Extending lean misfire limit of methane-air mixtures by means of an enhanced spark discharge

Reliable initiation of flame kernel development by an electrical spark in IC engines operating at ultra-lean air-fuel mixtures lays down specific demands to spark discharge variables. The demands become especially strict under conditions of intensive mixture motion through the spark gap. The main goal of this study was to determine experimentally the minimum values of spark duration and spark current in the glow phase of the discharge necessary for reliable ignition of methane-air mixtures with equivalence ratios of 0.7 down to 0.6. Different combinations of flow velocity and spark plug orientation with respect to mean flow vector have been considered. A special experimental ignition system was employed to set up spark discharge variables. Besides, a numerical study of early flame kernel development under conditions used in the tests has been carried out. Among other conclusions, the results of the study show that spark duration and energy typical of normal production ignition systems are insufficient for consistent ignition of ultra-lean mixtures rapidly flowing through the spark gap.