Soot Aggregates Research Articles

Mass concentration and morphological analysis of PM10 and PM2.5 particles in congested roads during day hours in three major cities of Oman

ABSTRACT PM10 and PM2.5 samples were collected using the particulates E-Sampler from congested roads in three major cities of Oman. The average PM10 concentration varied from 35.87 µg/m3 in Salalah during the monsoon season to 18.95 µg/m3 in Sohar. PM2.5 concentration ranged from 20.74 µg/m3 in Muscat to 7.20 µg/m3 in Sohar. Average concentrations of PM10 and PM2.5 in all cities were below NAAQS and WHO standards. Scanning Electron Microscopy coupled with energy dispersive spectrometer (SEM-EDS) of PM2.5 particles from all cities showed spherical like fly ash and chain like soot aggregates. These might have originated from fuel burning and vehicle emissions. Fe, O and Si are the major components present in the PM2.5 and PM10 particles while other elements are present in lower percentages. PM10 particles collected from Muscat and Salalah were irregular and chain like soot aggregates that are referred to originate from natural and anthropogenic emissions. However, PM10 collected from Sohar showed irregular shape containing aluminosilicate particles that might have initiated from natural sources.

Nanoscale inspection on carbon particles from commercial RP-3 kerosene combustion with different dilutions

RP-3 kerosene fuel is the dominant hydrocarbon fuel used in civilian airplanes in China. Lately, many administration and universal organizations imposed a stringent standard for civilian airplanes pollutants emission. The amount of pollutants emission can be affected by the introduction of a variety of additives into flames, such as inert diluents, gaseous additives. This paper reports the effects of different inert gases (nitrogen and helium) and carbon dioxide dilutions in the oxidizer side on soot characteristics generated from RP-3 kerosene inverse diffusion flames. Flame diluted by carbon dioxide produced less amount of soot compared to flames diluted by nitrogen and helium, possibly because of changes in flame shape and properties such as flame diameter and availability of oxygen atoms. Carbon dioxide suppressed soot precursors formation in inception zone and released particles with smaller diameter due to lack of hydrogen radicals, an increase of hydroxyl radicals pool concentration, and decrease in flame temperature. Flame diluted by helium generated much soot aggregates with bigger primary particles diameter compared to base flame (flame diluted by nitrogen) as a result of high temperature. Soot particles produced in carbon dioxide diluted flame had more amorphous nanostructure, longer interlayer spacing and nanocrystallite height, shorter nanocrystallite width, lesser number of layers, and higher oxygen content compared to flame diluted by nitrogen and helium, which reflected a better oxidation reactivity among other diluted flames.

Morphology and size of soot from gas flares as a function of fuel and water addition

A large-scale, laboratory turbulent diffusion flame was used to study the effects of fuel composition on soot size and morphology. The burner and fuels are typical of those used in the upstream oil and gas industry for gas flaring, a practice commonly used to dispose of excess gaseous hydrocarbons. Fuels were characterized by their carbon-to-hydrogen ratio (from 0.264 to 0.369) and their volumetric higher heating value (HHVv) (from 35.8 to 75.2 MJ/m3). Transmission electron microscopy (TEM) was used to assess primary particle and aggregate size, showing that the scaling of primary particle size to aggregate size was roughly the same for all of the considered fuels (dp = 16.3(da,100 [nm]/100)0.35). However, fuels with higher HHVv produced substantially larger soot aggregates. A scanning mobility particle sizer (SMPS) was also used (i) to measure mobility diameter distributions and (ii) in tandem with a centrifugal particle mass analyzer (CPMA) to determine the two-dimensional mass-mobility and effective density-mobility distributions using a new inversion approach. The new approach was shown to improve internal consistency of inferred morphological parameters, though with a shift relative to median-based analysis of the tandem data. Raman spectroscopy was used to quantify the degree of graphitization in the soot nanostructure. The addition of water to the fuel consistently reduced the soot yields but did not affect other morphological parameters. Larger aggregates also tended to have larger primary particles and higher Raman D/G ratios suggesting larger graphitic domains.

Fine Particulate Matter and Gaseous Compounds in Kitchens and Outdoor Air of Different Dwellings.

Passive diffusion tubes for volatile organic compounds (VOCs) and carbonyls and low volume particulate matter (PM2.5) samplers were used simultaneously in kitchens and outdoor air of four dwellings. PM2.5 filters were analysed for their carbonaceous content (organic and elemental carbon, OC and EC) by a thermo-optical technique and for polycyclic aromatic hydrocarbon (PAHs) and plasticisers by GC-MS. The morphology and chemical composition of selected PM2.5 samples were characterised by SEM-EDS. The mean indoor PM2.5 concentrations ranged from 14 µg m−3 to 30 µg m−3, while the outdoor levels varied from 18 µg m−3 to 30 µg m−3. Total carbon represented up to 40% of the PM2.5 mass. In general, the indoor OC/EC ratios were higher than the outdoor values. Indoor-to-outdoor ratios higher than 1 were observed for VOCs, carbonyls and plasticisers. PAH levels were much higher in the outdoor air. The particulate material was mainly composed of soot aggregates, fly ashes and mineral particles. The hazard quotients associated with VOC inhalation suggested a low probability of non-cancer effects, while the cancer risk was found to be low, but not negligible. Residential exposure to PAHs was dominated by benzo[a]pyrene and has shown to pose an insignificant cancer risk.

Three-dimensional tomography reveals distinct morphological and optical properties of soot aggregates from coal-fired residential stoves in China

Electron tomography (ET) is used to reconstruct the exact 3-dimensional morphologies of fractal-like soot aggregates sampled from a household heating stove commonly used in China. Conventional ET techniques suffer from “the missing wedge” problem caused by unreachable tilt angles, leading to noisy reconstructed tomograms. We overcame this problem by implementing a high-resolution object-edge identification method coupled with a novel voxel-filling algorithm to improve the reconstruction quality. Our reconstructed micron-length aggregates highlight the local non-idealities present throughout a particle's surface; these characteristics are almost impossible to account for in existing computational simulation exercises. Q-space analysis predicts the fractal dimension of our ET reconstructed aggregates to be in the range between 2.2 and 2.6, which deviates significantly from the universal value of 1.8 obtained using the widely adopted diffusion limited cluster-cluster aggregation (DLCA) model. The optical properties of our ET reconstructed aggregates are compared with those built with a DLCA model and equivalent spheres . The most striking optical characteristics of the ET reconstructed aggregates are their wavelength invariant mass absorption cross-sections of ~3.5 m2/g and single scattering albedo of ~0.5. The sample size investigated in this work is constrained by the extremely time-consuming object-edge identification process of electron tomography. This issue necessitates the development of more efficient computer vision algorithms for future research.

Physical properties of exhaust soot from dimethyl carbonate-diesel blends: Characterizations and impact on soot oxidation behavior

This study presents the physical properties and oxidation reactivity of exhaust soot from a modern direct injection diesel engine fueled with dimethyl carbonate (DMC)-diesel blends and discusses the relationship between physical properties and oxidation reactivity of soot. The soot morphology, size, fractal dimension and nanostructure were analyzed by transmission electron microscopy and Raman scattering spectrometry. The thermogravimetric analysis was carried out to characterize soot oxidation reactivity in the form of apparent activation energy. The results showed that soot aggregates from DMC/diesel blended fuels exhibited fewer and smaller primary particles as well as small-sized clusters than the diesel soot aggregates. Soot primary particles presented shorter fringe length, wider separation distance and greater tortuosity with increasing DMC blending amount, while the degree of graphitization for soot presented an increasing trend. It was also found that soot from DMC/diesel blends, or low loading operation had higher oxidation reactivity than those from pure diesel or heavy loading operation. Among the physical properties, fractal dimension and primary particle size appeared to be insignificant than the nanostructure for governing the soot oxidation reactivity. Further analysis showed the separation distance was more correlated with soot oxidation characteristics than fringe length and tortuosity. These results illustrated that the use of DMC blended diesel fuel affects the physical properties of soot, enhances soot particle oxidation reactivity, which will be significant for improving the regeneration efficiency of after-treatment device.

Influence of wall-wetting conditions on in-flame and exhaust soot structures in a spark ignition direct injection petrol engine

Great attention to the efficiency benefits of spark ignition direct injection engine has been averted due to its problematic particulate emissions. In the present study, the fundamental knowledge of wall-wetting-induced spark ignition direct injection soot particles is enhanced through direct particle sampling from pool fire on the piston top surface and cylinder liner as well as from the exhaust stream. The sampled soot particles are imaged using transmission electron microscope, and the image post-processing for statistical morphology and internal structure analysis is performed to better understand the soot formation and oxidation processes. The experiments were performed in a single-cylinder optical spark ignition direct injection engine where diffusion flame luminosity was recorded using a high-speed camera through the cylinder liner window, with which the overall sooting level was understood, and the pool fire location was identified. Given the in-flame soot sampling experiments in the spark ignition direct injection engine were new, error analysis was conducted in terms of the number of fuel injections and engine run-to-run variations. This sampling technique then was applied for various injection timings in the intake stroke. The data analysis and physical interpretation was focused on a piston-wetting condition at the most advanced injection timing of 320 °CA bTDC and a liner-wetting condition at the most retarded injection timing of 180 °CA bTDC in the present study. Between these two different wall-wetting conditions, it was found that the piston-wetting condition has larger soot primary particles and soot aggregates. The internal carbon-layer fringe shows longer length, less tortuosity and smaller gap, indicating more mature and carbonised soot. This was consistent with more significant and wider distributed pool fire and thus longer soot residence time within the flames. When the exhaust soot particles were analysed, however, it was found that the reduction in soot aggregate size was much higher and the carbonisation was more progressed for the piston-wetting condition than those of the liner-wetting condition. This suggested higher soot oxidation later in the expansion/exhaust stroke for the piston-wetting condition, which potentially can be better utilised for engine applications.

Simultaneous inversion of fractal morphology and particle size distribution of soot aggregate based on light scattering intensity

Simultaneous inversion of fractal morphology and particle size distribution of soot aggregate based on light scattering intensity

Absorption and scattering of light by soot aggregates with uniform and pendular ring coatings

The magnitude of radiative forcing by soot is strongly dependent on its morphology and mixing state, which continuously evolve during atmospheric aging. One of the major soot aging mechanisms is via interaction with condensable trace-gas chemicals, and our previous study has shown the formation of two distinct coating distributions on fractal soot aggregates, primarily depending on the radius of monomer spheres and supersaturation of the condensing vapor. The two coating distributions, spherical shells around monomers and pendular rings in junctions between monomers, differ profoundly in their ability to restructure soot aggregates. Here, we investigate the impact of these two distributions on the optical properties of soot, using Discrete Dipole Approximation (DDA) calculations, which are also compared against the Rayleigh Debye Gans (RDG) approximation and the core-shell model. For most optical parameters, the difference between the two coating distributions was minor, except for the asymmetry parameter, where it was significant (5–13%). We found that the placement of condensate in junctions significantly depressed the asymmetry parameter for most coating volumes, thus promoting isotropic scattering by soot. Compared to a uniform condensate distribution, the presence of coating between monomers always resulted in slightly larger absorption, scattering and single scattering albedo (SSA), with the difference reaching ~10% for scattering at high coating volumes. We found that the RDG approximation underestimated absorption, but was able to predict scattering to within ~3%. On the other hand, the core-shell model significantly overestimated absorption, scattering, and SSA, especially for thinly coated soot.

Inferring soot morphology through multi-angle light scattering using an artificial neural network

The morphological parameters of polydisperse aerosolized soot can be found by regressing modeled angularly-resolved elastic light scattering to experimental measurements, but this is an ill-posed problem in the presence of measurement noise or model error. Rayleigh-Debye-Gans Fractal Aggregate (RDG-FA) theory provides a closed-form solution for the light scattering kernel in the measurement model but can be subject to 30% model error (or more) compared to the exact solution, which is amplified by the ill-posedness of the inference problem into significant errors in the recovered morphological parameters. More precise approaches, e.g. the multi-sphere T-matrix method (MSTM), are too expensive for inference problems, which require repeated evaluation of the forward model; this is particularly true when computing posterior probability densities and credibility intervals. In this work, a computationally-efficient artificial feed-forward multi-layered neural network (ANN) is trained using MSTM scattering simulations on randomly-generated soot aggregates sampled from plausible morphological parameters. A fixed value is specified for the refractive index, while the monodisperse primary particle diameters are specified, and sintering, overlap or necking phenomena are ignored for the MSTM simulations. The ANN is then used to approximate the light scattering kernel in the measurement model, which is incorporated into the Bayesian inference procedure. The Bayesian/ANN approach is shown to be more accurate compared to a Bayesian approximation error technique. The Bayesian/ANN is then applied to in-flame measurements of soot and results are compared with transmission electron microscopy results from the literature. Parameters derived from electron micrographs of extracted soot are not contained within 90% credibility intervals; this is likely due to some of the simplifying assumptions in the scattering model, which points the way towards future work.

Quantitative high-resolution transmission electron microscopy nanostructure analysis of soot oxidized in diesel spray flame periphery

In order to better understand the in-flame diesel soot oxidation processes, soot particles at the oxidation-dominant periphery of diesel spray flame were sampled via newly developed suck type soot sampler employing a high-speed solenoid valve, and their morphology and nanostructure were observed and analyzed via high-resolution transmission electron microscopy. A single-shot diesel flame for the soot sampling experiment was achieved in a constant-volume vessel under a diesel-like condition (9.5 kg/m3, 2.5 MPa, 1070 K, and 21%O2). Morphology of soot aggregates, inner-core/outer-shell structure of primary particles within the aggregates, and carbon crystallite nanostructures within the primary particles were compared between the soot aggregates sampled at the diesel flame core near the central axis and the oxidation-dominant flame periphery. The morphology observation and the inner-core/outer-shell structure characteristics obtained by newly employed concentricity analysis showed that the flame core soot exhibits graphitic primary particles with clear outlines and boundaries similarly observed for engine exhaust soot. Each primary particle contained a well-defined inner core surrounded by thick graphitic outer shell. On the contrary, the flame periphery soot exhibited smaller primary particles with unclear and lumpy outlines containing multiple obscured inner cores surrounded by thinner outer shell. The analysis of carbon crystallite nanostructures within the primary particles showed that the in-flame soot nanostructure shifts toward amorphous from the flame core to the periphery. On the contrary, the engine soot nanostructure in the literature shifts toward graphitic from the in-cylinder TDC to the exhaust, exhibiting the opposite trend with the in-flame soot. These results suggest that the engine exhaust soot has not experienced the rapid in-flame oxidation by OH radicals and is therefore considered not to be the remains of incomplete or partial oxidation, but the runaways escaped from the flame core to the exhaust without being attacked by the in-flame OH radicals.

A comprehensive study of fuel composition, combustion and soot nanostructure characteristics of a diesel/light hydrocarbons premixed charge compression ignition engine

The present research concentrates on the fuel properties and engine operating conditions on combustion and emission characteristics especially for morphology and nano-structure of a light hydrocarbons PCCI engine. The experiments were conducted by using gas chromatography-mass spectrometry, thermogravimetric analysis and high-resolution transmission electron microscopy. Additionally, the performance, combustion and gaseous pollutant emissions characteristics were also performed. The results indicate that the carbon chain length of main compounds in light hydrocarbons sample is shorter and the volatile matter content is higher. TG/DTG curves of light hydrocarbons move to a lower temperature region compared to diesel, which is due to lower decomposition temperature and higher volatility of light hydrocarbons. The performance characteristics show that BSFC is higher and BTE is lower in light hydrocarbons PCCI engine compared to conventional diesel engine. The combustion and emission characteristics show that the in-cylinder peak pressure of light hydrocarbons PCCI engine is reduced by 18.1%, and the pressure rise rate and heat release rate present a consistent variation trend compared to conventional diesel engine. Light hydrocarbons PCCI engine exhibits higher THC emission with respect to different engine load, while CO and NOx emissions are lower. Compared with conventional diesel engine, the soot aggregate of light hydrocarbons PCCI engine exhibits more sparse, and it appears more chain-like. Additionally, the primary particles in light hydrocarbons PCCI engine represent more ordered graphitic and fullerenic nanostructure.

Soot formation and evolution in RP-3 kerosene inverse diffusion flames: Effects of flow rates and dimethyl carbonate additions

RP-3 kerosene fuel is the dominant hydrocarbon fuel used in civilian aeroplanes in China. In this study, the effects of fuel flow rates and dimethyl carbonate additions on the formation and evolution of young soot particle collected from RP-3 kerosene in inverse diffusion flames were studied comprehensively by several methods. Physical properties (nanostructures) of soot particles were evaluated by low-resolution transmission electron (TEM) microscopy, high resolution transmission electron microscopy (HRTEM), X-ray Diffraction (XRD) spectroscopy, and Raman spectroscopy. Chemical properties (oxidation reactivity and surface oxygen contents) of soot particles were studied over thermogravimetric analyzer (TGA) and X-ray photoelectron spectroscopy (XPS). When the fuel flow rate increased and dimethyl carbonate addition ratio decreased, the soot particles and aggregates were found to form a lot and grow faster with bigger primary particle diameter. The HRTEM, XRD, and Raman analyses have shown that the disorder and turbostratic structure with shorter fringe length and longer tortuosity were increased, which indicated higher oxidation reactivity rates, as the fuel flow rate and dimethyl carbonate addition ratio increased. The surface oxygen contents were found to decrease as the fuel flow rate increased, while were shown to increase as the dimethyl carbonate addition ratio increased.

Morphology of soot sampled from N2-diluted methane/air counterflow flames at elevated pressures via TEM imaging

An experimental work is carried out to investigate the influence of pressure on morphological parameters of soot in counterflow flames of N2-diluted methane and air. Flames are stabilized at 3, 5, 7 and 10 atm in a pressure vessel and a global strain rate of 30 s−1 is maintained at all pressures by adjusting the inlet mass flux. The mole fraction of methane is maintained at 0.7. The entire soot zone of the counterflow flames are sampled using a thermophoretic sampling device attached to the pressure vessel. Our sampling method minimizes the flow disturbances to a level that they are visually negligible during the sampling process. Collected samples are analyzed under a transmission electron microscope and information about mean primary particle diameter, fractal dimension (Df), fractal prefactor (kf) and aggregate size distribution is inferred at different pressures. To investigate the effects of carbon flux on primary particle size, fuel mole fraction is decreased to 0.5 and primary particle size is investigated at 5, 7 and 10 atm. Mean primary particle size increases by 70% when pressure is changed from 5 to 10 atm and remains independent of fuel mole fractions. Geometric mean and geometric width of aggregate size distributions also increase by increasing the pressure. Fractal properties of soot aggregates are found to be insensitive to the pressure. Fractal dimension varies between 1.56 and 1.65 while fractal prefactor values range between 1.96 and 2.1.

Light scattering matrix for soot aerosol: Comparisons between experimental measurements and numerical simulations

Fractal aggregate model has shown significant superiority in simulating integral optical properties (like optical cross sections etc.) of soot aerosol. In this study, angular distributions of scattering matrices for soot samples were measured at 532 nm wavelength. Experiments were conducted over scattering angles from 5° to 175° using an improved and validated apparatus. Soot particles emitted from burning of toluene and n-heptane were collected and re-aerosolized for matrix measurements. Electrical mobility diameter distributions of soot aggregates were measured and converted to volume equivalent diameter distributions according to various conversion factors. Size distributions of soot monomers and fractal parameters were obtained through statistical analyses of transmission electron microscope (TEM) images. Fractal aggregate models were generated by a tunable particle-cluster algorithm, using measured size distributions of aggregates and statistically obtained morphological parameters. Multiple sphere T-matrix (MSTM) method was employed for the calculation of individual particles, and bulk scattering matrices were integrated from particles with same morphology parameters. Results indicated that measured scattering matrices for these two soot samples show similar angular behaviors. Compared with fresh soot particles, the collection and re-aerosolization treatments lead to larger mobility diameters and more compact particle structures. Fractal parameter, conversion factor, refractive index and polydisperse monomer all have various effects on different matrix elements. Inter-comparisons between simulations and measurements focus more on the performance of ideal fractal model consisting of point-contact monomers in simulating measured scattering matrices, and there is no doubt that ideal fractal aggregates cannot simultaneously reproduce measured angular distributions of all matrix elements.

Key‐lock Ceria Catalysts for the Control of Diesel Engine Soot Particulate Emissions

AbstractA new concept, referred to as key‐lock catalyst, is presented in this article. Soot combustion ceria catalysts were prepared combining hard (polymethylmethacrylate colloidal crystals) and soft (Pluronic F127) templates, tuning the porosity of ceria in different size ranges to match the morphology of soot aggregates. The catalysts porosity was characterized in detail by N2 adsorption‐desorption isotherms and Hg‐porosimetry. XRD and H2‐TPR characterization ruled out that differences in activity are related neither with crystallographic nor with redox properties. As a proof of key‐lock catalyst concept, an optimum key‐lock ceria catalyst was synthesized by combining large macropores (100–300 nm) with mesopores (10–30 nm), because they fit to the large soot aggregates and to primary soot particles sizes, respectively. The best soot combustion activity of the optimum key‐lock catalyst is attributed to the optimum transfer of ceria active oxygen from catalyst to soot. The catalytic results confirmed that all ceria catalysts prepared with different porosity oxidize NO to NO2 at the same rate, and the NO2‐assisted soot combustion pathway is not affected by tuning ceria porosity. This double‐templated synthesis and the key‐lock concept opens a new synthesis approach to design noble‐metal free soot combustion catalysts based on the highly effective active oxygen mechanism.

Morphological and radiative characteristics of soot aggregates: Experimental and numerical research

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.

Source apportionment and health risk assessment of air pollution particles in eastern district of Chengdu.

This paper systematically studied the mass concentration levels of PM2.5 and PM10 and obtained the morphological characteristics and components of the particles through scanning electron microscopy (SEM-EDX) and discussed the sources of the particles. Meanwhile, the health risk was evaluated according to the mass concentration of particulate matter. The results showed that the average annual PM2.5 and PM10 in the eastern part of Chengdu were 101.99μg/m3 and 168.89μg/m3, respectively, exceeding the national second-level average annual air quality standard (GB3095-2012). Both of them were the highest in winter and the lowest in summer and had a significant positive correlation. The atmospheric particles in the study area were mainly composed of fly ash particles, soot aggregates, mineral particles (sulfate mineral particles, carbonate mineral particles, etc.), which mainly came from coal burning, dust, automobile exhaust and secondary products. The results of the health risk assessment showed that the mass concentration of PM2.5 and PM10 in the atmosphere of the eastern part of Chengdu exceeded the IT-1 target. The average annual air quality index was 185.84, and the air quality index was level 4, classified as medium pollution. PM10 and PM2.5 were both excessive pollutants, and PM10 was the primary pollutant. Relevant measures should be taken to control particulate matter sources to some extent.

Typical and Atypical Morphology of Non-volatile Particles from a Diesel and Natural Gas Marine Engine

Non-volatile particle emissions from a marine engine fueled by either diesel or natural gas (NG) blended with diesel pilot gas were investigated via transmission electron microscopy (TEM). The most common particles (> 95% by number) were soot aggregates. These “typical” aggregates exhibited primary particle diameters of 20.7 ± 1.9 and 26.9 ± 1.7 for 100 nm aggregates when diesel and NG fuel were used, respectively. Highly non-uniform aggregates, with distinct groups of smaller and larger monomers, were visible in all of the samples but occurred most frequently with diesel fueling at high loads. The observed “atypical” particles included super-aggregates, small compact aggregates, spheres, mineral-like polyhedral particles, and fibers. Such particles, although rare (averaging 3% by number, as calculated by counting the number of particles for each type depicted in all of the collected images), were found in most of the samples and could have been produced by a variety of mechanisms. For instance, the spheres (approximately 300 nm in diameter) most likely arose from metals within the lubricating oil.

煤烟凝聚粒子对紫外光散射信道的影响研究

煤烟凝聚粒子对紫外光散射信道的影响研究