Free-Piston Engine

A free-piston engine is a linear, crankless internal combustion engine in which the motion of the piston is not controlled by a crankshaft but is instead determined by the interaction of forces from the combustion chamber gases, a rebound device such as a piston in a closed cylinder, and a load device such as a gas compressor or a linear alternator. Rather than delivering power to a crankshaft, a free-piston engine extracts power either through exhaust gas pressure driving a turbine, by driving a linear load such as an air compressor, or by incorporating a linear alternator directly into the pistons to produce electrical power. Free-piston engines typically operate on a two-stroke cycle, and can be built with a single piston, dual pistons, or an opposed-piston configuration depending on the number of combustion cylinders involved.