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Mechanical Theory 1 > Diesel Engines > Flashcards

Diesel Engines Flashcards

1
Q

What is the difference between a petrol and a diesel engine?

A

A petrol engine takes in a mixture of air and fuel into the cylinder before it compresses the mixture and ignites it with a spark plug

A diesel engine takes in just air into the cylinder, it then compresses the air and fuel is injected into the hot compressed air and spontaneous combustion occurs.

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2
Q

Applications/purposes of a diesel engine include:

A

Diesel generators
Air compressors
Fire pumps
Main propulsion engines and motor boats

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3
Q

Cylinders are numbered from the …. Starting with 123 etc ending with the …

A

Free end

Drive end

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4
Q

With V engines whilst looking from the free end bank … Is on the left and bank …. Is on the right

A

A

B

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5
Q

Components of an engine include:

A 
Engine block
Cylinder head
Cylinder head joint/gasket
Sump
Piston
Piston ring
Con rods
Crankshaft
Camshaft
Valves
Push rod
Rocker arms
Injectors
Flywheel
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6
Q

A crank shaft turns…

A

Reciprocating motion into rotary motion

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7
Q

What do camshafts control?

A

The opening and closing of the inlet and exhaust valves in the correct sequence and is driven off the crankshaft at half crankshaft speed

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8
Q

Describe what a push rod does?

A

Transfers motion from the camshaft to the rocker arms

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9
Q

Describe how an injector works

A

Injects a measured amount of high pressure atomised fuel into the combustion chamber

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10
Q

Describe how the flywheel works?

A

Promotes smooth running during the non power strokes by storing kinetic energy

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11
Q

Name the four stroke cycle?

A

Induction
Compression
Power
Exhaust

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12
Q

Describe the induction stroke?

A

The inlet valve is open and the exhaust valve is closed. The piston moves from TDC (top dead centre) to BDC (bottom dead centre). The increase in volume causes a depression (vacuum) drawing air into the cylinder. The inlet valve closes just after BDC to improve “cylinder charging”

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13
Q

Describe the compression stroke?

A

The inlet and exhaust valves are both closed. The piston moves from BDC to TDC compressing the air trapped in the cylinder which causes a rise in pressure and temperature. When the piston is almost at TDC (end of the stroke) the injector sprays high pressure atomised fuel. This allows for an ignition delay of the fuel igniting.

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14
Q

Describe the power stroke:

A

Both valves remain closed for this stroke. Just as the piston passes TDC and starts to descend towards BDC the fuel has ignited and combustion occurs.the burning air/fuel mix causes a rapid increase in temperature and pressure and forces the piston down to BDC.

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15
Q

Describe the Exhaust stroke?

A

The exhaust valve is open, the inlet valve is closed. The piston rises from BDC to TDC pushing waste gassed through the exhaust.

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16
Q

Describe valve overlap?

A

The inlet valve starts to open just before TDC on the exhaust stroke and the exhaust valve remains open until slightly after TDC on the start of the induction stroke. This short period (10-12 degrees of crankshaft rotation) is known as valve overlap. This aids cylinder charging of fresh air for the next induction stroke and the fresh air entering the cylinder helps purge exhaust gassed and cool the exhaust valve

17
Q

Describe the components in a basic fuel system?

A

Fuel service tank

Fuel lift pump (provides clean ready to use fuel from the service tank to the diesel engine)

Fuel filters

Fuel injection pump

Fuel injector

Fuel spill return

18
Q

Describe components in a lubricating oil system?

A 
Engine block
Sump
Strainer
Priming pump
3 way cock
Non return valve
Pump
Filters
Reducing valve
Lub oil cooler
19
Q

How often are oil tests carried out and why?

A

Weekly to identify defects to enable repair before damage occurs.

20
Q

Where are oil test results logged?

A

Engine log book

21
Q

What types of tests are carried out with an oil test?

A

TBN (acidity)
Viscosity (thickness of the oil)
Water in oil
Insolubles

22
Q

What components are in a cooling system?

A 
(salt water)
Sea cock
Strainer
Salt water pump
Lub oil cooler
Heat exchanger
DOB
(Fresh water)
Engine block
Thermostat
Header tank
Heat exchanger
FW pump
23
Q

Coolant is a …. Mix of fresh water and …. . It is an antifre and corrosion inhibitor.

A

50/50

AL39

24
Q

How often are coolant tests carried out?

A

Weekly and when defects are suspected

25
Q

Coolant tests include:

A

Salinity (salt content)
Density (AL39 dilution)
Acidity (acids indicate an internal issue)

26
Q

List engine safety devices?

A 
Low lub oil pressure
Low coolant pressure
High lub oil temperature
High coolant temperature
Engine overspeed
27
Q

Before resetting trips you must:

A

Investigate the cause of the trip
Rectify the fault
Reset the trip

28
Q

List hazards whilst working around a diesel engine?

A

Fire/heat
Noise
Rotating machinery
Personal hygiene

Mechanical Theory 1 (2 decks)

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