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. (1) In order to avoid the increase of smoke, both a small-hole 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. NO_x is not reduced at 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) With pilot injection, the effect of NO_x reduction is generally small but the prevention of HC increase is obtained only under light-load, injection timing retard conditions.