The reactions of propanal/acetone with hydroperoxyl radicals: A theoretical and modeling study

Propanal (C 2 H 5 CHO) and acetone (CH 3 COCH 3 ), the C 3 carbonyl compound isomers, are the main byproducts of bio-alcohol combustion. In this work, the reaction rate coefficients between propanal/acetone and hydroperoxyl radicals (HO 2 ) over 500–2000 K and 0.01–100 atm were obtained by the RRKM/master equation method based on high-level quantum chemical calculations. The competition relationship among the H-abstraction, HO 2 addition, addition-dissociation reaction pathways and their temperature and pressure dependence were explored. The results show that for propanal + HO 2, the aldehydic H-abstraction reaction is highly favored over the addition-dissociation and other abstraction channels, while for acetone + HO 2 , the H-abstraction reaction is comparable with those of addition-dissociation reactions at low temperature. At temperatures ≤ 700 K and pressures ≥ 1 atm, collisional stabilization of the peroxy-alcohol radical is the dominant channel. To reveal the impact of the studied reactions on model predictions, the rate coefficients of various reaction channels calculated in this work and those of peroxy-alcohol radicals + HO 2 from the literature were incorporated into a recently proposed low-temperature mechanism of propanal. The results show that the aldehydic H-abstraction reaction of propanal by HO 2 greatly contributes to the combustion behavior in the negative temperature coefficient regime. The peroxy-alcohol radical favors its decomposition channel with temperatures ranging from 500 to 900 K at 1 atm in a JSR. Modified Arrhenius representations of the calculated rate coefficients are given and should be valuable for the future development of low-temperature oxidation mechanisms for aldehydes, ketones, and alcohols.