Impact of thermal diffusion on lean near-limit H2-CH4-air flames

In this research work, we investigate the influence of transport models and thermal diffusion (Soret effect) on numerical predictions of zero-gravity flame balls as well as normal-gravity steady and closed burner-stabilized reacting fronts for lean hydrogen-methane-air premixed mixtures, having a 40% hydrogen (H2) and 60% methane (CH4) fuel composition, specified on a molar basis. Three transport models are considered in the simulations: mixture-averaged, multicomponent, and multicomponent with inclusion of thermal diffusion. Although differences are found between the mixture-averaged and multicomponent solutions, they are not as prominent as those found when thermal diffusion is accounted for. The inclusion of thermal diffusion leads to predictions of larger flame sizes for both the zero-gravity flame balls and the normal-gravity burner-stabilized flames. Furthermore, lower lean limits are predicted when thermal diffusion is included in the computations.