The Influence of Surface Chemistry on the Development of Minor Species Profiles in the Premixed Boundary Layer Combustion of an H₂/Air Mixture

Abstract

The combustion of premixed hydrogen/air mixtures flowing over a hot catalytic and non-catalytic surface has been modelled using a modified Newton's method and an adaptive gridding algorithm for the solution of the governing boundary layer equations. Detailed transport, including thermophoretic effects, and gas phase chemical kinetics were included in the model. The surface boundary conditions in the catalytic case include a mass transport limited surface reaction of H₂ and O₂ to form H₂Oand OH. The relative amounts of H,0 and OH were taken from available experimental data and were varied to test the effect of the amount of desorbed OH on radical profile shapes. Heat release and O-atom profiles exhibit a double peak as a result of OH desorption. The heat release in the catalytic case is significantly lower near the leading edge of the plate resulting in slower flame propagation into the boundary layer. Recombination reactions of the unstable species (O, OH, H, HO₂, H₂O₂) on the wall were included in the non-catalytic case. The sticking coefficients of the recombination reactions were varied to test the effect of the recombination rate on radical profile shapes.