Premixed flames with nonbranching chain-reactions (structure and dynamics)

Abstract

A description of the flame structure, and its response to wrinkling and unsteady perturbations, is given for a simplified multiple step reaction mechanism (representative for example of halogen-hydrogen reactions), involving a dissociation reaction, a nonbranching chain reaction, both with high activation energy, and a recombination reaction. We describe the changes in flame structure that take place with increasing values of the flame temperature. We encounter first a "merged" flame regime, for which the chemical reactions are confined to a thin zone, on the hot side of the flame, and the quasi-steady state approximation, applicable at lower flame temperatures can no longer be used. Then, we reach a slow recombination regime for which the radical is produced in a thin zone and diffuses out to recombine in the outer transport zones. New effects, due to the radical diffusivity on the flame dynamics, are found in this regime. Finally, in describing the flame structure for high enough flame temperatures, the effects of radical recombination can be neglected, but no longer the endothermic effect of dissociation.