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In diesel engines, high-pressure fuel injection is very effective to reduce emissions of particulates and oxides of nitrogen. For this reason, all efforts have been directed to develop suitable high-pressure injection systems. However, high-pressure injection often increases internal leakage of the working fluid, increases power for pumping, and is sometimes still short of injection pressures at lower engine speeds. To remove these faults, the present authors developed a fuel injection system named KD-3 that relies on a novel principle using oil hammering in a convergent pipeline. The dynamic behavior of the proposed system was analyzed by the method of characteristics and computer simulations. A prototype injection system was designed and tested with success. Using a source pressure of 20 MPa, this system boosts pressure well to higher than 120 MPa at the inlet of injection nozzle.

In diesel engines, pilot injections and injections at a reduced initial injection rate with high-pressure fuel injection have a potential to reduce particulate, NOx and noise emissions simultaneously. For this reason, various shaping methods of injection rate waveform have been proposed. The present authors also propose such a high-pressure injection system with variable injection rate that relies on spool acceleration and oil-hammering in the injection pipeline. This paper first describes the injection rate shaping, including injections with pilot and reduced initial injection rate, and elucidates their effects on reducing exhaust and noise emissions. A pilot injection can be achieved by either installing a fuel spill path in a plunger body or elongating prelift of the spool. Computer simulations and bench tests of such injection systems show that pilot injection quantity is small enough and the pilot injection pressure is much lower than that of the main part of the injection.