Chemical nonequilibrium effects in hydrogen-air laminar jet diffusion flames

Abstract

A theoretical medel for the structure of hydrogen-air laminar jet diffusion flames has been developed. The model includes the effects of nonequilibrium chemical kinetics and realistic transport properties. The reaction zone in such flames is found to resemble the recombination zone in premixed flames. Distributions of the free radicals H, O, and OH are substantially in excess of local equilibrium values. The computed results show that the partial equilibrium approximation, which is often employed in premixed flames, is valid within the reaction zone but breaks down outside it. Hydroperoxyl is found to be an important intermediate species in the flame, being formed primarily by the reversible recombination reaction H + 0/sub 2/ + M ..-->.. HO/sub 2/ + M and destroyed by H, O, and OH radical attack. The absence of chemical equilibrium and the broadening of the energy release zone result in peak temperatures which are well below the adiabatic flame temperature. Broadening of the energy release zone is due significantly to the mobility of hydrogen atoms.