Experimental characterization of n-heptane low-temperature oxidation products including keto-hydroperoxides and highly oxygenated organic molecules (HOMs)
Résumé
The oxidation of n-heptane was performed in a jet-stirred reactor (JSR) 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 coolflame, 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® coupling were used to characterize hydroperoxides (C 7 H 16 O 2), keto-hydroperoxides (C 7 H 14 O 3), cyclic ethers (C 7 H 14 O), carboxylic acids (C 2 H 4 O 2 , C 3 H 6 O 2 , C 4 H 8 O 2), ketones (C 3-5 H 6-10 O), diones (C 7 H 12 O 2), and highly oxygenated molecules (C 7 H 14 O 5 , C 7 H 14 O 7 , C 7 H 14 O 9 , C 7 H 14 O 11) resulting from the addition of up to six O 2 molecules on fuel radicals. H/D exchange with D 2 O 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.
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