The Particle Emission Characteristics of a Light Duty Diesel Engine by Using Different Pilot Injections

Pilot injection has been used widely in diesel engines for its NO_x and noise reducing characteristics. In this paper, its impacts to the particle emissions were studied using a light-duty common-rail Euro 4 diesel engine with different pilot injection strategies. Three steady-state engine modes were selected from the EU legislative diesel engine test cycle to represent low, medium and high engine speeds and loads. The quantities and injection timings of the pilot injection strategies were then varied. The particle number concentration and size distributions were investigated along with the smoke and regulated gas emissions such as the NO_x trade-off. These results indicate how a pilot injection alongside a main injection can increase the particle size compared to a single main injection event. Furthermore, the split injection was closely related to the engine mode. Advancing the pilot injection generally reduces the particle size, which was made clearer when higher pilot fuel quantities were used. At lower fuel quantities, the opposite behavior was seen. Advancing the pilot injection also increased the nucleation mode particles but this impact was not clear at high engine loads. The increase of pilot fuel quantity increased the total particle number at the medium speed and load mode whilst reducing them at engine idle and the high speed and load mode. This was also reflected in the particle size and distributions as it tended to produce more large particles at middle speed/load while smaller and fewer ones at idle or high speed/load mode.