The two-stroke engine is an internal combustion engine. The two strokes are:
|Stroke||Number||Piston||Intake port||Exhaust port|
|bottom dead centre||open||open|
|top dead centre||closed||closed|
Unlike a four-stroke engine, there are no intake and exhaust strokes. When the piston is at bottom dead centre, fuel-air mixture is blown in under slight pressure. The incoming mixture forces out the exhaust gas at the same time. The animation shows an engine with crankcase compression to force in the fuel-air mixture. Some engines use a rotary blower instead.