A COMPUTATIONAL STUDY OF METHANE AIR COMBUSTION OVER HEATED CATALYTIC AND NONCATALYTIC SURFACES

A boundary layer model for the combustion of methane-air mixtures over a heated catalytic and noncatalytic surface maintained at constant temperature has been developed. Finite differences and a modified damped Newton's method were implemented to solve the coupled nonlinear parabolic partial differential equations for the conservation of total mass, momentum, energy, and chemical species. Adaptive gridding was used to obtain high resolution into the boundary layer and at the flame front. Detailed gas-phase chemistry was included in the model. The effect of different surface reaction boundary conditions on flame propagation and on the development of unstable species profiles in the gas-phase has been studied. An inert surface and a surface promoting gas-phase oxidation of the fuel to stable products have been simulated. In addition, the effect of desorption of hydroxyl radicals from the wall during the oxidation of the fuel on the unstable species profiles and on the propagation of the flame into the boundary layer was studied. The results illustrate the sensitivity of the predicted methane flame propagation on the surface boundary conditions used, which is more pronounced than for a hydrogen flame studied earlier.