The internal structure of hydrogen-air difussion flames

Abstract

The Internal Structure of Hydrogen-Air Diffusion Flames. Tho purpose of this paper is to study finite rate chemistry effects in diffusion controlled hydrogenair flames undor conditions appearing in some cases in a supersonic combustor. Since for large reaction rates the flame is close to chemical equilibrium, the reaction takes place in a very thin region, so thata "singular perturbation "treatment" of the problem seems appropriate.
It has been shown previously that, within the inner or reaction zone, convection effects may be neglocted, the temperature is constant across the flame,
and tho mass fraction distributions are given by ordinary
differential equations, whore tho only independent
variable involved is tho coordinate normal to the flame
surface. Tho solution of the outer problom, which is a
pure mixing problem with the additional condition that
fuol and oxidizer do not coexist in any zone, provides
t h e following information: tho flame position, rates of
fuel consumption, temperature, concentrators of species,
fluid velocity outside of tho flame, and the boundary
conditions required to solve the "inner problem." The
main contribution of this paper consists in the introduction
of a fairly complicated chemical kinetic scheme
representing hydrogen-oxygen reaction. The nonlinear
equations expressing the conservation of chemical
species are approximately integrated by means of an
integral method. It has boen found that, in the case
considered of a near-equilibrium diffusion flame, tho
role played by the dissociation-recombination reactions
is purely marginal, and that somo of the second order
"shuffling" reactions are close to equilibrium. The
method shown here may be applied to compute the
distanco from the injector corresponding to a given
separation from equilibrium, say ten to twenty percent. For the casos whore this length is a small fraction of the combustion zone length, the equilibrium treatment describes properly tho flame behavior.