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

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

Ozone-assisted combustion of hydrogen: A comparison with isooctane

International audienceHomogeneous Charge Compression Ignition (HCCI) engines have the potential to achieve low emissions of nitrogen oxides and particulate matter but the use of carbon-based fuels leads to significant emissions of carbon monoxide and unburned hydrocarbon which hinder the widespread development of HCCI. Nonetheless, HCCI engines have also the potential to use various types of fuel such as hydrogen, a carbon free fuel. The present study examined hydrogen combustion in an HCCI engine comparing hydrogen with isooctane. The sensitivities of CA05, CA50 and ringing intensity to intake pressure, intake temperature and ozone were investigated for both fuels. Results highlighted that hydrogen autoignites more easily than isooctane despite its higher-octane number. Ozone seeding was therefore used to shift the combustion region of isooctane in order to perform a viable comparison between the two fuels while starting with the same initial conditions. From this point, all of the three parameters were found to promote the HCCI combustion of both fuels but greater sensitivities were observed for hydrogen than for isooctane. Ozone was observed to have the strongest influence, making it a good strategy for a future control approach. The noise level of hydrogen was very high due its high reactivity. Finally, the use of hydrogen together with ozone should enable a very clean engine cycle to be achieved cycle with only water and nitrogen as engine-out emissions

Experimental and modeling study of the oxidation of n- and iso-butanal

Veloo PS, Dagaut P, Togbé C, et al. Experimental and modeling study of the oxidation of n- and iso-butanal. Combustion And Flame. 2013;160(9):1609-1626.Understanding the kinetics of large molecular weight aldehydes is essential in the context of both conventional and alternative fuels. For example, they are key intermediates formed during the low-temperature oxidation of hydrocarbons as well as during the high-temperature oxidation of oxygenated fuels such as alcohols. In this study, an experimental and kinetic modeling investigation of n-butanal (n-butyraldehyde) and iso-butanal (iso-butyraldehyde or 2-methylpropanal) oxidation kinetics was performed. Experiments were performed in a jet stirred reactor and in counterflow flames over a wide range of equivalence ratios, temperatures, and pressures. The jet stirred reactor was utilized to observe the evolution of stable intermediates and products for the oxidation of n- and iso-butanal at elevated pressures and low to intermediate temperatures. The counterflow configuration was utilized for the determination of laminar flame speeds. A detailed chemical kinetic interpretative model was developed and validated consisting of 244 species and 1198 reactions derived from a previous study of the oxidation of propanal (propionaldehyde). Extensive reaction pathway and sensitivity analysis was performed to provide detailed insight into the mechanisms governing low-, intermediate-, and high-temperature reactivity. The simulation results using the present model are in good agreement with the experimental laminar flame speeds and well within a factor of two of the speciation data obtained in the jet stirred reactor. (c) 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved

Modeling Challenges in Computing Aeronautical Combustion Chambers

International audienceThis article reviews the modeling challenges for performing Large Eddy Simulations of aero-nautical combustion chambers. Since the kerosene is injected in a liquid phase into the combustion chamber, the description of the atomization is of primary importance. The article first discusses the numerous numerical challenges encountered during this process, which leads to the formation of small droplets that constitute a spray. The existing numerical and modeling methods to describe a spray of kerosene droplets are then presented. The article then focuses on the description of the complex combustion kinetics. Hundreds of species and thousands of reactions have to beconsidered to predict ignition, flame stabilization and pollutant emissions. Due to lengthy computational times, detailed chemical schemes are too large to be directly used in CFD. This article then presents the major existing chemical reduction strategies. Significant interactions of the reactions layers with the flow vortices occur at the subgrid scale. The question of turbulent combustion modeling is therefore discussed in an LES context. Finally, the prediction of soot and NOx formation is presented. The review is illustrated by several examples representative of practical situations encountered in aeronautical combustors.On présente une revue des principales activités de recherche de l'ONERA sur la combustion supersonique et les superstatoréacteurs (ou statomixtes) dans le domaine civil depuis 1992. La première partie concerne les recherches de base sur la combustion supersonique, incluant l'acquisition de bases de données expérimentales et la modélisation de la combustion. Les études plus appliquées sur l'injection et la stabilisation de la flamme dans des foyers de recherche font l'objet de la deuxième partie. La troisième partie est consacrée aux activités de conception et de caractérisation de superstatoréacteurs pour diverses applications. L'ensemble des activités présentées a été mené soit sur financement interne, soit dans le cadre de trois programmes majeurs : PREPHA (1992-1997), JAPHAR (1997-2001) et LAPCAT II (2008-2013)

Effect of reduced two-dose (1+1) schedule of 10 and 13-valent pneumococcal conjugate vaccines (SynflorixTM and Prevenar13TM)) on nasopharyngeal carriage and serotype-specific immune response in the first two years of life: Results from an open-labelled randomized controlled trial in Indian children

Introduction: This study aimed to assess the effect of a reduced dose regime (1 + 1) of PCV10 and PCV13 along with 3-dose regimes on pneumococcal vaccine-type (VT) carriage and immunogenicity in the first two years of life in PCV-naïve Indian children. Methods: A total of 805 healthy infants aged 6–8 weeks were randomised to 7 groups (n = 115). Six groups received SynflorixTM(PCV10) or Prevenar13TM(PCV13) in the following schedules: 3 + 0 (three primary at 6, 10, and 14 weeks); 2 + 1 (two primary 6 and 14 weeks with booster at 9 months; 1 + 1 (one primary at 14 weeks with booster at 9 months). The 7th group was a PCV-naïve control group. Nasopharyngeal swabs were collected at 6, 18 weeks, 9, 10, 15, and 18 months of age. Venous blood samples were collected at 18 weeks, 9, 10, and 18 months of age for assessment of sero-specific IgG antibodies. Additionally, functional activity using a serotype specific opsonophagocytic assay (OPA) was assessed at 10 and 18 months of age in a subset (20%) of participants. Results: All schedules of PCV13 showed significant 13VT carriage reduction in the second year of life as compared to control. At 15 months of age, PCV13 (1 + 1) showed 45 % reduction in 13VT-carriage compared to the control [OR = 0.55 (95% CI; 0.31–0.97), p= 0.038]. None of the PCV10 schedules showed significant reduction in 10VT carriage in the second year. Although not powered for these outcomes, at 18 months of age, 1 + 1 and 2 + 1 schedules of both vaccines demonstrated higher sero-responders for all serotypes, higher geometric mean concentrations (GMC) for all serotypes except 23F [with both vaccines], higher percent OPA responders and OPA geometric mean titres (GMT) compared to the 3 + 0 schedules for all serotypes. Conclusion: The reduced dose schedule (1 + 1) of PCV13 results in significant VT-carriage reduction in the second year of life. Immune protection provided by 1 + 1 schedules of PCV10 and PCV13 in the second year of life is comparable to WHO-recommended 3-dose schedules

Identification and Quantification of Aromatic Hydrocarbons Adsorbed on Soot from Premixed Flames of Kerosene, Synthetic Kerosene, and Kerosene–Synthetic Biofuels

In the current study, the chemical characterization of polycyclic aromatic hydrocarbons (PAHs) adsorbed on soot from premixed flames of synthetic paraffinic kerosene (SPK), conventional kerosene (Jet A-1), and Jet A-1/synthetic biofuel blends was carried out. Jet A-1 and SPK liquid fuels were analyzed with NMR to provide supporting information on their chemical composition. The analytical procedure used to characterize PAHs fraction in soot samples includes the following: (i) filtration of the soot samples diluted into <i>n</i>-hexane through PTFE filters, (ii) automated solid-phase extraction (A-SPE) for fractioning and cleaning-up the soot extracts, and (iii) chromatographic analysis of every fraction by reverse high-performance liquid chromatography (RPLC) with photodiode array (PDA) detection. Application of the aforementioned methodology allowed the identification of 78 compounds including indene, toluene, and 76 PAHs. Moreover, the relative abundance of five-membered-ring PAHs and alkyl PAHs was evaluated, and 19 PAHs (16 EPA PAHs, 1-methylnaphthalene, 2-methylnaphthalene, and coronene) were quantified. The PAH characterization should contribute to improve our understanding of atmospheric reactivity of soot and other environmental aspects of aromatic compounds adsorbed on soot