Effect of CO₂/N₂ Dilution on Premixed Methane–Air Flame Stability Under Strained Conditions

The effects of adding N₂ or CO₂ as diluents to a premixed methane–air flames under strain conditions (associated with a stagnation plate) were examined for flame stand-off distance, stability, intensity, and global flame behavior at various equivalence ratios. A stagnation plate was used to simulate the flame behavior near a combustor wall that can help provide some insights into reducing thermal stresses and enhance combustor lifetime. Decrease in equivalence ratio at the same thermal intensity provided larger strain rates while maintaining a stable flame. At stoichiometric condition, a balance was provided between high strain rates and low oxygen concentration flames to mitigate the peak (maximum) flame temperatures, and the associated temperature-dependent pollutants emission, such as NO_x, CO, and unburnt hydrocarbons. Higher thermal intensities provided higher strain rates; however, the addition of diluents impacted in destabilization of flame. The flame stand-off behavior occurred at lower strain rates, low thermal intensity, and increased equivalence ratios. CO₂ dilution reduced flame intensity, increased flame stand-off distance and overall flame destabilization than that with N₂ dilution.