Search

International audience; The specific surface area of ultrafine particles is an important parameter affecting their physical and chemical properties. For example, the specific surface area of combustion-generated black carbon (BC) particles has been linked to their toxicity and identified to be a more relevant metric to assess their biological response than particle size or mass (Schmid and Stoeger, 2016). Several methods have been developed to measure or determine the specific surface area of aerosol particles, such as the Brunauer-Emmett-Teller (BET) method based on nitrogen adsorption, the diffusion charging (DC) method, scanning Mobility Particle Sizing (SMPS), and the laser-induced incandescence (LII). BET is used as a reference method; however, it is an off-line method and requires a large quantity of sample (several hundreds of milligrams). DC, SMPS, and LII are on-line and faster methods, however, they are indirect methods and rely on various assumptions. Although DC and LII hold a good potential for online determination of the specific surface area of irregular particles, they require further development and evaluation. Recently, it has been demonstrated that the specific surface area of combustion generated black carbon particles can also be determined based on transmission electron microscope (TEM) image analysis; fairly good agreement between the results of BET and TEM was shown in several recent studies (Bau et al., 2010; Bourrous et al., 2018; Ouf et al., 2019). The fairly good agreement between the specific surface areas determined by BET and TEM image analysis of various BC and carbon black (CB) aerosols is an indication that there are negligible internal voids in BC and CB particles. Although TEM image analysis is an off-line method, its main advantage is that it requires only a small amount of sample to be collected on the grid for TEM analysis. Combustion generated BC particles appear as fractal aggregates formed by primary particles that display certain degrees of polydispersity, overlapping, and necking, which in general vary with fuel and flame conditions. Although the specific surface area of BC particles is mainly related to the mean primary particle diameter, other parameters, such as the aggregate size, fractal parameters (pre-factor and fractal dimension), the distribution of primary particles, and the degrees of primary particle overlapping and necking are also relevant. It is important to point out that whereas primary particle overlap reduces both the particle surface area and volume, primary particle necking reduces the particle surface area but increases the particle volume. Figure 1 shows two typical TEM images of flame generated soot particles. Figure 1. Two typical TEM images of flame generated soot particles showing primary particle overlapping, a, and primary particle necking, b (Yon et al., 2015). The effect of primary particle overlapping on the specific surface area of BC particles inferred from TEM image analysis has been investigated recently by Bourrous et al. (2018) and Ouf et al. (2019). However, the potential importance of primary particle necking to BC particle specific surface area determined by TEM image analysis has not been previously investigated. In this study, the TEM images of BC particles produced in laboratory soot generators and from literature were analysed to obtain the primary particle size distribution, primary particle overlapping, and necking. Based on these parameters, the particle specific surface area was inferred, and the results are compared with those obtained from BET or reported previously in the literature. Bau, S., Witschger, O., Gensdarmes, F., Rastoix, O., and Thomas, D. (2010) Powder Technol. 200, 190-201.Bourrous, S., Ribeyre, Q., Lintis, L., Yon, Y., Bau, S., Thomas, D., Vallières, C., and Ouf, F.-X. (2018) J. Aerosol Sci. 126, 122-132. Ouf, F.-X., Bourrous, S., Vallières, C., Yon, J., and Lintis, L. (2019) J. Aerosol Sci. 137, 105436.Schmid, O., and Stoeger, T. (2016) J. Aerosol Sci. 99, 133-143.Yon, J., Bescond, A., Liu, F. (2015) J. Quantitative Spectroscopy & Radiative Transfer 162, 197-206.

European Aerosol Conference, September 6-11 2015, Milan Italy

A major shortcoming of LII is its inability to measure soot aggregate properties. Elastic light scattering, however, is a suitable method to provide these additional information [1]. The technique has been performed following different strategies, mainly in terms of the number of angles involved and the use of absolute or relative scattering intensities. The key quantity to express the relative angular scattering within Rayleigh-Debye-Gans (RDG) theory is the structure factor, which undergoes a subtle but significant modulation during the transition from a monodisperse to a polydisperse distribution, makingit difficult to determine the size and polydispersity parameters simultaneously., 4th International Workshop and Meeting on Laser-Induced Incandescence : Quantitative Interpretation, Modeling, Application, April 18-20, 2010, Varenna, Lecco, Italy

Fourth International Workshop and Meeting on Laser Induced Incandescence: Quantitative Interpretation, Modelling, Application, April 18-20, 2010, Villa Monastero, Varenna, Lecco, Italy

Aggregation of soot particles results in mass fractal structure. It has been established that the particle aggregation makes the total absorption cross section of an aggregated soot particle deviate from the Rayleigh-Debye-Gans theory. This not only affects the ability of soot aggregates to absorb laser energy, but also their emissivity. This study investigates how aggregaton affects the soot temperature derived from the signal ratio in two-color LII experiments, Fourth International Workshop and Meeting on Laser-Induced Incandescence: Quantitative Interpretation, Modeling, Application, April 18-20, 2010, Villa Monastero, Varenna, Lecco, Italy

Recovering the size distribution of aerosolized soot aggregates from multiangle elastic light scattering data requires solving an inverse problem. This paper presents a methodology that uses maximum à posteriori (MAP) inference to stabilize the inversion by introducing prior information about the size distribution of the soot aggregates., 6th International Symposium on Radiative Transfer, June 13-19, 2010, Antalya, Turkey

The 4th International Workshop and Meeting on LII, Varenna, Lecco, Italy, April 18-20, 2010

Combustion Institute, Canadian Section Spring Technical Meeting, May 9-12, 2010, Ottawa, ON

For the modeling and application of LII it is of interest to know whether there are species ablated from soot particles during IR irradiation, what kind of species are involved in these processes, and at which fluences the ablation occurs. This is highly demanded as current LII models for non-negligible sublimation conditions are not well predictive for the first tens of nanoseconds and strongly vary among different LII models [1]. A photolonization mass spectrometer, modified to allow IR and UV interrogation of a soot laden molecular beam and subsequent analysis of the ionized products, was employed to explore these questions. Autoionization Cn clusters were observed as a product of IR irradiation, while neutral ablation products were not detected via IR+UV conditions. A new size class of particles in the range of 1000 to 3000 amu appears promptly after IR excitation. These particles are most likely fragments of soot rather than agglomerates of Cn clusters., 4th International Workshop and Meeting on Laser-Induced Incandescence: Quantitative Interpretation, Modeling, Application, April 18-20, 2010, Varenna, Lecco, Italy

Combustion Institute, Canadian Section Spring Technical Meeting, May 9-12, 2010, Ottawa, ON

2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference, July 8-12, 2007, Vancouver, BC

The sooting behaviour of binary fuel mixtures was evaluated both experimentally and through computer simulations. The soot volume fraction in laminar diffusion flames of mixtures of ethylene/propane, methane/ethylene, methane/propane, methane/ethane, methane/butane, ethane/propane and ethane/ethylene fuels was measured using 2-dimensional line of sight attenuation. A synergistic effect was observed for the ethylene/propane, methane/ethylene, methane/ethane and ethane/ethylene mixtures. The synergistic effect translated into a higher soot concentration for a mixture fraction than could be yielded by the added contribution of both pure fuels. Such an effect was not observed for the methane/propane, methane/butane and ethane/propane mixtures. Through experiments in which the flame temperature was kept constant, it was determined that the synergistic effect in the methane/ethylene mixture is very temperature dependent whereas, that in the ethylene/propane mixture is not. This phenomenon was further studied through the modeling of the ethylene/propane mixture. Numerical simulations were carried out using two different soot models. The simulations confirmed the presence of a synergistic effect. It was found that the effect could be directly correlated to a synergistic effect in the concentration of n-C4H5 and n-C4H3, which could be traced back to an interaction between ethylene and methyl radical species. These results yield further insight into the pathways to soot formation and highlight the importance of further analyzing binary fuel mixtures as a means of understanding soot formation in practical devices using industrial fuels.

International audience

IMECE2005, 2005 ASME International Mechanical Engineering Congress and Exposition, November 5-11, 2005, Orlando, FL, available, unlimited, public

International Bunsen Discussion Meeting 2005: Laser-Induced Incandescence, Quantitative Interpretation, Modelling, Application, September 26-28, 2005, Duisburg, Germany, available, unlimited, public

Combustion Institute Canadian Section, 2004 Spring Technical Meeting, May 9-12, 2004, Kingston, Ontario, available, unlimited, public

Since many practical combustors operate at high pressures there is interest in understanding how pressure influences combustion phenomena and in particular, soot formation pathways. The scope of the present work is to study the influence of pressure on soot formation under laminar conditions. To this end, a combustion facility and annular diffusion flame burner have been built and were commissioned in the fall of 2002. The first goal with the new facility has been to achieve stable laminar flames at elevated pressures. This paper serves to describe the characterization and optimization of the pressure vessel and burner facility., Canadian Section, Spring Technical Meeting, May 11-14, Vancouver, BC

When different inert diluents are added to the fuel or oxidant of a diffusion flame, the local concentrations of various chemical species and the temperature profile of the flame may vary and thus the soot formation process may be altered due to the differences in diffusivities of inert diluents., Combustion Institute - Canadian Section, 2002 Spring Technical Meeting, May 13-15, 2002, Windsor, ON, available, unlimited, public

Combustion Institute Canadian Section, 2001 Spring Technical Meeting, May 13-16, 2001, Montreal, QC, Canada, available, unlimited, public