How does a diesel engine get its energy?

A diesel engine heats a volatile fuel or oil, and mixes it with hot compressed air, causing it to rapidly combust (explode). Whereas a gasoline engine uses much more flammable petroleum distillates, a diesel engine can use many types of refined oils, such as peanut oil or mineral oil.

The fuel is sprayed into a heated combustion chamber (cylinder) where air in the chamber has been trapped and compressed by a moving piston, leading to compressive heating of the air. The oil explodes, and it forces the cylinder back in the opposite direction (the power stroke, part of a measured cyclic motion). On the following stroke of the cylinder, the waste gases (mostly water and CO2) are forced out through a valve opening, and the cylinder is ready for more fuel.