Simultaneous temperature and CO-concentration time-history measurements during the pyrolysis and ultra-fuel-rich oxidation of ethanol, diethyl ether, n-heptane, and isooctane behind reflected shock waves

Abstract

Abstract This study used shock tube and laser absorption spectroscopy to simultaneously measure temperature and CO-concentration time-histories behind reflected shock waves during the pyrolysis and ultra-fuel-rich oxidation of ethanol, diethyl ether, n-heptane, and isooctane. Two transition lines (v \xa0=\xa00, P8 and v \xa0=\xa01, R21) in the fundamental vibrational band of CO were selected for temperature and CO-concentration measurements. The temperature simulated based on the measured pressure as inputs agreed well with the measured temperature. The temperature calculated based on the measured pressure and isentropic relationship cannot reveal the real thermodynamic states inside the shock tube for the research in this study. This study compared the measured CO concentration with predictions from several mechanisms. The simulated data agreed well with the measured data only in the limited temperature range. Evident deviations were found between the measured and the simulated data. CO sensitivity analyses were performed to highlight the key reactions influencing CO formation. It was found that: C2H5OH\xa0=\xa0CH3\xa0+\xa0CH2OH and C2H5OH\xa0=\xa0C2H4\xa0+\xa0H2O dominate the CO formation process during ethanol pyrolysis and ultra-fuel-rich oxidation; C4H10O (+ M)\xa0=\xa0C2H5\xa0+\xa0C2H5O (+ M) and C4H10O\xa0+\xa0H\xa0=\xa0C4H9O\xa0+\xa0H2 exert the most evident effects on CO formation during diethyl ether pyrolysis and ultra-fuel-rich oxidation; the selected mechanisms show different reactions influencing CO formation during n-heptane ultra-fuel-rich oxidation; H\xa0+\xa0O2\xa0=\xa0O\xa0+\xa0OH and C2H3 (+ M)\xa0=\xa0C2H2\xa0+\xa0H (+ M) show competing behaviors in influencing CO formation during isooctane ultra-fuel-rich oxidation. This study updated rate constant of certain reactions to improve the mechanism performance in predicting CO-formation processes. Further research is necessary to update the rate coefficients for the above-mentioned reactions and improve mechanism performance.