Two-stroke engine

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Animation of two-stroke engine

The two-stroke engine is an internal combustion engine. The two strokes are:

Stroke Number Piston Intake port Exhaust port
bottom dead center open open
compression 1 piston rising closed closed
top dead center closed closed
firing 2 piston descending closed closed

Unlike a four-stroke engine, there are no intake and exhaust strokes. When the piston is at bottom dead center, 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. These engines use mixed fuel (often 50:1) primarily high octane gasoline, partially two-stroke oil.