Premixed flame ignition by transient plasma discharges

Flame ignition by short-duration (≈ 50 ns) transient plasma, or corona, discharges was investigated for methane-air, propane-air and butane-air mixtures at atmospheric and elevated pressures. Such discharges produce a larger fraction of high-energy electrons, yield more spatially distributed energy and deposit energy in the gas more efficiently than conventional arc discharges do. We show that compared to conventional arc ignition, flames ignited by transient discharges yield significantly shorter (typically by a factor of 3) ignition delay and burn times. The major advantage of coronas was found to be the spatial distribution of ignition sites and more efficient use of wall-plug energy. Experimental evidence suggests that chemical effects of the ionized species and radicals generated are apparently minor. The observed effects of discharge energy, equivalence ratio, pressure and fuel type on ignition delay and burn times can all be explained using a simple mechanistic model that considers the spatial distribution of streamers and a hypothesized minimum streamer ignition energy that is analogous to the conventional minimum ignition energy. Applications to practical combustion devices such as lean-burn premixed-charge internal combustion engines are discussed. 1 Department of Aerospace and Mechanical Engineering 2 Department of Electrical Engineering Electrophysics