Combustion and PM emission characteristics of diesel ignited natural gas engine under various diesel injection timings and pilot delivery

The combustion and PM emissions under various pilot diesel injection timings and delivery were experimentally investigated in a modified diesel pilot-ignited natural gas engine to analyze the combustion and emission characteristics. Results indicate that particle size distribution curve with variation of pilot diesel injection timing and delivery exhibits unimodal shape, the peak of particle number concentration appears near diameter of 29nm, and the size distribution varies slightly. With injection timing advancing, the particle number concentration especially nanometer particle number concentration obviously increases, and the particle mass concentration exhibits a decrease-increase trend, ignition delay period increases and total combustion duration first shortens and then prolongs slowly, corresponding crank angle of the heat release rate curve center closes to and then leaves TDC gradually. With the pilot delivery increasing, both ignition delay period and total combustion continuously decrease, and the crank angle of heat release rate curve center closes to TDC gradually, meanwhile the particle number concentration evidently decreases and its mass concentration increases unexpectedly.