Experimental and Numerical Study of the Effect of CO₂ Replacing Part of N₂ present in Air on CH₄ Premixed Flame...

The effect of CO₂, which replaces part of N₂ present in air, on flame stability, laminar burning velocities (LBVs), and intermediate radicals (O OH) of CH₄/O₂/N₂/CO₂ premixed flames has been analyzed using detailed experiments and numerical studies. The numerical simulations were conducted using the PREMIX code with a detailed chemical reaction mechanism (GRI-Mech 3.0) and a reduced mechanism (39 species and 205 reactions) based on GRI-Mech 3.0 over a wide range of equivalence ratios (Φ = 0.7-1.3) and CO₂ substitution ratios (0-30%). The reduced mechanism showed a good agreement with the other detailed mechanisms and experimental data. The experimental and numerical results showed that the substitution of CO₂ diminishes the stability of the flame, and the flame blow-out speed is significantly reduced (the substitution ratio is 0-30%, and the corresponding flame blow-out velocity is 5.2-2.5 m/s). In addition, CO₂ inhibits the LBV of the flame owing to the decrease of O and OH mole fractions. It not only accelerates the consumption of these two free radicals but also inhibits the generation of these two free radicals. Further analysis concluded that the substituted CO₂ has the greatest influence on the LBV sensitivity coefficient of the HO₂ + CH₃ = OH + CH₃O reaction.