Ethane oxidation at elevated pressures in the intermediate temperature regime: Experiments and modeling

Ethane oxidation has been experimentally studied in the intermediate temperature regime under lean conditions using a flow reactor. Species profiles have been obtained for H₂, CO, CO₂, CH₂O, CH₄, C₂H₄, C₂H₆, C₂H₄O, and CH₃CHO at pressures of 3, 6, and 10 atm for temperatures ranging from 915 to 966 K using a constant equivalence ratio of ~ 0.2 (in air). To model this data a detailed chemical kinetic model for ethane oxidation was developed. An optimized reaction mechanism, originally developed to model natural gas combustion, was expanded to include reactions pertinent to the lower temperature, elevated pressure conditions encountered in the flow reactor. The expanded mechanism consists of 277 elementary reactions and contains 47 species. By adjusting the rate coefficients of two key reactions the model was brought into agreement with experiment at 6 atm; however, the model indicates a larger pressure sensitivity than was measured experimentally. Results indicate that HO₂ is of primary importance in the regime studied; controlling the formation of many of the observed intermediates including the aldehydes and ethylene oxide. The results also point to the importance of continued investigation of the reactions of HO₂ with C₂H₆, C₂H₅, and C₂H₄ to further the understanding of ethane oxidation in the intermediate temperature regime. The expanded mechanism has also been tested against shock-tube ignition delay and laminar flame speed data and was found to be in good agreement with both the original GRI-Mech and the experimental data for both methane and ethane.