A Computational Study on the Dynamics of Counterflow Hydrogen-Air Edge Flames

Abstract

Local quenching of diffusion flame and the dynamics of the edge flame are computationally studied by a model problem of interaction between a counterflow diffusion flame and two pairs of vortices. The numerical method employs detailed hydrogen-air kinetic mechanism and high order spatial differencing and time integration. A soft inflow boundary condition using the Navier-Stokes characteristic boundary conditions (NSCBC) is implemented to maintain a steady counterflow diffusion flame. A steady laminar diffusion flame in a two-dimensional counterflow is locally extinguished by the two impinging pair of counter-rotating vortices with sufficiently large strength of vorticity. It is found that the subsequent evolution of the flame edges depend on the flow conditions, in that the distance between the two edges can broaden leading to total extinction of the flame or it may close off to re-establish the original diffusion flame shape. The local flow parameters and flame propagation speed are examined and the existence of negative edge flame speed is investigated. The effect of preferential diffusion is also considered by varying the Lewis number of hydrogen, and the results are compared against the theoretical predictions.