Effects of Plasma Chemistry and Charge Stratification in Plasma Jet Ignition

Abstract

The ignition efficiency of methane-oxygen-argon mixtures was measured with plasma jet ignition over a range of equivalence ratios. Several plasma feed gases, including the mixture to be ignited, were used as the plasma feed. Measurements were made at different stages of filling of the plasma cavity with the plasma feed in order to separate the effect of plasma composition from the effect of local mixture alteration by the feed gas. Methane. acetylene, propane, and hydrogen as plasma feeds resulted in the highest ignition efficiencies in the leanest mixtures. Oxygen, nitrogen, and helium also produced an increase in the ignition efficiency over that obtained with no feed, although the effect was less for these feeds than with the fuels. Although the local charge alteration at the igniter exit was greatly reduced, if not eliminated, in these experiments compared to many plasma jet experiments previously reported, the results are qualitatively quite similar. This suggests that either local charge alteration has not been completely eliminated, or that the plasma products of the fuels are as effective in igniting the lean mixtures as is a mixture enriched in the ignition region by the fuel itself.