Why is a diesel engine also called an self-ignition engine?

A diesel engine is called a self-ignition engine because it operates based on the principle of compression ignition. In this type of engine, air is compressed to such a high degree that its temperature increases significantly. When diesel fuel is injected into this highly compressed, hot air, it ignites spontaneously, without the need for a spark plug. This distinguishing feature is crucial because it enables the engine to operate more efficiently and on a higher compression ratio compared to gasoline engines, which rely on spark ignition.

Understanding how diesel engines work is important in the context of German traffic regulations, particularly regarding emissions and fuel types. Diesel engines tend to produce less carbon dioxide but can emit higher levels of nitrogen oxides and particulate matter. Thus, regulations often focus on ensuring that diesel vehicles meet strict emission standards to minimize their environmental impact.