Numerical Investigation of CH₄/CO₂/Air and CH₄/CO₂/O₂ Counterflow Premixed Flames with Radiation Reabsorption

Effects of radiative heat loss on temperatures and extinction characteristics of CH₄/CO₂/air and CH₄/CO₂/O₂ counterflow premixed flames were numerically investigated by using the detailed chemistry and transport properties with emphasis on assessing the importance of radiation reabsorption. Radiative transfer was calculated using the discrete ordinate method along with the grey gas assumption. Results show that radiation reabsorption has little influence on the temperatures and extinction limits of CH₄/air counterflow premixed flames of low equivalence ratio. However the radiation reabsorption has a significant effect on the flame temperatures and extinction limits of CH₄/CO₂/air and CH₄/CO₂/O₂ counterflow premixed flames, especially on the radiation extinction limits. The flammable region of CH₄/CO₂/air counterflow premixed flames becomes smaller as the fraction of CO₂ added to air increases. Radiation extinction of CH₄/CO₂/O₂ flames occurs at higher stretch rates than that of CH₄/air flames.