Diesel Engines Flashcards
What is the difference between a petrol and a diesel engine?
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.
Applications/purposes of a diesel engine include:
Diesel generators
Air compressors
Fire pumps
Main propulsion engines and motor boats
Cylinders are numbered from the …. Starting with 123 etc ending with the …
Free end
Drive end
With V engines whilst looking from the free end bank … Is on the left and bank …. Is on the right
A
B
Components of an engine include:
Engine block Cylinder head Cylinder head joint/gasket Sump Piston Piston ring Con rods Crankshaft Camshaft Valves Push rod Rocker arms Injectors Flywheel
A crank shaft turns…
Reciprocating motion into rotary motion
What do camshafts control?
The opening and closing of the inlet and exhaust valves in the correct sequence and is driven off the crankshaft at half crankshaft speed
Describe what a push rod does?
Transfers motion from the camshaft to the rocker arms
Describe how an injector works
Injects a measured amount of high pressure atomised fuel into the combustion chamber
Describe how the flywheel works?
Promotes smooth running during the non power strokes by storing kinetic energy
Name the four stroke cycle?
Induction
Compression
Power
Exhaust
Describe the induction stroke?
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”
Describe the compression stroke?
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.
Describe the power stroke:
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.
Describe the Exhaust stroke?
The exhaust valve is open, the inlet valve is closed. The piston rises from BDC to TDC pushing waste gassed through the exhaust.
Describe valve overlap?
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
Describe the components in a basic fuel system?
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
Describe components in a lubricating oil system?
Engine block Sump Strainer Priming pump 3 way cock Non return valve Pump Filters Reducing valve Lub oil cooler
How often are oil tests carried out and why?
Weekly to identify defects to enable repair before damage occurs.
Where are oil test results logged?
Engine log book
What types of tests are carried out with an oil test?
TBN (acidity)
Viscosity (thickness of the oil)
Water in oil
Insolubles
What components are in a cooling system?
(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
Coolant is a …. Mix of fresh water and …. . It is an antifre and corrosion inhibitor.
50/50
AL39
How often are coolant tests carried out?
Weekly and when defects are suspected
