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Citation suggéréeAnses. (2022). Étude sur les pratiques de consommation des usagers de cigarettes électroniques en France : appui à la caractérisation des expositions. (saisine 2020-SA-0017). Maisons-Alfort : Anses, 68 p.; Arrivée sur le marché français au début des années 2010, la cigarette électronique, vapoteuse ou système électronique de délivrance de la nicotine (SEDEN), est un système portatif de délivrance d’un aérosol, contenant le plus souvent de la nicotine, destiné à être inhalé au moyen d'un embout buccal. Le dispositif électronique est composé de trois éléments principaux : un atomiseur, une batterie et un réservoir ou une cartouche contenant le liquide à vapoter («e-liquide »). Celui-ci est une solution composée majoritairement d’un support de dilution, propylène glycol (PG) et/ou de glycérol (glycérine végétale, VG) auquel sont ajoutés un mélange d’arômes et de la nicotine dans des concentrations variables. Lors de l’utilisation, le e-liquide est chauffé au contact de l’atomiseur, grâce à l’énergie fournie par la batterie. Il se forme alors un aérosol dont la composition finale varie non seulement en fonction de la composition du e-liquide mais aussi du dispositif électronique utilisé, de ses réglages, et du mode d’inhalation. Le terme générique « produit du vapotage » désigne aussi bien le e-liquide que le dispositif électronique utilisé par l’usager (« vapoteur »).Du fait de l’absence de combustion lors de son usage, la cigarette électronique est souventconsidérée comme une alternative préférable à la consommation de tabac fumé, voire uneaide à l’arrêt tabagique. Cet aspect reste controversé. En effet, selon les travaux du Cochranepubliés en 2021 et 2022, la cigarette électronique utilisée avec des produits à base de nicotine,augmenterait les taux d’abandon du tabac. Une autre revue systématique récente n’arrivait cependant pas à démontrer que la cigarette électronique favorise l’obtention d’un arrêt prolongé du tabac (au-delà de 6 à 12 mois) . En l’absence d’une efficacité clairement établie, le Haut Conseilde la santé publique (HCSP) recommandait en France en 2021 de ne pas utiliser la cigaretteélectronique pour le sevrage tabagique en première intention. Il admet néanmoins la possibilitéd’utiliser ce produit de consommation par choix individuel, en dehors ou en complément d’uneprise en charge pour arrêter de fumer dans le cadre du système de soin (HCSP, 2021). Lacontroverse sur l’utilisation des produits du vapotage tient aussi de la méconnaissance desrisques sanitaires à long terme liés à l’exposition aux substances chimiques contenues dansles émissions des cigarettes électroniques.Pour autant, depuis l’arrivée de ces dispositifs sur le marché, leur utilisation en Franceaugmente et cette tendance semble se maintenir dans le temps. En effet, les prévalencesd’usages actuel et quotidien1 de cigarette électronique restent stables depuis 2018, avecrespectivement 5,4 % et 4,3 % des 18-75 ans. Par ailleurs, d’après les données issues desbaromètres de Santé publique France entre 2014 et 2017 l’ancienneté moyenne dans levapotage a été multipliée par cinq, passant de 4 mois à 20 mois (Santé publique France,2019). Ces augmentations sont en partie liées au développement du produit à cette périodeet démontrent un intérêt durable de la part des consommateurs. L’utilisation de ces produits concerne également les mineurs, pour lesquels la vente est pourtant interdite depuis 2014selon la Loi n° 2014-344 du 17 mars 2014. Selon l’Observatoire français des drogues ettendances addictives (OFDT), les taux d’initiation à 16 ans étaient significativement plusélevés en France que dans le reste de l’Europe sur la période 2018-2019 ((46 % contre 40 %en moyenne) tandis que l’usage au cours du mois demeurait similaire, autour de 16 % (OFDT,2021).

International audience; A better understanding of the formation of soot particles is essential to improve combustion-related processes. For this purpose, this work reports for the first time the measurement of the size of soot particles under formation in a turbulent atmospheric flame in a planar configuration. This is ensured by the detection of the elastic scattering of a laser sheet thanks to two cameras positioned at different scattering angles (45° and 135°). The size information is then used to interpret the scattering signal collected by an additional camera positioned at 90° in order to evaluate the soot number concentration. This last step relies on a calibration ensured by soot volume fraction and primary particle size previously determined by autocompensating laser-induced incandescence in the same flame.Moreover, the use of a 1kHz repetition rate nanosecond laser and three high speed CMOS cameras enables the access to these physical parameters with a high temporal resolution. The 2D and time-resolved soot characterization is of interest because it enables the observation of the temporal and spatial modifications of soot structures when propagating in such turbulent flames. In particular, in this flame, the transport and mixing of soot pockets are clearly observed and the impact of these processes on the size and number concentration is quantified.

Ultrafine particles represent a growing concern in the public health community but their precise role in many illnesses is still unknown. This lack of knowledge is related to the experimental difficulty in linking their biological effects to their multiple properties, which are important determinants of toxicity. Our aim is to propose an interdisciplinary approach to study fine (FP) and ultrafine (UFP) particles, generated in a controlled manner using a miniCAST (Combustion Aerosol Standard) soot generator used with two different operating conditions (CAST1 and CAST3). The chemical characterization was performed by an untargeted analysis using ultra-high resolution mass spectrometry. In conjunction with this approach, subsequent analysis by gas chromatography–mass spectrometry (GC–MS) was performed to identify polycyclic aromatic hydrocarbons (PAH). CAST1 enabled the generation of FP with a predominance of small PAH molecules, and CAST3 enabled the generation of UFP, which presented higher numbers of carbon atoms corresponding to larger PAH molecules. Healthy normal human bronchial epithelial (NHBE) cells differentiated at the air-liquid interface (ALI) were directly exposed to these freshly emitted FP and UFP. Expression of MUC5AC, FOXJ1, OCLN and ZOI as well as microscopic observation confirmed the ciliated pseudostratified epithelial phenotype. Study of the mass deposition efficiency revealed a difference between the two operating conditions, probably due to the morphological differences between the two categories of particles. We demonstrated that only NHBE cells exposed to CAST3 particles induced upregulation in the gene expression of IL-8 and NQO1. This approach offers new perspectives to study FP and UFP with stable and controlled properties.

Combustion and other high-temperature processes frequently result in the emission of aerosols in the form of polydisperse fractal-like aggregates made of condensed-phase nanoparticles (soot for instance). If certain conditions are met, the emitted aerosol particles are known to evolve into important cloud condensation nuclei (CCN) in the atmosphere. In this work, the hygroscopic parameter κ of complex morphology aggregates is calculated from the supersaturation-dependent activated fraction Fa=Fa(SS) in the frame of κ-Köhler theory. The particle size distribution is approximated with the morphology-corrected volume equivalent diameter calculated from the electrical mobility diameter by taking into account the diameter of the primary particle and the fractal dimension of the aggregate experimentally obtained from transmission electron microscopy measurements. Activation experiments are performed in water supersaturation conditions using a commercial CCN-100 condensation nuclei counter. The model is tested in close-to-ideal conditions of size-selected, isolated spherical particles (ammonium sulfate nanoparticles dispersed in nitrogen), then with complex polydisperse fractal-like aggregates (soot particles activated by exposure to ozone with κ as low as 5×10-5) that represent realistic anthropogenic emissions in the atmosphere.

Air pollution has significant health effects worldwide, and airborne particles play a significant role in these effects. Ultrafine particles (UFPs) have an aerodynamic diameter of 0.1 μm or less, can penetrate deep into the respiratory tree, and are more toxic due to their large specific surface area, which should adsorb organic compounds. The aim of this study is to show the toxicological effects of UFPs with high organic content at low dose on BEAS-2B cells through at air-liquid interface (ALI) exposure using a Vitrocell® technology and a miniCAST (Combustion Aerosol Standard) generator. In conjunction with this approach, chemical analysis of particles and gas phase was performed to evaluate the presence of polycyclic aromatic hydrocarbons (PAHs). Chemical analyses confirmed the presence of PAHs in UFPs. With this experimental setup, exposure of the BEAS-2B cells induced neither cytotoxicity nor mitochondrial dysfunction. However, an increase of oxidative stress was observed, as assessed through Nrf2, NQO1, HO-1, CuZnSOD, MnSOD, and Catalase gene expression, together with significant induction of genes related to xenobiotic metabolism CYP1A1 and CYP1B1. Negative regulation of inflammatory genes expression (IL-6 and IL-8) was present three hours after the exposition to the UFPs. Taken together, this experimental approach, using repeatable conditions, should help to clarify the mechanisms by which organic UFPs induce toxicological effects.

Aerosols such as soot are a matter of concern in our daily life. Due to their impact on human healthbut also on global warming, their characterization is of extremely high relevance. In this context,extensive work has been done to characterize soot particles by optical techniques because suchapproaches enable an in-situ determination. These techniques essentially rely on the attenuationof the light (LOSA), on the scattering properties (Angular Light Scattering) or on their thermalbehaviour after laser heating (LII). In any cases, the signals are interpreted based on modelsrequiring precise light-particles theories in order to express the absorption and scattering crosssections. For nano-aerosols as soot, the Rayleigh-Debye-Gans (RDG) approximation for fractalaggregates (FA) is frequently used essentially due to its simplicity since it provides a simpleanalytical expression of the scattering and absorption cross sections. However, this approximationrelies on two strong assumptions. First, the monomers composing the aggregate behave asRayleigh spheres, i.e., they are small enough compared to the wavelength and transparentenough to make the phase shift negligible. Second, it is supposed that there is no electromagneticcoupling between the monomers (internal multiple-scattering), i.e., each one sees only the incidentlight and not the light scattered by its neighbours.Many studies have compared rigorous solutions with RDG-FA ones and observed importantdiscrepancies. Indeed, RDG-FA can lead to errors up to 45% on the predicted forward scattering[1, 2] and optical determination of the fractal dimension can be overestimated by a factor up to10% [3]. Also, impact on LII measurements has been shown to be potentially important [4].Nevertheless, the precise underlying mechanisms leading to these discrepancies were not well understood and thus, until now, no models where proposed to improve RDG-FA theory regarding the internal coupling effects.The present communication aims to show to the LII and soot communities the recent advances made on this topic which were achieved by the use of the phasor approach which enables a comprehensive description of the internal electric field and its link with corrections to bring to RDGFA. The internal coupling effects will be first illustrated for a pair of monomers [5] followed by fractal aggregates [6]. Correction factors will be proposed for absorption and forward scattering. Recent advances concerning the impact of internal coupling on scattering structure factor will be also presented.

It is well established that soot particles are harmful to the environment and health of living beings, mainly due to their small sizes and chemical composition. In this sense, development of advanced experimental diagnostics for detailed characterization of soot properties is fundamental. Unfortunately, accurate characterization of soot properties requires knowledge of its optical properties, which are difficult to obtain and are subject to ongoing debate and investigation in the community [1]. The soot optical properties can be related to its composition and internal nanostructure in terms of the amount of organic and graphitic compounds, which allows to define a level of maturity [2]. Indeed, soot maturity should be considered in the analysis of optical signals obtained experimentally. Particularly, the auto-compensating laser induced incandescence (ACLII) technique offers a great opportunity to obtain soot properties; however, large errors can be produced when converting these signals to soot volume fraction, temperature and sizes without considering soot maturity.The maturity of soot particles can be quantified as a power-law spectral dependence of the ratio of absorption function Em to the ratio of avelengths λ, which defines a maturity level β. This is closely related to the Angstrom exponent ξ that uses the ratio of absorption coefficients κabs or absorption cross section instead of ratio of Em [1]. The determination of ξ relies on a power-law fit of the data retrieved for the ratios of κabs at different pairs of wavelengths, which may vary according to the spectral range considered, especially if κabs is determined from extinction measurements and not corrected for scattering. Moreover, the multiple-scattering effects within soot aggregates can also play a role and should be accounted for. Nevertheless, these effects can be quantified using a numerical framework, where a reference can be established.In this study, the impact of composition, morphology, multiple-scattering and excitation wavelength on the determination of soot temperature, volume fraction and diameter of primary spheres through the ACLII technique is quantified. For this purpose, the numerical method considers the following. First, simulation of a canonical Gülder type flame is performed, using the CoFlame code, providing reference 2D fields of soot volume fraction, temperature, diameter of primary particles, number density of aggregates and primary particles. Next, these properties are used as input for solving the conservation equations of energy and mass of laser-heated soot aggregates. Last, the modelled temperature-time curve is used to simulate a pair of timeresolved LII signals at different detection wavelengths, which are then used to recover the input parameters, in particular, soot volume fraction, temperature and particle diameter. The effect of soot maturity is considered by imposing a β coefficient field based on recent results [2]. The scattered values of ξ found after a literature review are used as reference for the sensitivity analysis. Finally, multiple-scattering effects are taken into account through the corrections proposed by [3], and the effect of size distribution is also assessed. This framework allows to quantify the uncertainties associated with the hypotheses employed in laser-based techniques.

International audience; The main characteristics of pool fire flames are flame height, air entrainment, pulsation of the flame, formation and properties of soot particles, mass burning rate, radiation feedback to the pool surface, and the amount of pollutants including soot released to the environment. In this type of buoyancy controlled flames, the soot content produced and their subsequent thermal radiation feedback to the pool surface are key to determine the self-sustainability of the flame, their mass burning rate and the heat release rate. The accurate characterization of these flames is an involved task, specially for modelers due to the difficulty of imposing adequate boundary conditions. For this reason, efforts are being made to design experimental campaigns with well-controlled conditions for their reliable repeatability, reproducibility and replicability. In this work, we characterized the production of soot in a surrogate pool fire. This is emulated by a bench-scale porous burner fueled with pure ethylene burning in still air. The flame stability was characterized with high temporal and spatial resolution by using a CMOS camera and a fast photodiode. The results show that the flame exhibit a time-varying propagation behavior with a periodic separation of the reactive zone. Soot volume fraction distributions were measured at nine locations along the flame centerline from 20 to 100 mm above the burner exit using the auto-compensating laser-induced incandescence (AC-LII) technique. The mean, standard deviation and probability density function of soot volume fraction were determined. Soot volume fraction presents an increasing tendency with the height above the burner, in spite of a local decrease at 90 mm which is approximately the position separating the lower and attached portion of the flame from the higher more intermittent one. The results of this work provide a valuable data set for validating soot production models in pool fire configurations.

International audience; In-flame optical characterization of soot is of vital importance to understand soot formation mechanisms as well as to develop and validate accurate soot models. The present work introduces an unconventional methodology adapted to laminar axisymmetric flames that avoids the issue of variable measurement vol- ume with varying scattering angle in the existing light scattering techniques and thus enables the deter- mination of aggregate size with a higher spatial resolution. Coupled with multi-wavelength line-of-sight attenuation measurements, the proposed Horizontal Planar Angular Light Scattering at 532 nm was found able to provide radial profiles of aggregate size, number and diameter of primary spheres, soot volume fraction, and number density in a laminar axisymmetric coflow ethylene/air diffusion flame established over a Gülder burner. The spatial variation of soot optical properties associated with soot maturity was considered in data analysis.

International audience; Mature soot aggregates exhibit a morphology which is currently mimicked by diffusion-limited aggregation (DLCA) codes, i.e. with a sticking probability = 1 when two aggregates collide. Nevertheless, nascent soot particles may grow in the reaction-limited aggregation regime (RLCA), i.e. with a sticking probability ≪ 1. Yet, it remains to be seen how fast the transition from RLCA to DLCA occurs for soot particles and what is the impact on aggregation kinetics, particle size distribution and morphology. This work intends to fill this gap by exploring the aggregation of soot particles formed in a laminar premixed flame through numerical simulations. Results show that the transition from RLCA to DLCA is very fast and produces a moderate impact on soot formation dynamics and morphology. However, soot particles mass bulk density is found to play an important role and should be considered in future simulations of soot formation in flames.

Black carbon aerosol emissions are recognized as contributors to global warming and air pollution. There remains, however, a lack of in-situ techniques to remotely quantify black carbon aerosol particles with high range and time resolution. This article presents for the first time, to our knowledge, a direct and contact-free remote measurement of black carbon aerosol number and mass concentration less than ten of meters from the emission source. This is done with a novel picosecond short-range elastic backscatter lidar (PSR-EBL) technique. To address the complexity of retrieving lidar products at short measurement ranges, we apply a forward inversion method featuring radiometric lidar calibration. Our method is based on an extension of a well-established light-scattering model, the Rayleigh-Debye-Gans for Fractal-Aggregates (RDG-FA) theory, which computes an analytical expression for lidar parameters. These parameters are the backscattering cross-sections and the lidar ratio for black carbon fractal aggregates. Using a small-scale Jet A-1 kerosene pool fire, it is shown that our technique can quantify the aerosol number and mass concentration with centimetre range-resolution and millisecond time-resolution.; Les émissions d'aérosols de carbone noir sont reconnues comme contribuant au réchauffement climatique et à la pollution de l'air. Il reste cependant un manque de techniques pour quantifier à distance les particules d'aérosol de noir de carbone avec une plage et une résolution temporelle élevées. Cet article présente une technique à distance directe et sans contact pour quantifier le nombre d'aérosols de carbone noir et la concentration massique à quelques mètres de la source d'émission. Cela se fait à l'aide de l'instrument Colibri basé sur une nouvelle technique, appelée ici Picosecond Short-Range Elastic Backscatter Lidar (PSR-EBL). Pour faire face à la complexité de la récupération des produits lidar à de courtes plages de mesure, nous appliquons une méthode d'inversion directe avec étalonnage radiométrique du lidar. Notre méthode est basée sur une extension d'un modèle de diffusion de la lumière bien établi, la théorie Rayleigh-Debye-Gans for Fractal-Aggregates (RDG-FA), qui calcule une expression analytique des paramètres lidar. Ces paramètres sont les sections efficaces de rétrodiffusion et le rapport lidar pour les agrégats fractals de carbone noir. À l'aide d'un feu de nappe de kérosène Jet A-1 à petite échelle, nous démontrons la capacité de la technique à quantifier le nombre d'aérosols et la concentration en masse avec une résolution centimétrique et une résolution temporelle en millisecondes.

Laser-induced incandescence (LII) is an optical technique that is widely used for the in situ measurement of the soot volume fraction in flames. The low intensity of LII signals in low-sooting turbulent flames means that long camera acquisition times are needed to achieve sufficiently high signal-to-noise ratios. The direct application of auto-compensating LII (AC-LII) to infer the soot volume fraction from the measured LII signals can lead to large errors due to the significant decrease in the temperature of the soot particles over the duration of the camera gate. In order to reduce the measurement errors from AC-LII, we propose an improved approach in which the cooling of soot particles during the camera acquisition of LII signals is considered. The proposed methodology is applied to planar AC-LII measurements for the determination of soot volume fraction and primary particle diameter in a low-sooting turbulent flame, with the help of the open source LII software LIISim. This study represents the first application of planar AC-LII to a turbulent flame. A sensitivity analysis is also conducted in order to determine the main factors affecting the uncertainty of the proposed approach. Copyright © 2021 American Association for Aerosol Research

International audience; Knowledge of the optical properties of soot black carbon (BC) is required for the prediction of the radiative effects of freshly-emitted and aged BC particles. Here we review BC mass absorption cross section (MAC) and absorption function E(m) measurements, focusing on freshly-emitted BC. First, we review recently reported MACs at 550 nm wavelength as obtained from direct measurements of particulate absorption and mass concentration; we find an average of 8.0 ± 0.7 m2/g from ten measurements, not significantly higher (p > 0.26) than the widely used MAC of 7.5 ± 1.2 m2/g recommended by Bond and Bergstrom [Bond, T. C., and R. W. Bergstrom. 2006. Light absorption by carbonaceous particles: An investigative review. Aerosol Sci. Technol. 40(1):27–67]. Second, we review recently reported E(m), whose retrieval is more complex due to the need to combine measurements with numerical models to estimate the contribution of scattering to extinction. Third, we review recent numerical studies that have aimed to predict the BC MAC using various complex refractive indices (m = n + ik). Most of these studies have used m = 1.95 + 0.79i recommended by Bond and Bergstrom (2006), yet failed to predict a MAC as high as 7.5 or 8.0 m2/g at 550 nm wavelength. Fourth, we summarize a selected range of alternative values of m that has been reported by recent studies and place them in the context of measurements using a contour plot of E(m) on the n–k plane. We show that the widely used m = 1.95 + 0.79i corresponds to an E(m) that is too low to be consistent with the measured MAC values. We conclude that the E(m) of BC in the visible and near infrared should be greater than 0.32, and that the commonly used BC models or the refractive index, or both, are still in need of improvement.

The present study demonstrates the exploitation of the spectral elastic light scattering technique. Additional information provided by the spectral response of the light scattering signals enables the measurement of the soot size distribution with only two scattering angles. It also provides quantitative data on the spectral dependence of the soot optical index, which is related to the soot chemical composition. The measurement principle consists in dividing the scattered spectra collected at two scattering angles and processing this ratio using the Rayleigh–Debye–Gans theory for Fractal Aggregates (RDG-FA). It is shown that the median diameter of gyration and geometric standard deviation of a lognormal soot size distribution can be determined without any prior information on key parameters such as the fractal prefactor, particle primary diameter, aggregate number density and soot optical properties. A proof of concept was performed on soot particles produced by a miniCAST generator by comparing the optical results with the soot size distributions measured by SMPS. A statistical Bayesian inversion approach was used to determine posterior distributions with a particular emphasis on their uncertainty quantification.

Combustion generated soot appears as fractal aggregates formed by polydisperse nearly spherical primary particles. Knowledge of their radiative properties is a prerequisite for laser based diagnostics of soot. In this parametric study, the effect of primary particle polydispersity on soot aggregate absorption and scattering properties is investigated numerically. Two series of fractal aggregates formed by normal and lognormal distributed primary particles of different levels of standard deviation were numerically generated for typical flame soot with a fractal dimension and prefactor fixed to D f = 1.73 and kf ≈ 1.5, respectively. Three aggregate sizes consisting of N p = 15 , 50 and 150 monomers per aggregate were investigated. Due to the uncertainty in soot refractive index, radiative properties were calculated by considering two different refractive indices at λ ≈ 532 nm recommended in the literature using the Discrete Dipoles Approximation and the Generalized Multiparticle Mie method. The results are interpreted in terms of correction factors to the Rayleigh–Debye–Gans theory for fractal aggregates (RDG-FA) for the forward scattering cross section A and for the absorption cross section h. It is shown that differential cross section for vertically polarized incident light, total scattering and absorption cross sections are well predicted by the RDG-FA theory for all considered aggregates formed by normally ( σ / d p ¯ ≤ 30%) and lognormally (σgeo ≤ 1.6) distributed primary particles. The refractive index is found to be of greater impact than primary particle polydispersity on the importance of multiple scattering. The radiative force per unit laser power experienced by the soot aggregates was found primarily determined by the aggregate volume, regardless of the level of primary particle polydispersity.

A novel diagnostic is proposed to characterize the maturity of soot particles in a laminar axisymmetric coflow ethylene diffusion flame in terms of the spectral dependence of soot absorption function. The method relies on the combination of line-of-sight attenuation (LOSA) and emission measurements at four wavelengths (500, 532, 660 and 810 nm). The analysis of the measured signals enables the determination of soot temperature, soot volume fraction, soot maturity and the contribution of soot scattering to extinction. The analysis of extinction and emission measurements considers the spatial variation of soot optical properties. The introduction of a maturity index allows the evaluation of soot maturity based on the spectral variation of the soot absorption function. The maturity index is correlated with the organic or the mature soot content and finally in terms of the absolute value of absorption function at 810 nm. The methodology is validated using a set of synthetic spectral LOSA and emission signals representing experimental measurements based on numerical results obtained using the CoFlame code. A sensitivity analysis of the Abel inversion is also performed to properly address the effect of deconvolution procedure. Finally, the proposed method is applied to analyze the experimental data of spectrally-resolved LOSA and emission acquired in a laminar axisymmetric coflow ethylene diffusion flame established on a Gulder burner. The two-dimensional distributions of soot temperature, soot volume fraction, soot maturity, and the ratio of total scattering to absorption are determined. Mature soot particles are found on the top of the flame in the centerline region and also in the outer edge of the flame wing displaying strong gradients.

Rayleigh–Debye–Gans (RDG) theory is a commonly used approximation for light scattering and absorption by nanoparticles in the visible spectrum. The aim of this study is to advance our understanding for the origin of empirically observed deviations between accurate calculations of forward scattering and the absorption cross-sections and those predicted by RDG. For this purpose, we investigate the internal electric field within bi-spherical nanoparticles in several cases. The fixed-size constituent spheres of the bispheres are either separated or overlapped and are investigated using the discrete dipole approximation (DDA). To study the internal electric fields, we apply a phasor approach, which provides a semi-graphical way to understand the deviation of the forward scattering ( A ) and that of the absorption cross section ( h ) with respect to the RDG. The phasor approach reveals the influence of the bisphere orientation, absorption function E ( m ) , scattering function F ( m ) , and wavelength. It is observed that RDG tends to overestimate the forward scattering, i.e., A 1 , as well as absorption h 1 for larger size parameters, and thus, shorter wavelengths. At the opposite limit, a decreasing absorption function E ( m ) leads to RDG underestimating the true scattered intensity. An explanation for this effect is a competition between the non-uniformity of the internal electric field and the phase shift of the phasors, leading to different results than those predicted by RDG and the amount of dipoles scattering in-phase.

Soot particle surface growth may have a significant impact on aggregation kinetics, particle morphology, and both aggregate and monomer size distributions. Particularly, the morphological effects of surface growth are currently poorly understood. This is complex since surface growth also affects the kinetics of aggregation resulting in a time-dependent competition between both phenomena, producing very different morphological markers. The present study aims at improving our understanding of the morphological impact of surface growth by implementing this effect in a Monte Carlo discrete element code for the simulation of soot formation in an ethylene premixed flame. An asymptotic average primary particle overlapping ∼ 30 % is observed for different flame conditions. The primary particle coordination number is highly sensitive to surface growth rate and particle volume fraction, and maximum values are on average within the 4 - 8 range. The particle local compacity, as quantified by the packing factor, is also considerably increased when aggregates experience surface growth, contrarily to the fractal structure of individual aggregates that seems more dependent on the aggregation regime. Finally, surface growth narrows both the primary particle and aggregate size distributions.

International audience; Soot formation and oxidation are investigated in swirl stratified premixed ethylene/air flames at atmospheric pressure. The effects of both swirl and stratification are studied to understand the relationship between the flame structure, soot precursors and soot. The topology of the flame is obtained with particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) on hydroxyl radical (OH). The production of polycyclic aromatic hydrocarbons (PAHs) is investigated using PLIF by mainly probing the aromatic compounds with two benzene rings (i.e. naphthalene) that are known to actively participate in soot nucleation and growth. Soot production is investigated using laser-induced incandescence (LII), giving quantitative data on the soot volume fraction. Extensive information on the flame structure and the mechanisms of formation/consumption of soot is gathered based on the coupling of these laser diagnostics. An image analysis of velocity, OH, PAHs and soot distributions enables us to propose a scenario that describes the link between the inception, growth, aggregation and oxidation processes. In particular, the data reveal the presence of distinct zones for these processes: a thermal decomposition region in which PAHs contributes to nascent soot formation, organised as filaments along the interface between the PAH region and the inner recirculation zone (IRZ); a mixing region controlled by large moving structures that favour the growth and aggregation of nascent soot into mature soot; and an oxidation region leading to the fast consumption of soot particles. These processes are impacted to varying extents by the intensities of swirl and stratification.

The present work investigates the effect of jet-exit Reynolds number ( R e ) on soot particle size and flame temperature in n -butane jet flames. Correlation of temperature with soot volume fraction ( f v ), soot precursor (polycyclic aromatic hydrocarbons or PAH), and reaction zone (OH) is also examined. The investigated flames ( R e = 5000 –21,500) are identical as of the companion work (Part 1). The temperature was measured in a low-sooting region using a fine-wire thermocouple. The soot particle size distribution was obtained using a scanning mobility particle sizer (SMPS). Temporal evolution (with 0.1 s resolution) of f v in the extracted aerosol sample was monitored with a Pegasor particle sensor (PPS). f v from LII and PPS are compared, and the reasons for differences are discussed in detail. The radial location of peak temperature is biased towards the fuel-rich side. At R e 5000 , peak-PAH occurs at 650 K , whereas in lifted turbulent flame ( Re 21 , 500 ), peak-PAH shifts to 940 K . PAH formation temperature is influenced by air/fuel mixing. Despite the variation of turbulence level ( Re = 5000 − 21 , 500 ), peak- f v in the soot inception region occurs at a nearly identical temperature of 1400 K . Peak- f v shifts towards lower temperature with increasing height, likely due to oxidation by diffused OH. The soot mode diameter ( D m ) was measured along the axis. D m increases with height and reaches a maximum near peak- f v region. D m at moderate R e ( 5000 − 7200 ), varies between 12 and 28 nm along the flame axis. At high R e (21,500), D m range decreases to 12 − 24 nm . The decrease in peak- D m with R e is likely due to reduced residence time and enhanced reactant mixing. The comprehensive database containing a wide range of parameters from the present and companion (Part 1) papers will aid in the development and validation of turbulence and soot chemistry models, especially for fuels of practical relevance.

The study is aimed at investigating the radiative properties of soot aggregates at determined morphological features using both experimental and numerical methods. Soot aggregates collected from air monitoring stations in different locations were examined. The locations were divided into three groups. The first group (Case 1) included the coastal and industrial zone; the second group (Case 2) consisted of small and large cities; and the third group (Case 3) included areas in the neighbourhood of thermal power plants. The absorbance measurements of the soot aggregates were conducted in the visible and near-infrared spectra, and in the wavelength range of 2 μm-20 μm. The samples were characterised by scanning electron microscopy (SEM), and their radiative properties were assessed using the discrete dipole approximation (DDA) for numerically generated fractal aggregates with two popular refractive indices of m = 1.60 + 0.60i and m = 1.90 + 0.75i. Calculations were conducted for primary particles in point-contact, with 20% overlapping and with a coating (50% and 80%) in the wavelength range of 0.4–1.064 μm. The largest measured absorbance values in both the winter and summer seasons were found in the cities in Case 1, and the x-ray diffraction (XRD) phases of the samples were also presented. The radiative properties of the aggregates, i.e., Df = 1.78 and kf = 2.0 representing Case 3, were close to those of aggregates with Df = 2.1 and kf = 2.35 representing Case 1 in the investigated wavelength range. The calculated radiative properties and the experimental absorbance measurements for point-contact and overlapping situations showed the same trend in the examined wavelengths. The absorbance properties of the samples of coastal and industrial zones were distinctively higher than others in the wavelength range of 2 μm-20 μm which could be attributed to the PAH effects.

During the agglomeration of nanoparticles and in particular, soot, a change in both the flow regime (from free molecular to near continuum) as well as the change of agglomeration regime (from ballistic to diffusive) is expected. However, these effects are rarely taken into account in numerical simulations of particle agglomeration and yet, they are suspected to have an important impact on the agglomeration kinetics, particle morphologies, and size distributions. This work intends to study these properties by using the Monte Carlo Aggregation Code (MCAC) presented in the preceding work (part 1), focusing on the physical impacts of varying the particle volume fraction and monomers size and polydispersity. The results show an important sensitivity of the kinetics of agglomeration, coagulation homogeneity, and agglomerate morphology to the size of monomers. First, for smaller monomer diameters, the agglomeration kinetic is enhanced and agglomerates are characterized by larger fractal dimensions. Second, for large monomer diameters, fractal dimensions down to 1.67 can be found being smaller than the classical 1.78 for Diffusion Limited Cluster Agglomeration (DLCA) mechanism. One important conclusion is that variation in time of both regimes has to be considered for a more accurate simulation of the agglomerate size distribution and morphology.

The application of Monte Carlo methods to simulate the agglomeration of suspended nanoparticles is currently limited to specific agglomeration regimes with reduced accuracy in terms of the particle's physical residence time. The definition of specific particles persistent distance, its corresponding time step and subsequent probabilities for particle displacements may improve the accuracy of this method. To solve these issues, a new persistent distance and its corresponding time step based on Langevin dynamics simulations are introduced. Additionally, a probability of particle displacements, not restricted to a specific agglomeration regime, is introduced. All the modifications are validated by comparison with Langevin dynamics simulations. Finally, the above mentioned modifications considerably improve the accuracy of Monte Carlo methods to predict the dynamics and agglomeration of suspended nanoparticles.

The influence of the fire exposure on the degradation mechanism of thin carbon/epoxy and carbon/polyphenylene sulphide (PPS) laminates has been investigated using a propane burner. The burner used in this work is able to provide a controlled and repeatable heating condition, with the test condition of 106 kW/m2 representative of a severe fire condition. Mass loss and temperature measurements made during the fire aggression coupled with post-fire microscopic analysis aim at providing a better understanding of the physical and mechanical changes on laminates depending on matrix nature and different fire-exposure times. For a high heat flux, a 300s fire exposure is more detrimental for the carbon/epoxy sample (22% mass loss) than for the carbon/PPS (6% mass loss) although ATG results show a similar char yield of around 75% under nitrogen for both materials. Observation and analysis of microscopic images after different fire-exposure times fire suggest that the thermal behaviour of the 2 mm thin laminates is driven by the formation of major delamination and macroscopic pores forming a thermal barrier as the analysis of the images indicates a void content 2 to 5 times higher for the carbon/PPS sample than for the carbon/epoxy specimens. On the one hand, the degradation of the thermoplastic PPS matrix into a viscous product seems to trap pyrolysis gases into macroscopic gaseous cells. These porosities provide an efficient thermal barrier protecting the back surface from the flame high thermal flux. On the other hand the degradation of the thermosetting epoxy matrix forms a dry network of carbon fibres and porous char.

International audience; Experimental studies of soot morphology based on analysis of transmission electron microscopy (TEM) images usually neglect the potential effects of primary particle polydispersity and overlapping. In this study, fractal aggregates of different sizes consisting of polydisperse and overlapping primary particles were numerically generated using typical fractal dimension and prefactor relevant to soot. A total of 3600 simulated two-dimensional projections for each primary particle size distribution and level of overlapping considered was produced and analyzed using two TEM image analysis methods commonly used in the literature to evaluate the effects of primary particle polydispersity and overlapping on the recovered morphological parameters of soot. Fairly large deviations in the recovered number of primary particles in aggregates were obtained by both methods considered using the procedure commonly used in the literature. A recommendation was proposed to improve the accuracy of the retrieved number of polydisperse primary particles in an aggregate. We show that the results obtained by using both the Tian et al. (2006) and Brasil et al. (1999) methods can be significantly improved by using the recommended modification for primary particle polydispersity levels commonly encountered in flame soot. Finally, we recommend to use the modified Tian et al. 2006 method for recovering the number of primary particles of aggregates consisting of both polydisperse and overlapped primary particles.

Combustion of hydrocarbons produces both particulate and gas phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose to couple a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate and gas phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through, and then trap the most volatile components on a second black carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling/multi-technique approach in conjunction with advanced statistical methods we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry.

A validation of the ISO 787-23 method for measuring true density on reference black carbon samples and combustion emitted particles is proposed and compared to alternative methods. New measurements of true density on samples representative of fire emissions at different scales are presented and discussed, according to their respective experimental uncertainties. These results are compared to the values of soot true densities reported in the literature. An interesting correlation between the true density of combustion emitted particles and the Organic Carbon (OC) content is observed and commented: the true density significantly decreases as OC content increases. Three different ranges of true densities are then proposed as a function of the OC/Total Carbon (TC) ratio of combustion emitted particles. For low OC contents (i.e. below 5%) and high OC contents (i.e. above 20%), respective mean values of 1834 ± 187 kg/m3 and 1285 ± 217 kg/m3 are proposed. For intermediate OC content values, a fit is applied based on a mixing law. Finally, there is a discussion on the relevance of using these values for true densities of combustion emitted particles for temperatures representative of those reported in industrial fires, ranging from 25 °C to 240 °C.

In this study, the tunable algorithm of cluster–cluster aggregation developed by Filippov et al. (2000) for generating fractal aggregates formed by monodisperse spherical primary particles is extended to polydisperse primary particles. This new algorithm, termed FracVAL, is developed by using an innovative aggregation strategy. The algorithm is able to preserve the prescribed fractal dimension ( D f ) and prefactor ( k f ) for each aggregate, regardless of its size, with negligible error for lognormally distributed primary particles with the geometric standard deviation σ p , g e o being as large as 3. In contrast, for polydisperse primary particles the direct use of Filippov et al. (2000) method, as is done by Skorupski et al. (2014), does not ensure the preservation of D f and k f for individual aggregates and it is necessary to generate a large number of aggregates to achieve the prescribed D f and k f on an ensemble basis. The performance of FracVAL is evaluated for aggregates consisting of 500 and 1000 monomers and for fractal dimension variation over the entire range of D f between 1 and 3 and k f between 0.1 and 2.7. Aggregates consisting of 500 monomers are generated on average in less than 2.4 min on a common laptop, illustrating the efficiency of the proposed algorithm. Program summary Program Title: FracVAL Program Files doi: http://dx.doi.org/10.17632/mgf8wdcsfb.1 Licensing provisions: GNU General Public License v3 Programming language: Fortran 90 Nature of problem: Generation of fractal-like aggregates, consisting of point-touching, polydisperse primary particles Solution method: Hierarchical cluster–cluster random aggregation Additional comments including restrictions and unusual features: Possible combinations of fractal dimension and prefactor depend on monomers polydispersity

In the last two to three decades, many efforts have been made to evaluate the radiative properties of soot in flames. Due to the strong impact of soot on global warming and the aging process of soot particles in the atmosphere, it is necessary to gain a better understanding on how the radiative properties of soot are affected by coating with nonabsorbing organic aerosol compounds. In the present study, the aging process is experimentally mimicked in the laboratory by coating oleic acid onto freshly generated soot particles. The morphological restructuring of soot particles is determined by nonoptical techniques for mobility diameter and effective density and by angular light scattering for gyration radius and fractal dimension. Both approaches give results in good agreement. Moreover, spectrally resolved scattering measurements between 500 and 700 nm have been carried out. The experimental data are in satisfactory agreement with previously published numerical results and enable the validation of a Rayleigh-Debye-Gans theory for coated fractal aggregates (RDG-CFA) that could be integrated in climate models or for the interpretation of scattering based measurements.

The fractal-like black carbon particles emitted from combustion systems and biomass burning are short-lived pollutants that contribute significantly to climate forcing. To accurately quantify the forcing and interpret optical measurements of uncoated and coated black carbon (BC) particles, it is indispensable to know the refractive index m = n + ki of BC in the visible and near infrared. In this study the effects of various morphological parameters and structure defects of black carbon particles on their mass absorption cross section (MAC) were first investigated using the generalized Mie-solution method (GMM) and discrete dipole approximation (DDA). The accuracy of the Rayleigh-Debye-Gans (RDG) approximation is also evaluated. Based on recent measurements of the soot absorption function E(m) and freshly emitted BC MAC in the visible and near-infrared, the most probable range of E(m) was recommended. A criterion was proposed to determine the valid range of refractive index of freshly emitted BC based on the contour plot of E(m) on the n-k plane., The 9th International Symposium on Radiative Transfer, RAD-19, June 3-7, 2019, Athens, Greece

The high reactivity of nanostructured materials makes their use very attractive for various industrial applications. However, these materials may also have an important impact on health / environment / climate and on the performances of protective devices (i.e. high efficiency particulate air filters, electrostatic precipitators). Those properties are mainly due to their high specific surface area, which is directly related to the size of the non-porous primary nanoparticles and to the nature of the bridging between them (from point contact for agglomerates to partial fusion for aggregates). In this paper, a straightforward image processing has been developed to measure, assuming a log-normal size distribution, the primary particle diameter (Dpp), the geometric standard deviation GSD (or σg), the projected overlap coefficient (Cov, p) and the specific surface area (SS) directly from TEM images according to the approach introduced by Bau, Witschger, Gensdarmes, Rastoix, and Thomas (2010) . Measurements have been performed from TEM images obtained for 22 different kinds of nanoparticles, from simple spheres to soot particles and virtual aggregates. The results show a good agreement (within ± 20%) between automatic and manual analysis of Dpp, σg and SS while the overlap coefficient has been compared to the manual analysis showing a reasonable agreement (within ± 40%).

International audience; The morphological description of fractal agglomerates is generally reduced to only two parameters,namely the mass fractal dimension and its prefactor. In the most evolved approaches, a stretching exponent is also introduced, while a packing factor is preferred to the fractal prefactor. In any case, the current analytical description of agglomerates morphology is accurate only for sufficiently large agglomerates, which is due to the limited spatial extension of the clusters that are actually quasi-fractal. In the present study, a cutoff function of the pair correlation function is considered for both larger and smaller scales. This enables a more accurate morphological description valid for any cluster size is to be given taking into account the polydispersity of the primary spheres. This new analytical morphological description relying on 5 parameters, is presented here for the first time. The physical range covered by these morphological parameters is determined based on virtually generated Diffusion Limited Cluster Agglomeration. Finally, the model is used to express the fractal prefactor and structure factors and their dependence on agglomerate size and morphological parameters is investigated.

WOS:000373250400012; International audience; The effects of weakly absorbing material coating on soot have attracted considerable research attention in recent years due to the significant influence of such coating on soot radiative properties and the large differences predicted by different numerical models. Soot aggregates were first numerically generated using the diffusion limited cluster aggregation algorithm to produce fractal aggregates formed by log-normally distributed polydisperse spherical primary particles in point-touch. These aggregates were then processed by adding a certain amount of primary particle overlapping and necking to simulate the soot morphology observed from transmission electron microscopy images. After this process, a layer of WAM coating of different thicknesses was added to these more realistic soot aggregates. The radiative properties of these coated soot aggregates over the spectral range of 266-1064 nm were calculated by the discrete dipole approximation (DDA) using the spectrally dependent refractive index of soot for four aggregates containing N-p =1, 20, 51 and 96 primary particles. The considered coating thicknesses range from 0% (no coating) up to 100% coating in terms of the primary particle diameter. Coating enhances both the particle absorption and scattering cross sections, with much stronger enhancement to the scattering one, as well as the asymmetry factor and the single scattering albedo. The absorption enhancement is stronger in the UV than in the visible and the near infrared. The simple corrections to the Rayleigh-Debye-Gans fractal aggregates theory for uncoated soot aggregates are found not working for coated soot aggregates. The core-shell model significantly overestimates the absorption enhancement by coating in the visible and the near infrared compared to the DDA results of the coated soot particle. Treating an externally coated soot aggregate as an aggregate formed by individually coated primary particles significantly underestimates the absorption enhancement by coating in the visible and the near infrared. Crown Copyright (C) 2015 Published by Elsevier Ltd. All rights reserved.

The aim of the present study is to evaluate experimentally the impact of a non-absorbing coating material on the spectral radiative properties of freshly produced carbonaceous aerosols. Once emitted into the atmosphere, carbonaceous particles are prone to interact with organic chemical compounds to acquire a certain amount of non-absorbing or weakly absorbing coating on their surface. In the present study, oleic acid is used as a surrogate for the coating material and applied to aerosols produced by a miniCAST (soot particles of different chemical and morphological properties) and a spark discharge aerosol generator. A simple analytical model is presented to evaluate the coating thickness. Furthermore, the spectrally resolved extinction cross sections of uncoated and coated particles are determined enabling the evaluation of the mass specific extinction coefficient and the extinction enhancement factor over a wide spectral range ( 200 − 1100 nm). Influences of the coating thickness and the type of core carbonaceous particles are also discussed.

This paper addresses how well and under what conditions the Rayleigh-Debye-Gans (RDG) approximation describes scattering and absorption of light by fractal aggregates (FA) including soot. The RDGFA theory, which is the prevailing, first order description of this problem, has two assumptions: the monomers, or primary particles, of the aggregate scatter and absorb in the Rayleigh regime, and the aggregate scatters in the diffraction limit weighted by this Rayleigh scattering and absorbs as a system of independent monomer particles. The aggregates studied here are formed via Diffusion Limited Cluster Aggregation (DLCA) and have a fractal dimension D = 1.78 ± 0.04 and prefactor of k0 = 1.35 ± 0.10. The aggregates are a collection of monodisperse spherical monomers with point contacts. Optical calculations were performed with the multiple sphere T-matrix (MSTM) and DDSCAT codes for incident light polarized perpendicular to the scattering plane. The scattering considered is the forward scattering intensity and the angular scattering as parameterized by the scattering wave vector. The total absorption cross section for aggregates is also calculated. This work stresses the systematic study of the effects of the variables of monomers per aggregate, which ranged from one to 502, two monomer size parameters of 0.157 and 0.314, and a wide range of refractive index real and imaginary parts. It also considers soot refractive indices with three representative dispersions. A summary of results for both scattering and absorption includes deviations from RDGFA theory ranging as large as 35% with positive deviations increasing with the real part of the refractive index and negative deviations growing with the imaginary part. These deviation from the RDG limit are shown to be similar to deviations for spheres.

WOS:000358626000003; International audience; Effective density measurements are used extensively to convert submicron particle sizes based on a particle's mobility diameter into mass. Measurements of the effective density also provide information concerning the particle morphology. For example, the effective density curves of fractal aggregates reveal a scaling factor that seems to correlate with the fractal dimension of the particles. The present paper proposes a simple semi-empirical model that permits the quantitative interpretation of these measurements to determine parameters such as the fractal dimension, the primary particle size, and the bulk density of an aggregate particle. The proposed model is based on the assumption that the hydrodynamic drag force of an aggregate is proportional to the drag force applied to isolated primary spheres and to the number of primary spheres in the aggregate at power a. The model was applied to soot particles produced by either a spark discharge (PALAS GFG1000) or by combustion (miniCAST 5206)-both mechanisms enable the generation of aggregates or agglomerates with very different primary sphere diameters. The proposed model showed a good fit for all of the effective density measurements obtained in this study; the a parameter was driven by the aggregate fractal dimension and by the Knudsen number that was determined based on the primary particle diameter. Finally, for a known primary particle diameter, the fractal dimension and the bulk density were determined successfully with the proposed model. (C) 2015 Elsevier Ltd. All rights reserved.

WOS:000357543800021; International audience; There is a strong interest in accurately modelling the radiative properties of soot aggregates (also known as black carbon particles) emitted from combustion systems and fires to gain improved understanding of the role of black carbon to global warming. This study conducted a systematic investigation of the effects of overlapping and necking between neighbouring primary particles on the radiative properties of soot aggregates using the discrete dipole approximation. The degrees of overlapping and necking are quantified by the overlapping and necking parameters. Realistic soot aggregates were generated numerically by constructing overlapping and necking to fractal aggregates formed by point-touch primary particles simulated using a diffusion-limited cluster aggregation algorithm. Radiative properties (differential scattering, absorption, total scattering, specific extinction, asymmetry factor and single scattering albedo) were calculated using the experimentally measured soot refractive index over the spectral range of 266-1064 nm for 9 combinations of the overlapping and necking parameters. Overlapping and necking affect significantly the absorption and scattering properties of soot aggregates, especially in the near UV spectrum due to the enhanced multiple scattering effects within an aggregate. By using correctly modified aggregate properties (fractal dimension, prefactor, primary particle radius, and the number of primary particle) and by accounting for the effects of multiple scattering, the simple Rayleigh-Debye-Gans theory for fractal aggregates can reproduce reasonably accurate radiative properties of realistic soot aggregates. (C) 2015 Elsevier Ltd. All rights reserved.

WOS:000394199200005; International audience; The French national project MERMOSE gathers the capabilities of seven organizations to better characterize commercial aircraft engine emissions and to better understand their impact on nucleation processes in the atmosphere. In this frame, a measurement campaign has been performed on a Snecma/NPO Saturn SaM146-1S17 turbofan. During this work, we used a complete set of on-line and off-line techniques to measure radial and angular profiles of particulate matter (PM) properties in the engine exhaust hot flow. We studied different engine thrust settings, selected to match the aircraft main operating conditions (idle, climb, take-off, approach and "ground" cruise). The mode of the emitted particles size distribution ranged from 17 nm to 55 nm and was sensitive to the thrust. The sampled PM showed a complex morphology and were formed by primary nanoparticles of about 15 rim in diameter. They were mainly composed of carbon (with traces of oxygen, sulfur and calcium) and their organic carbon to total carbon ratio (OC/TC) ratio showed a decrease as a function of the maximum thrust from similar to 80% for 30% thrust setting to similar to 12% for 100%.

WOS:000397458900179; International audience; The study used a vertical porous burner fueled with a CH4/C2H4 mixture burning in quiescent ambient air to measure the soot content of a vertical turbulent wall flame. Soot volume fractions were determined by planar laser induced incandescence (LII). Particle image velocimetry (PIV) was used to measure the vertical velocity of the mean flow. The mean soot volume fraction and vertical velocity values were mapped with a two-dimensional (2D) imaging technique. Soot volume fraction flux was analyzed as a function of height. The results show that, in the top zone of the flame, the soot formation was counterbalanced by oxidation with air. In addition, each instantaneous 2D soot sheet was analyzed to determine two parameters: the soot volume fraction maximum f(v,max) and the horizontal width delta(FWHM). For both parameters, average and RMS (root mean square) values were calculated at each height. Except for the bottom zone of the burner, average values varied little with height, whereas RMS values remained persistently high. It is found that, with increasing heights, there exist far from the burner and in the lean side of the flame more and more soot sheets with high values of f(v,max) and delta(FWHM). (C) 2016 by The Combustion Institute. Published by Elsevier Inc.

International audience; The present work reports soot volume fraction determined in turbulent sooting non-premixed jet flames using a Pegasor particle sensor (PPS) and also using the non-intrusive laser-induced incandescence (LII) technique. Additionally, soot particle size distribution is determined using Scanning Mobility Particle Sizer (SMPS). Turbulent flames with different fuels, namely: butane (Re = 26,000), 70% butane + 30% ethylene by volumes (Re = 20,000), and ethylene (Re = 10,000) are investigated. The axial distribution of PPS derived soot volume fraction is qualitatively in excellent agreement with that obtained using LII. The possible sources of quantitative discrepancy between soot concentration obtained through LII and that of the PPS are discussed. Axial evolution of the soot size along with the volume fraction is presented. These results form part of the proposed comprehensive database to validate advanced soot models.

The Institute of Radioprotection and Nuclear Safety (IRSN in French) is conducting research on the impact of a fire on the behaviour of containment devices such as high efficiency particulate air (HEPA) pleated filters for radioactive materials. This work aims to study the clogging of HEPA filters in case of fire involving realistic materials (polymers making up gloves boxes, waste treatment solvent, hydraulic oil, solid material mixtures making up a trash bin, electrical cables, and cabinets) used in nuclear facilities, from the medium to large scale. The clogging kinetics of industrial pleated HEPA filters is monitored by measuring the pressure drop of the filters and the filtered air temperature at a given filtration velocity (from 0.23 to 2.1 cm/s). Upstream HEPA filters, combustion aerosols are characterized in terms of size distribution, mass concentration, composition, and particle morphology using, respectively, a DMS500 (CambustionLTD), glass fiber filter sampling, and transmission electron micro...