Abstract: A rotary internal combustion engine includes four generally oval-shaped rotors which rotate in the same angular direction at the same angular speed. The peripheries of adjacent rotors rotate past one another to confine a working volume therebetween. Two of such rotors have a truncated end to periodically open the working volume to exhaust combusted gases and to intake fresh air. A fuel injector mixes fuel with fresh air trapped in the working volume to form a combustible mixture. The four rotors are surrounded by a shroud having strakes for creating directed vorticity within the shroud. Turning vanes direct incoming air from an intake manifold into the working volume and also direct exhaust gases toward an exhaust manifold.