Alkyl radicals rule the low temperature oxidation of long chain aldehydes

A detailed knowledge of aldehydes oxidation at high and low temperatures is of concern in exploring the viability of biofuels such as alcohols. A reliable and simple approach for the description of aldehydes low temperature oxidation is proposed based on fundamental studies available in the literature, previous high temperature kinetic studies and acetaldehyde low temperature cool flames. The high reactivity of the weakly bound aldehydic H-atom leads to the predominant formation of carbonyl radicals. While acetyl-radical addition to oxygen is a key step in the low temperature reactivity of acetaldehyde, heavier carbonyl radicals are rapidly decomposed to CO and alkyl radicals. Therefore, the observed reactivity of C3-C4 aldehydes is ruled by the well established low temperature branching pathways of the corresponding alkyl radicals. Based on these assumptions, a comparison of the relative reactivity of alkanes and aldehydes is also discussed. The approach and the kinetic mechanism here presented are supported by several comparisons with experimental data in Jet Stirred Reactor, and allow easy extension to heavier aldehydes.