1 PCM
2 High pressure pump
3 High pressure chambers for high pressure generation
4 Fuel feed
5 Fuel metering valve
6 Fuel pressure sensor
7 Fuel rail
8 Solenoid valve
9 Injector needle
The engine management system on the common rail injection system is capable of providing the optimum injection pressure for each operating condition.Via the high pressure chambers of the common rail high-pressure pump, fuel is compressed and fed to the fuel rail. In the process, the delivery quantity is regulated by the fuel metering valve by varying the opening cross section of the fuel metering valve accordingly. The fuel pressure is regulated in such a way that the optimum pressure is available for each operating condition. On the one hand, this reduces the noise emission during fuel combustion.
On the other hand, the engine management system can meter the fuel very precisely, which has a positive effect on exhaust emissions and fuel consumption. The fuel pressure sensor continuously informs the PCM about the current fuel pressure. Pressure is regulated via the fuel metering valve by reducing the cross section of this valve accordingly. As a result, the high-pressure pump delivers a smaller quantity of fuel (or no fuel at all, depending on the requirements) until the desired fuel pressure is reached. Fuel pressure is dependent on engine speed and engine load.
Switching off the engine
Because of the way the diesel engine works, the engine can only be switched off by interrupting the fuel supply. In the case of fully electronic engine management this is achieved by the PCM specifying an injected quantity of 0. The solenoids for fuel injection are therefore no longer energized and the engine is switched off.
Pressure drop after engine is switched off
After the engine has been switched off, pressure is reduced through leakage past the fuel injectors. The rate of pressure reduction depends on how high the fuel pressure and fuel temperature are. For safety reasons, a certain period of time has to elapse before the high-pressure system is opened after the engine is stopped.