A Numerical Study on Effects of Electrode Gap and Heat Loss on Flame Kernel Formation in Spark Ignition Process for Methane/Air Mixtures

Abstract

The effect of the electrode on the flame kernel initiation in the spark ignited methane/air mixtures has been numerically investigated. The electrode gap was thought to have strong effects on the flame kernel initiation and was varied as a parameter. The equivalence ratio of the mixture was also varied. A detail reaction mechanism of methane and a detail transport mechanism including thermal diffusion were taken into account in the numerical model. The effect of the heat loss to the electrode was investigated for the several condition of the electrode surface. Results indicated that the heat loss to the electrode for the isothermal condition of the electrode surface was not different from that for the thermal condition including the heat transfer to the electrode and the heat conduction in the electrode although the flame kernel initiation for the adiabatic surface of the electrode gap was rather different from them. The flame kernel initiation in the stoichiometric mixture was enhanced with increase in the electrode gap for the same ignition energy. The OH production rate in the lean mixtures was smaller than that in the stoichiometric mixture for the same ignition energy. Even in the lean mixture, OH production rate became much greater when the electrode gap was broadened only from 3 to 4 mm.