The operation of a Diesel Engine

Diesel engines are designed to operate on the four-stroke or the two-stroke principle, just like petrol engines. In respect of their design features diesel engines differ more particularly in the manner in which the fuel and air are brought together and ignited.

In a diesel engine with direct injection (or solid injection) the fuel is injected directly into the cylinder (or sometimes into a spherical combustion chamber formed in the piston). The injection nozzle must be so designed that its spray pervades all the air in the combustion chamber, so that complete combustion of the fuel can take place.

In a diesel engine provided with a swirl chamber the air is forced into this chamber by the piston and thereby acquires a rapid swirling motion, so that mixing with the fuel is promoted. What mainly occurs in the pre-combustion chamber of a diesel engine is mixing of the fuel and air and preliminary combustion of the mixture.

As a result of the rise in pressure during this pre-combustion, the incompletely burned fuel-and-gas mixture flows at high velocity from the pre-combustion chamber into the cylinder, where it can undergo complete combustion with the air there.