Impact of detailed multicomponent transport on planar and counterflow hydrogen/air and methane/air flames

Freely propagating and counterflow laminar premixed steady hydrogen/air and methane/air flames are investigated numerically using complex chemistry an d detailed transport models. All the transport coefficients in the mixture, including thermal diffusion coefficients, are evaluated using cost-effecti ve, accurate algorithms derived recently by the authors from the kinetic th eory of gases. Our numerical results provide a quantitative assessment of t he impact of thermal diffusion on planar flame speed as a function of equiv alence ratio and on extinction limits of counterflow flames as a function o f either strain rate or equivalence ratio. In some cases, such as rich hydr ogen/air flames, the effect of thermal diffusion is actually opposite to th e one expected from a qualitative viewpoint or obtained with empirical mode ls. In addition, we observe relevant effects of thermal diffusion on extinc tion of methane/air counterflow flames.