Operating principles of diesel engine control systems (BMW 7 Series E38)

When a diesel engine is running, clean air is sucked into its cylinders and compressed to high pressure. The air temperature rises above the ignition temperature of diesel fuel. The fuel is injected into the cylinder a little ahead of its time and ignites spontaneously. Thus, spark plugs are not used to ignite the fuel in a diesel engine.

When the engine is cold, the compressed air temperature may not reach the value required for ignition. In this case, additional preheating is required. For this purpose, a glow plug is installed in each cylinder, which heats the combustion chamber. The duration of heating depends on the ambient temperature and is regulated by the engine control unit and the preheating relay.

Before entering the injection pump, the fuel is cleaned of impurities and water in the fuel filter. Therefore, it is important to remove water from the fuel filter or replace it in accordance with the requirements of the maintenance schedule (see chapter Vehicle settings and routine maintenance).

To increase power, some engines use turbocharging.

Diesel engines are controlled by an electronic system similar to that of petrol engines (see section Fuel system of gasoline engines).

(This publication was borrowed from an online resource BMWman)