Numerical investigation and CSP analysis of laminar V-flames of H₂-CH₄-air mixtures

A numerical study of steady, rod-stabilized, V-type, CH₄-air and H₂-CH₄-air premixed laminar flames is conducted, particularly addressing the peculiar stabilization/blow-off of H₂-CH₄-air flames reported by Shoshin et al. (2013). For the CH₄-air flames, either decreasing the inlet equivalence ratio or increasing the mean inflow velocity leads to a larger standoff distance and a lower heat flux to the rod, 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; however, increasing the inflow velocity reduces the standoff distance and increases the heat flux to the rod. The predicted behaviour of the flames is fully 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. Moreover, algorithmic tools from computational singular perturbation (CSP) are used to investigate the reactive dynamics and identify the dominant physical processes of the flames.