Experimental characterization of n-heptane low-temperature oxidation products including keto-hydroperoxides and highly oxygenated organic molecules (HOMs)

The oxidation of n-heptane was performed in a jet-stirred reactor USR) at 10 atm, an equivalence ratio of 0.5, and an initial fuel concentration of 1000 ppm at a residence time of 1 s in the temperature range 580-790 K (from cool-flame, negative temperature coefficient NTC, to intermediate temperature oxidation regime), and with 5000 ppm of fuel at 647 K and a residence time of 1.5 s. Low-temperature products formed in JSR were characterized using high-resolution mass spectrometry analyses (HRMS). Atmospheric pressure chemical ionizations (APCI) was used in positive and negative modes for MS analyses. Both flow injection analyses (FIA) or ultra-high-pressure liquid chromatography-Orbitrap (R) coupling were used to characterize hydroperoxides (C7H16O2), keto-hydroperoxides (C7H14O3), cyclic ethers (C7H14O), carboxylic acids (C2H4O2, C3H6O2, C4H8O2), ketones (C3-5H6-10O), diones (C7H12O2), and highly oxygenated molecules (C7H14O5, C7H14O2, C7H14O9, C2H14O11) resulting from the addition of up to six O-2 molecules on fuel radicals. H/D exchange with D2O was used to confirm the presence of -OH or -OOH groups in the products. Several available kinetic reaction mechanisms were tested against the present measurements of keto-hydroperoxides showing significant discrepancies. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The oxidation of n-heptane was experimentally investigated using jet-stirred reactor at different temperatures and fuel concentrations, with low temperature products characterized by high-resolution mass spectrometry analyses. Various oxygenated molecules were identified, showing significant discrepancies with existing kinetic reaction mechanisms.