CNRS Atmospheric and Combustion Chemistry Laboratory

Lille, France

CNRS Atmospheric and Combustion Chemistry Laboratory

Lille, France

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Fenard Y.,CNRS Atmospheric and Combustion Chemistry Laboratory | Boumehdi M.A.,CNRS Atmospheric and Combustion Chemistry Laboratory | Vanhove G.,CNRS Atmospheric and Combustion Chemistry Laboratory
Combustion and Flame | Year: 2017

The oxidation of 2-methyltetrahydrofuran (2-MTHF) has been experimentally studied in a rapid compression machine. The ignition delays of stoichiometric 2-MTHF/O2/inert mixtures were measured for a wide range of conditions: Top dead center pressure ranging from 0.3 to 2.1 MPa and core gas temperatures between 640 K and 900 K. Two-stage ignition is observed for temperatures between 685 K and 790 K, leading to a deviation from Arrhenius behavior of the evolution of ignition delays with temperature. Sampling of the reacting mixture was performed for different times between the top dead center and the ignition. Stable reaction intermediates were separated by gas chromatography, identified by mass spectrometry and quantified with a flame ionization detector. More than 20 species were identified and used to identify major reaction pathways. Among species of importance, 2-methyl-dihydrofurans, 2-methylfuran, methyldihydrofuranones, 1-cyclopropanylethanone, 3-penten-2-one and methylvinylketone were detected. Mole fraction profiles were obtained and used alongside first stage and total ignition delays to validate a detailed kinetic model for the oxidation of 2-MTHF. The resulting model takes in account 507 species involved in 2425 reactions. The validity of this model was extended to the high temperature range using existing ignition delays and low pressure laminar flame speciation data. © 2017 The Combustion Institute


Yi J.,Pohang University of Science and Technology | Bahrini C.,CNRS Atmospheric and Combustion Chemistry Laboratory | Schoemaecker C.,CNRS Atmospheric and Combustion Chemistry Laboratory | Fittschen C.,CNRS Atmospheric and Combustion Chemistry Laboratory | Choi W.,Pohang University of Science and Technology
Journal of Physical Chemistry C | Year: 2012

Hydrogen peroxide (H 2O 2) is an important reactive oxygen species (ROS) involved in photocatalysis. To study the photocatalytic behavior of H 2O 2, the decomposition of H 2O 2 on illuminated TiO 2 films was investigated using cavity ring down spectroscopy (CRDS). A mixture of H 2O 2 and O 2 gas was flowed through a cavity reactor which contained a TiO 2-coated plate. The removal of H 2O 2 and the accompanying production of HO 2 radicals were monitored in the gas phase just above the TiO 2 film which was irradiated by a UV light-emitting diode (LED) (375 nm). The TiO 2 films tested in this study were mainly Degussa P25 TiO 2 (DP), Aldrich anatase (AA), and Aldrich rutile (AR). The photocatalytic production of HO 2 was observed only in the presence of H 2O 2, which indicates that the HO 2 radicals were generated from the decomposition of H 2O 2, not from the photocatalytic reduction of O 2. The direct photolysis of H 2O 2 in the absence of TiO 2 was not observed at all under the present irradiation conditions. The degradation of H 2O 2 and the accompanying production of HO 2 was not retarded at all in the absence of O 2 (a common electron acceptor), which implies that H 2O 2 itself should serve as an electron acceptor. Although the HO 2 radicals were originated from the decomposition of H 2O 2, the removal of H 2O 2 and the production of HO 2 were not correlated. H 2O 2 could be rapidly degraded on illuminated DP with little production of HO 2, whereas H 2O 2 was photodegraded much more slowly over AA and AR but with a marked production of HO 2. On illuminated DP, the in situ generated HO 2 radicals seem to be rapidly degraded with little chance of desorption into the gas phase, while those on AA and AR are long-lived enough that some desorb into the gas phase. This implies that the fate of HO 2 radicals, which are universally involved in all photocatalytic reactions in the presence of O 2, should be sensitively influenced by and dependent on the kind of TiO 2. The photocatalytic decomposition of H 2O 2 with different TiO 2 films was investigated with varying the experimental parameters such as light intensity, [H 2O 2], carrier gas composition (O 2 vs N 2), and alternative electron donor and acceptor (methanol, EDTA, silver ions). The result implications for photocatalytic mechanism and atmospheric chemistry are discussed. © 2012 American Chemical Society.


Thiebaud J.,CNRS Atmospheric and Combustion Chemistry Laboratory | Thiebaud J.,SRI International | Thevenet F.,Ecole Des Mines de Douai | Fittschen C.,CNRS Atmospheric and Combustion Chemistry Laboratory
Journal of Physical Chemistry C | Year: 2010

The formation of OH radicals and their diffusion into the gas phase after UV-excitation of TiO2 in the presence of H2O has been studied using the very sensitive and selective detection method of laserinduced fluorescence (LIF). The time-resolved evolution of the OH radical concentration has been observed at different pressures and at varying distances between the photocatalytic surface and the detection volume. H2O2 has been indirectly detected by LIF. The influence of O2, hydrocarbons, and excitation laser wavelength on the evolution of both species profiles has been studied in this work. The quantum yield for the formation of OH and H2O2 has been estimated by comparison with signals obtained after photolysis of H2O2 in the gas phase. © 2010 American Chemical Society.


Lamoureux N.,CNRS Atmospheric and Combustion Chemistry Laboratory | Desgroux P.,CNRS Atmospheric and Combustion Chemistry Laboratory | El Bakali A.,CNRS Atmospheric and Combustion Chemistry Laboratory | Pauwels J.F.,CNRS Atmospheric and Combustion Chemistry Laboratory
Combustion and Flame | Year: 2010

We report an experimental and modeling study on prompt-NO formation in low-pressure (5.3kPa) premixed flames. Special emphasis is given to the quantitative detection (and prediction) of NCN, whose role in prompt-NO formation has recently been confirmed in alkane flames. Here a rich (Φ=1.25) CH4-O2-N2 flame and rich (Φ=1.25) and stoichiometric C2H2-O2-N2 flames have been investigated. Absolute concentration profiles of CH and NCN radicals and NO species are obtained by combining laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CRDS). Temperature profile is determined in each flame using OH and NO-LIF thermometry. Flame modeling is performed to determine the role of NCN in prompt-NO formation and to test the capacity of the present chemical mechanisms to predict some intermediate species involved in prompt-NO formation. The methane flame is modeled using GDFkin®3.0_NCN mechanism [El Bakali et al., Fuel 85 (2006), 896-909]. The acetylene flames are modeled using the Lindstedt and Skevis C/H/O mechanism [Lindstedt and Skevis, Proc. Combust. Inst. 28 (2000), 1801-1807], completed by the submechanism issued from GDFkin®3.0_NCN for nitrogen chemistry. This submechanism includes the initiation reaction CH+N2=NCN+H. Rate constants of NO-sensitive reactions of the submechanism are modified by taking into account the recent literature. In particular, the C2O route could be explored thanks to a significant presence of C2O in acetylene flames. Globally, the modified submechanism of nitrogen chemistry coupled with the two hydrocarbon mechanisms leads to a satisfying prediction of NCN and NO mole fraction profiles, even though refinements of rate constant determination is still required. The role of NCN in prompt-NO formation in acetylene flames is demonstrated. © 2010 The Combustion Institute.


Louis F.,CNRS Atmospheric and Combustion Chemistry Laboratory
International Journal of Chemical Kinetics | Year: 2015

The rate constants of the H-abstraction reactions from cyclopropane by H, O (3P), Cl (2P3/2), and OH radicals have been calculated over the temperature range of 250-2500 K using two different levels of theory. Calculations of optimized geometrical parameters and vibrational frequencies are performed using the MP2 method combined with the cc-pVTZ basis set and the 6-311++G(d,p) basis set. Single-point energy calculations have been carried out with the highly correlated ab initio coupled cluster method in the space of single, double, and triple (perturbatively) electron excitations CCSD(T) using either the cc-pVTZ, aug-cc-pVTZ, and aug-cc-pVQZ basis sets or the 6-311++G(3df,3pd) basis set. The CCSD(T) calculated potential energies have been extrapolated to the complete basis limit (CBS) limit. The Full Configuration Interaction (FCI) energies have been also estimated using the continued-fraction approximation as proposed by Goodson (J. Chem. Phys., 2002, 116, 6948-6956). Canonical transition-state theory combined with an Eckart tunneling correction has been used to predict the rate constants as a function of temperature using two kinetic models (direct abstraction or complex mechanism) at two levels of theory (CCSD(T)-cf/CBS//MP2/cc-pVTZ and CCSD(T)-cf/6-311++G(3df,3pd)//MP2/6-311++G(d,p)). The calculated kinetic parameters are in reasonable agreement with their literature counterparts for all reactions. In the light of these trends, the use of the Pople-style basis sets for studying the reactivity of other systems such as larger cycloalkanes or halogenated cycloalkanes is recommended because the 6-311++G(3df,3pd) basis set is less time consuming than the aug-cc-pVQZ basis set. Based on our calculations performed at the CCSD(T)-cf/CBS//MP2/cc-pVTZ level of theory, the standard enthalpy of formation at 298 K for the cyclopropyl radical has been reassessed and its value is (290.5 ± 1.6) kJ mol-1. © 2015 Wiley Periodicals, Inc.


Bejaoui S.,CNRS Atmospheric and Combustion Chemistry Laboratory | Mercier X.,CNRS Atmospheric and Combustion Chemistry Laboratory | Desgroux P.,CNRS Atmospheric and Combustion Chemistry Laboratory | Therssen E.,CNRS Atmospheric and Combustion Chemistry Laboratory
Combustion and Flame | Year: 2014

In this work, laser induced fluorescence (LIF) has been applied to probe PAHs in two atmospheric sooting flames: a premixed flat flame of methane and a Diesel turbulent spray one. Different laser excitation wavelengths have been used. UV excitations at 266 and 355 nm have been operated from the fourth and the third harmonic frequencies of an Nd: YAG laser while visible excitations were emitted by an OPO pumped by the third harmonic of the YAG laser. Because of the different nature of the flames, the recorded fluorescence spectra highlight different spectral properties. The diffusion flame appears to provide a better selectivity to the LIF measurements because of the stratification of the PAHs size classes along the flame height. In the premixed flame, all PAHs size classes spatially coexist making the analysis of LIF measurements more complex. Upon visible excitations, it is highlighted in this paper that PAHs can absorb and fluoresce up to 680 nm. Fluorescence emission spectra are shown to present Stokes and anti-Stokes components. Discussion of these non-conventional absorption and fluorescence features are provided on the basis of the knowledge of PAH spectroscopy and flame kinetics. Hence, different families of PAHs are successively envisaged and discussed to elucidate the experimental spectra recorded in both flames. It is shown that only a limited number of PAHs are able to lead to such spectral features. From this discussion, it appears that large pericondensed PAHs are unlikely to give rise to such signals. Some other possibilities are therefore discussed which could potentially correspond to the latest fluorescent gaseous species at the origin of the soot formation. © 2014.


Faccinetto A.,CNRS Atmospheric and Combustion Chemistry Laboratory | Faccinetto A.,CNRS Atomic and Molecular Physics Laboratory | Desgroux P.,CNRS Atmospheric and Combustion Chemistry Laboratory | Ziskind M.,CNRS Atomic and Molecular Physics Laboratory | And 2 more authors.
Combustion and Flame | Year: 2011

Species adsorbed at the surfaces of soot particles sampled at different locations in a low-pressure methane flame have been analyzed. The analysis method is laser desorption/laser ionization/time-of-flight mass spectrometry (LD/LI/TOF-MS) applied to soot particles deposited on a filter after probe extraction in the flame. In order to fully characterize the experimental apparatus, a strategy of systematic investigations has been adopted, beginning with the study of less complex systems constituted by model soot (standard polycyclic aromatic hydrocarbons, PAHs, adsorbed on black carbon), and then natural soot sampled from a literature reference ethylene flame. This characterization allowed a good understanding of the analytical response of PAHs to the desorption and ionization processes and the definition of the optimal experimental conditions. The soot PAH content was then investigated on a low-pressure methane/oxygen/nitrogen premixed flat flame (φ= 2.32) as a function of the sampling height above the burner (HAB). The obtained mass spectra are reproducible, fragment-free, well resolved in the analyzed m/. z range and they are characterized by an excellent signal-to-noise ratio. They all feature regular peak sequences, where each signal peak has been assigned to the most stable high-temperature-formed PAHs. The structure of the mass spectra depends on the sampling HAB into the flame, i.e., on the reaction time. An original contribution to the data interpretation comes from the development of a new sampling method that makes it possible to infer hypotheses about the PAH partition between the gas phase and the soot particles. This method highlights the presence of high-mass PAHs in the soot nucleation zone, and it suggests the importance of heterogeneous reactions occurring between flame PAHs and soot particles. © 2010 The Combustion Institute.


Lamoureux N.,CNRS Atmospheric and Combustion Chemistry Laboratory | El Merhubi H.,CNRS Atmospheric and Combustion Chemistry Laboratory | Gasnot L.,CNRS Atmospheric and Combustion Chemistry Laboratory | Schoemaecker C.,CNRS Atmospheric and Combustion Chemistry Laboratory | Desgroux P.,CNRS Atmospheric and Combustion Chemistry Laboratory
Proceedings of the Combustion Institute | Year: 2015

In the present work, measurements of absolute mole fraction profiles of CN and HCN were jointly performed in low pressure (5.3 kPa) premixed CH4/O2/N2 flames of three equivalent ratios (φ = 0.8-1.25). These species were the missing link of the database comprising CH, NCN, NCO and NO species previously acquired in Lille to improve detailed mechanisms of prompt-NO formation. For that purpose, LIF and pulsed CRDS techniques were implemented to measure in the flames absolute mole fraction of CN by probing the B-X(1,0) vibrational band around 356 nm. This combination of techniques allows reaching a detection limit as low as tenth of ppbv that was necessary to measure CN in lean flame condition could be achieved. HCN molecules were measured by using cw-CRDS technique around 1.5 μm (in the (2 0 0)-(0 0 0) vibrational band) after gas probe sampling. The required sensitivity equal to 15 ppbv of HCN was achieved using a long absorption cell (about 1 m). These CN and HCN profiles were simulated by considering two detailed mechanisms of prompt-NO formation from literature (Konnov0.6 (Combust. Flame 156 (2009) 2093-2105) and GDFkin®3.0-NCN (Combust. Flame 157 (2010) 1929-1941)). © 2014 The Combustion Institute.


Carteret M.,CNRS Atmospheric and Combustion Chemistry Laboratory | Pauwels J.-F.,CNRS Atmospheric and Combustion Chemistry Laboratory | Hanoune B.,CNRS Atmospheric and Combustion Chemistry Laboratory
Indoor Air | Year: 2012

Laboratory measurements of the gaseous emission factors (EF) from two recent kerosene space heaters (wick and injector) with five different fuels have been conducted in an 8-m3 environmental chamber. The two heaters tested were found to emit mainly CO2, CO, NO, NO2, and some volatile organic compounds (VOCs). NO2 is continuously emitted during use, with an EF of 100-450μg per g of consumed fuel. CO is normally emitted mainly during the first minutes of use (up to 3mg/g). Formaldehyde and benzene EFs were quantified at 15 and 16μg/g, respectively, for the wick heater. Some other VOCs, such as 1,3-butadiene, were detected with lower EFs. We demonstrated the unsuitability of a 'biofuel' containing fatty acid methyl esters for use with the wick heater, and that the accumulation of soot on the same heater, whatever the fuel, leads to a dramatic increase in the CO EF, up to 16mg/g, which could be responsible for chronic and acute CO intoxications. © 2011 John Wiley & Sons A/S.


Gasnot L.,CNRS Atmospheric and Combustion Chemistry Laboratory | Dao D.Q.,CNRS Atmospheric and Combustion Chemistry Laboratory | Pauwels J.F.,CNRS Atmospheric and Combustion Chemistry Laboratory
Energy and Fuels | Year: 2012

An experimental and kinetic study of the influence of additives on the selective noncatalytic reduction (SNCR) process is presented. Experiments were performed on a lab-scale reactor suitable to investigate the influence of important operating parameters (flue gas temperature, residence time, amount of reducing agent, initial NO x concentration, etc.) on the SNCR efficiency. Several chemical compounds such as CH 4, C 2H 6, C 2H 4, C 2H 2, CH 3OH, C 2H 5OH, and CO, which are usually used in the literature as additives for the SNCR process, have been evaluated. The experimental results prove that the use of such additives allows the NO reduction process to be more efficient at lower temperatures. Furthermore, they induce a downward shift up to more than 100 K of the optimal temperature window for the reduction process. Four detailed kinetic mechanisms available in the literature have been tested to model our experimental results. The one that presents the better agreement between experiment and modeling has been optimized to explain the kinetic influence of the additives on the classical SNCR process. The main reaction pathways involved have been pointed out, illustrating the important role of OH radical. © 2012 American Chemical Society.

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