Compared to conventional fuel injection characteristics, ideal fuel injection characteristics should fulfil the following requirements:
• It should be possible to independently determine the injection pressure and injection volume for every operating point of the engine (additional degree of freedom for ideal mixture preparation)
• After restart of combustion, the injection pressure should be freely selectable during the entire fuel injection procedure.
• The injection quantity and pressure should be as low as possible at the start of injection (during the spark delay between injection start and combustion start)
These requirements have been fulfilled in the common rail accumulator injection system with preliminary and main injection.
The noise and vibration characteristics are also decisively influenced by the degree of combustion severity. Therefore, a carefully planned adaptation of fuel injection has taken on an important role.
Preferably, influencing engine combustion takes place by means of a preliminary injection in the common rail system. This makes disturbance-free combustion at low noise levels possible (refer to Fig.).
In addition, active and passive acoustic measures contribute to the sonic performance being considerably enhanced, even over high-performance IDI-engines, e.g. offsetting the pin axle from the centre of the piston to the counter pressure side (see Fig.).
The common rail system has a modular design. The following components are mainly responsible for the injection characteristics:
• Solenoid valve-controlled injectors which are screwed into the cylinder head
• Pressure accumulator (rail)
• High pressure pump
To a lesser extent, the following components are also important:
• Electronic control unit (DDE)
• Crankshaft speed sensor
• Camshaft speed sensor
