by changing the amount of injected fuel (quality torque control), rather than varying the amount of intake air. Stratified charge mode also keeps the flame away from the cylinder walls, reducing thermal losses.

Since mixtures that are too lean cannot be ignited with a spark plug (due to the lack of fuel), the charge must be stratified, i.e., a small zone of fuel-air mixture must be created around the spark plug. To achieve this, a stratified charge engine injects fuel during the later stages of the compression stroke. A "swirl cavity"