... the centerline of the centerline of the engine crankshaft, piston stroke equal to twice the crank radius. Piston ... symbols express VL. Four-stroke cycle engine work, including four piston stroke both the intake stroke, compression stroke, expansion stroke (Zuogong trip) and ... as the residual gas. To sum up, four-stroke gasoline engine through the intake, compression, combustion Zuogong, exhaust four ...