How Does An Engine Work?

Stroke 1: Intake
The piston starts at the top, the intake valve opens and the piston moves down to let the engine take in a cylinder-full of air and gasoline. Only the tiniest drop of gasoline needs to be mixed into the air for this to work.

Stroke 2: Compression
The piston moves back up to compress the gasoline/air mixture.

Stroke 3: Combustion
When the piston has moved up and compressed the gasoline/air mixture, the spark plug provides a spark that ignites the gasoline. The gasoline charge in the cylinder explodes, driving the piston back down again.

Stroke 4: Exhaust
Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust gas is pushed out of the cylinder as the piston moves back up. It goes through the catalytic converter before going through the tailpipe. Now the engine is ready for the next cycle, so it takes in another charge of air and gasoline.