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

Abstract

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.

Experimental Characterization of Tetrahydrofuran Low-Temperature Oxidation Products Including Ketohydroperoxides and Highly Oxygenated Molecules

“…The present study confirms the occurrence of extended oxidation pathways 25,57 deduced from JSR experiments with synchrotron-based MS. 25,57 In these experiments, several products of the second and third addition of molecular oxygen were detected. More recently, 26,27 Their formation was observed here (Table 3). The variation of the integrated C 4 H 9 O 3 + signal obtained by FIA versus temperature is presented in Figure 2.…”

“…With the recent development of analytical techniques, e.g., synchrotronbased MS 25,40,41 and ultrahigh-pressure liquid chromatography (UHPLC) coupled to Orbitrap, it becomes possible to better characterize cool flame products. 26,27,42 As part of continuing efforts in this laboratory to better understand the chemical kinetics of fuel combustion, a series of experiments have been carried out recently for the oxidation of several ethers. 26,27 presenting results of kinetic experiments completed to identify the products of THF cool flames in a JSR.…”

“…26,27,42 As part of continuing efforts in this laboratory to better understand the chemical kinetics of fuel combustion, a series of experiments have been carried out recently for the oxidation of several ethers. 26,27 presenting results of kinetic experiments completed to identify the products of THF cool flames in a JSR. Among the products detected, we paid particular attention to the detection of KHP isomers because discrepancies between kinetic modeling and measurements have been reported recently.…”

Oxidation of diethyl ether: Extensive characterization of products formed at low temperature using high resolution mass spectrometry

“…Because of its high sensitivity and high resolution, Orbitrap® mass spectrometer is a very appropriate tool for the characterization and identification of complex organic molecules, especially when they are present at trace amounts within complex matrices. Recently, flow injection analyses and ultrahigh-pressure liquid chromatography both coupled to high-resolution mass spectrometry (HRMS) has been used in our laboratory to attempt identifying different KHPs and HOMs isomers formed by oxidation of di-n-propyl ether, di-n-butyl ether, tetrahydrofuran, n-heptane, and a nheptane-iso-octane mixture [7][8][9][10]. In order to better characterize the low-temperature oxidation of diethyl ether, new experiments were performed in a jet-stirred reactor at 10 bar, over a range of temperatures.…”

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

“…Back pressure was regulated at 1.05 bar to allow exhausts gas flow through the bubbler. As in previous works 9, [16][17][18] , liquid samples were stored in a freezer at -15 °C for HRMS analyses. elsewhere 9,[19][20][21] .…”