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Low-temperature oxidation of a gasoline surrogate: Experimental investigation in JSR and RCM using high-resolution mass spectrometry

  • Belhadj, Nesrine
  • Benoit, Roland
  • Dagaut, Philippe
  • Lailliau, Maxence
  • Moreau, Bruno
  • Foucher, Fabrice
Publication Date
Jun 01, 2021
DOI: 10.1016/j.combustflame.2021.01.037
OAI: oai:HAL:hal-03221825v1
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The oxidation of a gasoline model-fuel (2500 ppm of n-heptane and 2500 ppm of iso-octane), called RON 50, was studied in a jet-stirred reactor (JSR) over the temperature range 560-700 K, at a total pressure of 10 atm, at a residence time of 1.5 s, and an equivalence ratio of 0.5. Gas samples were collected as a function temperature. Ignition of RON 50/air mixtures was also studied in a rapid compression machine (RCM) under the same fuel-lean conditions, 20 bar, 640 K. Gas samples were collected at variable reaction time. Products of low-T oxidation formed in a jet-stirred reactor and a rapid compression machine were dissolved in acetonitrile and analyzed by highresolution mass spectrometry. Flow injection analyses and ultrahigh-pressure liquid chromatography coupled to an Orbitrap® were used to characterize a wide range of species such as hydroperoxides, diols, ketohydroperoxides, carboxylic acids, diketones, cyclic ethers (C n H 2n O) formed by decomposition of alkyl hydroperoxy radicals, and highly oxidized species formed via up to six O 2 additions on alkyl radicals (C n H 2n O 11). Mass spectrometry analyses were conducted using atmospheric pressure chemical ionization running in negative and positive ionization modes. For confirming the presence of-OH or-OOH groups in the products, we performed H/D exchange by addition of D 2 O to samples. Under JSR conditions, we observed a wide range of n-heptane oxidation products: C 7 H 14 O x (x=1-11), C 7 H 12 O x (x=1-11), C 7 H 10 O x (x=1-9), C 7 H 8 O x (x=1-9), C 7 H 6 O x (x=1-8), and C 7 H 4 O x (x=1-6). Similarly, the following products of iso-octane oxidation were observed: C 8 H 16 O x (x=1-12), C 8 H 14 O x (x=1-11), C 8 H 12 O x (x=1-12), C 8 H 10 O x (x=2-10), C 8 H 8 O x (x=2-8), C 8 H 6 O x (x=1-7). Finally, C n H 2n (n=4-8), C n H 2n-2 (n=4-8), C n H 2n O (n=3-8), C n H 2n-2 O (n=3-8), C n H 2n-4 O (n=3-8), C n H 2n+2 O 2 (n=3-8), C n H 2n O 2 (n=2-8), C n H 2n-2 O 2 (n=3-8), C n H 2n-4 O 2 (n=3-8), and C n H 2n O 3 (n=2-8) were also observed. Most of these products were also detected in RCM samples. Products measurements indicated that RON 50 oxidation routes are similar under RCM and JSR experimental conditions. A kinetic reaction mechanism was used to compare the formation of products versus temperature in a JSR. New pathways need to be introduced in existing reaction schemes for predicting newly detected cool-flame products.

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