The Four-Stroke Engine Cycle
Most car engines are four-stroke internal combustion engines. Each piston completes four strokes per cycle:
- Intake stroke: Piston moves down; intake valve opens; air-fuel mixture is drawn into the cylinder.
- Compression stroke: Both valves close; piston moves up and compresses the mixture, raising temperature and pressure.
- Power stroke: The spark plug fires at the top of compression, igniting the mixture. The explosion pushes the piston down — this is the only stroke that produces power.
- Exhaust stroke: Exhaust valve opens; piston moves up and pushes burned gases out.
The spark plug fires during the compression stroke, at top dead center (TDC).
Cylinder configurations: Inline (single row), V-type (two angled banks), Flat/Boxer (two horizontal banks), Rotary (triangular rotor).