On the similarities and differences between the products of oxidation of hydrocarbons under simulated atmospheric conditions and cool-flames

Abstract

Abstract. Whereas the kinetics of oxidation of limonene has been extensively studied and mechanisms for its oxidation by OH and/or ozone have been proposed, more studies are required for better understanding its oxidation pathways. The oxidation of limonene-oxygen-nitrogen mixtures was studied using a jet-stirred reactor at elevated temperature and atmospheric pressure. Samples of the reacting mixtures were collected and analyzed by high resolution mass spectrometry (Orbitrap) after direct injection or after separation by reverse-phase ultra-high-pressure liquid chromatography and soft ionization by (+/−) HESI and (+/−) APCI. The results indicate that among the 1138 detected products, many oxygenates found in earlier studies of limonene oxidation by OH and/or ozone are also produced under the present conditions. Other highly oxygenated products and oligomers were also detected in the present work. The results are discussed in terms of reaction pathways involving the initial formation of peroxy radicals, isomerization reactions yielding keto-hydroperoxides and other oxygenated intermediates and products up to C25H32O17. The possible occurrence of the Waddington mechanism and of the Korcek mechanism are also discussed. The present work demonstrates similarities between the oxidation products and oxidation pathways of limonene under simulated atmospheric conditions and in those encountered during the self-ignition of hydrocarbons at low temperatures, which should stimulate future interactions between communities of atmospheric chemistry and combustion chemistry to improve current chemical models.

Insight into the Ozone-Assisted Low-Temperature Combustion of Dimethyl Ether by Means of Stabilized Cool Flames

“…As explained above, the initiation of the reactivity takes place through H-atom abstraction on the fuel molecule, assisted by the decomposition of O 3 above the burner, and followed by addition to O 2 . At 5% fuel conversion, it is noticed that the most influential reaction of consumption of ROO• is not the H-atom migration as expected from the low temperature combustion of DME 56 representative of atmospheric chemistry, this confirms the recently pointed out link between kinetic studies of low temperature combustion and atmospheric chemistry 57 . A change in the branching ratio is observed when the temperature has increased, at 20% fuel conversion, where the ROO• isomerization into •QOOH becomes more predominant, as commonly observed in LTC studies 56 .…”

Gasoline Surrogate Oxidation in a Motored Engine, a JSR, and an RCM: Characterization of Cool-Flame Products by High-Resolution Mass Spectrometry

“…Back pressure was regulated at 1.05 bar to allow exhausts gas flow through the bubbler. As in previous works 9, [16][17][18] , liquid samples were stored in a freezer at -15 °C for HRMS analyses. elsewhere 9,[19][20][21] .…”