the invention relates to a fuel injection system for self - ignition internal combustion engines . the noise reduction of diesel engines requires new injection systems . according to the invention a pre - injection and a main injection is achieved by employing to injection lines of different lengths . the difference in length is selected such that the time difference of the pressure waves for travelling the respective lengths corresponds to the desired time delay between the pre - injection and the main injection . in order to account for the compressibility of the fuel both injection lines are maintained at a standing pressure . the hydraulic effect of the injection lines on each other is prevented by check valves and by - pass valves . the controlled injection significantly reduces the combustion noise .