Four-Stroke Cycle

Automobile engines actually have multiple cylinders. The movement of the piston from the top of its travel to the bottom of its travel is called stroke. Each cycle required to burn the air-fuel mixture has four strokes. Hence the name, four-stroke cycle. During the intake stroke, the piston is pulled down by the turning crankshaft, creating a vacuum above it. Because the intake valve is open while the piston is moving down, the air-fuel mixture is drawn into the cylinder through the intake valve port. The mixture is supplied to the cylinder by the fuel system. Gasoline is especially combustible when one part of it is atomized with about 15 parts of air. Atomization makes the mixture like fog.