Pictured are the front and back view of a half cylinder with air concentrations. Red indicates high air concentration and blue indicates low air concentration. This engine geometry shows a central intake valve in the cylinder head, and exhaust ports attached to the side of the cylinder wall at the bottom. Air flows through the central valve at the top, and exhaust flows into the cylinder through the ports at the bottom.

This different engine geometry has a helical intake port/valve in the center of the cylinder head, and four exhaust ports/valves on the periphery of the cylinder. Air flows through the central intake port in a swirling motion, and exhaust flows into the cylinder through the four ports in the cylinder head. Both the central port and exhaust ports produce a swirling motion. Bassem Ramadan and his team at Kettering University have found that when both air and exhaust are swirling, mixing between the two is delayed during the compression stroke.