Effect of CO2 dilution on thermal characteristics and chemiluminescence for CH4/O2 diffusion flame: A numerical simulation based on detailed mechanism

The effect of CO2 dilution on the reaction kinetics of chemiluminescence and the local thermodynamic properties is a critical way to deeply understand the combustion mechanism of CO2 dilution flames. In this work, numerical simulations of CO2* and C2* chemiluminescence were performed. Spatial correlations between temperature and keystone species were explored. CO2* and C2* can effectively characterize the high-temperature zone in a flame. Through calculations of thermal diffusion flux, the inhibiting effect of thermal diffusion caused by CO2 dilution was discussed. CO2 dilution inhibited the thermal diffusion of the key products CH2 and O. Further analysis was conducted on the local characterization of CO2* and C2* on the distribution of heat release rate. CO2* and C2* can indicate the endothermic zone. The influencing mechanism of CO2 dilution on the formation of H, O and OH was revealed. The important roles of H and OH in the decomposition of CH4 and the formation of OH from O2 were demonstrated. The main formation pathways of CO2* and C2* reactants were revealed. O2 was mainly involved in the combustion reaction through the formation of OH. In addition, the inhibition of CO2* and C2* chemiluminescence by the chemical effect of CO2 dilution was discussed.