INFLUENCE OF MOMENTUM AND HEAT-LOSSES ON THE LARGE-SCALE STABILITY OFQUASI-2D PREMIXED FLAMES

We consider premixed gaseous flames propagating between parallel plate s (Hele-Shaw cell) and qualitatively analyze how the resulting losses of momentum and heat affect the flame stability for wavelengths of wri nkling that noticeably exceed the plate spacing. Modelling the flame a s an effective interface and using Euler-Darcy equations for the gas o n both sides, we firstly show that friction to adiabatic walls modify the Landau-Darrieus instability in two ways: a damping coefficient is brought in, along with a Saffman-Taylor type of instability. Being due to friction-induced pressure gradients, the latter may even dominate the stabilizing influence of gravity for downwardly propagating fronts in narrow channels. Because they ultimately make the gas density resu me its upstream value, heat losses tend to moderate these effects, as well as the Landau-Darrieus instability and the influence of gravity, but the long wavelengths of wrinkling may remain unstable in downward propagations when heat losses are acounted for. This last conclusion i s reached upon analysis of the weak-expansion limit. We also outline a flame-dynamics type of experiment to estimate the heat and momentum e xchanges that are involved in our analysis.