Modeling Study of the Impact of Blending N₂, CO₂, and H₂O on Characteristics of CH₄ Laminar Premixed Combustion

N 2, CO 2, and H 2 O 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 NO x and soot precursors [polycyclic aromatic hydrocarbons (PAHs)]. In this paper, using N 2, CO 2, and H 2 O 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 NO x emissions of CH 4 . 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 FN 2, FCO 2, and FH 2 O. The results show that the laminar burning velocity and adiabatic flame temperature of CH 4 were decreased by adding N 2, CO 2, and H 2 O, and the influence of the three diluents increases with the increase of the blending ratios, following the order of CO 2 > H 2 O > N 2 . 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 H 2 O leads to the adiabatic flame temperatures of CH 4 gradually increasing as the dilution ratio ( D r ) 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 CH 4 is reduced after adding N 2, CO 2, and H 2 O, depressing the generation of NO. The generation path of NO is mainly prompt NO x, and the responsible reactions are reactions R38, H + O 2 ⇄ O + OH; R240, CH + N 2 = HCN + N; and R52, H + CH 3 (+M) ⇄ CH 4 (+M).