Primary Particle Diameter Research Articles

Measurement of soot volume fraction and primary particle diameter in oxygen enriched ethylene diffusion flames using the laser-induced incandescence technique

The paper presents an experimental investigation of the effect of oxygen concentration in the oxidizer (O2+N2) on distributions of soot volume fraction (SVF) and flame centerline primary particle size in laminar coflow ethylene diffusion flames. The base flame has an oxygen index (OI, oxygen mole fraction in the oxidizer stream) of 21%. Three additional flames, with OI of 30%, 40% and 50%, are also examined. The fuel flow rate was maintained constant in all the experiments. The two-dimensional laser-induced incandescence (2D-LII) and two-color spectral band measurement based on the response spectrum of R, and G bands of a color 3-CCD camera are applied to measure distributions of SVF. The time resolved laser-induced incandescence (TIRE-LII) is used to measure SVF and primary particle size along the flame centerline at different heights above burner (HAB). The results of SVF are compared among the two-color method, 2D-LII, and light-of-sight attenuation (LOSA) from the literature in the base flame and compared between TIRE-LII and two-color spectral band method in oxygen enriched flames. Good agreements are observed in the measured SVF from different methods. Soot primary particle sizes, measured by TIRE-LII, are compared with those based on transmission electron microscopy (TEM) image analysis from the literature and a fairly good agreement is observed. The results indicate that soot yields increase and the flame becomes shorter and brighter with increasing OI. The primary particle diameter increases firstly and then decreases with the normalized HAB by the visible flame height (hf). At the same HAB/hf, the primary particle diameter generally increases with increasing OI from 21% up to 50%.

Effects of Silica-Particle Coating on a Silica Support for the Fabrication of High-Performance Silicalite-1 Membranes by Gel-Free Steam-Assisted Conversion.

Silicalite-1 membranes with high pervaporation performance were prepared successfully on a silica-particle-coated tubular silica support using a gel-free steam-assisted conversion (SAC) method. The effects of the silica-particle layer formed on the top surface of the silica support and the physical properties of the silica particles themselves on the membrane-formation process were investigated. The silica particles coated served as the additional silica source for growing the silicalite-1 seed crystal layer into the silicalite-1 membrane. As a result, it was possible to form a dense and continuous membrane even under gel-free conditions. Furthermore, it was found that the properties of the silica particles, such as their primary particle diameter, had a determining effect on their solubility during the steam treatment, that is, on the supply rate of the silica source. The silicalite-1 membrane obtained using the spherical-silica-particle-coated support had an approximately 9-μm-thick separation layer and showed very high pervaporation performance, exhibiting a separation factor of 105 and a flux of 3.72 kg m−2 h−1 for a 10 wt % ethanol/water mixture at 323 K. Thus, the gel-free SAC method can be used with a silica support coated with silica particles to readily prepare high-performance membranes without producing any chemical waste.

Size distribution and chemical composition of primary particles emitted during open biomass burning processes: Impacts on cloud condensation nuclei activation

As a major source of fine particles, open biomass burning can affect climate and the hydrological cycle via the formation of cloud condensation nuclei (CCN) and their deposition. This study investigated the effect of aerosol size and chemical composition (water-soluble compounds, elemental carbon, and organic carbon) on CCN activation during the complete combustion of six commonly used crop (rice, wheat, corn, soybean, and cotton) and leaf residues in a simulation chamber developed for this study. Geometric mean diameters (GMD) of emitted primary particles ranged from 68 to 130 nm and water-soluble compound (WSC) content ranged from 33 to 50%. Although GMDs and WSCs possessed similar temporal tendencies during the combustion process, their average values were dependent on the type of biomass. Number concentration ratios of CCN and particle (CCN/CN) ranged from 1.4–2.1% and 5.8–8.3% at supersaturations of 0.2% and 1.0%, respectively. The CCN/CN value increased during the combustion process when the GMD and WSC content increased. Correlation coefficients for GMD and CCN activation ranged from 0.62 to 0.93, while correlations for WSC and CCN activation ranged from 0.33 to 0.95. Soybean biomass had the highest correlations for both GMD and WSC with CCN activation at various supersaturations. These results suggest that the size and chemical composition of biomass aerosols are important in CCN formation, while the aerosol size has a higher impact.

The chemical structure effects of alkylbenzenes on soot formation in a laminar co-flow flame

Alkylbenzene isomers are often used in transportation fuel surrogates but have different sooting tendencies. There is a need to understand how their chemical structures affect the soot formation mechanism. In this study, the chemical structure effects of alkylbenzenes (1,2,4-trimethylbenzene (124TMB) and n-propylbenzene (PBZ)) on soot formation in a laminar diffusion flame were experimentally and numerically investigated. In the experiment, the optical time-resolved laser-induced incandescence (LII) and spectral soot emission (SSE) diagnostics were used to measure radial soot volume fraction, primary particle diameter and flame temperature profiles. The radial number density was also experimentally derived. The results are consistent with the literature as 124TMB exhibits higher soot concentration than PBZ. From the analyses of the primary particle diameters and the derived number density, this is caused by the higher soot nucleation rate for 124TMB. This conclusion is supported by numerical modeling, which utilized the detailed CoFlame code with a moderately reduced CRECK mechanism. The simulation results show that 124TMB has earlier soot inception and Polycyclic Aromatic Hydrocarbon (PAH) addition than PBZ. Consistent with both earlier soot inception and PAH addition, the 124TMB model predicts earlier pyrene (A4) formation, suggesting 124TMB has alternative reaction pathways for pyrene formation. The reaction pathway analysis suggests that pyrene is formed via the aromatic radical recombination route, as opposed to the conventional HACA mechanism. Bypassing the formation of the second ring could be the reason for 124TMB having earlier soot nucleation. In contrast, the PBZ model predicts that the formation of pyrene follows the slower HACA pathways, leading to later soot nucleation.

Influence of ethanol blending ratios on in-flame soot particle structures in an optical spark-ignition direct-injection engine

This study shows how ethanol addition impacts in-flame and exhaust soot in spark-ignition direct injection (SIDI) engines through direct and simultaneous sampling of particles from the flames and exhaust stream. The thermophoresis-based soot sampling and transmission electron microscope (TEM) imaging was performed for various ethanol blending ratios ranging from 0 to 60%. A quantitative analysis is performed in the images obtained from a standard TEM by yielding the in-flame and exhaust soot number counts, projection area, as well as morphological parameters such as soot primary particle diameter, aggregate radius of gyration, and fractal dimension. In addition, the internal structures and reactivity status of in-flame and exhaust soot particles are unveiled using a high-resolution TEM with carbon fringe length, tortuosity and fringe-to-fringe separation extracted from processed carbon layer fringe images. The results show that both the number counts and projection areas of exhaust soot are much lower than those of the in-flame soot at any fixed ethanol blending ratios. The exhaust soot is smaller in size for both the primary particles and aggregates with more compact aggregate structures, longer and straighter fringe, and lower fringe separation, all indicating significant soot oxidation occurred inside the cylinder before the particles exit through the exhaust. With increasing ethanol blending ratio, almost linear reduction in number counts and projection area is found for both the in-flame and exhaust soot particles, while both soot aggregates and primary particles become smaller with more stretched aggregate structures and shorter, more curved, and narrower gap fringe structures, indicating soot particles with higher reactivity. The significantly lower soot emissions achieved with higher ethanol blending ratio is found to be due primarily to the suppression of soot formation within the flame as evidenced by higher reduction rate of number counts, projection area, and primary particle and aggregate sizes for the in-flame soot than that of the exhaust soot.

Effects of water addition on soot properties in ethylene inverse diffusion flames

The effects of H2O addition on the evolutions of soot morphology, nanostructure, and oxidation reactivity were investigated in ethylene inverse diffusion flames. The thermophoretic sampling and transmission electron microscopy (TEM) analysis were used to evaluate the soot morphological characteristics including primary particle diameter, projected area of agglomerates, and fractal dimension. High-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) were utilized to gain the nanostructure and crystallite features and thermogravimetric analyzer (TGA) was adopted for oxidation reactivity by analyzing the soot collected via quartz plate sampling. A reduction in soot production was found with increasing H2O concentration, which illustrated an inhibition effect of H2O on soot formation. The soot morphology evolutions further demonstrated that H2O addition could decrease soot inception process from the reduced sizes of primary particles and agglomerates, and fractal dimension. The HRTEM and XRD results showed that the increasing H2O addition led to larger fringe length, lower fringe tortuosity, and smaller interlayer spacing of soot, which indicated a higher carbonization degree in soot nanostructure. The soot oxidation reactivity was slightly reduced with H2O addition.

Properties of carbon black produced by the thermal decomposition of methane in the products of premixed flames

The thermal decomposition of methane is a technique used to manufacture hydrogen gas and carbon black. The physical properties of carbon black produced by the thermal decomposition of methane (TDM) in the O2-deficient gas products of two premixed flames (propane- or methane-air) were investigated under different flow rates of decomposing methane injection (0.5–5 SLPM). An inverted burner was designed to provide a fuel-rich, laminar premixed flame, to produce hot gas into which methane was injected to thermally decompose inside a reactor. Particles from TDM were extracted by a nitrogen dilution system at the immediate exit of the reaction chamber, where another branch of the exhaust was dried and directed to a gas chromatograph. The carbon black particles were characterized by size resolved number concentration, mass concentration, effective density, volatility, and internal mixing state using different arrangements of a differential mobility analyzer, catalytic denuder, centrifugal particle mass analyzer, and condensation particle counter, as well as by morphology and primary particle size using transmission electron microscopy. A bimodal number-size distribution was observed at all conditions with count median diameters (CMDs) less than 58 nm and 21 nm when using propane- or methane-air premixed flames as the heat source, respectively. Higher number concentrations and mass concentrations with larger CMDs were achieved under lower flow rates of decomposing methane injection. For a given flow rate of decomposition methane, mass concentration and CMD increased significantly when using propane as the fuel, compared to the methane fuel. The size segregated mass fraction of internally mixed volatile content in particles was similar for both heat sources, showing a roughly constant fraction of volatile material in particles produced by the decomposition of 0.5 and 5 SLPM of methane (10%–30%) but a measurably larger fraction (55%–30%) with a decreasing trend as a function of particle size from the decomposition of 1 SLPM of methane. The effective density of denuded particles was similar, but slightly higher, than the effective density of soot from a wide range of internal combustion engines. A higher denuded effective density was observed in the particles with higher volatile contents (particles from decomposition of 1 SLPM of methane), suggesting the restructuring of carbon black into more compact clusters due to excessive volatile condensation. TEM analysis revealed some similarity between the produced carbon black and engine soot in terms of morphology and primary particle diameter (both below 40 nm). Beside the carbon black properties, the efficiency of TDM in this configuration was also investigated by evaluation of methane destruction efficiency, as well as carbon black and hydrogen production efficiencies, based on the product gas composition and the particle mass concentration. It was found that longer residence times corresponding to lower flow rates resulted in higher conversion efficiencies in terms of methane destruction efficiency (maximum of ∼95%), hydrogen production efficiency (maximum of ∼80%), and carbon black production efficiency (maximum of ∼1%). It was concluded that the significantly low efficiency of carbon black production is due to the high amount of CO formation, likely through the gasification process.

Soot morphology and nanostructure in complex flame flow patterns via secondary particle surface growth

While the majority of studies explore soot formation in relatively simple, one-dimensional flames, most real-world flames consist of complex flows defined by large-scale turbulent eddies, recirculating flow patterns, and buoyancy effects. The effects of complex flow on soot physicochemical properties are poorly understood. This work employs an inverted gravity flame reactor (IGFR) to compare differences in soot growth between a one-dimensional laminar diffusion flame and a recirculating flame. Computational fluid dynamics (CFD) and experimental observations show particle oscillations between (i) a rich region with a high concentration of surface growth species, and (ii) a high-temperature oxidation region. Transmission electron microscopy (TEM) shows a significant difference in final primary particle diameter, where the one-dimensional flame produces primary particles 10–25 nm in diameter and the recirculating flame produces primary particles 25–75 nm in diameter. Additionally, larger primary particles from the recirculating flame contain both single and multiple cores. We propose that due to the spheroidal shape of the large primary particles, the secondary surface growth is primarily a result of polyaromatic hydrocarbon (PAH) condensation during re-entrainment of mature soot into the fuel-rich region followed by subsequent liquid layer carbonization in the high-temperature environment of the flame front. The recirculating flow patterns in the IGFR and repeated particle growth/oxidation cycle can serve as a model for soot formation in the large-scale flames with complex flow patterns, such as forest fires, coal fire plants, and other sources.

Magnetic One-Step Purification of His-Tagged Protein by Bare Iron Oxide Nanoparticles.

Magnetic separation is a promising alternative to conventional methods in downstream processing. This can facilitate easier handling, fewer processing steps, and more sustainable processes. Target materials can be extracted directly from crude cell lysates in a single step by magnetic nanoadsorbents with high-gradient magnetic fishing (HGMF). Additionally, the use of hazardous consumables for reducing downstream processing steps can be avoided. Here, we present proof of principle of one-step magnetic fishing from crude Escherichia coli cell lysate of a green fluorescent protein (GFP) with an attached hexahistidine (His6)-tag, which is used as the model target molecule. The focus of this investigation is the upscale to a liter scale magnetic fishing process in which a purity of 91% GFP can be achieved in a single purification step from cleared cell lysate. The binding through the His6-tag can be demonstrated, since no significant binding of nontagged GFP toward bare iron oxide nanoparticles (BIONs) can be observed. Nonfunctionalized BIONs with primary particle diameters of around 12 nm, as used in the process, can be produced with a simple and low-cost coprecipitation synthesis. Thus, HGMF with BIONs might pave the way for a new and greener era of downstream processing.

Chemical and nanostructural characteristics of the particulate matter produced by renewable diesel fuel in an automotive diesel engine

Renewable diesel (RD), a paraffinic fuel produced by the hydrotreating of palm oil, was used neat and blended at 10% and 30% (by volume) with ultra-low sulfur diesel (ULSD) to generate particles in an automotive diesel engine operating at two engine speeds (1890 and 2410 min−1) under the same engine load (95 Nm). Particulate matter was characterized using thermogravimetric analysis (TGA), Raman spectroscopy, X-Ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), and X-Ray photoelectron spectroscopy (XPS). Oxidation profiles showed that diesel soot is slightly more reactive than the soot produced by RD and its blends, independently of the engine speed (the maximum mass loss rate temperature –MLRTmax– was 6.6 °C lower for ULSD than neat RD). This behavior was in agreement with the active surface area (ASA) of the particles, which varied between 10.8 m2/g for RD to 13.9 m2/g for ULSD at the same engine speed. Soot nanostructure (ratio of Raman peaks) and interlayer distance show a slightly higher degree of order of the particles when RD was added into diesel fuel. The mean primary particle diameter of neat RD soot was around 26 nm and fractal dimension of the agglomerates was around 1.66, which were both lower in comparison with ULSD (32 nm and 1.97, respectively). Fringe analysis applied to HRTEM micrographs revealed no clear trend in the fringe length and tortuosity among soot samples. Finally, it was found that, independently of the fuel tested, all particle samples gathered at 2410 min−1 were slightly more reactive and smaller than those collected at 1890 min−1. From this engine configuration and specific experimental setting, it can be expected that the use of RD blends would not markedly affect the performance of aftertreatment devices like diesel particulate filters.

Retrieval of fractal dimension and size distribution of non-compact soot aggregates from relative intensities of multi-wavelength angular-resolved light scattering.

A new technique is developed to retrieve the fractal dimension and size distribution of soot aggregates simultaneously from the relative intensities of multi-wavelength angular-resolved light scattering. Compared with other techniques, the main advantage of this method is its independence of knowing complex refractive index, number density of aggregate, fractal prefactor and primary particle diameter. The forward light scattering procedure of soot aggregate is described by Rayleigh-Debye-Gans polydisperse fractal aggregate (RDG-PFA) scattering theory, and the retrieval process is performed by using the covariance matrix adaption-evolution strategy algorithm (CMA-ES). Three different measurement models, i.e. absolute scattering and transmittance, absolute scattering, relative scattering (RS), are investigated in present research. Numerical experiments have been performed to test the feasibility of the CMA-ES algorithm. Combined with the multi-wavelength RDG-PFA strategy, the retrieval accuracy of soot aggregate size distribution is proved to be more effectively by using the RS model. Satisfactory results under 10% Gaussian measurement noise have demonstrated the feasibility of the proposed method.

Particle Characterization of Soot Aggregates Emitted by Gasohol Fueled Direct Injection Engine

In this study, two gasohols, namely, E15 [15% v/v ethanol blended with 85% v/v gasoline] and M15 [15% v/v methanol blended with 85% v/v gasoline] with respect to baseline gasoline were investigated for the characteristics of their soot particles. An in-depth comparative analysis for morphological characteristics of particulate matter emitted by a GDI engine using a high-resolution transmission electron microscope (HRTEM) was performed. Soot particles were collected using a partial flow dilution tunnel, and the effect of engine load and fuel oxygenated content on soot morphology was investigated. For soot samples from different test fuels, primary particle diameter (Dp), length, and width of the soot agglomerate and high angle annular dark field were investigated. At the macroscale (ratio of length to width of agglomerate L/W), the HRTEM images of gasoline soot agglomerates were observed to be remarkably similar to the agglomerates from gasohols; however, a detailed analysis of these images on the microsca...

A feasible and accurate method for calculating the radiative properties of soot particle ensembles in flames

The accurate calculation of the radiative properties of soot particle ensembles in flames needs to exactly reconstruct the geometric structures of all soot particles and accurately calculate the radiative properties of all soot particles based on their reconstructed geometric structures. However, the enormous number of soot particles in real ensembles makes it practically impossible to implement this task. To solve this problem, a feasible and accurate method is proposed for calculating their main radiative properties except scattering matrix and depolarization ratio. Experimental and numerical results show that soot particles with the same number of primary particles from the same sampling point can be considered as equivalent soot particles, which have almost the same volume, absorption cross-section, scattering cross-section and scattering asymmetry cross-section. Moreover, the average values of these quantities of equivalent soot particles approximately linearly increase with the number of primary particles. These findings can dramatically reduce the difficulty of reconstruction and calculation. The radiative properties of 37 different morphologies of soot particle ensembles in the visible and near-infrared regions (λ = 0.40–3.00 µm) are calculated using this method, and it is shown that the increasing of the average diameter of primary particles and the average number of primary particles per soot particle can enhance the absorption coefficient, scattering coefficient, asymmetry factor and single-scattering albedo of soot particle ensembles 0.1–900 times. In addition, these radiative properties are found to decrease by at least 70% with the increasing of λ from 0.40 µm to 3.00 µm.

The evolution of soot morphology and nanostructure along axial direction in diesel spray jet flames

This study aims at providing new insights into the soot formation and oxidation processes in diesel spray jet flames under the diesel-like conditions. Soot particles are sampled within a reacting diesel jet spray flame in a constant-volume combustion chamber under diesel-like high-temperature and pressure ambient conditions. The experiments are conducted with an injector hole of 0.28 mm and injection mass of 30 mg per shot. Soot particles at different locations along the axis of the diesel jet flame are sampled by a thermophoretic probe, and the variation of soot morphology and nanostructure of the sampled soot particles along the axial location in the flame is analyzed by using the transmission electron microscopy (TEM). At upstream of the jet flame, large “liquid-like” particles are observed in the TEM images. As these particles are delivered to the downstream, (1) there are many immature primary particles formed on the surface of large “liquid-like” particles, and (2) they are carbonized into the larger soot aggregates with the matured structure, and then at last, (3) the larger soot aggregates gradually break up into the smaller particles with relatively compact structure. Both the diameter of primary particles and radius of gyration of the soot aggregates decrease as the distance between the injector nozzle tip and the center of TEM grid is increased, while the opposite trend is found in the behavior of the fractal dimensions of soot aggregates. The high resolution TEM images show that the soot primary particles exhibit the turbostratic state at the upstream of the jet flame, while more matured structures with the graphitic crystallite in outer shell and several fine particles in the inner core are observed as the sampling distance from orifice is increased. The average fringe length increases while the average tortuosity and separation decrease with the distance from the nozzle. These results suggest that the mechanism of mature soot aggregates generated directly from the large “liquid-like” particles should be one of the ways of soot particle formation along the axis of diesel jet flames.

Characterization of biomass PM emissions using thermophoretic sampling: Composition and morphological description of the carbonaceous residues

In this paper, a complete characterization of particulate matter (PM) emitted by a low-scale biomass combustor was performed. Samples were collected in three different zones of the installation (in-flame, boiler outlet and chimney outlet) using the thermophoretic sampling (TPS) method, and the different particle structures present in the biomass were studied from a chemical and a morphological point of view. Five types of particles were found: soot agglomerates, organic films, organic particles with imbibed fibrous structures, condensed tars and condensed inorganic salts. Transmission electron microscopy (TEM) was used for shape description, and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX) was used for determining elementary composition. Specifically, soot agglomerates were submitted to a deeper characterization in terms of fractal descriptors, obtaining values for primary particle diameter, dpo, of 21.7 ± 8.4 nm, 21.4 ± 6.6 nm and 26.0 ± 5.9 nm for the three sampled zones, as well as values for fractal dimension, Df, between 1.40 and 2.60 and fractal prefactor, kf, between 2.20 and 2.40. The results were in agreement with other soot formation sources and showed an increasing tendency to cluster growth and compaction with the residence time inside the facility, being higher as they went further from the combustion zone. Fractal descriptors were not fairly influenced by the applied thermal treatment.

Brownian dynamics simulation of soot primary particle aggregation in laminar ethylene diffusion flames

The aggregation of soot primary particles along the centerline of laminar ethylene diffusion flames is simulated using the Brownian dynamics method incorporating the cluster–cluster aggregation model. Unlike previous studies, this simulation approach takes more key parameters into account, such as the temperature, dynamic viscosity and velocity of the flame gas, the primary particle diameter distribution and the soot volume fraction. Given that the change in the O2 concentration would greatly affect these simulation parameters, three aggregation simulations for flames at different O2 concentrations are implemented to check the applicability of this simulation approach for different sets of simulation parameters. These simulations dynamically display the soot morphology evolution from isolated mature primary particles to fractal-like aggregates along the flame centerline, and simulation results indicate that the fractal properties of simulated soot aggregates are almost identical, yielding a fractal dimension of 1.70-1.74 and a fractal prefactor of 2.13-2.23, and the mean number of primary particles per simulated soot particle is in the range of 1-83. Moreover, as the O2 concentration increases from 21% to 40%, the simulated height of the soot aggregation region along the flame centerline decreases from 25 mm to 10 mm, and the simulated time of soot aggregation reduces from 18.5 ms to 8.8 ms. On the whole, these simulation results agree well with the experimental data.

Experimental investigation of soot evolution in a turbulent non-premixed prevaporized toluene flame

The formation, growth, and oxidation of soot in turbulent prevaporized toluene diffusion flames stabilized on a jet-in-hot-coflow (JHC) burner are investigated in this study. Flame structure, local gas temperature as well as local soot volume fraction and primary soot particle diameter, are simultaneously detected by means of OH planar laser-induced fluorescence (PLIF), non-linear excitation regime two-line atomic fluorescence (nTLAF) of indium, and time-resolved (TiRe) laser-induced incandescence (LII), respectively. The collected data sets were used to generate joint statistics of soot properties and flame characteristics and provided new insights into the interaction of the OH layer and soot in turbulent flames. The interaction of OH and soot as a driving mechanism for soot oxidation is of particular interest as it has been proven to be challenging to model. Statistics of soot volume fraction and primary particle size in the OH layer are employed to gain deeper insights into the soot oxidation process. Mean soot volume fraction and primary soot particle size conditioned on temperature and OH signal intensity indicate that, due to differential diffusion of soot with respect to the chemical species, high soot volume fraction and primary soot particle diameter of up to 50 nm are present at low temperatures and low OH concentration. In the soot oxidation region, statistical analysis of the soot parameters disclose that clusters of high soot volume fraction mostly consist of large primary particles. Observations from instantaneous images and the presence of large primary particles inside the OH layer suggest that the oxidation is not sufficiently fast to burn the soot completely.

Determining fractal properties of soot aggregates and primary particle size distribution in counterflow flames up to 10 atm

Abstract Experimental investigations of soot morphology are performed in counterflow flames of N2-diluted ethylene and air, up to 10 atm. A thermophoretic sampling device is attached to a pressure vessel containing a counterflow burner where flames with an ethylene mole fraction of 0.3 are stabilized at 3, 5, and 6 atm. To allow measurements at higher pressures, the fuel mole fraction is lowered to 0.2 to reduce the soot loading and flames are studied at 5, 7, and 10 atm. Thermophoretic sampling of the soot zone is performed using TEM grids. The sampling process causes minimal flame disturbances. Soot collected on TEM grids is analyzed under transmission electron microscope (TEM). Primary particle size distributions are inferred at each pressure by manually analyzing the primary particles from TEM images. Fractal properties of soot at each pressure are also obtained by analyzing the TEM images at comparatively low magnifications. Mean primary particle diameter increases from 17.5 to 47.1 nm as the pressure is increased from 3 to 10 atm, whereas the fractal dimension and prefactor do not change with pressure up to 10 atm. For the flames studied here, fractal dimension lies between 1.61 and 1.67 whereas fractal prefactor varies between 1.68 and 1.86 without following any apparent trend with pressure.

Impact of bio-alcohol fuels combustion on particulate matter morphology from efficient gasoline direct injection engines

The requirements for controlling particulate emissions in gasoline direct injection (GDI) engines, particularly in hybrid vehicles (where frequent cold-start event impact on both, particles characteristics and catalytic aftertreament efficiency), nesesitates the need for understanding their formation mechanism and their morphological characteristics. The findings described in this investigation have significance in the design of efficient Gasoline Particulate Filters (GPFs) and the development of computational models that predict particle filtration and oxidation processes.Morphological analysis of the particulate emissions from the combustion of commercial gasoline and two bio-alcohol blends: of 25% v/v ethanol in gasoline and 33% v/v butanol and 67% v/v gasoline, in a modern GDI engine has been carried out using a transmission electron microscopy. The primary particle size distribution from the combustion of butanol-gasoline blend was slightly smaller compared to gasoline, while the mean primary particle diameter was 3 nm smaller from the combustion of ethanol-gasoline fuel. This decrease in primary particle size for ethanol-gasoline blend was also reflected in a reduction of the mean radius of gyration and mean number of primary particles per agglomerate.The combustion of butanol-gasoline blend induced improved particle oxidation rates during the combustion process and post-oxidation stage, and led in 80% and 60% reduction in particle concentration in the engine exhaust when compared to the combustion of gasoline and ethanol-gasoline blend, respectively. Additionally, the estimation of the particle fractal dimension through the use of fractal equation, minimum bonding rectangle method and root form factor showed comparable results for butanol-gasoline and gasoline, with the particle agglomerates being more compact than the ethanol-gasoline fuel, where more chain like particles are seen. Therefore, particles emitted from the combustion of ethanol-gasoline fuel are easier to be trapped (lower fractal dimension) and present a higher reactivity (high surface/volume ratio) compared to particles emitted from gasoline combustion.

A semi-automatic analysis tool for the determination of primary particle size, overlap coefficient and specific surface area of nanoparticles aggregates

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%).