Measurement of the reaction rate of H + O2 + M → HO2 + M, for M= Ar, N2, CO2, at high temperature with a sensitive OH absorption diagnostic

The reaction rate of H + O2+M = HO2+M in the low-pressure limit was determined in the temperature range of 1450– 2000 K, with Argon, Nitrogen, and Carbon Dioxide as the third-body collision partners, by measuring the OH time-history after the induction time during lean oxidation of Hydrogen. Test conditions were optimized to suppress the sensitivity of OH to interfering reactions after the induction time, using dilute and extremely lean mixtures at these temperatures. The strong Q1(5) transition in the A-X(0,0) band of OH was used as the probing wavelength for the diagnostic. Calibration measurements were performed prior to the experiments to estimate the effects of pressure shift and collision broadening on the absorption coefficient of OH for each of the bath gas species, which enabled a reduction in the uncertainty in the absorption cross-section of OH. Aided by the calibrated and improved OH diagnostic, the reaction rate constants were determined at high temperatures, with low scatter, and tight uncertainty bounds. The measured rate constants also agree with the extrapolation of previous investigations at lower temperatures. Combined rate constant expressions based on the lower temperature measurements of Shao et al. (2018) and the current high-temperature measurements are proposed, which are valid over the temperature range of 1000–2000 K:k2,Ar=(2.66*1019)*T−1.36cm6mol−2s−1(±9%)k2,N2=(2.25*1021)*T−1.95cm6mol−2s−1(±23%)k2,CO2=(2.23*1018)*T−0.79cm6mol−2s−1(±28%)