How a Car Engine Works Quiz
The four strokes
Most gasoline car engines work in four steps, called strokes, inside metal tubes called cylinders. A piston slides up and down inside each cylinder.
First comes intake: the piston moves down and pulls in a mix of air and fuel. Then compression: the piston moves up and squeezes the mix. Then power: a spark plug lights the mix, and the burning gas expands and shoves the piston down. Finally, exhaust: the piston rises again and pushes the burned gases out.
This four-stroke cycle was first built into a working engine by the German engineer Nikolaus Otto in 1876, so it's sometimes called the Otto cycle.
From pistons to wheels
Pistons move up and down, but wheels turn round and round. A crankshaft, a bent shaft linked to all the pistons, turns their up-and-down motion into spinning.
Most car engines have four, six or eight cylinders, firing one after another so the push is smooth. The gearbox then matches the engine's speed to the wheels.
Diesel engines work in a similar way but have no spark plugs. They squeeze air so hard that it gets hot enough to light the fuel on its own when it's sprayed in.
Electric cars
Electric cars don't burn fuel at all. A battery powers electric motors, which use magnets and electricity to spin. An electric motor has far fewer moving parts than a gasoline engine.
When an electric car slows down, its motor can work in reverse, as a generator, turning some of the car's motion back into electricity for the battery. This is called regenerative braking.
Hybrid cars carry both a gasoline engine and an electric motor and switch between them to save fuel.