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

The overall rate constants for the reactions of hydroxyl radicals (OH) with a series of aldehydes, formaldehyde (CH 2 O), acetaldehyde (CH 3 CHO), propionaldehyde (C 2 H 5 CHO) and n-butyraldehyde (n-C 3 H 7 CHO), were studied behind reflected shock waves at temperatures of 950–1400 K and pressures of 1–2 atm. 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 R 1 (5) line in the OH A-X (0, 0) band near 306.69 nm. 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 cm 3 mol −1 s −1 and K, as k CH 2 O = 1.02 × 10 7 T 1.92 exp ( 779 / T ) ± 13 % k CH 3 CHO = 4.32 × 10 6 T 2.02 exp ( 716 K / T ) ± 22 % k C 2 H 5 CHO = 5.94 × 10 6 T 1.98 exp ( 823 K / T ) ± 27 % k nC 3 H 7 CHO = 5.36 × 10 6 T 2.06 exp ( 658 K / 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 C 2 –C 4 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 (200–1400 K) 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. [ABSTRACT FROM AUTHOR]