Low-Temperature Oxidation of di-n-Butyl Ether in a Motored Homogeneous Charge Compression Ignition (HCCI) Engine: Comparison of Characteristic Products with RCM and JSR Speciation by Orbitrap
Résumé
Earlier, 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 to 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 ultra-high-pressure liquid chromatography. Flow injection analyzes 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-dinitrophenyl hydrazine. A large set of chemical products of DBE cool flame were detected in the engine exhausts. They include hydroperoxides and diols (C8H18O3), unsaturated diols or unsaturated hydroperoxides (C8H16O3), ketohydroperoxides (C4H8O3 and C8H16O4), di-keto ethers (C8H14O3), olefinic di-keto ethers (C8H12O3), cyclic and keto-ethers (C8H16O2), 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), 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 a common oxidation mechanism proceeds in JSR, RCM, and motored engine, leading to the formation of products having the same chemical formulas and retention times.
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