Extinction Limits of Premixed Catalyzed Flames in Stagnation Point Flows

The steady premixed laminar flame in the stagnation point flow of a flat adiabatic catalytic surface is examined. The fuel-oxidizer mixture is represented as a one-reactant mixture with chemical kinetics controlled by the mass fraction of the deficient reactant. The study is performed for non-unity Lewis numbers. Flame structures and extinction curves are determined with activation energy asymptotics. When the Lewis number (thermal diffusivity over mass diffusivity of the deficient reactant) is below a critical Lewis number (greater than one) extinction occurs with the flame front at the stagnation surface. In this case extinction curves are found to be C-shaped or exceptionally ∑-shaped and an extension of extinction limits is possible if the catalytic surface reaction is sufficiently strong. Activation energy asymptotic results are compared to exact calculations based on Newton iterations and adaptive grids. The qualitative agreement is good and the general trends are well described by activation energy asymptotics but quantitative errors are found in the predicted extinction limits.