A Generalized Burke-Schumann Formulation for Hydrogen-Oxygen Diffusion Flames Maintaining Partial Equilibrium of the Shuffle Reactions

Abstract

Under a wide range of conditions of ambient pressures, temperatures, dilutions and strain rates, non premixed combustion in hydrogen-oxygen systems maintains partial equilibrium of the four two-body chain-carrying reactions while experiencing finite rates of the three-body radical-recombination reactions H + O₂ + M → HO₂ + M and H + H + M → H₂ + M. There then exists a three-step reduced mechanism, with H as the only intermediate species and concentrations of the radicals O, OH and HO₂ related to that of H through steady states. The conservation equations corresponding to this chemical description arc formulated here in terms of generalized coupling functions that account for species diffusivities that differ from the thermal diffusivity. providing a set of equations that describe the flame structure for strain conditions ranging from ncar extinction to weakly strained flames. As a model example, the formulation is applied 10 the analysis of name development in the hydrogen-air laminar mixing layer with free-stream temperatures above the crossover temperature corresponding to the second explosion limit. The formulation can be used for many other model problems as well as for computational studies of nonpremixed combustion in complex configurations involving both laminar and turbulent flows.

Keywords:

• Diffusion flames
• hydrogen
• Burke-Schumann
• reduced mechanisms
• conserved scalars