High temperature measurements for the rate constants of C1–C4 aldehydes with OH in a shock tube

Abstract

The overall rate constants for the reactions of hydroxyl radicals (OH) with a series of aldehydes, formaldehyde (CH2O), acetaldehyde (CH3CHO), propionaldehyde (C2H5CHO) and n-butyraldehyde (n-C3H7CHO), were studied behind reflected shock waves at temperatures of 950–1400K and pressures of 1–2atm. OH radicals were produced by rapid thermal decomposition of tert-butyl hydroperoxide (TBHP), and OH time-histories were monitored by narrow-linewidth UV laser absorption of the well-characterized R1(5) line in the OH A-X (0, 0) band near 306.69nm. The overall rate constants were inferred by fitting simulated OH profiles to the measured OH time histories using detailed mechanisms of Veloo et al. (2013), USC Mech-II (2007) and GRI Mech 3.0. The measured high-temperature aldehydes+OH rate constants can be expressed in modified Arrhenius equations, in units of cm3mol−1s−1 and K, askCH2O=1.02×107T1.92exp(779/T)±13%kCH3CHO=4.32×106T2.02exp(716K/T)±22%kC2H5CHO=5.94×106T1.98exp(823K/T)±27%knC3H7CHO=5.36×106T2.06exp(658K/T)±25%No pressure dependence was observed in these measurements. The measured rate constant for the formaldehyde+OH reaction is consistent with previous experimental work from Vasudevan et al. (2005) within ±25%. For C2–C4 aldehydes+OH, this study provides the first direct rate constant measurement at high temperatures. More general rate constant expressions covering a much wider temperature range (200–1400K) were also determined by combining current measurements with existing low temperature data in the literature. These wide-range expressions were seen to be in excellent agreement with most existing experimental data.