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

The oxidation of a primary reference fuel 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 under both conditions. The present work extends that investigation by oxidizing an IF Ar heptane/iso-octane mixture under motored engine conditions. Exhaust gases were collected through bubbling in cooled acetonitrile. The samples were analyzed by ultra-high-pressure liquid chromatography 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 (C7H14O and C8F16O), ketohydroperoxides (KHPs; C7H14O3 and C8H16O3), diketones (C7F12O2 and C8H14O2), and ketodihydroperoxides (C7H14O5 and C8H16O3), presented in our previous work, a large set of newly detected or rarely considered lowtemperature products are presented here. They include hydroperoxides and diols (C7H16O2 and C8H18O2), olefinic hydroperoxides/ diols (C7H14O2 and C8H16O2), dihydroperoxides (C7H16O4 and C8H18O4), olefinic dihydroperoxides (C7H14O4 and C8H16O4), olefinic cyclic ethers/carbonyls (C7H12O and C8H14O), di- and tri-olefinic cyclic ethers/ketones/aldehydes (C7H10O and C7H8O), olefinic KHPs (C7H12O3 and C8H14O3), di-olefinic KHPs (C7H12O3), triketones (C(8)H(14)O(3)and C8H12O3), olefinic diketones (C7H10O2 and C8H12O2), di-olefinic diketones (C7H8O2), and diketo-hydroperoxides (C7H12O4 and C8H14O4). 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 the motored engine, JSR, and RCM.

Automated summary

This study compares the oxidation products of a gasoline surrogate fuel under motored engine conditions with those obtained in a jet-stirred reactor (JSR) and rapid compression machine (RCM). The results show that despite the different experimental conditions, similar products are formed, indicating a common chemical mechanism operates in all three conditions.