Particulate emission and combustion characteristics of a direct-injection natural gas engine under various injection and ignition timings

The particulate emission under various injection timings and ignition timings was experimentally investigated on a natural gas direct-injection spark-ignition engine, and the corresponding combustion and emission characteristics were also analyzed. The results show that the particulate emission increases with the advance of fuel injection timing and ignition timing, the peak of particle number concentration appears around the particle diameter of 29 nm with the value of 1×10⁷ cm^-3, but the size distribution varies slightly. The flame development duration decreases with the fuel injection timing advancing, and the rapid flame duration reaches the minimum value at the fuel injection timing of 190°. With the ignition timing advancing, the flame development duration increases. The rapid combustion duration firstly decreases with the advancing ignition timing, and then increases. Both NO_x and HC concentrations increase with the advanced fuel injection timing and ignition timing.