A Numerical Study on Early Stage of Flame Kernel Development in Spark Ignition Process for Methane/Air Combustible Mixtures

Abstract

A numerical analysis with a detail description of flow dynamics and chemical kinetics on the effect of the equivalence ratio of methane/air mixtures on the minimum ignition energy is carried out. In the early stage, the behavior of the flame kernel is dominated by a flow which is induced by the blast wave. Although a high temperature gas, which spurts out from the electrode gap, quenches, the gas at the electrode gap is self-sustained with an application of small ignition energy near the minimum. After a certain period of time, the flame kernel gradually grows out of the electrode gap. In the case of high-energy application, hot gas region, which spurts out from the electrode gap, doesn't quenches and propagatable flame kernel is formed at the early stage of spark ignition process. The local equivalence ratio at the electrode gap is larger than that in the outer region with an application of small energy although its effect is not so strong in an application of high energy. In addition, calculated profile of the minimum ignition energy as a function of the equivalence ratio for methane-air mixtures shows a minimum value below the equialence ratio of 1.0. An effect of preferential diffusion for lighter molecules is confirmed.