A numerical investigation of CO2 dilution on the thermochemical characteristics of a swirl stabilized diffusion flame

The turbulent combustion flow modeling is performed to study the effects of CO2 addition to the fuel and oxidizer streams on the thermochemical characteristics of a swirl stabilized diffusion flame. A flamelet approach along with three well-known turbulence models is utilized to model the turbulent combustion flow field. The k-omega shear stress transport (SST) model shows the best agreement with the experimental measurements compared with other models. Therefore, the k-omega SST model is used to study the effects of CO2 dilution on the flame structure and strength, temperature distribution, and CO concentration. To determine the chemical effects of CO2 dilution, a fictitious species is replaced with the regular CO2 in both the fuel stream and the oxidizer stream. The results indicate that the flame temperature decreases when CO2 is added to either the fuel or the oxidizer stream. The flame length reduction is observed at all levels of CO2 dilution. The H radical concentration indicating the flame strength decreases, following by the thermochemical effects of CO2 dilution processes. In comparison with the fictitious species dilution, the chemical effects of CO2 addition enhance the CO mass fraction. The numerical simulations show that when the dilution level is higher, the rate of the flame length reduction is more significant at low swirl numbers.