Dynamics and Morphology of Premixed Flame Propagation in Channels: Effects of the Lewis Number and Thermal Boundary Conditions

Abstract

Equidiffusive combustion is a model, which is widely employed in analytical and computational studies, including those on premixed flame acceleration. However, realistic combustible mixtures are oftentimes far from the stoichiometry, being thereby strongly non-equidiffusive and thus requiring extra analyses. The present work addresses this demand by means of the computational simulations of the basic fully-compressible hydrodynamic and combustion equations. Specifically, here we focus on the non-equidiffusive flames at various thermal boundary conditions, including adiabatic or isothermal walls of the channels. A detailed parametric study is performed, with the key parameters of the problem being the Lewis number, Le, taken in the range 0.2 ≤ Le ≤ 2.0, the thermal expansion factor Θ, being 5 ≤ Θ ≤ 8, and the flame propagation Reynolds number, Re = R/PrL_f, where L_f is the thermal flame thickness and Pr the Prandtl number. We used Re in the range 5 ≤ Re ≤ 30. It is shown that while Θ ~ 8 flames tend to accelerate exponentially in channel with adiabatic, nonslip walls; acceleration moderates to a linear trend for Θ ~ 5. Moreover, with the isothermal walls, acceleration moderates (with hot walls) or even terminates (with cold walls). Furthermore, it is found that a non-unity Le influences the flame dynamics notably in both adiabatic and isothermal channels. Namely, Le < 1 flames get extra strong corrugation and thereby spread much faster than equidiffusive ones. In contrast, Le > 1 flames are thickened and propagate slower.