Diesel Engines Flashcards
What is the difference between petrol and diesel engines?
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 engines 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.
What are 4 applications of diesel engines?
Diesel generators
Air compressors
Fire pumps
Main propulsion engines and motor boats
What are the two ends of the engine called?
Free end (where the cylinders are numbered from) and drive end (connected to the flywheel)
What are the components of a diesel engine?
Engine block
Cylinder head
Cylinder head joint/gasket
Sump
Piston
Piston rings
Connecting rod (Con Rod)
Crankshaft
Camshaft
Valves
Push rod
Rocker arms
Injector
Flywheel
What is the purpose of a crankshaft?
Turns reciprocating motion into rotary motion
What is the purpose of a camshaft?
Controls the opening and closing of the inlet and exhaust valves in the correct sequence and is driven off the crankshaft at half crankshaft speed
What is the purpose of push rods?
Transfers motion from the camshaft to the rocker arms
What is the purpose of fuel injectors?
Injects a measured amount of high pressure, atomised fuel into the combustion chamber
What is the purpose of the flywheel?
Promotes smooth running during the non-power strokes by storing kinetic energy
What are the four parts of the 4 stroke cycle?
Induction (Suck)
Compression (Squeeze)
Power (Bang)
Exhaust (Blow)
What is the induction stroke?
The inlet valve is open, the exhaust valve is closed. The piston moves from TDC to BDC. The increase in volume causes a depression (vacuum) drawing air into the cylinder. The inlet valve closes just after BDC to improve “cylinder charging”
What is the compression stroke?
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
What is the power stroke?
Both valves remain closed for this stroke. Just as the piston passed 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
What is the exhaust stroke?
The exhaust valve is open, the inlet valve is closed. The piston rises from BDC to TDC pushing waste gasses through the exhaust
What is 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 overlap lasts for approximately 10 or 12 degrees of crankshaft rotation.
