Combined effects of nongray radiation and pressure on premixed CH₄/O₂/CO₂ flames

The combined effects of non-gray radiation and pressure on the propagation and flammability limits of premixed CH₄/O₂/CO₂ flames were investigated numerically at an ambient temperature of 300 K over the pressure range of 0.04-0.50 MPa and the CO₂ dilution range of 0.40-0.79 molar fraction of CO₂ in the oxidant. A statistical narrow-band (SNB) model and an optically thin model (OTM) were used to describe flame radiation heat transfer in conjunction with a detailed chemical mechanism and transport properties. Results show that the effects of non-gray radiation and pressure on the burning velocity and flammability limits of the flame become significant as the amount of CO₂ added is increased. Moreover, the flammability limits based on the OTM can be significantly extended by the spectral reabsorption mechanism described by the SNB model. Comparisons of the calculated results based on the SNB model with the experimental results in microgravity by Abbud-Madrid and Ronney show reasonable agreement.