Oxy-combustion is a clean combustion technology that can reduce greenhouse emissions by increasing oxygen concentration and replacing N₂ with CO₂. This paper constructed a mechanism coupled with the OH*/CH*/C₂*/CO₂* formation and quenching reactions to simulate counterflow diffusion flames. Different stoichiometric mixed fraction (Z_st = [1+(Y_FW_Oν_O/Y_OW_Fν_F)]^-1) with the same adiabatic flame temperature (2279 K) was set by adjusting the CO₂ concentration on the oxidant and fuel side. Soot formation and chemiluminescence were interpreted based on the carbon-to-oxygen (C/O) ratio space. Because compared with the physical space and the mixture fraction space, the C/O ratio space is not affected by boundary conditions and flame configuration. With Z_st increases (0.064 to 0.4), the soot zone shrinks and moves toward the oxidant side, but chemiluminescence and temperature move in opposite directions. The peak temperature decreases by 50 K, while the soot volume fraction (SVF) decreases by 85% due to a significant decrease in the concentration of soot precursors (A1, etc.). The reduction of chemiluminescence is much lower than SVF, making chemiluminescence apparent in high Z_st flames. In C/O ratio space, the soot precursor boundary starts at 0.50. Due to the high concentration of oxidizing components, A1 is almost non-existent at positions less than 0.5, the very low polycyclic aromatic hydrocarbons concentration is not conducive to soot formation. While the chemiluminescence is mainly distributed in the range of 0.45-0.55 between the radical pool (< 0.5) and the soot precursor zone (> 0.5), because the CH₂, CH, and C₂H produced by the oxidation of C₂H₂ are distributed here, which are the reactants producing chemiluminescence radicals.

oxy-combustion,soot formation,chemiluminescence,C/O ratio,counterflow diffusion flame