LAUSR

N₂, CO₂, and H₂O are impurity components in the biogas fuel production process, which are added at an appropriate amount to the combustion of hydrocarbon fuel that can effectively reduce the emissions of NOₓ and soot precursors [polycyclic aromatic hydrocarbons (PAHs)]. In this paper, using N₂, CO₂, and H₂O as dilution gas, the CHEMKIN-II/PREMIX code with detailed chemical reaction mechanism GRI-Mech 3.0 was chosen to calculate the premixed combustion characteristics and NOₓ emissions of CH₄. At different equivalence ratios (Φ = 0.8, 1.0, and 1.2) and blending ratios (0–40%), the physical and chemical effects of different dilution gases were systematically studied through the introduction of hypothetical substances FN₂, FCO₂, and FH₂O. The results show that the laminar burning velocity and adiabatic flame temperature of CH₄ were decreased by adding N₂, CO₂, and H₂O, and the influence of the three diluents increases with the increase of the blending ratios, following the order of CO₂ > H₂O > N₂. Moreover, the physical and chemical effects are greatest at stoichiometric conditions, and physical effects are much greater than chemical effects. In particular, at Φ = 1.2, the chemical effect of H₂O leads to the adiabatic flame temperatures of CH₄ gradually increasing as the dilution ratio (Dᵣ) increases. The sensitivity analysis of the main elementary reactions, which play a leading role in the influence of NO generation, shows that the adiabatic flame temperature of CH₄ is reduced after adding N₂, CO₂, and H₂O, depressing the generation of NO. The generation path of NO is mainly prompt NOₓ, and the responsible reactions are reactions R38, H + O₂ ⇄ O + OH; R240, CH + N₂ = HCN + N; and R52, H + CH₃ (+M) ⇄ CH₄ (+M).