The Soret Effect in Naturally Propagating, Premixed, Lean, Hydrogen-Air Flames

Comparatively little attention has been given to multicomponent diffusion effects in lean hydrogen-air flames, in spite of the importance of these flames in safety and their potential importance to future energy technologies. Prior direct numerical simulations either have considered only the mixture-averaged transport model, or have been limited to stabilized flames that do not exhibit the thermo-diffusive instability. The so-called full, multicomponent transport model with cross-diffusion is found to predict hotter, significantly faster flames with much faster extinction and division of cellular structures. Accepted for presentation at the 32nd International Symposium on Combustion, paper 2B13, and for publication in the Proceedings of the Combustion Institute, volume 32. Nomenclature Dk,` binary diffusion coefficient Dk,` species diffusion coefficient Dmix k species mixture-averaged diffusion coefficient θk species thermal diffusion coefficient δT thermal flame thickness hk specific enthalpy of the species j k species diffusive flux vector, the superscript i = 0, 1, 2 indicating the degree of approximation j cor k corrected flux, derived from j (i) k for i = 1, 2 κ curvature of the flame surface (positive when the flame is convex toward the fresh mixture) k, ` species indices L Markstein length λ thermal conductivity (of the mixture) λ′ partial thermal conductivity p pressure q heat flux vector ρ mass density ρk species mass density, ρYk