by the newer electronic fuel injection systems. Fuel is supplied to the high-pressure fuel pump from a low-pressure fuel delivery pump and associated pipework. The fuel flows into the high-pressure pump where it fills the internal spaces in the delivery chamber. As the pump is operated by a can on the camshaft the delivery chamber becomes closed off and the fuel pressure starts to rise dramatically following a few degrees of rotation of the cam operating the plunger. Fuel is delivered directly to spring-loaded injectors via the pump’s delivery valve and high-pressure pipework. The fuel injectors are opened up by the hydraulic action of the fuel after the high-pressure fuel pump plunger movement has generated sufficient fuel pressure to overcome the spring pressure keeping the fuel valve closed. The action is designed to be rapid as an aid to the timing and atomisation of the fuel ready for combustion.

Answer 31

Although this is now an obsolete system it is worth a mention here to show the student that good systems that fell out of favour in the past could make a return to efficiency especially with the advancement of material science and electronics. This very early system had fuel pumps to deliver fuel to a pressure main and various cylinder valves were opened to the main which allowed fuel injection to the appropriate cylinder. The system required either mechanically operated fuel valves (e.g. older Doxford engines) or mechanically operated timing valves (e.g.) newer Doxford engines) allowing connection between rail and hydraulic injector at the correct injection timing.

Answer 32

Modern engine designers are coming under increasingly more pressure to build engines that are considerably more fuel efficient than they were just a few years ago. The most important strategy to achieve this is to use sophisticated and very close combustion control which cannot be achieved by the use of mechanical systems such as described in the first section here – mechanical fuel injection systems.The fuel is supplied – via a low-pressure delivery pump and associated pipework – to a high-pressure pump and piping system running the entire length of the engine. The electrically operated fuel valves (injectors) are connected to the high-pressure ‘rail’ pipework. When combustion within a given cylinder is required an electrical signal from the electronic control unit operates the correct fuel valve.The important aspect about the EFI system is that the start, duration, quantity and end of fuel delivery are all completely controllable to a very fine degree and they are parameters that can be modified independently of each other and independent of any other consideration such as engine speed or ambient temperature.

Answer 33

The general rate of heat release (ROHR) for residual fuel is affected by the quality of the refining process and any other types of fuel that are used in the process. For example, if there is any gas oil left over from the process then this will start to burn first and may affect the overall efficiency of the combustion process. There are three distinct phases to the heat release process. The naphtha ignites first starting the process, a middle section where gas oil is ignited next which is followed by the main event where the residual fuel starts to burn.

Answer 34

To achieve effective combustion the fuel must be atomised and then distributed throughout the combustion space. It is the function of the fuel valve to accomplish this. Most fuel valves on the current generation of marine diesel engines are still of the hydraulic type. The opening and closing of this type of valve is controlled by the fuel pressure delivered by the fuel pump. The fuel pressure acts on the needle in the lower chamber and when the force is sufficient to overcome the force of the spring keeping the valve shut, the needle lifts. Full lift occurs quickly as an extra area of the needle is exposed to the fuel pressure, after initial lift, placing additional force against the closing force of the spring. The full action of lift is limited by the needle shoulder which halts against a thrust face on the injector’s body. The injector lift pressure varies with the different designs but may be about 140 bar on average with some designs reaching as much as 250 bar. The fuel valve will require a seal, intended to be a face-to-face seal.

Answer 35

Care must be taken here as in the past bad practice has led to additional copper rings being added or thicker ones being used than the system was designed to have. The exact design system must be used because adding a copper ring will change the height of the nozzle tip and thus will change the point of injection relative to the rest of the combustion space which will have a dramatic effect on the engine’s performance due to poor combustion. Coolant is circulated in the annular space between the injector holder and the holder itself. Direct cooling of the fuel valve as an alternative to this is easily arranged. Coolant connections on the main block would supply and return through drillings similar to that shown for fuel. The choice of oil or water for cooling depends on the engine and valve design and is also affected by the type of fuel. With hot boiler oil it is necessary to cool right to the injector tip so as to attempt to keep metal temperatures below 200°C. Hydraulic fuel valves usually have a lift of about 1 mm and the action is almost instantaneous.

Answer 36

Pilot injection and phased injection of charge is now not a problem with modern engines that have electronic combustion control systems.

Answer 37

Traditionally, diesel engine fuel delivery, injection and atomisation has been carried out by using totally mechanical systems with the majority operating by varying the amount of fuel injected per stroke which is controlled by varying the effective plunger stroke of the high-pressure fuel pump Mechanical systems achieve this by: 1.Varying the beginning of delivery 2.Varying the end of delivery 3.Varying the beginning and the end of delivery.

Answer 38

Currently the most popular method of mechanical fuel injection on larger marine engines is by using a single high-pressure fuel pump for each cylinder. Regulation of the quantity of fuel is matched to the load of the engine by a governor operating various linkages that control the output from the pump. The pump is a single piston moving inside a barrel or cylinder. As the piston is at the bottom of the stroke the space above fills with fuel. As the plunger rises the inlet port is closed and the fuel is delivered from the delivery valve at the top of the pump. The control method is to change the effective length of the pump’s delivery stroke by altering the end of delivery. This method is more suited to constant speed engines which would require a fixed start of injection and the amount of fuel required would increase as the load increased. They are regularly fitted to auxiliary engines and give fuel injection early in the cycle at light load which not only gives higher efficiency but also leads to higher firing pressures. They have also been used with large direct drive engines such as the older Burmeister & Wain (now MAN Diesel & Turbo). However, the large two-stroke engine is a variable speed engine and therefore requires a variable time for the start of injection. Therefore, the valve-type pump is favoured for large engines which had a constant end of delivery and regulation of the start of injection accomplished by varying the suction valve closure.

Answer 39

Fuel injection pumps can be a problem especially when running on residual fuel oil and also when running at the same load over a prolonged period. Impurities in the fuel cause wear on the barrels and plunger of individual fuel pumps. This may happen to pumps in different amounts. Therefore, one pump might wear more than another and pumps may also wear at different points on their load operating range. This means that as an engine increases in load and all the fuel pumps are operated in the same relationship not all the pumps will be delivering fuel in the same way due to the different wear characteristics of each pump. Individual fuel pumps can be adjusted in relation to the other pumps on the engine however this must be done with great care. A balanced engine is one where each of the cylinders is taking its fair share of the load. The problem is that one of the pumps could be pumping low at one part of the range but just a small movement further it will be pumping the full amount. Therefore, any slight adjustment might cause a pump to move from under pumping to pumping more than it should. In many cases only a small adjustment is possible and the best cause of action is to change the pump.

Answer 40

The previous section dealt with variable fuel delivery having a constant beginning of injection. This system is no longer acceptable in modern engines because the part load and low load performance produced does not meet the needs of current legislation relating to engine emissions. Also in the quest for better fuel economy it is modern practice to now vary both the beginning and end of injection. Also With a constant start of injection system the maximum firing pressure of the engine will fall almost linearly as the power of the engine is reduced.

Answer 41

In order that the thermal efficiency and hence the specific fuel consumption can be maintained at optimum it is necessary to maintain maximum firing pressures as the engine load is reduced. This is accomplished by advancing the timing of the fuel injection, and the start of combustion, as the engine load is reduced. The advancement of the injection timing continues until about 65–70%, thereafter the injection is retarded. The ability to retard the fuel injection is extremely important, especially when used to control the emissions from the engine. Retarding the fuel injection delays the heat released and controls the highest peak temperatures in the combustion process. The ability to advance and retard the fuel injection process will reduce the ‘diesel knock’ at low engine loads that is sometimes experienced in engines without VIT. The inclusion of a ‘knock’ sensor will provide feedback to the engine control unit that will then be able to vary the timing accordingly in real time while the engine is in service.

Answer 42

See figure 3.9 motor EK book for sketches The sketch numbered 1 in Figure 3.9 shows the plunger moving down. The pressure in the barrel falls and as the suction and spill ports open to the fuel rail the fuel flows into the barrel. In sketch 2 the plunger is moving upwards. The fuel is displaced from the barrel through the spill and suction ports. This displacement will continue until the plunger completely covers both ports. Sketch 3 shows the plunger continuing to move upwards and just covering the spill and suction ports. This is the effective beginning of delivery and any further upward movement of the plunger will pressurise the fuel that has already filled the high-pressure pipe between the pump and the fuel valve, and it will open the fuel valve injecting fuel to the engine. In sketch 4 the plunger continues to move upwards. Injection continues until the point when the lower helical edge of the groove on the plunger uncovers the spill port. The high pressure in the barrel is immediately connected to the low pressure of the fuel suction. There is no longer sufficient pressure to keep the fuel valve needle open and injection ceases. Sketch 5 shows the plunger turned by means of the rack and pinion control arm so that the longitudinal groove of the plunger is aligned with the spill port. In this position the plunger is unable to deliver any fuel since the spill port does not close during the cycle. Sketch 6 shows a sectional plan view to illustrate how the plunger can be rotated in order to vary the effective height of the helix relative to the spill port. The plunger base is slotted into a control sleeve which is rotated by quadrant and rack bar that are both under the control of the engine’s governor.

Answer 43

With both valve and helical spill designs there can be problems of fuel cavitation due to very high velocities. Velocities near 200 m/s can create low-pressure vapour bubbles if pressure drops below the vapour pressure. These bubbles can subsequently collapse during pressure changes which results in shock waves and erosion attack as well as possible fatigue failure. A spring-loaded piston and orifice design can absorb and damp out fluctuation. Many manufacturers utilise a form of the above pump. The adjustment of the start of injection timing is carried out on Bosch-type fuel pumps by varying the relative height of plunger and suction/spill ports in the barrel. This may be accomplished in two ways: Adjusting the height of plunger relative to the barrel Adjusting the height of the barrel relative to the plunger Adjustment of plunger height can be accomplished in some installations by adjusting the cam follower. Lowering the plunger has the effect of retarding the injection. Raising the plunger advances the injection. In earlier B&W designs adjustment of injection timing was carried out by raising the fuel pump barrel in relation to the plunger. In this design the fuel pump top flange has an external threaded portion projecting towards the barrel (figure 3.11). This thread matches with the external thread of the adjusting ring. The adjusting ring has external gear teeth cut on its upper part which are engaged by the adjusting pinion. To adjust the injection timing the pinch bolts are released and the adjusting pinion is turned to either raise or lower the barrel. Lowering the barrel will advance the injection timing while raising the barrel will retard the injection timing.

Answer 44

Efforts are continually being made to improve the reliability and economy of medium-speed engines which operate on heavier grades of fuel. One way of achieving this is by having a carefully controlled, reliable combustion process. This requires good atomisation with short injection periods but this results in high injection rates at high engine loads with commensurate high rates at intermediate and low loads where increased ignition delays may be experienced. Indeed, research has shown that, at low loads, the injection process may be completed before ignition commences. As the fuel is well mixed with the air, the combustion is very intense and almost instantaneous when ignition does eventually occur. This uncontrolled energy release will cause ‘diesel knock’ and possibly destructive thermal and mechanical stresses. As a solution to this problem Wärtsilä developed a two-stage injection process in which the fuel injected during the pilot stage is constant and independent of engine load. The quantity of fuel injected during the pilot phase is set at about 2–6% of the MCR, which is marginally less than the amount required to compensate for frictional loses when the engine is idling. The pilot fuel is injected in advance of the main injection phase but the quantity involved is too small to damage the combustion chamber components. The injection and ignition of the pilot fuel minimises the ignition delay because it raises the temperature of the combustion air. The fuel injected during the main stage enters a favourable environment with combustion commencing as soon as the first fuel droplets enter the combustion chamber. This eliminates the possibility of unburnt fuel being stored in the combustion chamber and hence the destructive uncontrolled release of energy. Both fuel valves are supplied by the same fuel pump. The fuel pump, however, has two plungers to supply pilot and main injection. The main plunger of this fuel pump is of the conventional scroll, or Bosch type. The pilot plunger is positioned above the main plunger, but since the quantity of fuel injected in the pilot stage is constant this plunger has no helix. As the pilot plunger covers the suction/spill port injection commences and ceases as the lower edge of the plunger uncovers the suction/spill port (figure 3.15) This arrangement has the advantage that the emission of NOx are reduced and allows the use of low Cetane fuels.

Answer 45

Common rail systems permit a continuous, load-independent control of injection timing, pressure, volume and phasing. This means that common rail technology achieves the highest levels of flexibility for all engine loads and gives significantly better results than a conventional fuel injection system. Reliable and efficient CR systems have been developed for an extensive range of marine fuels, including residual fuels such as heavy fuel oil (HFO). This gives the added advantage of using a single fuel for both two-stroke and four-stroke engines. then common rail system is quite simple. High-pressure fuel – as much as 2,000 bar – is circulated around the engine close to the fuel injectors. There will be a short length of pipe from the ‘common rail’ to the fuel injector. When the fuel injector is opened the high-pressure fuel flows into the combustion space through the small holes in the injector. The fuel will atomise well due to the very high pressure of the fuel in the fuel rail and due to the very small angled holes in the injector outlet. The major advance with this system comes from the ability to open and close the fuel injector so quickly. This enables very close control over the timing, duration and sequencing of the fuel injection process. Therefore, so much more can be done to influence the combustion process.

Answer 46

The first and very obvious statement to make is that we have high-pressure fuel inside pipework that stretches over longer distances. Due to the high pressure if any fuel does escape then it also has the potential to spray over a larger area, over the years fuel spraying onto hot surfaces has started a good number of serious engine room fires. all high-pressure piping will be shielded in a double casing and care will be taken at the design stage to ensure that the fuel lines run in as safe a place as possible. However, it is the EOOW responsibility to point out that this is a potential source of danger and that particular attention should be paid to the integrity of the pipework and associated fixings. Good maintenance practices must also be followed. It will be vitally important that the correct ‘high-pressure’ fittings, couplings and seals are used – unapproved alternatives are not acceptable. The pipework must be supported correctly after any maintenance work and it is important that any supports, which were removed to ease the dismantling of the pipework, are replaced. Sub-standard workmanship could lead to failure in the pipework or could allow leaks of fuel out of the system or air into the system. Either of these faults will affect the operation of the engine and if the engine stopped it could endanger the vessel as well.

Answer 47

Main engine fuel must be supplied to a specification which is set out in the ISO standard 8217. The two latest revisions from 2005 and 2010 are the most important. The standard sets out the specification for the fuel characteristics including viscosity, density, flash point, pour point, sulphur, carbon residue, water and ash. The new (ISO8217:2010) specification addresses some of the residual fuel quality problems that has been experienced by the industry, with the inclusion of acid number limits as well as a limit on hydrogen sulphide. The distillate grades have had the inclusion of oxidation stability and a lubricity requirement introduced and the residual marine fuels have a calculated carbon aromaticity index added as an indicator of ignition delay. There is also a limit on sodium content as well as stricter limits for ash and vanadium and there has been a significant reduction in limits for aluminium and silicon, which are also known as cat fines. The knock on effect from taking on ‘off spec’ (unisutiable fuel not fit to to standard) is that filters start clogging due to sludge, sticking or seized fuel pumps and even piston ring breakages will occur due to the quality of the fuel. When this does happen there is always a cost Involved. It is the job of the engineering officers to ensure that they have evidence to support any claim on insurance, or against a third party, that the ship owner might wish to make. Fuel should now be supplied according to the specification set out in ISO 8217 and preferably the 2010 version of the standard. Residual fuel sold for ship bunkers outside the sulphur-controlled zones continues to have a high sulphur content. Marine fuels are covered by an ISO specification and there are controls on various parameters. The standard also specifies that fuel shall not contain any added substance or chemical waste which jeopardises the safety of ships or adversely affects the performance of machinery or is harmful to personnel or contributes overall to air pollution.

Answer 48

Different manufacturers will design their own modification upon the basic system. For example MAN Diesel have completed extensive studies on the consequences of any failure of their system, before fitting it to the engine. Verification of their studies have been completed by a research and development (R&D) programme carried out in their test laboratories and on their research engines. MAN Diesel for example have followed the following design concepts: * The fuel injectors are only pressurized during injection. Meaning that there is no danger of uncontrolled injection, even if a control valve or injection valve leaks. * All high-pressure components are double-walled. Any fuel from leaking or broken pipes is contained within the double-walled pipework. The leaking fuel can then be led to an accumulator that is fitted with an alarm. * Flow-limiting valves are fitted to the fuel pipe for each cylinder. The valves will limit the quantity of fuel to be injected, even in case of leaking or broken components. * Non-return valves fitted in the line for each cylinder. These valves prevent backflow from the low-pressure system into the cylinder, for example, if there is a fuel valve seizure or breakage. * There are between two and four high-pressure pumps fitted to the systems. Therefore, there is redundancy in the system and should one pump fail, emergency operation is possible. * Pressure-limiting valves are fitted. These have the additional pressure control function and act as a safety valve. This design characteristic means that emergency operation is possible, even in case of any failure in fuel rail pressure. * Emergency stop valve/flushing valve included in the design. The valve, which is actuated by compressed air, stops the engine in case of emergency. * Surplus rail-pressure sensors and TDC speed pick-ups are fitted. No interruption of engine operation will occur due to pick-up or sensor error. The Wärtsilä approach with their RT Flex engine is to control the fuel injection process with a ‘volumetric fuel injection control unit’ which controls the timing and volume of the fuel to be injected. Wärtsilä do have a common rail which is fed with heated fuel oil at high pressure (nominally 1,000 bar) ready for injection. Fuel supply is via a number of high-pressure pumps driven by multi-lobe cams. Fuel is delivered from the common rail through the injection control unit, which is placed next to each cylinder, to the standard fuel injection valves. The fuel injectors are hydraulically operated by the high-pressure fuel oil. The control unit uses quick-acting valves to regulate the timing of fuel injection, control the volume of fuel injected and set the shape and phase of the injection. The three fuel injection valves in each cylinder cover are separately controlled so that, although they normally act in unison, they can also be programmed to operate separately as necessary.

Answer 49

To minimise the effects from some of these problems careful design consideration has been given to the design of the overall fuel system as well as the bunkering system. Modern residual fuels tend to have a high viscosity and may also have a high pour point so it is important that upon the completion of the bunkering process, it is checked that that the fuel has drained freely into the bunker tanks. If the vessel is loading bunkers in cold climates it may be necessary to include insulation on the exposed bunker lines. An indication of a fuel with a high pour point may be a high loading temperature. If a waxy fuel is suspected then a pour point test should be carried out. Due to the problems associated with incompatibility, fuels from different sources should not be mixed. The importance of segregation of fuels from different sources cannot be overstated and should be practiced, wherever possible, by transferring remaining fuel into smaller tanks prior to bunkering in order that the total quantity of fuel loaded can be received into empty tanks. Even if a vessel is equipped with adequate storage to ensure segregation mixing may occur in the settling and service tanks when fuels are changed over. If compatibility problems are suspected then fuel change-overs should be accomplished by running down the settling tank before pumping in the next, possibly incompatible, fuel. With the introduction of the new emission regulations and the requirements for vessel to operate on ‘LSF’, fuel suppliers are using more blending techniques to comply with the regulations and for this reason the risk of incompatibility will only increase. Fuels supplied to a ship must be treated before use. In fact comment has been made that this is one of very few products which is purchased but is not ‘fit for purpose’ and must have additional treatment by the purchaser before it can be used. Technically bunker fuel is any grade of fuel that is used by the ship but the term main bunker fuel has come to mean the fuel used for powering the main engine. The term comes from the days when the ships were powered by coal and this was loaded into a ‘bunker’. The temperature of the stored fuel must be monitored to ensure that it does not fall to near its pour point. This is important, especially when fuel is stored in double bottoms, since it is not uncommon for fuels to have a pour point of 25°C and approaching that point the fuel becomes un-pumpable, which can happen when the vessel is in climates that can be considered temperate. The heating capacity of the fuel system, including the tank heating, trace heating and main system heating should be able to deal with the viscosity of any fuel the vessel is likely to encounter. Tank heating must be able to maintain temperatures above the maximum likely pour point.

Answer 50

Communication - The engineering officers must make sure that the rest of the ship company know at which port bunkering is likely to be taking place. Engineering officers must work with other relevant officers and crew during the actual operation so that they can all keep a watch on the process while carrying out their own tasks such as loading cargo or taking on stores and spare gear. Communication between the ship and the bunkering vehicle (barge or road tanker) is vital to completing a safe operation. Efficient lines of internal ship communication are also extremely important. Resources - The bunker station which is the point where the vessel’s fixed pipework is connected to the flexible bunkering hose usually provided by the bunker suppliers should be ’manned’ at all times during the operation. The engine room valve operating station of valve chest should be manned at all times and the officer stationed here should be in constant communication with the officer at the bunker station. Adequate ‘drip trays’ should be placed under the final flange where the ship’s pipework meets the flexible bunkering pipe. Appropriate ‘oil spill’ dispersant and absorbent material should be placed close to the bunkering station. Any water freeing holes in the ship’s bulwark around the site of the bunker station should be temporally blocked so that if there was a spill the oil would be retained on-board where it can be cleaned up without incurring a financial penalty. Other actions - The chief engineer should check and agree the order quantity and quality with the manager in charge of the bunker barge or tanker. Samples should be taken ideally at the start and at the end of the operation but random samples could also be taken during the bunkering process. The quantity being delivered needs to be checked – the traditional way has been to check the bunker fuel in the ship’s tanks before and after delivery of the fuel. Alternatively, an engineer could go to the bunker barge or road tanker and check the quantities there before and after delivery (see below for the more modern approach). Chief engineer needs to record where the bunkers from that load are stored and that the records are understood by all the ship’s senior management team. Chief engineer needs to update his/her standing orders so that the engineers know the sequence for drawing the fuel during the next voyage. MARPOL Annex VI gives minimum values for the emissions from the flue of ships that come under the jurisdiction of countries that are signatories to IMO. Regulation 18 states that fuel of the correct standard should be available. However, it also recognises that there will be bunker ports in countries that are not party to the MARPOL agreement. When purchasing fuel from such ports IMO recommend that ship managers have a clause inserted in their agreement detailing the specification of the fuel, ideally to meet the IMO requirements. A Bunker Receipt Note with specific contents must be issued for each delivery together with a sample that is fully representative of the fuel delivered. These must be retained, not necessarily on-board, for 3 years in the case of the documentation and at least 12 months in the case of the fuel sample, in case they are required as proof of compliance. Furthermore, the regulation gives steps that must be taken in the event of non-compliance. Flag states issue guidance for ship operators about the requirements for meeting the MARPOL Annex VI regulations. Classification societies also issue assistance to their members about the necessary steps needed to comply with good practice.

Answer 51

Keeping the flash point of a fuel within specification is a legal requirement. The flash point is the temperature at which any vapour that is given off will ignite when an external flame is applied. This is usually quoted as the temperature measured under standardised conditions. The fuel’s flash point is defined, and kept within tolerance, to minimise fire risk during normal storage and handling. The minimum flash point for fuel in the machinery space of a merchant ship is governed by international legislation and set at the value of 60°C. For fuels used for emergency purposes, external to the machinery space the flash point must still be greater than 43°C. However even when residual fuels are at a temperature below their measured flash point they are still capable of producing light hydrocarbons, and could still be flammable. The normal maximum storage temperature of a fuel is 10°C below the flash point, unless special arrangements are made. Storage tank heating as well as settling and service tank heating should maximise the separation of water and solid matter from the fuel and still be able to maintain the correct post-purification temperature. This is important given the requirement for fuel to be stored at 10°C below the flash point which could be 60°C. However, the purification and clarification temperatures of high viscosity fuels may be substantially higher than this; 100°C for example. To comply with this regulation a post-purifier fuel cooler may be required to return the fuel to below its flash point-related value, as it is returned back to the storage tank. If a fuel storage temperature is allowed to drop close to its pour point at any stage during the storage, then wax can start to form which may not readily be absorbed into the fuel again when the temperature is raised. The wax forms a sludge which can block filters and the small passages in the fuel injection equipment. When operating with high viscosity fuels it may be necessary to employ high rates of heat transfer during fuel heating. This could lead to thermal cracking of the fuel resulting in carbon deposits on the heating surfaces causing reduced heating capacity. To maintain optimum heat transfer and heating steam consumption there should be a facility to enable the oil side of the heater to be cleaned periodically by circulating with a proprietary carbon remover.

Answer 52

See motor EK BOOK fuel systems - figure 3.18.

Answer 53

1. Representative samples of fuel, in addition to the suppliers’ sample, taken at loading. These should be sealed, clearly labelled and retained on-board for 3 months after the fuel has been consumed. 2. Segregation of fuels from different sources by loading into empty tanks. This may involve the transfer of remaining fuels into smaller tanks prior to loading. 3. Draining bunker lines at the completion of loading. Closing all bunker valves when this is accomplished. 4. Maintaining storage temperatures at least 5°C above the pour point and 10°C below the flash point. 5. Sending a representative fuel sample for analysis and taking the appropriate action upon receipt of the results. 6. Fitting a certified mass flow meter to accurately measure the quantity of bunkers delivered free of contamination. 7. Draining water from tanks at regular intervals. 8. Monitoring fuel consumption against fuel remaining on-board. This should be achieved by daily measurement of all fuel tanks: on older ships dipping the fuel tanks will probably provide the most accurate results. However, on a vessel fitted with accurate depth gauges the remote readings will provide the data required. 9. Regular checks of the fuel purification plant to see if excess water or solid impurities are being removed by the purifiers. 10. Temperature and viscosity control of the fuel from the storage tanks to the point of use by the machinery is very important. If the fuel temperature drops close to its pour point that the fuel filters could become clogged. 11. If the bunker tanks are filled to the very top and the temperature is slightly low, then as the temperature rises so will the volume. It will not take much for the fuel to rise up the vent pipe and cover the vessel with fuel which could spill into the water causing the vessel to be fined or the master and chief engineer arrested.

Answer 54

Some problems identified could be as follows: Low flash point: Regulations require a flash point above 60°C. If the flash point is found to be below this level then the owners and classification society should be informed. A lower flash point fuel will render the vessel ‘out of class’. The addition of a higher flash point fuel will not raise the flash point of the original stock. To avoid the generation of a flammable vapour heating temperatures should be regulated carefully. High sulphur: Sulphur is present in crude oil and the specific amount depends on the original source of crude oil used and the type of refining process. During combustion, sulphur is converted into sulphur oxides which become corrosive upon contact with water and if left unchecked will damage engine pistons and cylinder liners. The acids produced must be neutralized by the cylinder lubricant and marine engine lubricants are especially developed with a high BN to cope with this acidity. If the correct lubricant is used, the sulphur content of a marine fuel is technically not important but the increasing environmental implications is now of great concern to the legislators. Annex VI of MARPOL 73/78 sets out the sulphur content of any fuel oil used on-board ships which originally were not to exceed 4.50% m/m max. After 2010 both Annex VI and the EU directive 2005/33/EC restricted the SOx emissions of ships sailing in the Baltic Sea SECA to 6 g/kWh which corresponds to a fuel oil sulphur content of maximum 1.5% m/m. In addition, the EU directive extended the 1.5% m/m sulphur limit to ferries operating to and from any EU port. The North Sea and English Channel have now become a SECA area where the 1.5% m/m sulphur limit applied. The EU directive has further set a limit of 0.1% m/m max on the sulphur content of marine fuels used by ships at berth (and by inland waterways), which was effective from 1 January 2010 which also becomes a SECA area requirement from 2015.The knock on effect is that from 2015 the current generation of marine engines will not achieve these low levels of emission without additional ‘after engine’ technology such as selective catalytic reduction (SCR) (see p. 313). High water content: This may separate when heated, however water could also form a stable emulsion which is difficult to separate without the addition of emulsion breaking chemicals. If the water contamination is salt water, not uncommon in the marine environment, serious problems associated with sodium-vanadium corrosion and turbo-charger fouling may be experienced. Water contamination also introduces the risk of bacteria into the fuel. Bacterial growth can occur at the oil/water interface which if allowed to proliferate can cause blockage of filters and fuel system. The problem of bacterial, or microbial attack, is greater in fuel which is unheated, especially diesel oil, since the temperatures involved when heating high-viscosity fuels will pasteurise the fuel and thus kill off bacteria. Since prevention is better than cure, draining the water from the oil is by far the best course of action. High vanadium: May cause high temperature corrosion. The use of an ash-modifying chemical additive to maintain the vanadium oxides in a molten state will prevent adhesion to high temperature components. However, vanadium is bound chemically within the fuel and as a consequence cannot be removed. The vanadium deposits are very hard and can cause extensive damage to turbo-chargers. Instability and incompatibility: Instability refers to tendency of the fuel to produce a sludge by itself. Incompatibility is the tendency of the fuel to produce a sludge when blended with other fuels. These sludges form when the asphaltene content of the fuel can no longer stay in solution and so precipitates out, sometimes at a prodigious rate. The deposited sludge blocks tank suctions, filters and pipes and quickly chokes purifiers. In engines the blockage of injector nozzles, late burning and coking can result in damage to pistons, rings and liners. Therefore fuels from different sources should not be mixed on-board. High aluminium content: This contamination is a result of carry-over of ‘catalytic fines’ from the refining process of the initial oil. These ‘fines’ are an aluminium compound ranging in size from 5 mm to 50 mm and are extremely abrasive. Very low levels of aluminium indicate the presence of catalytic fines in the fuel which, if used, will lead to high levels of abrasive wear in the fuel system, piston, rings and liner in an extremely short period of time; 30 ppm of aluminium is generally considered as the maximum allowable level in fuel oil bunkers before purification. As a result of the small size of these compounds they are difficult to be removed completely by centrifuge. The purification plant, in correct operation, will reduce the aluminium content to about 10 ppm before it is used in the engine. It has been found that if the aluminium content is above 30 ppm difficulties will be experienced in attaining a safe level of 10 ppm after purification. Due to the problem of ‘cat fines’ the 2010 version of the ISO 8217 specification for fuel oil was introduced.

Answer 55

changing over fuel To protect the fuel oil injection equipment against rapid temperature changes which may damage and cause risk of sticking of the fuel valves and or fuel pump plunger and suction valves. the change over for fuel must be done in the correct manner. When you change from heavy fuel oil (HFO) to marine diesel oil (MDO) or back, you must keep the thermal stresses of the related fuel components as low as possible. Thermal stress occurs because of the large temperature changes. Too fast change of the temperature can cause damage to the fuel pump plungers and can cause leakages in the fuel pipes. During the change-over procedure the temperature of the fuel must not change more than 2°C each minute. This prevents damage to the system, specially when you do the procedure frequently. The small change rate is also because of the large difference of viscosity between HFO and MDO/ MGO. You can do a change-over of the fuel only when the engine is running. While the engine has stopped, there is no fuel flow through the fuel rail. In this situation a change-over is not possible. Fuel of this type requires the purifiers to have a smaller gravity disk fitted in order to maintain the water-oil interface, finer filters are also fitted within the fuel treatment system to enable effective particle separation. The visco-therm controller must also be adjusted in order not to over-heat the fuel reducing its viscosity too much risking carbonisation or gassing up the fuel lines. The engine fuel injection timing must also be adjusted to compensate for less viscous fuel.

Answer 56

Fuel pump lead is the distance travelled by the plunger from the point at which rise of the fuel cam starts (or the follower start lifting) till the piston of the unit in question reaches top dead centre or TDC (ignition DC).

Answer 57

The primary method of checking fuel pump timing would be using the manufacturer’s instructions of setting the fuel pump with the engine stopped. For the Bosch type fuel pumps, a small window is present at the base of the fuel pump. Within this window an engraved line can be seen on the spring holder of the fuel pump. When the cam follower is displaced by the cam, it pushes the spring holder up. When the engraved line coincides with the line on the fuel pump body, then the fuel pump plunger is at the position where it is just covering the spill ports. Hence at this moment the fuel pump is starting to pressurize the trapped fuel volume, and hence fuel delivery will commence. Thus the engine is rotated to the point where the two lines coincide, and this indicates the commencement of fuel delivery. The actual crank angle would be read off the flywheel.

Answer 58

Should the fuel pump timing be required to be changed, then the shims fitted underneath the fuel pump would be changed. If shims are added the fuel pump will inject later, and visa versa for removing the shims. The fuel pump is attached to the fuel rack, and the fuel control lever set to the same readings as the other fuel pumps. This should deliver the same fuel quantity. The fuel pump rack should always read zero when the governor is in the no-fuel position, to ensure the engine will stop when required. To enable the actual fuel quantity delivered from each fuel pump to be measured, indicator cards would be required. Indicator cards would be taken from each cylinder and the power developed would be found, either directly from the software for the electronic cylinder units, or using a planimeter to determine the area of the power card for the mechanically taken indicator cards.

Answer 59

Checking and Adjusting Variable Injection Timing (VIT) Fuel Pump A variable injection fuel pump can also be adjusted for fuel timing with the engine running. Thus whilst the engine is running the fuel pump timing can be checked by the draw card type of indicator card. On this type of card the position when the fuel has ignited can be seen by either The point at which the pressure-volume curve moves away from the normal compression curve, or The point on the pressure derivative curve on the electronic indicator when the rate of pressure rise suddenly increases. The derivative curve makes the point of fuel ignition much easier to determine. Once the point of fuel timing is determined, then the fuel pump can be adjusted either Collectively for the whole engine by adjusting the sensor which determines the quantity of fuel timing advancement by measuring the position of the fuel rack position. Any adjustment of this sensor will advance or retard the fuel timing of all fuel pumps at once. Individually by adjusting the linkage from the individual fuel timing servo to the fuel pump. This adjustment will adjust the fuel timing of an individual fuel pump. The fuel pumps would need to be adjusted collectively, when the fuel combustion quality reduces. Hence if combustion was slower than normal, possibility due to a high level of Conradson Carbon or Ashalptenes, then the fuel timing could be advanced. This will allow more time for combustion, and should reduce exhaust temperatures and smoke levels. When fuel timing is advanced it is important that the cylinder maximum pressures are measured to ensure that they are not excessive. Should the ignition quality of the fuel be lower than normal, then the initial raise in cylinder pressure when combustion occurs will be higher than normal, and may even lead to bearing damage. In these cases the fuel timing would be retarded to depress the rate of pressure rise. Individual fuel pump timing adjustment would be required when the fuel pump is internally worn. This will cause a lower amount of fuel to be injected, but also later in the engine cycle. Hence the performance of the pump could be regained by increasing the quantity delivered at the fuel rack, and advancing the individual fuel pump timing.

Answer 60

Yes On-board testing of the fuel could be carried out during the bunker operation by one of the engineering staff not required to supervise or monitor the bunkering operation. The following tests could be carried out: Water content Viscosity Density Compatibility Check for abrasive fines Although the tests are not as accurate as a shore based laboratory the tests would indicate whether the fuel loaded is the same as the fuel quality ordered and therefore the bunker receipt.

Answer 61

Oxides of nitrogen are formed when the nitrogen in the fuel, and some of the nitrogen in the air combines with the oxygen present during combustion in the heat of the combustion process. The quantity of NOx produced is dependent on the temperature and duration of combustion, and the quantity of oxygen present in the combustion space. Carbon monoxide is formed when the level of oxygen within the combustion space is insufficient to provide complete combustion to carbon dioxide. As usually there is ample oxygen within a diesel engine, readings of carbon monoxide indicate the present of pockets of fuel rich mixtures burning locally without enough oxygen, hence poor fuel/air mixing from incorrect atomization and air turbulence will cause carbon monoxide levels to rise. Sulphur oxides are formed when the sulphur in the fuel reacts with the oxygen to form sulphur monoxide and dioxide. Increasing levels of fuel sulphur content will increase the sulphur oxides produced.

Answer 62

In order to reduce the effects of the sulphurous products the following can be used: Reduce the level of sulphur in the fuel by using low sulphur fuels Counteract the condensation rate of the sulphur oxides by elevating metal temperatures at the cylinder walls, and the skin temperature of the exhaust gas boiler tubes Use of high alkaline lubricating oils to counteract-neutralise the acids formed on condensation. Increased frequency of cleaning of the exhaust gas boiler and turbocharger gas turbine

Answer 63

When the fuel injector needle valve seizes, this can be when the needle is 1.Shut – causing a smaller amount of fuel to be injected (on multi valved engines) causing low cylinder power developed. 2.Partly open – causing less fuel to be injected and the injector to dribble causing exhaust smoke and low cylinder power developed. 3.Open – causing the injector to inject earlier and the injector to dribble. The possible cause could be either: 1.Overheating of the fuel injector due to inadequate cooling 2.Abrasives in the fuel from inadequate fuel preparation

Answer 64

The following actions to be taken to minimize the seizing of fuel injector needle valve: 1.Take a sample of the fuel entering the engine and send it for analysis to investigate possible contamination from metal elements 2.Remove all of the other injectors at the earliest opportunity to examine for defects and to test the injectors. 3.Examine the injector tips looking for overheating. If this is present, then check the operation of the injector cooling system (if fitted) and the cylinder head cooling system. Inspect the same system for internal fouling of the heat transfer surfaces. Ensure that the high temp alarms are functioning. 4.Ensure that the flow rates for the fuel oil purifiers are as low as possible whilst still maintaining the service tank level. If a gravity disc is used, check that the largest sized disc is fitted without causing water seal failure. Both of these actions will reduce the level of contamination in the purifier clean phase outlet. 5.If two settling tanks are available, ensure that the filling of one settling tank differ from that with the active FO separator suction. This will maximize fuel settling time and provide cleaner fuel at the purifier suction. 6.Check the condition of the cold and hot fuel oil filters for physical damage, that would allow dirt to pass through the filtering unit. 7.Check the correct operation of the fuel injector test unit, with regard to the correct calibration/protective oil.

Answer 65

To supply accurate metered amount of fuel with sufficient pressure to open fuel injector in correct timing.

Answer 66

1.Reduce the engine speed 2.By lifting the pump roller form cam peak and securing the pump roller guide 3.By making pump rack to zero position

Answer 67

Difficult to start the engine Abnormal exhaust temperature reading Black smoke coming out Irregular running of engine.

Answer 68

Lock off the starring mechanism Start L.O pump Open all indicator cock then By hair line method 1.Turn the engine so that the unit to be checked is toward the TDC of compression stroke (plunger upstroke) so that hair line marking on plunger and pump body are coincided. 2.When hair lines are coincided, stop turning and check the mark on the fly wheel whether timing is correct or not. By removing deflector from fuel pump Take out deflector on both sides of the fuel pump Put hand torch on one side of pump and mirror on the other side The light from torch will be visible on the mirror Turn the engine so that the unit to be check is toward the TDC of compression (at plunger upstroke) At one instant the light on mirror disappears. (When plunger covers the deflector port) At this time, stop engine turning & check the mark on flywheel.

Answer 69

In Main Engine 1.Make a marking between cross head and guide shoe while they are before TDC and also mark at the flywheel. 2.Turn the crank shaft in the same direction until the crosshead and guide shoe are at the previous mark (coincide) 3.Make the second marking on the fly wheel. We got two marks on the flywheel mid point between the two points is TDC. 4.Now 360º can be divided around the flywheel. In Auxiliary Engine 1.Remove the fuel valve 2.Insert the rod onto the piston (mark on rod and flywheel) 3.Turn crank until the rod previous mark 4.Make the second marking on the fly wheel 5.Mid point between the two points is TDC

Answer 70

Check plunger guide wear & tear Check spring (length & stiffness, crack) Plunger & barrel wear & tear, check clearance (5 microns for DO, 15 microns for HO) by dropping the plunger into the barrel it fall down slowly is OK Check control sleeve and rack teeth for crack Check the Delivery valve face Check ‘O’ ring of fitted.

Answer 71

Controlling the fuel amount in two ways, by means of a helix groove on the plunger or by means of control valves. The quantity of fuel delivered is regulated by the vertical length of the helix where it is in line with the suction port. This setting may be altered by rotating the plunger. In stop position, the vertical slot of the plunger is in lined with the spill port where then ports are opened and thus no injection occurred.

Answer 72

When overhauling fuel injectors it is important that the work area is very clean. Lay paper out on the work bench, disused charts are ideal. Do not use rags or cloths for cleaning components. Wash all items thoroughly in kerosene and blow dry with compressed air. Inspect all sealing faces for any damage. Small scratches can be removed by lapping in against a special surface plate, using a fine lapping paste such as jewelers rouge. Any pitting or indentation of the sealing face mean the nozzle should be replaced or sent to specialists for reconditioning. Clean the nozzle bore with a special drill and use specially supplied needles for cleaning the nozzle holes. If the holes are too large, or appear oval when inspected with a magnifying glass, the nozzle should be discarded. The nozzle needle and guide are matched a pair and should not be interchanged. The needle should be free to move in the guide and when lifted it should drop down into the guide under its own weight. Reassemble the injector and tighten the cap nut down to the correct torque. Note that some engine manufacturers supply different sets of nozzles for the same engine. An example of this would be slow steaming nozzles, which may have different size holes. Always make sure the correct nozzle has been fitted.

Answer 73

Testing of fuel injector is carried out as follows. Mount the fuel injector in its test rig and connect up the oil supply. Under no circumstances should hands be placed under the injector spray. The high velocity oil jet can penetrate the skin and cause blood poisoning. With the injector priming valve open, operate the hand pump to prime the injector. Once the fuel flows from the priming valve it can be closed. Operate the pump rapidly for several strokes. The injector should open with a high pitched chatter and fuel should be emitted in a fine cloud. After the injector opens, check to make sure the pressure does not fall off too quickly. To test for the tightness between the nozzle needle and seat, operate the hand pump slowly to gradually increase the pressure until it is just below opening pressure. Maintain the pressure for a few seconds and ensure injector is not dripping. To test for tightness between needle and guide, operate the hand pump to increase pressure until it is just below opening pressure. See how long it takes the pressure to fall off. If the pressure falls quickly the needle and guide should be replaced. Where nozzles are cooled internally, these spaces should be pressure tested to check for tightness. Blank off one of the fuel valve cooling connections and fill the injector cooling space with water or fuel, depending upon the cooling medium. Then connect a low pressure air supply to the other connection. Leave the air on for a short period of time and test for internal or external leakage. Testing of fuel injector is usually carried out at an interval of 2000 running hours for marine diesel engines. Following points to be remembered while testing of fuel injector: 1.Visually examine the injector just after taken from cylinder head. Pressure test and find opening pressure in service. 2.Check injector setting pressure, formation of trumpets and carbon accumulation, corrosion at the nozzle, etc. 3.Spray pattern assessment and prompt re-seating. 4.Drip proof. No droplet formation at set pressure minus 10 bar, held steady and also upon closing. 5.Injector lift diagram may be taken. 6.Recommended assembly procedure to be followed (Like tightening torque, etc.) and handle parts carefully.

Answer 74

A fuel injector valve is a device which receives pressurized fuel as a liquid and sprays it into engine cylinder as a fine mist. It consists of a nozzle and nozzle holder and a body. The nozzle has a series of small orifices around its tip used for atomizing the injected fuel. So, the purpose of injection valves is to precisely inject the fuel quantity calculated by the control unit in all engine operating states. To ensure the fuel is atomized effectively while minimizing condensation losses, a certain engine-specific distance and injection angle need to be observed. Fuel injector valves, like any other machinery or devices that are under continuous load and stress, tend to malfunction and ultimately to fail while in service if maintenance plan is not properly followed. Accelerated wear/damage to nozzle tips are in most cases caused by poor fuel oil quality, fuel contamination and this will cause poor combustion which in turn will result in poor engine performance and eventually may result in major damage to the engine. As the fuel injection valve should be operated for 8000 hrs. without removal and as per Wartsila for 6000 hrs. , unless a specific reason dictates so. To ensure safe operation, the heavy fuel oil operating instructions and treatment, including correct filtration must be strictly observed. Performance check is strongly recommended at least once a week. The fuel injection valve should be cleaned from the outside without dismantling the fuel valve, check should be done in fully assembled condition. Correct cleaning procedure of the nozzle is necessary to ensure proper atomisation of the fuel in the combustion chamber. For judgment of the fuel nozzle condition, only opening pressure and leakage should be used as criteria for acceptance or rejection. Spray pattern test should not be used as a criteria, as the test bench injection capacity is too small to produce the same condition as exits is in the engine. Drop in opening pressure is typically caused by wear in the needle seat in the fuel injection valve or setting of the spring. Setting of the spring cannot be avoided, however wear in the seat area is the result of wear from abrasive particles and can be reduced by proper treatment of the fuel. In case of leakage or low opening pressure, the valve should be opened for internal check of parts. If leakage is the reason for opening the fuel valve, typically the nozzle will have to be replaced as a minimum, while a low opening pressure normally dictates a replacement of the spring. In both situations replacement of other parts may be required based on condition.

Fuel Injection and Fuel Pumps Flashcards

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