Optimization of Pilot Injection Pattern and Its Effect on Diesel Combustion with High-Pressure Injection.

The pilot injection pattern was optimized, and some effects of pilot injection on combustion and exhaust emissions were investigated using a single-cylinder DI diesel engine. The results are as follows. (1) In order to avoid the increase of smoke, both a small-hole-diameter nozzle and very accurate control of pilot injection quanTITY and pilot-main interval are essential. These improve the atomization of the pilot fuel and the air entrainment into the main spray. (2) With pilot injection, NOx is not reduced at the injection timing of TDC but is gradually reduced at more retarded injection timing. This is because the main combustion is accelerated at early injection timing but is decelerated at retarded injection timing, due to the promotion of ignition. (3) The effect of pilot injection on NOx reduction is generally small ; however, pilot injection well prevents HC increase under light-load, injection-timing-retard conditions.