Ethane ignition and oxidation behind reflected shock waves

Several diluted C2H6/O2/Ar mixtures of varying concentrations and equivalence ratios (0.5<ϕ<2.0)(0.5<ϕ<2.0) were studied at temperatures between 1218 and 1860 K and at pressures between 0.57 and 3.0 atm using a shock tube. The argon dilution ranged from 91 to 98% by volume. Reaction progress was monitored using chemiluminescence emission from OH∗ and CH∗ at 307 and 431 nm, respectively. The dependence of ignition delay time on temperature, activation energy, and reactant concentrations is given in a master correlation of all the experimental data. The overall activation energy was found to be 39.6 kcal/mol over the range of conditions studied. For the first time in a shock-tube C2H6 oxidation study, detailed species profile data and quantitative OH∗ time histories were documented, in addition to ignition delay times, and compared against modern detailed mechanisms. Because of the comprehensive scope of the present study and the high precision of the experimental data, several conclusions can be drawn that could not have been reached from earlier studies. Although there is some discrepancy among previous ethane oxidation data, the present work clearly shows the convergence of ignition delay time measurements to those herein and the remarkable accuracy of current kinetics models over most of the parameter space explored, despite the variation in the literature data. However, two areas shown to still need more measurements and better modeling are those of higher pressures and fuel-rich ethane–air mixtures. After appropriate OH∗ and CH∗ submechanisms are added, two modern chemical kinetics mechanisms containing high-temperature ethane chemistry are compared to the data to gauge the current state of C2H6 oxidation modeling over the conditions of this study. The reproduction of the OH∗ and CH∗ profiles, together with τignτign predictions by these models, are compared against the profiles and ignition times found in the experimental data. The models are then used to identify some key reactions in ethane oxidation and CH formation under the conditions of this study.