Extinction of diffusion flames with nonunity Lewis numbers

Abstract

Quasisteady extinction of diffusion flames with nonunity Lewis numbers is analyzed for counterflow diffusion flames in the diffusion-flame regime of activation-energy asymptotics. Particular attention is placed on an excess or deficiency of the total energy in the reaction region, associated with leakage of the reactants. If the Lewis number is less than unity, there is diminished diffusive loss of thermal energy that leads to an increase of the total energy in the reaction zone as reactants penetrate. The resulting excess total energy strengthens the chemical reaction, so that the flame becomes more robust and resistant to extinction. On the other hand, flames with Lewis numbers greater than unity are found to extinguish more easily. An extinction criterion is provided that is valid for nonunity Lewis numbers.