Numerical investigation on the effect of CO2 and steam for the H2 intermediate formation and NOX emission in laminar premixed methane/air flames

One-dimensional premixed freely-propagating flames for (CH₄+CO₂/H₂O)/air(79%N₂+21%O₂) mixtures were modeled using ChemkinⅡ/Premix Code with the detailed mechanism GRI-Mech 3.0. The investigation of the effects of CO₂ and steam addition on the H₂ intermediate formation and NO emission was conducted at the initial conditions of 1 atm and 398 K. Both physical and chemical effects of CO₂, H₂O on laminar burning velocities and adiabatic flame temperatures were also analyzed. The calculations show that with the increase of α_CO2 and α_H2O, both physical and chemical effects of CO₂ and H₂O result in the reduction of laminar burning velocities (LBVs) and adiabatic flame temperatures (AFTs) in which the chemical effects of CO₂ addition are more significantly than H₂O. Especially, the chemical effects of steam promote the increase of AFTs and the influence in rich BG65 flames are larger than in methane. With a proper amount of H₂O addition, the chemical effects of H₂O on the peak concentration of H₂ are more significantly than physical at Φ = 1.2. Moreover, CO₂, steam and their mixture addition have significant reduction on the NO emission. The most sensitive reaction for the formation of H₂ and NO emission were determined. The responsible reactions for H₂ formation and NO emission are R84 OH + H₂ <=> H + H₂O and R240 CH + N₂ <=> HCN + N (a prompt routine), respectively.