Experimental study on the effects of the ignition parameters on the spark characteristics and the flame propagation of premixed methane–air mixtures

Abstract

The charging time and the electrode gap distance are very important ignition parameters for the spark ignition process. The effects of these two parameters on the spark characteristics and the flame propagation of premixed methane–air mixtures were investigated experimentally at a constant pressure and a constant temperature by using a constant-volume bomb and a high-speed schlieren system. The parameters of the spark characteristics, including the spark voltage, the spark current, the spark duration and the lean burn ignition limit, were experimentally measured, and the spark resistance and the ignition energy were calculated on the basis of these parameters. By comparing the schlieren photographs of laminar flame propagation in different conditions taken by the high-speed schlieren devices, the effects of the ignition parameters on the cross-sectional area of the flame, the flame radius and the speed of flame propagation were analysed. The results show that the charging time and the electrode gap distance have important influences on the early kernel formation. Increasing the charging time or the electrode gap distance can significantly increase the influences of the effective radius of ignition and the original kernel size, can increase the ignition energy and can promote kernel development and flame propagation. Increasing the charging time or the electrode gap distance can effectively increase the lean burn ignition limit but, when the electrode gap distance increases to a certain extent, only increasing the charging time can increase the lean burn ignition limit further.