The oxidation of a PRF 50 gasoline surrogate (n-heptane/iso-octane) performed earlier in a jet-stirred reactor (JSR) and a rapid compression machine (RCM), showed that oxidation proceeds similarly in both conditions. The present work extends that investigation by oxidizing a n-heptane / isooctane mixture under motored engine conditions. Exhaust gases were collected through bubbling in cooled acetonitrile. The samples were analyzed by ultra-high-pressure liquid chromatography (UHPLC) coupled to high-resolution mass spectrometry (HRMS-orbitrap Q-Exactive™). Low-temperature oxidation intermediates were characterized using tandem mass spectrometry (MS/MS), H/D exchange, and 2,4-dinitrophenyl hydrazine derivatization. In addition to cyclic ethers/ketones/aldehydes (C 7 H 14 O, C 8 H 16 O), ketohydroperoxides (C 7 H 14 O 3 , C 8 H 16 O 3 ), diketones (C 7 H 12 O 2 , C 8 H 14 O 2 ), and ketodihydroperoxides (C 7 H 14 O 5 , C 8 H 16 O 5 ), presented in our previous work, a large set of newly detected or rarely considered low-temperature products are presented here. They include hydroperoxides and diols (C 7 H 16 O 2 , C 8 H 18 O 2 ), olefinic hydroperoxides/diols (C 7 H 14 O 2 , C 8 H 16 O 2 ), dihydroperoxides (C 7 H 16 O 4 , C 8 H 18 O 4 ), olefinic dihydroperoxides (C 7 H 14 O 4 , C 8 H 16 O 4 ), olefinic cyclic ethers/carbonyls (C 7 H 12 O, C 8 H 14 O), di-and tri-olefinic cyclic ethers/ketones/aldehydes (C 7 H 10 O, C 7 H 8 O), olefinic ketohydroperoxides (C 7 H 12 O 3 , C 8 H 14 O 3 ), di-olefinic ketohydroperoxides (C 7 H 10 O 3 ), triketones (C 7 H 10 O 3 , C 8 H 12 O 3 ), olefinic diketones (C 7 H 10 O 2 , C 8 H 12 O 2 ), di-olefinic diketones (C 7 H 8 O 2 ), and diketohydroperoxides (C 7 H 12 O 4 , C 8 H 14 O 4 ). Motored engine's low-temperature oxidation intermediates were compared to those obtained in JSR and RCM. Despite the strong differences in the experimental conditions, the results indicate the formation of the same products. This indicates that a common chemical mechanism operates in motored engine, JSR, and RCM.
Previously, the oxidation of di-n-butyl ether (DBE) carried out in a jet-stirred reactor (JSR) and in a rapid compression machine (RCM) revealed that it proceeds similarly under both conditions (Belhadj et al, Combust. Flame 2020, 222, 133–144). Here, we extend that study to DBE oxidation in a motored homogeneous charge compression ignition engine, conditions under which this fuel has never been studied. Samples of exhaust gas were obtained by bubbling in acetonitrile maintained at 0 °C. The samples were analyzed using atmospheric pressure chemical ionization in positive and negative modes, high-resolution mass spectrometry (Orbitrap), and ultrahigh-pressure liquid chromatography. Flow injection analyses of samples before and after H/D exchange using D2O were also performed to verify the presence of isomeric products containing OH or OOH groups. Carbonyls were identified through derivatization with 2,4-dinitrophenylhydrazine. A large set of chemical products of the DBE cool flame were detected in the engine exhausts. They include hydroperoxides and diols (C8H18O3), unsaturated diols or unsaturated hydroperoxides (C8H16O3), keto hydroperoxides (C4H8O3 and C8H16O4), diketo ethers (C8H14O3), olefinic diketo ethers (C8H12O3), cyclic and keto ethers (C8H16O2), and olefinic cyclic and keto ethers (C8H14O2). Also, highly oxygenated chemicals, i.e., keto dihydroperoxides (C8H16O6) resulting from three O2 additions on radicals from the fuel, diketo hydroperoxides (C8H14O5) resulting from decomposition of keto dihydroperoxides (C8H16O6), in addition to other oxygenated intermediates i.e., hydroxy-DBE (C8H18O2) and organic peroxides ROOR′ (C16H34O4, C11H24O3, C11H22O3, and C10H22O3), were observed in the engine exhausts. The present speciation results of the engine exhausts were compared to those obtained for samples of the oxidation of DBE in an RCM and a JSR. Despite the significant differences in physical experimental conditions, the present study indicates thata common oxidation mechanism proceeds in JSR, RCM, and a motored engine, leading to the formation of products having the same chemical formulas and retention times.
Low-temperature experiments on the oxidation of limonene−O 2 −N 2 mixtures were conducted in a jet-stirred reactor (JSR) over a range of temperatures (520−800 K) under fuel-lean conditions (equivalence ratio φ = 0.5) with a short residence time (1.5 s) and a pressure of 1 bar. Collected samples of the reaction mixtures were analyzed by (i) online Fourier transform infrared spectroscopy (FTIR) and (ii) Orbitrap Q-Exactive high-resolution mass spectrometry after direct injection or chromatographic separation using reversed-phase ultra-high-performance liquid chromatography (RP-UHPLC) and soft ionization (with positive or negative heated electrospray ionization and atmosphericpressure chemical ionization). H/D exchange using deuterated water (D 2 O) and a reaction with 2,4-dinitrophenylhydrazine (2,4-DNPH) were performed to probe the presence of OH, OOH, and C�O groups in the oxidized products. A broad range of oxidation products ranging from water to highly oxygenated products containing five and more O atoms were detected (C
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