Impact of Thermal Expansion and Lewis Number on Premixed Flame Propagation in Channels with Adiabatic and Isothermal, Nonslip Walls

摘要

The impacts of the Lewis number (Le), the thermal expansion factor (Θ), and the flame propagation Reynolds number (Re) on the flame dynamics induced by wall friction in adiabatic and isothermal channels is studied by means of the comprehensive computational simulations of the reacting flow equations with a fully-compressible hydrodynamics and an Arrhenius chemical kinetics. We employed the quantiles Le and Re in the ranges 0.2 ≤ Le ≤ 2.0 and 5 ≤ Re ≤ 30. With adiabatic, nonslip walls, flames accelerate exponentially for typical hydrocarbons, 6 ≤ Θ ≤ 8, though acceleration weakens to a linear trend for smaller Θ. The situation is conceptually different in isothermal channels, where flames spread steadily or near-steadily (slow acceleration) or may even extinguish. A non-unity Lewis number influences the flame dynamics substantially in both adiabatic and isothermal channels. Specifically, Le < 1 flames get extra strong folding due to the diffusional-thermal instability and thereby spread much faster than Le = 1 ones. In contrast, Le > 1 flames are thickened and propagate slower.