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How Does the Car Engine Piston Work?

Updated April 17, 2017

A car engine piston is anchored to and powered by a car engine crankshaft. An engine crankshaft spins in a circular motion deep inside an engine block; a piston rod, which anchors a piston to a crankshaft, converts the circular motion of an engine crankshaft into the up and down movement of a piston. An engine piston is wholly dependent on an engine crankshaft for power and movement; a piston moves up and down only as fast as a crankshaft spins.

Piston Operates Inside Engine Cylinder

An engine block consists of a series of hollow, elongated channels known as cylinders. Cylinders are the heart of an engine's operation and function. Each engine cylinder has one engine piston. A piston moves up and down inside of an engine cylinder. As an engine crankshaft spins, the piston, which is connected to the spinning crankshaft via the piston rod, moves through a continual cycle of up and down movements within an engine cylinder.

Piston Compresses Air/Fuel Mixture

All gasoline-powered engines use pistons to compress the engine air/fuel mixture, which is a specific ratio of air to gas. When the air/fuel mixture enters a vehicle engine on the downward motion of a piston, the air/fuel mixture gets compressed by the rising movement of a piston during a vehicle engine's power stroke. At the top of the power stroke, the air/fuel mixture gets pushed between the top, or head, of a piston and the top of the engine cylinder. This compression readies the air/fuel mixture for ignition by the spark plugs.

Piston Creates Cylinder Vacum

Besides compressing the air/fuel mixture of an engine, a piston is responsible for creating a vacuum, or an area of low pressure, within an engine cylinder. When a piston moves down inside an engine cylinder, the air pressure inside the cylinder is lower than air pressure outside of the cylinder. This low pressure area pulls a vehicle's air/fuel mixture into the cylinder where it eventually gets compressed and ignited.

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