Edinburgh Napier University

  A computational study of steady, rod-stabilized, inverted, lean, CH4-air and H2-CH4-air flames is conducted. For the CH4-air flames, either decreasing the inlet equivalence ratio or increasing the mean inflow velocity leads to a larger standoff distance, and below a critical value of the inlet equivalence ratio or above a critical value of the inflow velocity, the flame blows off. For the H2-CH4-air flames, decreasing the inlet equivalence ratio has similar effects as those on the CH4-air flames; however, increasing the inflow velocity reduces the standoff distance. Though counter-intuitive, the predicted behaviour of the flames is consistent with the experimental observations. Both the CH4-air and H2-CH4-air flames exhibit preferential diffusion effects such as superadiabatic temperatures and local equivalence ratio variations, which are more pronounced for the H2-CH4-air flames, displaying non-uniform and localized consumption rates of the fuel components. The strong diffusion of H2 plays an important role to maintain and even strengthen the reaction processes in the anchoring region and the counter-intuitive stabilization/blow-off of the H2-CH4-air flames.