Some aspects of stabilization and structure of laminar premixed hydrogen-air flames in a microchannel

Abstract

In the present paper, flame stabilization and structure are investigated numerically for non-adiabatic hydrogen-air flames at different equivalence ratios and inlet velocities. A cylindrical microcombustor in which combustion occurs in the annular region between two concentric tubes is investigated. The inner hollow tube contains static nitrogen gas and this combination acts as a thermal reservoir that stores and recirculates heat to the incoming mixture. Investigations are carried out using detailed numerical model incorporating two-dimensional transport, thermal radiation, multi-step kinetics, and conjugate heat transfer. Flame is sustained by the continuous ignition mechanism activated by an uninterrupted temperature field between gas mixture and wall developing at steady state. Heat losses from flame resulted in a crossover temperature higher than that of the lean-limit and stoichiometric free flames due to slow radical build-up. Thermal diffusion of hydrogen is shown to be responsible for enhancing the burning intensity of leading edge. Diffusion and reaction kinetics at the flame tip result in twin-peaked heat release rate distribution, most prominently for fuel rich flame (ϕ = 1.7).