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M1 > Diesels > Flashcards

Diesels Flashcards

1
Q

State the function of a crankshaft?

A

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

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2
Q

Describe the requirements of a shell bearing?

A

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

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3
Q

Describe the operation of the TVD?

A

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

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4
Q

Give occasions for testing a TVD?

A

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

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5
Q

Give precautions to be taken with TVDs?

A

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

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6
Q

What is the routine for testing TVDs?

A

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

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7
Q

Describe the function of the con rod?

A

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

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8
Q

Describe the construction of the con rod?

A

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

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9
Q

Describe the function of a piston?

A

To transmit the power from combustion

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10
Q

Describe the requirements of a piston?

A

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

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11
Q

Why are there shaped piston crown?

A

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

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12
Q

What are the functions of piston rings?

A

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

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13
Q

List the types of piston rings?

A

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

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14
Q

Describe the function of the gudgeon pin?

A

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

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15
Q

List the different methods of securing a gudgeon pin?

A

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

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16
Q

Describe the function of the cylinder liner?

A

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

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17
Q

What are the types of cylinder liners used?

A

Wet
Dry

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18
Q

What are the requirements of a cylinder liner?

A

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

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19
Q

What is the function of the cylinder head?

A

To seal off the top of the cylinder

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20
Q

List the components associated with the cylinder head?

A

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

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21
Q

What are the requirements of a cylinder head gasket?

A

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

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22
Q

Describe the function of the camshaft?

A

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

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23
Q

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

A

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

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24
Q

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

A

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

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

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25
Q

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

A

Advantages :
- To provide a positive drive
- Engine timing is very accurate

Disadvantages :
- Noisy
- Forced lubrication system is required
- They are expensive

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26
Q

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

A

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

27
Q

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

A

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

28
Q

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

A

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

29
Q

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

A

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

30
Q

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

A

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

31
Q

State the requirements of a governor?

A

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

32
Q

Describe the basic principles of a governor?

A

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

33
Q

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

A

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

34
Q

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

A

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

35
Q

What are the principle components associated with the power amplifier?

A

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

36
Q

What are the principle components associated with the speed setting?

A

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

37
Q

List the common types of governors used in the RN?

A

Centrifugal
Hydraulic
Pneumatic
Electronic
Combination of above

38
Q

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

A

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

39
Q

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

A

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

40
Q

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

A

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

41
Q

State the function of the intake and exhaust system?

A

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

42
Q

State two methods of controlling emission levels?

A

By fuelling design
By treatment of the exhaust gases

43
Q

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

A

Positive displacement
Mechanically driven
Exhaust gas driven

44
Q

Explain positive displacement?

A

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

45
Q

Explain mechanically driven?

A

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

46
Q

Explain exhaust gas driven?

A

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

47
Q

List the three types of scavenge blower?

A

Gearwheel/lobe type
Plunger type
Centrifugal type

48
Q

State what checks are made to turbo blowers?

A

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

49
Q

What are the two methods of cooling turbo blowers?

A

Water cooling
Air cooling

50
Q

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

A

Self contained oil pump
Main engine lubricating oil pressure circuit

51
Q

List the components of a typical charged air system?

A

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

52
Q

Describe how a fuel injector nozzle operates?

A

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

53
Q

Explain correct fuel pump timing?

A

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

54
Q

Where is the certificate stored for new fuel injection pumps?

A

BR3630 when the new pump is fitted into the engine

55
Q

What are the categories of safety devices fitted to ICE?

A

Starting
Normal running
Shutdown
Safety devices

56
Q

List safety devices fitted to ICE in the RN?

A

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

57
Q

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

A

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

58
Q

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

A

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

59
Q

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

A

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

60
Q

What are the possible causes of low lub oil pressure?

A

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

61
Q

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

A

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

62
Q

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

A

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

63
Q

What is a fingerprint test?

A

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

64
Q

When are fingerprint tests carried out?

A

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

M1 (4 decks)

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