a rotary engine utilizes an expansion chamber and crescent piston to capture the energy of expanding combustion gases through out substantially all of each revolution of the piston . the rotary engine uses a crescent piston , the movement of which is guided by the combined action of a hub having a saddle supporting the piston and a can track . the invention burns fuel in a separate combustion chamber charged from a coaxially mounted compressor and controlled by a pass gate sentry valve . the rotary engine of the invention is cooled by an internal coolant injection system . the coolant solution may contain a alkaline reagent to react with and neutralize acidic components of the combustion gases which would otherwise remain in the exhaust and contribute to air pollution . the rotary engine of the present invention is adaptable to compression ignition fuels and spark ignition fuels . the invention may be constructed of conventional metallic materials as well as composites and ceramics .