Analysis of Nonequidiffusive Premixed Flames in Obstructed Channels

摘要

The impact of the Lewis number, Le, which characterizes the (non)equidiffusivity of a combustible premixture, on the dynamics and morphology of a premixed flamefront, propagating through a toothbrush-like array of obstacles in a semi-open channel, is studied by means of the computational simulations of reacting flow equations with fully-compressible hydrodynamics and Arrhenius chemical kinetics. The computational approach employs a cell-centered, finite-volume numerical scheme, which is of 2nd-order accuracy in time, 4th-order in space for convective terms, and of 2nd-order in space for diffusive terms. The channels of blockage ratios 0.33～0.67, with the scaled spacing between the obstacles being Δz/R = 0.25, and of widths 48 ≤ D/L_f ≤ 96, where L_f is the flame thickness, are considered. The Lewis numbers employed are in the range 0.2 ≤ Le ≤ 2.0. It is shown that Le influences the flame evolution substantially. Specifically, flame acceleration weakens for Le > 1 (inherent to fuel-lean hydrogen or fuel-rich hydrocarbon burning), presumably, due to a thickening of the flamefront. In contrast, Le < 1 flames (such as that of rich hydrogen or lean hydrocarbon) acquire an extra strong folding of the front and thereby accelerate even much faster. The later effect can be devoted to the onset of diffusional-thermal combustion instability.