Probing the fuel-specific intermediates in the low-temperature oxidation of 1-heptene and modeling interpretation

Low temperature (low-T) oxidation of 1-heptene was evaluated in a jet-stirred reactor (JSR) over the temperatures of 450 K–800 K, 770 Torr and equivalence ratios of 0.5–2.0. The intermediates were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) and gas chromatography combined with mass spectrometry (GC–MS). The SVUV-PIMS experiment combined with quantum chemistry calculation of ionization energy enabled the identification of fuel-specific intermediates, including C7 alkenylperoxy radical and hydroperoxides. Among them, alkenylperoxy radical, diolefinic-hydroperoxide and cyclic ether hydroperoxide have not been detected in alkene oxidation before. To accurately identify and quantify other fuel-specific intermediates, e.g., aldehyde and cyclic ether isomers, the GC–MS experiment was carried out under the same conditions as the SVUV-PIMS experiment. A detailed low-T oxidation model of 1-heptene was developed, which could reasonably capture the fuel oxidation rate and negative temperature coefficient behaviors observed. The present model could not only interpret the formation of different kinds of hydroperoxides and predict their temperature windows, but also capture the formation of 2-heptenal, hexanal and heptanal, and branched tetrahydrofurans, which are derived from the H-abstraction by OH, OH addition and H addition reactions of 1-heptene, respectively, revealing that the competition between these reactions can be well characterized.