described in detail infra that the accordingly reduced travel time of the front of the pressure wave of the main injection allows for the reduction of the active length of the time delay member 17 the control cross section which is required for the opening of the main injection and is represented by the stroke of the piston u03b4s 2 u03b4s 3 must be kept as small as possible by providing a circumferential annular groove within the metering piston unit 11 for transferring the fuel into the radial bore 10a which feeds into the time delay member 17 in order to provide a maximized pressure steepness over time of the front flank of the main injection the movements of the piston 10 over time is normed by the pressure wave generator 4 since the generator 4 always provides a constant pressure the desired pre injection quantity is defined by the cylinder chamber 10b as the product of the piston cross section and the stroke u03b4s 2 of the piston 10 in the following paragraphs the function of the system will be described in detail after the pre injection quantity has been metered by the piston 10 and the displacement of.