05/04/2020
How does a diesel engine turn fuel into power?
Four-stroke engines
Like a gasoline engine, a diesel engine usually operates by repeating a cycle of four stages or strokes, during which the piston moves up and down twice (the crankshaft rotates twice in other words) during the cycle.
Intake: Air is drawn into the cylinder through the open air inlet valve as the piston moves down.
Compression: The inlet valve closes, the piston moves up, and compresses the air mixture, heating it up. Fuel is injected into the hot gas through the central fuel injection valve and spontaneously ignites. Unlike with a gas engine, no sparking plug is needed to make this happen.
Power: As the air-fuel mixture ignites and burns, it pushes the piston down, driving the crankshaft that sends power to the wheels.
Exhaust: The outlet valve opens to let out the exhaust gases, pushed out by the returning piston.
Two-stroke engines
In a two-stroke diesel, the complete cycle happens as the piston moves up and down just once. Confusingly, there are really three stages in a two-stroke cycle:
Exhaust and intake: Fresh air is blown into the side of the cylinder, pushing the old exhaust out through valves at the top.
Compression: The inlet and exhaust valves close. The piston moves up, compresses the air, and heats it up. When the piston reaches the top of the cylinder, fuel is injected and spontaneously ignites.
Power: As the air-fuel mixture ignites, it pushes the piston down, driving the crankshaft that sends power to the wheels.
Two-stroke engines are smaller and lighter than four-stroke ones, and tend to be more efficient since they produce power once during each rotation (instead of once during every two rotations, as in a four-stroke engine). This means they need more cooling and lubrication and suffer higher wear and tear.