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How does a combustion engine work?

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Quick answer

A combustion engine works by burning a fuel-air mixture inside cylinders to create rapidly expanding gas. That expansion pushes pistons, and a crankshaft converts their up-and-down motion into the rotation that turns the wheels — repeating in a four-stroke cycle many times a second.

Step by step

  1. Intake: a piston moves down, drawing in a mix of air and fuel.
  2. Compression: the piston rises, squeezing the mixture so it burns more powerfully.
  3. Power: a spark (or heat, in a diesel) ignites the mixture, and expanding gas forces the piston down.
  4. Exhaust: the piston rises again, pushing out the burnt gases — then the cycle repeats.

People also ask

What's the difference between petrol and diesel engines?
Petrol engines ignite the mixture with a spark plug; diesel engines compress air until it is hot enough to ignite the fuel on its own.
Why do engines have multiple cylinders?
Staggering several cylinders' power strokes delivers smoother, more continuous turning force than a single cylinder could.
Why does an engine need a cooling system?
Burning fuel produces intense heat; a coolant loop and radiator carry it away to keep parts from overheating and warping.

Part of the guide: Cars, Trains, Planes & Ships →