Technology
How does a combustion engine work?
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.
See it in motion.
Watch a 2-minute animated lesson that shows exactly how a combustion engine works.
Step by step
- 1Intake: a piston moves down, drawing in a mix of air and fuel.
- 2Compression: the piston rises, squeezing the mixture so it burns more powerfully.
- 3Power: a spark (or heat, in a diesel) ignites the mixture, and expanding gas forces the piston down.
- 4Exhaust: the piston rises again, pushing out the burnt gases — then the cycle repeats.
Frequently asked questions
- 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.