Abstract: A free piston combustion chamber coupled to air compression and gas expansion chambers are combined with a rotary motor. The rotary motor shaft drives the air compressor, receives power from the expanding gases in the expansion chamber and provides residual torque and power for external use. Two combustion chambers located at each end of the free piston receive compressed air and fuel for combustion outside of the rotary motor assembly. The motion of the free piston between the two combustion chambers is independent of the motor rotary motion. The air admission inside the combustion chambers, the fuel injection and the combustion initiation process are all controlled and timed by the free piston movement back and forth. The compressed air exiting from the compression chamber is heated by the gases exiting from the combustion chambers, before they are admitted into the expansion chamber of the rotary motor.