Abstract: This invention relates to a combustion engine which is cooled internally. Combustion occurs in primary combustion chambers and the gas combustion products are released into secondary chambers after combustion to mix with cooler fluids. These fluids cool the engine body during engine operation. A preferred form of the invention consists of a semi-rotary engine and means for joining the rotor of this engine to the output power shaft. Preferred engines of this invention will not require external cooling or use poppet valves and will be able to operate as both a four-stroke and two-stroke engine.