Hot surface ignition of H2-air and CH4– H2-air mixtures for various equivalence ratios and heating Rates

Abstract

Gaseous mixtures ignite when they come in contact with a surface with the ignition threshold temperature of the mixture. The hot surface ignition of fuels like hydrogen poses a safety threat due to its wide flammability range and high diffusivity. The present study numerically investigates hot surface ignition of H2-air and CH4/H2/air mixtures using detailed chemistry. The effects of the equivalence ratio (φ), composition and heating rate on the ignition threshold temperature of the mixture are studied. At rich mixture conditions, the ignition occurs at the side of the heated surface (glow plug). On the other hand, the lean mixtures ignite at the top of the heated surface. The variations in heating rates significantly affect the ignition temperature of rich mixtures. In contrast, the ignition temperature of the lean mixture does not show any considerable deviation concerning the variation in heating rates. The phenomenon of puffing flame is observed at lean extinction limits of H2-air mixtures. Lower ignition thresholds are observed in CH4/H2/air mixtures with high concentrations of H2. Mixtures having higher CH4 concentrations show higher ignition thresholds. The role of local equivalence ratio and heat release rate on the ignition characteristics has been studied to predict the behaviour of ignition kernel at various mixture conditions.