Hydroperoxide Measurements During Low-Temperature Gas-Phase Oxidation of n-Heptane and n-Decane

A wide range of hydroperoxides (C₁-C₃ alkyl hydroperoxides, C₃-C₇ alkenyl hydroperoxides, C₇ ketohydroperoxides, and hydrogen peroxide (H₂O₂)), as well as ketene and diones, have been quantified during the gas-phase oxidation of n-heptane. Some of these species, as well as C₁₀ alkenyl hydroperoxides and ketohydroperoxides, were also measured during the oxidation of n-decane. These experiments were performed using an atmospheric-pressure jet-stirred reactor at temperatures from 500 to 1100 K and one of three analytical methods, time-of-flight mass spectrometry combined with tunable synchrotron photoionization with a molecular beam sampling: time-of-flight mass spectrometry combined with laser photoionization with a capillary tube sampling, continuous wave cavity ring-down spectroscopy with sonic probe sampling. The experimental temperature at which the maximum mole fraction is observed increases significantly for alkyl hydroperoxides, alkenyl hydroperoxides, and then more so again for hydrogen peroxide, compared to ketohydroperoxides. The influence of the equivalence ratio from 0.25 to 4 on the formation of these peroxides has been studied during n-heptane oxidation. The up-to-date detailed kinetic oxidation models for n-heptane and for n-decane found in the literature have been used to discuss the possible pathways by which these peroxides, ketene, and diones are formed. In general, the model predicts well the reactivity of the two fuels, as well as the formation of major intermediates.