Effect of Molecular Gas Radiation on a Planar, Two-Dimensional, Turbulent-Jet-Diffusion Flame

Non-gray radiation described by the exponential model for molecular gas bands was added to the numerical solution of turbulent combustion of methane in a planar, enclosed, jet-diffusion flame. The planar jet of methane is injected with velocity u_fuel into a stream of air flowing with velocity u_air parallel to the fuel. Diffusion-controlled combustion occurs in the mixing region of the jet. Plane-parallel, isothermal, black walls symmetrically located above and below the jet form the combustion chamber. A soot-free flame is assumed to exist so that molecular gas bands determine the thermal radiative transfer to the walls. Velocity, composition, and temperature fields and heat flux at the wall are obtained numerically. Approximately 40 percent of the requisite computation time is expended on the radiation calculation. Solutions are obtained to show the effect of channel size, air preheat, and product recirculation. Also the effect of reaction zone thickness was examined by varying an effective first Damko¨hler or mixing number which parameterizes the mixing-controlled reaction rate. It is found that a given reduction in maximum combustion temperature to reduce nitric oxide formation can be accomplished with a much less detrimental reduction on heat transfer by recirculating exhaust product into the combustion air than by reducing air preheat.