Experimental and kinetic modeling study of the laminar burning velocity of CH₄/H₂ mixtures under oxy-fuel conditions

The oxy-fuel combustion of coke oven gas generates CH₄/H₂/O₂/CO₂ mixtures, and this study focuses on measuring the laminar burning velocities of these mixtures which are rarely studied previously. The investigation encompasses a range of equivalence ratios from 0.6 to 1.5, O₂/(O₂ + CO₂) ratios varying between 0.25 and 0.38, and H₂/(H₂ + CH₄) ratios ranging from 0.25 to 0.6, under normal temperature and pressure conditions. Employing the experimental data, five established detailed kinetic mechanisms (Konnov 2023, AramcoMech 3.0, GRI 3.0, USC II, and San Diego) are evaluated, revealing that the Konnov 2023 mechanism exhibits the best performance in predicting the laminar burning velocities. Notably, the thermal effect of H₂ demonstrates a small impact on laminar burning velocity, with the chemical effect being considerably more significant, since the addition of H₂ directly increases concentrations of H, O, and OH, thereby accelerating the global reaction rates of both H₂ and CH₄ oxidation. Conversely, the thermal effect of CO₂, attributable to its high specific heat, results in a reduction of the laminar burning velocity. Furthermore, the chemical effect of CO₂ is found to be comparable to the thermal effect, primarily arising from the elementary reaction CO + OH <=> CO₂ + H. It is noteworthy that the third-body reactions involving CO₂ exhibits relatively small effects.