CDI preinjection function

Preinjection on engine with direct injection is the principal parameter for maintaining the noise and exhaust emission levels.

An important element is that the preinjection quantity does not exceed a relatively small injected quantity level. Above this limit (1.5 mm3/stroke at 200 bar in the rail), there is a significant increase in the particulate emissions, with the result that there is still a noise benefit, but no further exhaust emission benefit. The minimum preinjection quantity which is required for effective fuel atomization, is 0.5 mm3/stroke.

Preinjection is used practically throughout the entire operating range, up to an engine speed of approx. 3500 rpm. This means that an adequately small preinjection quantity has to be assured even at high rail pressures (of around 1200 bar).

Start of actuation of preinjection

An actuation base value, dependent on the current engine operating point (and on the last start of actuation of main injection) is calculated, and adjusted in line with the coolant temperature.

Duration of actuation of preinjection

Calculation of the duration of preinjection is determined by the engine operating point and the rail pressure and is adjusted on the basis of the coolant temperature, the atmospheric pressure and the intake air temperature.