Numerical study of CH* chemiluminescence and heat release rate in methane inverse diffusion flame

Flame optical diagnostic method based on CH* chemiluminescence is often used in the combustion process monitoring. In this work, a numerical study of CH* chemiluminescence was conducted for the laminar methane inverse diffusion flame with a range of global oxygen/fuel equivalence ratios. CH* chemiluminescence is mainly distributed in the upstream of the inverse diffusion flame and the CH* concentration increases with the global oxygen/fuel equivalence ratio. CH* is generated by C2H, which mainly comes from the reactions OH + C2H2<=>C2H + H2O and H + C2H2<=>C2H + H-2. In addition, most CH* is quenched by collisions with H2O, CO, CO2 and H-2, and the CH* collision quench is enhanced with increasing global oxygen/fuel equivalence ratios. The CH* generated in the peak reaction zone will diffuse to the fuel and oxidizer sides due to the mass diffusion and the thermal diffusion. Moreover, the correlation between CH* and local heat release rate distribution is explored and CH* can characterize the local heat release rate on the fuel side.