Abstract: Features of this apparatus include a carrier ring with attached concentrically rotating pistons which tangentially couple forces from expanding gasses to a power transfer means, a rotating head with windows to allow piston passage, fuel admittance and exhaust ports to provide fuel intake and combusted gas removal without using reciprocating action, a power transfer means to couple power from the rotating pistons to a power output shaft, a means of simultaneous fuel admittance and exhaust gas removal, a unique sealing apparatus, and a balanced firing arrangement where two or more pistons symmetrically arranged with respect to their axis of rotation are simultaneously forced by expanding gases to rotate about their center of rotation in a concentric fashion. These features enable the apparatus to utilize maximum torque through the entire power stroke, do not require reciprocating motion, eccentric piston surface motion or angular deflection.