New reaction classes in the kinetic modeling of low temperature oxidation of n-alkanes

Due to the rapid advance in analytical methods, a large detail of intermediate products from the low temperature oxidation of hydrocarbon fuels in jet stirred reactors became recently available in the literature. This new comprehensive information allowed to highlight systematic deviations between model predictions and experimental measurements, both in some oxygenated species and in fuel conversion at very low temperatures (550-650 K). These discrepancies are largely reduced by including new reaction classes in the oxidation mechanism. Successive H-abstraction and molecular reactions of hydroperoxide species are proved to play a relevant role at very low temperatures, in competition with the chain branching decomposition reactions. Several recombination and disproportionation reactions of peroxy radicals are also of interest in explaining some intermediate oxygenated components. The aim of this paper is to discuss and analyze the ability of these new reaction classes to explain the formation of oxygenated species, such as organic acids and dicarbonyl species. Rate constants were determined using similarity and analogy rules for consolidated reactions, while theoretical calculations were performed to determine preliminary estimates for reaction channels lacking a reference reaction. Detailed comparisons with several experimental data of propane and n-butane oxidation at low temperatures support these assumptions. This kinetic study points out the need of further research activities in the investigation of successive reactions of hydroperoxide species.