Swirl

The orderly swirling motion of the charge air inside the combustion space, to aid mixing of this air with the atomized fuel as it is injected. Thorough mixing of the air and fuel is essential to good combustion. Swirl is achieved by designing cylinder heads, air inlet ports, valves, and piston crowns so the required motion is set up in the charge air as it enters the combustion space and is then compressed.