Diesels

Question 1

State the function of a crankshaft?

Answer 1

To change from reciprocating motion to rotary motion
To drive the auxiliaries

Question 2

Describe the requirements of a shell bearing?

Answer 2

Adequate fatigue and compressive strength to carry the load with the lining thickness envisaged
Material to be as soft as possible, consistent with a
Adequate corrosion resistance
Materials to be capable of being strongly bonded to a suitable backing
Inherently good anti friction and wear properties in the presence of a lubricant
To provide a replaceable bearing surface

Question 3

Describe the operation of the TVD?

Answer 3

When engine shaft rotates, the frictional drag of the silicone fluid imparts motion to the inertia ring, but at a slower speed than the engine
During normal operation, both housing and inertia disc revolves at the same speed
On the power stroke when the twisting motion tends to occur, the heavy inertia ring tends to act as a brake due to running at a slower speed
On the exhaust stroke, when untwisting tends to occur, the inertia ring tends to act as a flywheel taking the crankshaft over that point, so dampers out the vibrations

Question 4

Give occasions for testing a TVD?

Answer 4

Maintenance schedule item
If at any time it is suspected that the vibration damper is defective
On replacement of damper
Installation of new or refitted engine
Prior to and after major overhaul
As part of a baseline VA survey

Question 5

Give precautions to be taken with TVDs?

Answer 5

Extreme care to be exercised working near or on TVD, if removal is needed, care to be taken to protect TVD against damage
Never run an engine without its damper
Never lay an engine on its side, as this will cause the silicone fluid to be displaced and the side clearance lost
Never hit casing with a hammer or side clearance will be lost

Question 6

What is the routine for testing TVDs?

Answer 6

Consult makers handbook or BR
Check the concentricity of the spigoted coupling which is fitted for this purpose
Eccentricity of 0.002” or more should be corrected
Vibration analysis monitoring equipment

Question 7

Describe the function of the con rod?

Answer 7

To transmit reciprocating motion of the piston to rotary motion of crankshaft
Provides housing for bearings, piston, crankshaft

Question 8

Describe the construction of the con rod?

Answer 8

Connecting rod must be strong to withstand the gas pressures on the piston and the varying tension and compression loading yet must be light to minimise inertia effects
Therefore the most common types are forged from steel, medium carbon steel, or nickel chrome molybdenum stampings in the cross sectional shape of a H or oval
Small engine bearings are fitted at the piston end and large end bearings on the crankshaft end

Question 9

Describe the function of a piston?

Answer 9

To transmit the power from combustion

Question 10

Describe the requirements of a piston?

Answer 10

The has to be a minimum friction when reciprocating
A gas tight seal must be formed, yet there must be running clearances
The piston must be light to minimise the effects of inertia
The piston has to be strong to transmit the combustion loads without distortion
There should be no distortion when heat is dissipated
Piston tapered towards the crown to allow for expansion
Piston machined oval in way of the gudgeon pin bosses to allow for expansion
Excess metal relieved or scalloped around the gudgeon pin boss, strength being retained by extensive use or ribs or webs to reduce inertia
Split piston skirt, usually found on small cheap engines, to accommodate expansion
Pistons are cooled by the following combination of methods :
- Air flow across the top of the piston
- Through the piston rings to the cylinder walls
- Oil sprayed through jets on top of connecting rod to the underside of the piston crown
- Fins cast into the underside of the piston crown
- Oil circulated through a dummy piston

Question 11

Why are there shaped piston crown?

Answer 11

To form a combustion chamber
To deflect the induction or exhaust gasses flow, to give good mixing of fuel and air
To allow valves to remain open on supercharged engines as pistons pass through TDC
To allow for injector protuberance

Question 12

What are the functions of piston rings?

Answer 12

To align the piston in its travel up and down the cylinder liner
To form a gas tight seal between the piston and cylinder walls
To regulate the amount of oil onto the liner walls and scrape off any excess
To transfer heat of combustion from piston to liner and hence the cooling medium

Question 13

List the types of piston rings?

Answer 13

Compression rings
Oil scraper rings
Composite fire rings
Air rings
Oil band control

Question 14

Describe the function of the gudgeon pin?

Answer 14

To transmit power from the piston to the connecting rod
Forms a bearing journal for the small end of the connecting rod

Question 15

List the different methods of securing a gudgeon pin?

Answer 15

Semi floating - split small end and clamp bolt, set screw in piston boss
Fully floating - circlips, soft metal pads

Question 16

Describe the function of the cylinder liner?

Answer 16

To contain and guide the piston
To form the walls of the combustion chamber
To aid dissipation of heat

Question 17

What are the types of cylinder liners used?

Answer 17

Wet
Dry

Question 18

What are the requirements of a cylinder liner?

Answer 18

Strength to resist stressed due to pressure and temperature
Must be as symmetrical as possible to prevent distortion by unequal expansion
Hardness to resist wear
Good resistance to corrosion
Be able to form a good bearing surface
Be a good conductor of heat
Retain oil for lubrication
Good resistance to erosion

Question 19

What is the function of the cylinder head?

Answer 19

To seal off the top of the cylinder

Question 20

List the components associated with the cylinder head?

Answer 20

Valves
Rocker gear
Injectors
Combustion chambers
Exhaust passages
Inlet passages
Cooling passages
Air start valves
Decompression devices
Relief valves
Explosion valves
Oil/fuel transfer lines

Question 21

What are the requirements of a cylinder head gasket?

Answer 21

To form a gas, water and oil tight seal between the cylinder head and cylinder block
To withstand heat
Malleable to take up slight differences between surfaces produced in manufacture and by temperature differences

Question 22

Describe the function of the camshaft?

Answer 22

To transfer the rotary drive of the crankshaft to the reciprocating action of the engine operating gear in a correctly timed sequence

Question 23

What are the advantages and disadvantages of a belt driven camshaft?

Answer 23

Advantages :
- Light and cheap
- Quiet
- Can be used to power other components pulley wheels
- Relatively easy to change

Disadvantages :
- Extra oil seals required for external pulley wheels
- Belt cover needs to be good fit to exclude dirt
- Liable to stretch

Question 24

What are the advantages and disadvantages of a chain driven camshaft?

Answer 24

Advantages :
- Light and cheap
- Absorb noise and vibration
- Suitable for long distances

Disadvantages :
- Chains are liable to stretch and break
- A tensioner is required

Question 25

What are the advantages and disadvantages of a gear driven camshaft?

Answer 25

Advantages : - To provide a positive drive - Engine timing is very accurate Disadvantages : - Noisy - Forced lubrication system is required - They are expensive

Question 26

Describe what the profile of the cam is designed to attain?

Answer 26

The profile of the cam is designed to attain the correct opening and shutting times for the engine valves thus it will determine how wide and for how long the valve remains open The profile must account for the forces exerted by valve springs and those created by the generated gas pressure in the cylinder when the valve opens The cam curve is shaped to limit the compression strain from those forces as much as possible

Question 27

With reference to the phases of combustion, describe the uncontrolled pressure/temperature rise?

Answer 27

During this phase the pressure and temperature rise proceeds at a rapidly increasing rate and continues until most of the fuel injected has been burnt The longer the delay period, the greater the amount of fuel that enters the cylinder There is a consequent steep pressure rise as burning rapidly spreads with uncontrolled violence through the combustion chamber during this phase The rapid increase in pressure makes itself apparent as the noise known as diesel knock

Question 28

With reference to the phases of combustion, describe the controlled pressure/temperature rise?

Answer 28

Due to high pressure existing in the combustion space, the fuel still being injected burns almost instantaneously Any further pressure increases in the cylinder is directly controllable by the rate and volume of the fuel entering during this period This rate and volume is solely determined by the fuel injection pump design The combustion process is complete when the piston reaches the bottom of its effective stoke and the exhaust valves open

Question 29

Describe the effects on combustion of an advantage point of injection?

Answer 29

There is a longer delay period due to fuel being injected early, this fuel will not ignite until SIT is reached, this is always at the same point of crankshaft rotation This then gives a higher and steeper uncontrolled pressure/temperature rise due to the increased violence of initial combustion because of the surplus fuel in the cylinder A high and early peak pressure will result from the higher uncontrolled pressure/temperature rise, diesel knock will be more pronounced The cycle will have a longer power stroke than normal because of the early peak pressure Lower exhaust temperatures will be seen because the longer power stroke allows the gas more time to cool before the exhaust valves open

Question 30

Describe the effects on combustion of a retarded point of injection?

Answer 30

In this instance there is a shorter delay period due to the fuel being injected later in the cycle, SIT will occur at the same point of crankshaft rotation This then gives a shallow and lower uncontrolled pressure/temperature rise because less fuel is injected in the shorter delay period therefore the burning ferocity is below the designed rate The shallow uncontrolled pressure/temperature rise results in a low and late peak pressure, hence the engine will be quieter The cycle will have a shorter power stoke due to the late peak pressure Higher exhaust temperatures will be seen due to the shorter power stroke

Question 31

State the requirements of a governor?

Answer 31

To maintain a desired speed with varying loads To maintain a variable/set speed whilst allowing for changes in load

Question 32

Describe the basic principles of a governor?

Answer 32

A governor is in fact an automatic control and to do this it must be able to sense the error between the desired engine speed and the actual engine speed and in doing this, move the FIP control rack/lever to correct the difference in the speed error To do this, the governor must have some method of receiving and setting the desired speed level, a means of measuring actual speed and a method of comparing this value against the desired value It must also provide some method to move the fuel control lever to achieve desired speed, so to do this may require some kind of power amplification to move the FIP fuel lever This can be presented as a basic loop system The governor can be considered as a closed control loop

Question 33

List the requirements of the linkages connecting the governor to the fuel pumps?

Answer 33

Move the fuel pump rack proportionally regarding governor output lever movement Transfer governor arm rotational output movement to longitudinal fuel rack position Operate freely, without causing resistance Have means of adjustment to allow on engine tuning of fuel pumps Facilitate hand operation, especially for local shutdown of the engine Facilitate maximum fuel stops Facilitate overload indicators Facilitate measurements of fuel rack position Facilitate governor output arm movement beyond maximum fuel stop position without damaging governor or other components

Question 34

What are the principle components associated with the speed measuring device?

Answer 34

Centrifugal weights Hydraulic pressure provided by engine fuel oil/lubrication oil system Pneumatic air flow providing vacuum or air pressure Electronic speed sensing such as phonic probes

Question 35

What are the principle components associated with the power amplifier?

Answer 35

Springs, individual or multiple Hydraulics, via engine fluid system or self contained Electronic components through potentiometers

Question 36

What are the principle components associated with the speed setting?

Answer 36

Simple lever, rotary or sliding scale device Remote electrical devices such as a stepper motor Electronically operated device via signal or potentiometer

Question 37

List the common types of governors used in the RN?

Answer 37

Centrifugal Hydraulic Pneumatic Electronic Combination of above

Question 38

Describe what happens with reference to a simple centrifugal governor when load is removed from an engine?

Answer 38

Load removed from the engine will cause the engine to increase in speed This will move the weights outward and overcome spring tension causing the sliding sleeve to move upwards, thus moving the fuel rack towards a decreased fuel setting, allowing the engine to slow until a new balance is achieved

Question 39

Hand operated and stop buttons are fitted as normal shutdown devices, briefly explain how each one operates to shut down the engine?

Answer 39

Hand operated: - Shutdown levers are fitted directly to the fuel rack linkage system directly to the fuel pump - They are usually designed to operate the injection pumps to a no fuel position Stop buttons: - Electrical stop buttons are fitted to engine panels, and when pressed can either open a circuit to operate a shutdown device such as solenoid or break a circuit to carry out the same performance - Electrical stop buttons can also influence the governor to operate a no fuel position - They are buttons when operated which will use the engine lub oil system as an oil relay system and will operate shutdown devices and operate the same way as hand levers

Question 40

Name the three categories of mechanical overspeed trips used in the RN?

Answer 40

Trip bolt type Trip unit and fuel pump spragging Trip unit and fuel limiter type

Question 41

State the function of the intake and exhaust system?

Answer 41

To provide sufficient quantity of clean air to follow efficient combustion of the fuel up to the engines full power rating To remove exhaust gases from the engine to the safe area Air intake can be ducted from the upper deck direct to air manifold or taken from the engine compartment

Question 42

State two methods of controlling emission levels?

Answer 42

By fuelling design By treatment of the exhaust gases

Question 43

What are the three types of air charging used in the RN?

Answer 43

Positive displacement Mechanically driven Exhaust gas driven

Question 44

Explain positive displacement?

Answer 44

The output depends on the speed of rotation and size of pump

Question 45

Explain mechanically driven?

Answer 45

Engine driven axial flow fan type compressor Service use limited to submarines and hunt deltic engines Charge output only varies with speed change, not load change Energy required to drive compressor reduces efficiency, increase obtained from supercharging

Question 46

Explain exhaust gas driven?

Answer 46

Kinetic energy of the exhaust gases is utilised to rotate a turbine at high speeds and thus in turn drives a centrifugal compressor mounted on the same shaft Known as a turbocharger and is the most common means of supercharging used in the services The increase in overall efficiency of the engine is enhanced by utilisation of the waste heat and no resultant mechanical loss

Question 47

List the three types of scavenge blower?

Answer 47

Gearwheel/lobe type Plunger type Centrifugal type

Question 48

State what checks are made to turbo blowers?

Answer 48

Upkeep policy is generally UxE Some blowers have lub oil reservoirs, which periodically need refilling Some blowers fitted with tachos, speed should be recorded during performance trials Periodic VA surveys

Question 49

What are the two methods of cooling turbo blowers?

Answer 49

Water cooling Air cooling

Question 50

List the methods of lubricating oil systems used for turbo blowers in the RN?

Answer 50

Self contained oil pump Main engine lubricating oil pressure circuit

Question 51

List the components of a typical charged air system?

Answer 51

Air intake ducting or filters Blower Air charge intercooler Manifold Exhaust manifold Exhaust uptake Silencer

Question 52

Describe how a fuel injector nozzle operates?

Answer 52

Fuel is fed to the mouth of the nozzle through small holes drilled vertically in the nozzle body The nozzle valve is raised from its seating in the nozzle body by pressure of fuel The top face of the body is a lapped mirror finish and carries an angular groove The vertical drillings lead from this annular groove to the annular gallery A hole or holes of minute diameter are drilled in the end of the nozzle body allowing the fuel to pass into the combustion chamber in a very fine spray

Question 53

Explain correct fuel pump timing?

Answer 53

Achieved by: Spill timing Gauges Timing marks Bump timing DTI Combination of above

Question 54

Where is the certificate stored for new fuel injection pumps?

Answer 54

BR3630 when the new pump is fitted into the engine

Question 55

What are the categories of safety devices fitted to ICE?

Answer 55

Starting Normal running Shutdown Safety devices

Question 56

List safety devices fitted to ICE in the RN?

Answer 56

Start interlocks Overspeed Air flap Emergency stop Pressure and temperature trips MCAS

Question 57

What warning alarms are typically fitted to engines on watchkeeping panels?

Answer 57

Lub oil temperature limits Coolant temperature limits Pressure limits Exhaust temperature limits Overspeed limits Overload limits Air temperature limits Engine speed

Question 58

What requirements need to be met before mount heights are measured?

Answer 58

All alignment between engine and prime mover has been achieved The engine is in a standby condition The ship is afloat Crankshaft readings are within fit tolerances The mountings are left to settle for 24 hours Corrective shimming on mountings are carried out

Question 59

List the occasions when an engine is required to conduct a heat run?

Answer 59

On completion of top overhaul When significant work has been carried out on engine When establishing engine condition and performance for possible extension to release life

Question 60

What are the possible causes of low lub oil pressure?

Answer 60

Low sump level Suction strainer choked Oil pressure gauge faulty Oil filter or cooler dirty or blocked Oil pump worn or leaking Engine bearings worn Oil over heated Fuel dilution

Question 61

What actions can be taken to minimise the effects of light load running on an engine?

Answer 61

Maintaining the engine coolant and lub oil temperatures as near as practical to the maximum limits permitted IAW BR Controlling the coolant flow to the intercoolers of pressure charged engines where applicable as specified in the BR On completion of light running the engine should be run at or above 50% full load for at least 30 minutes

Question 62

In order to maintain correct performance of an engine, what parameters should be monitored?

Answer 62

Exhaust temperatures Coolant temperatures Lub oil temperatures Lub oil pressures Power Speed Dirt and corrosion Loss of lub oil or low oil pressure Abnormal wear Overheating Overspeed

Question 63

What is a fingerprint test?

Answer 63

Measures and records finger print of the generator set when particular loads are applied

Question 64

When are fingerprint tests carried out?

Answer 64

On completion of load trials for base line data Carried out by ships staff Results recorded in D346(F)