Numerical simulation of propagating circular and cylindrical lean premixed hydrogen/air flames

The wrinkling of premixed flame fronts propagating in gravity-free, quiescent, diffusionally imbalanced mixtures results from the combined influence of hydrodynamic and thermodiffusive instabilities. In this paper, the evolution of expanding, lean (equivalence ratio phi = 0.6), premixed 2-D circular and 3-D cylindrical H-2/air flames is investigated numerically using a single-step reaction and detailed transport. The Lewis number of the deficient reactant is sufficiently low so that the flame is subjected to both instability mechanisms. Instead of following a monotonically accelerating behavior, the flame is found to switch between a self-accelerating fully wrinkled shape when the cellular structures are amplified and a decelerating flame when the cell amplification saturates and the flame surface becomes almost smooth. This behavior is more intense in the 3-D case. In order to elucidate the effect of the perturbation in the third direction, two 3-D cases with varying perturbation wavelength along the z-direction are considered. Finally, the effect of stretch rate on the local propagation characteristics of the flame is investigated for both 2-D and 3-D cases. It was observed that due to a wider range of curvatures, the 3-D flames experience negative displacement speeds relative to the flow along positively-curved flame segments. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.