Analysis of nonequidiffusive premixed flames in obstructed channels

The impact of the Lewis number, Le, on the dynamics and morphology of a premixed flame front, spreading through a toothbrushlike array of obstacles in a semiopen channel, is studied by means of the computational simulations of the reacting flow equations including fully compressible hydrodynamics and one-step Arrhenius chemical kinetics. The channels of blockage ratios alpha = 1/3, 1/2, 2/3 are considered, with the Lewis numbers in the range 0.2 <= Le <= 2 employed. It is shown that the Lewis number influences flame evolution substantially. Specifically, flame acceleration weakens for Le > 1, inherent to fuel-rich hydrogen or fuel-lean propane burning. In contrast, Le < 1 flames, corresponding to lean hydrogen-air or rich propane-air mixtures, acquire strong folding of the front and thereby accelerate even faster. The latter effect can be devoted to the onset of the diffusional-thermal combustion instability.