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/H-2/O-2/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, O-2/(O-2 + CO2) ratios varying between 0.25 and 0.38, and H-2/(H-2 + 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 H-2 demonstrates a small impact on laminar burning velocity, with the chemical effect being considerably more significant, since the addition of H-2 directly increases concentrations of H, O, and OH, thereby accelerating the global reaction rates of both H-2 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.