Analysis of ignition mechanism of combustible mixtures by composite sparks

Abstract

Formation process of flame kernels produced by composite sparks in a quiescent propane-air mixture is numerically simulated by using a set of partial differential equations on two-dimensional cylindrical coordinates. Simulation is done with emphasis on physical effects such as gas movements generated by spark discharge and heat transfer from the flame kernel to spark electrode surfaces. Although chemical reaction is considered only by an overall reaction, the present simulation is found to be useful for understanding of physical effects in the following points: the flow pattern near spark gaps is an important factor that governs the flame kernel structure, the flow pattern is affected by the spark electrode diameter, gap width, and spark duration, and the calculated variation in the minimum ignition energy agrees qualitatively with the experimental variation, and the existence of the optimum spark duration is well confirmed. As for composite sparks, it is found that the superiority in ignition ability of composite sparks over capacitance sparks depends on spark electrode diameter and gap width.