Effects of H2, CO2, and H2O on the laminar burning velocity and reaction kinetics of methane/air flames under lean combustion conditions

Abstract

With increasing focus on clean energy, the combustion characteristics of methane, especially its laminar burning velocity, have garnered significant attention. This study presents a numerical investigation of the laminar burning velocity of methane/air mixtures incorporating various additives, using three different models. In addition to the laminar burning velocity, peak mole fractions of O, OH, and CH₃ at their maximum concentrations were analyzed, along with a sensitivity analysis conducted under the maximum temperature gradients. The results indicate that the behavior of methane flames varies with the addition of different gases. The addition of H₂ leads to a nearly linear increase in laminar burning velocity, accompanied by a slight rise in the mole concentrations of H and OH, while the concentration of CH₃ remains nearly unchanged. However, the addition of CO₂ and H₂O results in a decrease in laminar burning velocity, radical mole concentrations, and flame temperature. Furthermore, the impact of overall activation energy and overall activation order on the laminar burning velocity of the global one-step reaction is also discussed in detail. In summary, the addition of H₂ does not significantly affect either the overall activation energy or overall activation order, whereas CO₂ and H₂O contribute to reductions in both parameters. These findings could be beneficial to practical applications, including Exhaust Gas Recirculation (EGR) and Carbon Capture Utilization Storage (CCUS).