Evaluation, development, and validation of a new reduced mechanism for methane oxy-fuel combustion

The chemical kinetics under oxy-fuel combustion is significantly different from that of conventional air-combustion due to the effect of the high CO2 concentration. Although previous studies have made substantial achievement in reaction mechanisms for air-combustion, their performance under oxy-fuel conditions is still unknown. This study proposes a new 22-species, 19-step reduced mechanism for methane oxy-fuel combustion, developed using comprehensive mechanism evaluation, reduction, and validation methods. First, through quantitative error evaluation against a large experimental data set, for the first time we find that USC-Mech II obtains the best overall predictions among seven detailed combustion mechanisms in oxy-fuel conditions, particularly for the prediction of CO concentration. This detailed mechanism is then thoroughly simplified (including both skeletal and time-scale reduction) with error control under both atmospheric and pressurized oxy-fuel conditions. The obtained reduced mechanism is systematically validated using the detailed mechanism and the relative errors are found to be less than 10%. Relative to other mechanisms, this specially developed reduced mechanism for oxy-fuel combustion not only has minimal species, but also significantly improves the prediction of CO formation. The chemical influence of CO2 under oxy-fuel conditions is further discussed to identify dominant elementary reactions for CO formation, which is important for future development of methane oxy-fuel combustion.