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The oxidation of a stoichiometric diethyl ether-oxygen-nitrogen mixture containing 5000 ppm of fuel was studied in a jet-stirred reactor at 10 atm and a residence times of 1 s. Experimental temperatures varied stepwise for 440 to 740 K and products were quantified by gas chromatography with TCD and FID, gas chromatography-mass spectrometry, and FTIR. Other experiments in the temperature range 480 to 570 K were performed for characterizing elusive cool flame products. To this end, gas samples were trapped in acetonitrile for flow injection analyses and liquid chromatography-mass spectrometry (Orbitrap Q-ExactiveⓇ). For ionization, we used positive and negative atmospheric pressure chemical ionization (APCI). Among fuel-specific products, hydroperoxides and diols (C 4 H 10 O 3), carbonyl hydroperoxides (C 4 H 8 O 4), acetic acid, di-keto ethers (C 4 H 6 O 3), cyclic ethers (C 4 H 8 O 2) and highly oxygenated molecules, i.e., keto-dihydroperoxides (C 4 H 8 O 6), keto-trihydroperoxides (C 4 H 8 O 8), di-keto-hydroperoxides (C 4 H 6 O 5), and diketo-dihydroperoxides (C 4 H 6 O 7), were detected. To confirm the presence of –OH or –OOH groups in oxidation products, H/D exchange with D 2 O was used. DNPH derivatization was used to identify carbonyls present in samples, especially those with a molecular weight below 50 amu which cannot be detected directly by the mass spectrometer. Chemical kinetic modeling using a mechanism taken from the literature was performed. Although reasonable agreement between the data and the simulations was observed for several species, some discrepancies between experimental and computed mole fractions were observed. [ABSTRACT FROM AUTHOR]

The oxidation of a gasoline model-fuel (2500 ppm of n-heptane and 2500 ppm of isooctane), 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 high-resolution 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 isooctane 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. [ABSTRACT FROM AUTHOR]

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 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Ⓡ 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. [ABSTRACT FROM AUTHOR]

The oxidation of di-n-butyl-ether (DBE) was performed in a jet-stirred reactor (JSR) at 1 atm, 520 and 530 K, and from 480 to 670 K at 10 atm, at a residence time of 1 s, an equivalence ratio of 0.5, and an initial fuel concentration of 5000 ppm. Ignition experiments on DBE/air mixtures were also performed in a rapid compression machine (RCM) under stoichiometric conditions, 5 bar, and from 550 to 630 K. Low-temperature products formed in JSR and RCM experiments were characterized. To this end, high-resolution mass spectrometry analyses (HRMS) with flow injection analyses or ultra-high pressure liquid chromatography coupling were used to characterize hydroperoxides and diols (C 8 H 18 O 3), ketohydroperoxides (C 8 H 16 O 4), carboxylic acids (C 2 H 4 O 2 , C 3 H 6 O 2 , C 4 H 8 O 2), di-keto ethers (C 8 H 14 O 3), and highly oxygenated molecules (C 8 H 14 O 5 , C 8 H 16 O 6 , C 8 H 14 O 6 , C 8 H 14 O 7 , C 8 H 16 O 8 , and C 8 H 14 O 9) resulting from up to five O 2 additions on fuel's radicals. Whereas HOMs are of minor importance in combustion, they are considered key species for the formation of secondary organic aerosols. In addition, cyclic ethers and esters (C 8 H 16 O 2) were observed. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative modes for MS analyses. H/D exchange with D 2 O was used to confirm the presence of –OH or –OOH groups in the products. The present results show that DBE oxidation proceeds similarly under JSR and RCM conditions. Whereas the CH 2 groups neighboring the ether group are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates and products. Our kinetic reaction mechanism needs to be extended for simulating the formation of newly detected species. [ABSTRACT FROM AUTHOR]

Renewable feedstock such as biomass derivatives (hemicellulose, furfural) can be used to produce synthetic fuels, e.g., n-pentane, of interest for enhancing performance of diesel and gasoline engines. Whereas numerous studies of n-pentane have been published, its low temperature oxidation is not fully characterized and even recent kinetic models do not incorporate extended oxidation pathways which still need to be observed for n-pentane. In this context, a continuous flow fused-silica jet-stirred reactor (JSR) was used for studying the oxidation of 2500 ppm of n-pentane at 520‒800 K, 10 atm (representative of piston engines operating conditions), an equivalence ratio of 0.5, and a residence time of 1.5 s. Oxidation products were analyzed in the gas phase using gas chromatography (thermal conductivity, TCD and flame ionization, FID), Fourier-transform infrared spectrometry (FTIR), and electron impact ionization-quadrupole mass spectrometry (EI-qMS). Gaseous products were also dissolved in acetonitrile for characterization using flow injection analysis (FIA), high-pressure and ultra-high-pressure liquid chromatography (HPLC and UHPLC) coupled to atmospheric pressure chemical ionization (APCI) and Q-Exactive®-Orbitrap high resolution mass spectrometry (HRMS). This allowed detecting lower and higher mass oxygenated molecules such as methyl vinyl ketone (MVK) and 2,5-dihydrofuran (C 4 H 6 O), 2-butanone (C 4 H 8 O), 3-pentene-2-one (C 5 H 8 O), pentanediones (C 5 H 8 O 2), cyclic ethers and pentanones (C 5 H 10 O), C 3 ‒C 5 alkylhydroperoxides (C 3 H 8 O 2 , C 4 H 10 O 2 , C 5 H 12 O 2), C 2 ‒C 5 alkenylhydroperoxides (C 2 H 4 O 2 , C 3 H 6 O 2 , C 4 H 8 O 2 , C 5 H 10 O 2), C 3 ‒C 5 keto-hydroperoxides (C 3 H 6 O 3 , C 4 H 8 O 3 , C 5 H 10 O 3), and highly oxygenated molecules (C 5 H 8 O 4 , C 5 H 12 O 4 , C 5 H 10 O 4 , C 5 H 10 O 5, C 5 H 10 O 7) produced through multiply O 2 addition on fuel's radicals and internal H-shifts. Among these products 15 had not been reported before. Simulation of the present experiments showed discrepancies between experimental results and predictions. [ABSTRACT FROM AUTHOR]

This study concerns the oxidation of n -hexane. It was conducted in continuous flow fused-silica jet-stirred reactor (JSR) at 10 atm and an equivalence ratio of 0.5. n -Hexane initial concentrations were (i) 2500 ppm with a mean residence time of 1.5 s and (ii) 1000 ppm with a mean residence time of 0.7 s; we operated in the cool-flame regime for temperatures ranging from 540 to 720 K and 530 to 800 K, respectively. Products were analyzed and quantified in the gas phase using gas chromatography (with flame ionization, thermal conductivity, and quadrupole mass spectrometry) and Fourier transform infrared spectrometry. Products of low-temperature oxidation were sampled in the JSR and trapped in acetonitrile for characterization using an Orbitrap Q-Exactive®. Flow injection analyses (FIA) and ultra-high pressure liquid chromatography (UHPLC) coupled with atmospheric pressure chemical ionization (APCI +/- modes)- high resolution mass spectrometry (HRMS) analyses were used to characterize hydroperoxides (C 6 H 14 O 2), keto-hydroperoxides (C 6 H 12 O 3 , C 3 H 6 O 3 , C 4 H 8 O 3 , and C 5 H 10 O 3), cyclic ethers (C 6 H 12 O), carboxylic acids (C 2 to C 6), ketones (C 3 to C 6), diones (C 6 H 10 O 2), unsaturated ketones (C 6 H 10 O and C 6 H 8 O), unsaturated diones (C 6 H 8 O 2), and highly oxygenated molecules (C 6 H 12 O 4-8) produced by addition of three and four oxygen molecules on fuel's radicals. To confirm the presence of hydroxyl or hydroperoxyl groups in the oxidation products we used H/D exchange with D 2 O. 2,4-Dinitrophenylhydrazine (2,4-DNPH) derivatization was used to characterize and confirm the presence of different carbonyls which can be formed during the low temperature oxidation of n -hexane. An available kinetic reaction mechanism including 3rd O 2 addition on fuel's radicals was used to simulate the formation of the presently detected keto-hydroperoxides (KHP) and highly oxygenated molecules (HOMs). [ABSTRACT FROM AUTHOR]