How a gasoline engine turns fuel into motion

A four-stroke gasoline engine converts the chemical energy of fuel-and-air combustion into rotational mechanical work through a repeating four-step cycle ^[1][2]. Inside the engine, a piston moves up and down inside a metal tube called a cylinder ^[3]. That piston is linked by a connecting rod to a crankshaft, transforming the piston's up-and-down reciprocating motion into spinning rotational motion just like a bicyclist's legs turning the pedals ^[4][5].

The cycle proceeds through four distinct movements of the piston:

1. Intake: As the piston moves downward, the valves (specifically the intake valve) open to let a fresh mixture of air and fuel into the cylinder ^[6][7].
2. Compression: The intake valve closes, sealing the chamber while the piston moves back upward to compress that fuel-and-air mixture into a much smaller space, raising its temperature and pressure ^[8][9].
3. Power: Just as the compression reaches its peak, a spark plug fires an electric arc to ignite the mixture ^[10][11]. The resulting controlled explosion creates rapid high-pressure gas expansion that forcefully drives the piston downward ^[12][13]. This downward force pushes the connecting rod to spin the crankshaft, which produces the actual power used to move the vehicle ^[14][15].
4. Exhaust: Finally, the piston travels upward once more while the exhaust valve opens, pushing the spent combustion gases out of the cylinder and clearing the chamber so the cycle can begin again ^[16][17].Would you also like to know why compressing the air and fuel mixture before ignition makes the engine more efficient?AskAnswer complete. One follow-up option available.