Nonequidiffusive premixed-flame propagation in obstructed channels with open, nonreflecting ends

Equidiffusive premixed combustion in obstructed channels with both open, nonreflecting ends exhibits various forms of flame propagation: oscillations, acceleration or a combination of both regimes. Given the limited practicality of equidiffusive premixed combustion, it is important to understand how these modes of combustion are altered at nonequidiffusive conditions, characterized by a nonunity Lewis number (thermal to mass diffusivity ratio) Le not equal 1. To achieve this, the impacts of Le on the flame dynamics and morphology are analyzed by means of the computational simulations of the reacting flow equations, with Arrhenius chemical kinetics, fully compressible hydrodynamics, and transport properties. In addition to varying Le, the parametric study includes various blockage ratios, channel widths, obstacle spacing and thermal expansion ratios. It is identified how these parameters influence the burning velocities as well as the scaled oscillation amplitude and frequency. Specifically, in the narrow channels with small blockage ratios, the amplitude and frequency of the oscillations vary with Le, with the frequency decreasing and the amplitude increasing as Le grows from 0.3 to 2. In other conditions, a transition from the flame oscillations to sudden flame acceleration or its propagation at a constant velocity is singularly influenced by Le, or by the interplay of Le with the geometric parameters of a channel. The delay time before the onset of flame acceleration, especially at Le < 1, also varies as the channel width and the blockage ratio change. In all cases, Le has both quantitative and qualitative effects on flame propagation in obstructed channels with both open, nonreflecting ends.