Four-stroke engine
![Four-stroke cycle used in gasoline/petrol engines.
1 = Intake, 2 = Compression, 3 = Power, 4 = Exhaust. The right blue side is the intake port and the left brown side is the exhaust port. The cylinder wall is a thin sleeve surrounding the piston head which creates a space for the combustion of fuel and the genesis of mechanical energy.](/Images/godic/202501/14/4StrokeEngine_Ortho_3D_Small0922.gif")
![An Otto Engine from 1920's US Manufacture](/Images/godic/202501/14/PSM_V18_D500_An_american_internal_combustion_otto_engine0922.jpg")
![The Atkinson Gas Cycle](/Images/godic/202501/14/T_cycle_AtkinsonMiller0922.png")
![Audi Diesel R15 at Le Mans](/Images/godic/202501/14/1_Audi_R150922.jpg")
A four-stroke engine (also known as four cycle) is an internal combustion (IC) engine in which the piston completes four separate strokes while turning a crankshaft. A stroke refers to the full travel of the piston along the cylinder, in either direction. The four separate strokes are termed: