how does a diesel engine ignite
In a diesel engine, however, the air is compressed first, and then the fuel is injected. Because air heats up when it's compressed, the fuel ignites. The following animation shows the diesel cycle in action. You can compare it to the animation of the gasoline engine to see the differences. Image courtesy Baris Mengutay. The diesel engine uses a four-stroke combustion cycle just like a gasoline engine. The four strokes are: 1  Intake stroke -- The intake valve opens up, letting in air and moving the piston down. Â­. 2  Compression stroke -- The piston moves back up and compresses the air.