EXPERIMENTAL AND KINETIC MODELLING STUDY OF THE OXIDATION OF CYCLOPENTANE AND METHYLCYCLOPENTANE AT ATMOSPHERIC PRESSURE

International audienceCyclopentane and methylcyclopentane oxidation was investigated in a jet-stirred reactor at 1 atm, over temperatures ranging from 900 K to 1250 K, for fuel-lean, stoichiometric, and fuel-rich mixtures at a constant residence time of 70 ms. The initial mole fraction of both fuels was kept constant at 1000 ppm. The reactants were highly diluted by a flow of nitrogen to ensure thermal homogeneity. Samples of the reacting mixture were analyzed on-line or off-line by Fourier transform infrared spectroscopy and gas chromatography. A detailed kinetic mechanism consisting of 590 species involved in 3469 reversible reactions was developed and validated against these new experimental results and previously reported ignition delays. Reaction pathways analysis as well as sensitivity analyses were performed to get insights into the differences observed during the oxidation process of cyclopentane and methylcyclopentane

ON THE IMPACT OF THE O-ATOM ON THE IGNITION OF A 5-MEMBERED RING: A COMPARATIVE STUDY BETWEEN CYCLOPENTANE AND TETRAHYDROFURAN

International audienceCyclopentane (CPT) is one of the simplest cycloalkanes with five membered carbon ring, which has high-octane and knock-resistant characteristics, and it is commonly found in commercial gasoline. Tetrahydrofuran (THF) is a saturated cyclic ether compound, and has been shown to be as a promising bio-fuel for internal combustion engines. The molecular structure of CPT and THF is similar excluding the oxygen heteroatom in THF ring which induces lower bond dissociation energies of the C-H bonds on the α-sites, but higher BEDs on the β-sites. This work aims at comparing the auto-ignition delay times of CPT and THF measured in shock tube, and explain the differences and similarities observed with the help of a unique detailed kinetic mechanism. The ignition delay times have been measured in a high-pressure shock tube over a wide temperature range for various mixture compositions. The kinetic model used in the simulations was developed by introducing a sub-mechanism for CPT from Lokhachari et al. (2021) into the THF mechanism from Fenard et al. (2018). The present mechanism contains 1322 species and 6709 reactions. It was observed that despite differences in terms of bond dissociation energies, CPT and THF have very similar ignition delay times at the same equivalence ratio. However, when XFuel/XO2 is kept constant, it turns out that a discrepancy appears between CPT and THF when the mole fraction of O2 decreases, CPT becoming longer than THF to ignite. This observation indicates that CPT is more sensitive to the O2 content than THF

Ketohydroperoxides and Korcek mechanism identified during the oxidation of dipropyl ether in a JSR by high-resolution mass spectrometry

International audienceWith the growing interest for biomass-derived fuels the understanding of the combustion chemistry of ethers becomes of major scientific importance. Ethers usually develop strong cool flames at relatively low temperatures. Very complex processes occur there, with the formation of peroxidized intermediates such as ketohydroperoxides and highly oxidized molecules. Such chemicals are relatively unstable and difficult to analyze.We studied the low-temperature oxidation of dipropyl ether in a jet-stirred reactor. The experimental conditions were selected to maximize the production of ketohydroperoxides, based on the kinetic model of Serinyel et al. (2019). We oxidized 5000 ppm of dipropyl ether at 1 bar, T = 520–530 K, an equivalence ratio of 0.5, and at a residence time of 1 s. Analyses were performed on solubilized products of dipropyl ether oxidation in cooled acetonitrile. The samples were analyzed using soft HESI electrospray ionization (+/-) and an Orbitrap mass spectrometer (resolution: 140,000, mass accuracy RO2 QOOH; QOOH + O2 OOQOOH HOOQ’OOH followed by HOOQ’OOH + O2 (HOO)2Q’OO (i) (HOO)2POOH → OH + (HOO)2P=O (i.e., C6H12O6) and (ii) (HOO)2POOH + O2 → (HOO)3POO (HOO)3P’OOH → OH + (HOO)3P=O (i.e., C6H12O8).The so-called Korcek mechanism through which ketohydroperoxides are transformed into stable products, namely propanoic acid here, was also observed. Hydrogen–Deuterium exchange reactions using D2O served to confirm the presence of –OH groups in the products

Highly oxygenates molecules formed by oxidation of terpenes in a jet-stirred reactor

International audienceWith the growing interest for biomass-derived fuels the understanding of the combustion chemistry of terpenes becomes of major scientific importance. Terpenes have been proposed as biofuels for aviation because of their high energy density. They usually develop cool flames below 800 K. Very complex processes occur there, with the formation of peroxides intermediates such as ketohydroperoxides and highly oxidized molecules (HOMs) containing both hydroperoxy and carbonyl groups. Such chemicals are relatively unstable and difficult to analyze.We studied the low-temperature oxidation of alpha-pinene, beta-pinene, and limonene (C10H16) in a jet-stirred reactor. The experimental conditions were selected to maximize the production of ketohydroperoxides. We oxidized 5000 ppm of these three terpenes at 1 bar, T = 590 K, an equivalence ratio of 0.5, and at a residence time of 1 s. High-resolution mass spectrometry analyses were performed on solubilized products of terpenes oxidation in cooled acetonitrile. The samples were analyzed using soft HESI electrospray ionization (+/-) and an Orbitrap® mass spectrometer (resolution: 140,000, mass accuracy RO2 QOOH; QOOH + O2 OOQOOH HOOQ’OOH followed by HOOQ’OOH + O2 (HOO)2Q’OO (i) (HOO)2POOH → OH + (HOO)2P=O (i.e., C10H14O5) and (ii) (HOO)2POOH + O2 → (HOO)3POO (HOO)3P’OOH → OH + (HOO)3P=O (i.e., C10H14O7). Fourth oxygen addition yielding C10H14O9 was also observed in the present work. Hydrogen–Deuterium exchange reactions using D2O were used to confirm the presence of –OH groups in the products