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In order to improve the ignition stability and reduce the cycle-to-cycle variation, it is necessary to understand the mechanism of the flame kernel development and the local quenching effect during the spark ignition process. In this study, experiments for the spark ignition process in a high-speed lean gasoline-air mixture turbulent flow field were conducted. OH* chemiluminescence measurement and focusing Schlieren photography was applied to observe the development of flame kernel and discharge channel behaviors simultaneously. Results indicated that flame kernel fragments, generated by the restrike and short- circuit of discharge channels, quenched due to the local turbulence, which led to slow flame propagation or misfire. In that cases, the initial flame kernels showed stretched behaviors, along with high curvatures.

1 In this work, a microwave-assisted spark ignition was investigated for premixed lean methane/air mixtures. Experiments were performed in a combustion chamber with a constant volume. The initial pressure of the chamber was set to 0.1MPa and 1Mpa. Equivalence ratio Ø was varied from 0.51 to 0.6 to investigate the ignition behavior near the lean limit. High temperature regions in flames were visualized by the Schlieren photography using a high speed video camera. When the irradiation delay of microwave is 200 μs and the pulse frequency is 10 kHz, the probability of ignition reached maximum. A microwave irradiation to the mixture enable to ignite the mixture of equivalence ratio of 0.52. Table 1Nomenclature