Investigation of C2* chemiluminescence based on improved CH4/O2 diffusion flame combustion reaction mechanism

The chemiluminescence of C2* can effectively characterize the global and local combustion characteristics of flame. In this work, numerical simulation of C2* chemiluminescence was carried out based on the improved GRI-Mech 3.0 mechanism. The background emission of C2* was effectively deducted by the 535 nm filter, and the simulated two-dimensional distributions of C2* chemiluminescence were in good agreement with the experimental results. The species C2, C3, C3H, C3H2, C2O and their detailed chemical reaction kinetic mechanisms were added to the GRI-Mech 3.0 mechanism. The importance of the additional reaction kinetic mechanisms in the CH4 reaction mechanism was revealed. The C2* reaction characteristics were analyzed based on numerical simulation results. It was found that R1(CH2+C=C2*+H2) was the dominant formation reaction and R5(C2*+H2O=C2+H2O) was the dominant quenching reaction of C2*. Furthermore, the effect of equivalence ratio on the C2* reaction mechanism was further examined, revealing that the equivalence ratio affected the reactions R1 and R2 to different degrees under different combustion conditions. Additionally, C2* can characterize the complete pyrolysis height and global pyrolysis rate of CH4, and the C2* profile can determine the location of CH4 complete pyrolysis.