HAL (Le Centre pour la Communication Scientifique Directe), Jan 22, 2019
Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre... more Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre compréhension de l'évolution des propriétés radiatives des suies une fois émises dans l'atmosphère. Dans cette étude, le vieillissement atmosphérique est simulé expérimentalement par l'ajout d'un revêtement contrôlé d'acide oléique. La restructuration morphologique est quantifiée à l'aide de mesures non optiques (SMPS et masse volumique effective) et par diffusion angulaire. Des mesures de diffusion spectrales ont également été menées sur la gamme 500-700 nm, permettant la quantification d'un facteur d'amplification dépendant de la longueur d'onde. Les résultats sont comparés avec succès avec des résultats numériques précédemment publiés et ont rendu possible la validation d'une théorie « RDG-CFA » qui pourra être intégrée dans des modèles climatiques ou pour l'interprétation de mesures reposants sur la diffusion de la lumière.
HAL (Le Centre pour la Communication Scientifique Directe), Jan 26, 2021
La pollution de l'air a des effets sanitaires importants et les particules en suspension y contri... more La pollution de l'air a des effets sanitaires importants et les particules en suspension y contribuent de façon majeure. Les particules ultrafines (PUFs) ont un diamètre aérodynamique égal ou inférieur à 0.1µm et peuvent pénétrer profondément dans l'arbre respiratoire et atteindre d'autres organes comme le foie, le coeur et le cerveau. Les PUFs seraient plus toxiques en raison de leur surface spécifique qui absorberait davantage des composés organiques. L'objectif de cette étude est de montrer les effets toxicologiques des PUFs avec une teneur importante en composés organiques sur le modèle BEAS-2B, en utilisant une exposition à l'interface air-liquide afin de maintenir leurs caractéristiques microphysiques.
Gasoline emissions contain high levels of pollutants, including particulate matter (PM), which ar... more Gasoline emissions contain high levels of pollutants, including particulate matter (PM), which are associated with several health outcomes. Moreover, due to the depletion of fossil fuels, biofuels represent an attractive alternative, particularly second-generation biofuels (B2G) derived from lignocellulosic biomass. Unfortunately, compared to the abundant literature on diesel and gasoline emissions, relatively few studies are devoted to alternative fuels and their health effects. This study aimed to compare the adverse effects of gasoline and B2G emissions on human bronchial epithelial cells. We characterized the emissions generated by propane combustion (CAST1), gasoline Surrogate, and B2G consisting of Surrogate blended with anisole (10%) (S+10A) or ethanol (10%) (S+10E). To study the cellular effects, BEAS-2B cells were cultured at air-liquid interface for seven days and exposed to different emissions. Cell viability, oxidative stress, inflammation, and xenobiotic metabolism were...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 18, 2017
The present work reports soot volume fraction determined in turbulent sooting non-premixed jet fl... more 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.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 11, 2018
La mesure optique in-situ de distribution de taille de suies est une tâche complexe en particulie... more La mesure optique in-situ de distribution de taille de suies est une tâche complexe en particulier lorsque les accès angulaires sont limités car c'est une limitation critique pour l'utilisation de techniques basées sur la diffusion élastique de la lumière. Dans cette étude, une démonstration de l'exploitation de mesures de diffusion spectrale est présentée. Les informations supplémentaires apportées par la réponse spectrale du signal de diffusion à une lumière incidente polychromatique permettent la mesure in-situ de distribution de taille de suies.
Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir n... more Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre compréhension de l'évolution des propriétés radiatives des suies une fois émises dans l'atmosphère. Dans cette étude, le vieillissement atmosphérique est simulé expérimentalement par l'ajout d'un revêtement contrôlé d'acide oléique. La restructuration morphologique est quantifiée à l'aide de mesures non optiques (SMPS et masse volumique effective) et par diffusion angulaire. Des mesures de diffusion spectrales ont également été menées sur la gamme 500-700 nm, permettant la quantification d'un facteur d'amplification dépendant de la longueur d'onde. Les résultats sont comparés avec succès avec des résultats numériques précédemment publiés et ont rendu possible la validation d'une théorie « RDG-CFA » qui pourra être intégrée dans des modèles climatiques ou pour l'interprétation de mesures reposants sur la diffusion de la lumière.
La diffusion élastique de la lumière est une technique optique permettant la mesure in-situ de di... more La diffusion élastique de la lumière est une technique optique permettant la mesure in-situ de distribution de taille des particules de suie. Cependant, sa mise en ?uvre devient complexe voire impossible lorsque les accès angulaires sont limités. Dans cette étude, une démonstration de l'exploitation de mesures de diffusion spectrale est présentée. Nous montrons que l'information supplémentaire apportée par la réponse spectrale du signal de diffusion à une lumière incidente polychromatique permet la détermination de la distribution de taille avec une collection réduite à deux angles de diffusion.
Soot emitted from various combustion systems and fires into the atmosphere have been considered a... more Soot emitted from various combustion systems and fires into the atmosphere have been considered as the second largest contributor to global warming just after CO2 (Bond, Doherty et al. 2013) and found harmful to human health. This second point can be explained by their nanosize and large specific area (Brown, Wilson et al. 2001) favoring the transfer of toxic compounds as PAH (Lighty, Veranth et al. 2000) to the organism. For these reasons and for a better understanding of soot formation and growth during combustion processes, it is important to develop techniques able to follow the growth of soot particles and their chemical composition. This hard task is rarely achieved by in situ optical techniques. Furthermore, a single optical technique can not inform us about all parameters of soot. Therefore it is important to couple techniques to properly characterize these nanoparticles. LII is a powerful laser based technique that allows obtaining information on the soot volume fraction an...
1 UMR 6614 CORIA, CNRS, Université et INSA de Rouen, Saint Etienne du Rouvray, BP12, 76801, Franc... more 1 UMR 6614 CORIA, CNRS, Université et INSA de Rouen, Saint Etienne du Rouvray, BP12, 76801, France 2 Black Carbon Metrology, Measurement Science and Standards, National Research Council Ottawa, Ontario, Canada 3 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSN-RES, SCA, LPMA, Gif-Sur-Yvette, 91192, France.
Soot size measurement in a swirl stratified flame using high-speed angular light scattering RESUM... more Soot size measurement in a swirl stratified flame using high-speed angular light scattering RESUME Les travaux presentes dans cette etude concernent des mesures de tailles de particules de suie produites lors de la combustion de l'ethylene. La flamme etudiee est representative des conditions aeronautiques, c'est-adire turbulente, stratifiee (fort gradient spatial de richesse) et swirlee (ecoulement rotatif). La diffusion elastique de la lumiere est utilisee afin de determiner la taille des particules de suie. Cette technique est appliquee ici dans un plan a l'aide d'une nappe laser ainsi que de trois cameras disposees a trois angles de diffusion differents. En effet, l'intensite de la lumiere diffusee, resultante de l'interaction entre un faisceau laser et l'aerosol, varie en fonction de l'angle auquel on collecte le signal. Cette variation angulaire est une signature de la taille des particules etudiees. Puisque la flamme etudiee est turbulente donc ...
The present work investigates the effect of jet-exit Reynolds number (Re) on soot particle size a... more The present work investigates the effect of jet-exit Reynolds number (Re) 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 (Re = 5000 to 21500) 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 Re 5000, peak-PAH occurs at 650 K, whereas in lifted turbulent flame (Re 21500), peak-PAH shifts to 940 K. PAH formation temperature is influenced by air/fuel mixing. Despite the variation of turbulence level (Re = 5000-21500), 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 Re
The morphological description of fractal agglomérâtes is generally reduced to only two parameters... more The morphological description of fractal agglomérâtes 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 agglomerates size and morphological parameters is investigated.
During the agglomération of nanoparticles, notably soot, a change in both the flow régime (from f... more During the agglomération of nanoparticles, notably soot, a change in both the flow régime (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 particles 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 MCAC presented in the preceding work (part 1) by focusing on the physical impact 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 agglomerates morphology to the size of monomers. First, for smaller monomers diameters the agglomeration kinetic is enhanced and agglomerates are found to be more compact, characterized by larger fractal dimensions. Secondly, for large monomer diameters, fractal dimensions down to 1.67 can be found being therefore, smaller than the classical 1.78 for DLCA mechanism. One important conclusion is that variation in time of both the agglomeration and flow regimes has to be considered for a more accurate simulation of the agglomerates size distribution and morphology.
Experimental studies of soot morphology based on analysis of transmission electron microscopy (TE... more 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
Combustion generated soot appears as fractal aggregates formed by polydisperse nearly spherical p... more 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 k f ≈ 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 multi-sphere 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 (σ geo ≤ 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.
Many studies have been conducted on the environmental impacts of combustion generated aerosols. D... more Many studies have been conducted on the environmental impacts of combustion generated aerosols. Due to their complex composition and morphology, their chemical reactivity is not well understood and new developments of analysis methods are needed. We report the first demonstration of in-flight X-ray based characterizations of freshly emitted soot particles, which is of paramount importance for understanding the role of one of the main anthropogenic particulate contributors to global climate change. Soot particles, produced by a burner for several air-to-fuel ratios, were injected through an aerodynamic lens, focusing them to a region where they interacted with synchrotron radiation. X-ray photoelectron spectroscopy and carbon K-edge near-edge X-ray absorption spectroscopy were performed and compared to those obtained for supported samples. A good agreement is found between these samples, although slight oxidation is observed for supported samples. Our experiments demonstrate that NEX...
HAL (Le Centre pour la Communication Scientifique Directe), Nov 7, 2011
The aim of this work is to propose a new method for determining the size distribution of submicro... more The aim of this work is to propose a new method for determining the size distribution of submicronic particles by inversion of the measured angular scattering of light. This method relies on the determination of a function R * g by angular scattering. The variation of this function informs us about the polydispersity of the aggregates size. We show that, by supposing the nature of the size distributions (lognormal), it is possible to determine the governing parameters of these distributions.
for deriving the relative soot absorption function variation with wavelength at different locatio... more for deriving the relative soot absorption function variation with wavelength at different locations in a rich premixed methane flat flame at atmospheric pressure. The present analysis showed that the soot absorption function varies with the height above the burner exit and can be correlated with the degree of soot maturation.
HAL (Le Centre pour la Communication Scientifique Directe), Jan 22, 2019
Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre... more Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre compréhension de l'évolution des propriétés radiatives des suies une fois émises dans l'atmosphère. Dans cette étude, le vieillissement atmosphérique est simulé expérimentalement par l'ajout d'un revêtement contrôlé d'acide oléique. La restructuration morphologique est quantifiée à l'aide de mesures non optiques (SMPS et masse volumique effective) et par diffusion angulaire. Des mesures de diffusion spectrales ont également été menées sur la gamme 500-700 nm, permettant la quantification d'un facteur d'amplification dépendant de la longueur d'onde. Les résultats sont comparés avec succès avec des résultats numériques précédemment publiés et ont rendu possible la validation d'une théorie « RDG-CFA » qui pourra être intégrée dans des modèles climatiques ou pour l'interprétation de mesures reposants sur la diffusion de la lumière.
HAL (Le Centre pour la Communication Scientifique Directe), Jan 26, 2021
La pollution de l'air a des effets sanitaires importants et les particules en suspension y contri... more La pollution de l'air a des effets sanitaires importants et les particules en suspension y contribuent de façon majeure. Les particules ultrafines (PUFs) ont un diamètre aérodynamique égal ou inférieur à 0.1µm et peuvent pénétrer profondément dans l'arbre respiratoire et atteindre d'autres organes comme le foie, le coeur et le cerveau. Les PUFs seraient plus toxiques en raison de leur surface spécifique qui absorberait davantage des composés organiques. L'objectif de cette étude est de montrer les effets toxicologiques des PUFs avec une teneur importante en composés organiques sur le modèle BEAS-2B, en utilisant une exposition à l'interface air-liquide afin de maintenir leurs caractéristiques microphysiques.
Gasoline emissions contain high levels of pollutants, including particulate matter (PM), which ar... more Gasoline emissions contain high levels of pollutants, including particulate matter (PM), which are associated with several health outcomes. Moreover, due to the depletion of fossil fuels, biofuels represent an attractive alternative, particularly second-generation biofuels (B2G) derived from lignocellulosic biomass. Unfortunately, compared to the abundant literature on diesel and gasoline emissions, relatively few studies are devoted to alternative fuels and their health effects. This study aimed to compare the adverse effects of gasoline and B2G emissions on human bronchial epithelial cells. We characterized the emissions generated by propane combustion (CAST1), gasoline Surrogate, and B2G consisting of Surrogate blended with anisole (10%) (S+10A) or ethanol (10%) (S+10E). To study the cellular effects, BEAS-2B cells were cultured at air-liquid interface for seven days and exposed to different emissions. Cell viability, oxidative stress, inflammation, and xenobiotic metabolism were...
HAL (Le Centre pour la Communication Scientifique Directe), Apr 18, 2017
The present work reports soot volume fraction determined in turbulent sooting non-premixed jet fl... more 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.
HAL (Le Centre pour la Communication Scientifique Directe), Jun 11, 2018
La mesure optique in-situ de distribution de taille de suies est une tâche complexe en particulie... more La mesure optique in-situ de distribution de taille de suies est une tâche complexe en particulier lorsque les accès angulaires sont limités car c'est une limitation critique pour l'utilisation de techniques basées sur la diffusion élastique de la lumière. Dans cette étude, une démonstration de l'exploitation de mesures de diffusion spectrale est présentée. Les informations supplémentaires apportées par la réponse spectrale du signal de diffusion à une lumière incidente polychromatique permettent la mesure in-situ de distribution de taille de suies.
Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir n... more Du fait de leur impact for sur le réchauffement climatique, il est nécessaire d'approfondir notre compréhension de l'évolution des propriétés radiatives des suies une fois émises dans l'atmosphère. Dans cette étude, le vieillissement atmosphérique est simulé expérimentalement par l'ajout d'un revêtement contrôlé d'acide oléique. La restructuration morphologique est quantifiée à l'aide de mesures non optiques (SMPS et masse volumique effective) et par diffusion angulaire. Des mesures de diffusion spectrales ont également été menées sur la gamme 500-700 nm, permettant la quantification d'un facteur d'amplification dépendant de la longueur d'onde. Les résultats sont comparés avec succès avec des résultats numériques précédemment publiés et ont rendu possible la validation d'une théorie « RDG-CFA » qui pourra être intégrée dans des modèles climatiques ou pour l'interprétation de mesures reposants sur la diffusion de la lumière.
La diffusion élastique de la lumière est une technique optique permettant la mesure in-situ de di... more La diffusion élastique de la lumière est une technique optique permettant la mesure in-situ de distribution de taille des particules de suie. Cependant, sa mise en ?uvre devient complexe voire impossible lorsque les accès angulaires sont limités. Dans cette étude, une démonstration de l'exploitation de mesures de diffusion spectrale est présentée. Nous montrons que l'information supplémentaire apportée par la réponse spectrale du signal de diffusion à une lumière incidente polychromatique permet la détermination de la distribution de taille avec une collection réduite à deux angles de diffusion.
Soot emitted from various combustion systems and fires into the atmosphere have been considered a... more Soot emitted from various combustion systems and fires into the atmosphere have been considered as the second largest contributor to global warming just after CO2 (Bond, Doherty et al. 2013) and found harmful to human health. This second point can be explained by their nanosize and large specific area (Brown, Wilson et al. 2001) favoring the transfer of toxic compounds as PAH (Lighty, Veranth et al. 2000) to the organism. For these reasons and for a better understanding of soot formation and growth during combustion processes, it is important to develop techniques able to follow the growth of soot particles and their chemical composition. This hard task is rarely achieved by in situ optical techniques. Furthermore, a single optical technique can not inform us about all parameters of soot. Therefore it is important to couple techniques to properly characterize these nanoparticles. LII is a powerful laser based technique that allows obtaining information on the soot volume fraction an...
1 UMR 6614 CORIA, CNRS, Université et INSA de Rouen, Saint Etienne du Rouvray, BP12, 76801, Franc... more 1 UMR 6614 CORIA, CNRS, Université et INSA de Rouen, Saint Etienne du Rouvray, BP12, 76801, France 2 Black Carbon Metrology, Measurement Science and Standards, National Research Council Ottawa, Ontario, Canada 3 Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PSN-RES, SCA, LPMA, Gif-Sur-Yvette, 91192, France.
Soot size measurement in a swirl stratified flame using high-speed angular light scattering RESUM... more Soot size measurement in a swirl stratified flame using high-speed angular light scattering RESUME Les travaux presentes dans cette etude concernent des mesures de tailles de particules de suie produites lors de la combustion de l'ethylene. La flamme etudiee est representative des conditions aeronautiques, c'est-adire turbulente, stratifiee (fort gradient spatial de richesse) et swirlee (ecoulement rotatif). La diffusion elastique de la lumiere est utilisee afin de determiner la taille des particules de suie. Cette technique est appliquee ici dans un plan a l'aide d'une nappe laser ainsi que de trois cameras disposees a trois angles de diffusion differents. En effet, l'intensite de la lumiere diffusee, resultante de l'interaction entre un faisceau laser et l'aerosol, varie en fonction de l'angle auquel on collecte le signal. Cette variation angulaire est une signature de la taille des particules etudiees. Puisque la flamme etudiee est turbulente donc ...
The present work investigates the effect of jet-exit Reynolds number (Re) on soot particle size a... more The present work investigates the effect of jet-exit Reynolds number (Re) 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 (Re = 5000 to 21500) 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 Re 5000, peak-PAH occurs at 650 K, whereas in lifted turbulent flame (Re 21500), peak-PAH shifts to 940 K. PAH formation temperature is influenced by air/fuel mixing. Despite the variation of turbulence level (Re = 5000-21500), 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 Re
The morphological description of fractal agglomérâtes is generally reduced to only two parameters... more The morphological description of fractal agglomérâtes 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 agglomerates size and morphological parameters is investigated.
During the agglomération of nanoparticles, notably soot, a change in both the flow régime (from f... more During the agglomération of nanoparticles, notably soot, a change in both the flow régime (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 particles 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 MCAC presented in the preceding work (part 1) by focusing on the physical impact 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 agglomerates morphology to the size of monomers. First, for smaller monomers diameters the agglomeration kinetic is enhanced and agglomerates are found to be more compact, characterized by larger fractal dimensions. Secondly, for large monomer diameters, fractal dimensions down to 1.67 can be found being therefore, smaller than the classical 1.78 for DLCA mechanism. One important conclusion is that variation in time of both the agglomeration and flow regimes has to be considered for a more accurate simulation of the agglomerates size distribution and morphology.
Experimental studies of soot morphology based on analysis of transmission electron microscopy (TE... more 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
Combustion generated soot appears as fractal aggregates formed by polydisperse nearly spherical p... more 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 k f ≈ 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 multi-sphere 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 (σ geo ≤ 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.
Many studies have been conducted on the environmental impacts of combustion generated aerosols. D... more Many studies have been conducted on the environmental impacts of combustion generated aerosols. Due to their complex composition and morphology, their chemical reactivity is not well understood and new developments of analysis methods are needed. We report the first demonstration of in-flight X-ray based characterizations of freshly emitted soot particles, which is of paramount importance for understanding the role of one of the main anthropogenic particulate contributors to global climate change. Soot particles, produced by a burner for several air-to-fuel ratios, were injected through an aerodynamic lens, focusing them to a region where they interacted with synchrotron radiation. X-ray photoelectron spectroscopy and carbon K-edge near-edge X-ray absorption spectroscopy were performed and compared to those obtained for supported samples. A good agreement is found between these samples, although slight oxidation is observed for supported samples. Our experiments demonstrate that NEX...
HAL (Le Centre pour la Communication Scientifique Directe), Nov 7, 2011
The aim of this work is to propose a new method for determining the size distribution of submicro... more The aim of this work is to propose a new method for determining the size distribution of submicronic particles by inversion of the measured angular scattering of light. This method relies on the determination of a function R * g by angular scattering. The variation of this function informs us about the polydispersity of the aggregates size. We show that, by supposing the nature of the size distributions (lognormal), it is possible to determine the governing parameters of these distributions.
for deriving the relative soot absorption function variation with wavelength at different locatio... more for deriving the relative soot absorption function variation with wavelength at different locations in a rich premixed methane flat flame at atmospheric pressure. The present analysis showed that the soot absorption function varies with the height above the burner exit and can be correlated with the degree of soot maturation.
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Papers by Jérôme Yon