Primary soot particles

In a combustion chamber, soot volume fraction or number densities are usually not known. It is generally accepted that the primary soot particles are spherical in shape and about 20-60 nm in diameter (see the review by Charalampopoulos [185]). However, depending on the flow and combustion characteristics of the system, they agglomerate to form irregularly shaped large particles. The shape can be clusters of spheres or cylindrical long tails attached to burning coal particles. 

For agglomerates of small spheres, a solution technique developed by Jones [198,199] has received considerable attention [191, 200-205]. In this approach, the primary soot particles are assumed to be in the Rayleigh limit. The accuracy of the model decreases significantly as the individual soot spheres become larger compared to the wavelength of radiation, i.e., when... 

The reaction probabilities for O and OH with soot particles have been measured by Roth and co-workers in a series of shock tube experiments [58-60], They have found that both radicals react with soot particles with a collision efficiency of between 0.10 and 0.20. In contrast, the reaction probability with 02 is at least an order of magnitude lower [55], Of course, at lower temperatures and sufficiently lean mixtures, soot oxidation by radical species becomes small and oxidation by 02 is important (though slow). Consequently, soot that passes through or avoids the primary reaction zone of a flame (e.g., due to local flame quenching) may experience oxidation from 02 in the post-flame gases. Analysis of soot oxidation rates in flames [54-57] has supported the approximate value of the OH collision efficiency determined by Roth and co-workers. 

The physical and chemical complexity of primary combustion-generated POM is illustrated in Fig. 10.1 (Johnson et al., 1994), a schematic diagram of a diesel exhaust particle and associated copollutants. The gas-phase regime contains volatile (2-ring) PAHs and a fraction of the semivolatile (3- and 4-ring) PAHs. The particle-phase contains the remainder of the semivolatile PAHs ( particle-associated ) along with the 5- and 6-ring heavy PAHs adsorbed/absorbed to the surface of the elemental carbon spheres that constitute the backbone of the overall diesel soot particle. Also present is sulfate formed from oxidation of sulfur present in the diesel fuel and gas- and particle-phase PACs. 

Luminous Flames Luminosity conventionally refers to soot radiation. At atmospheric pressure, soot is formed in locally fuel-rich portions of flames in amounts that usually correspond to less than 1 percent of the carbon in the fuel. Because soot particles are small relative to the wavelength of the radiation of interest in flames (primary particle diameters of soot are of the order of 20 nm compared to wavelengths of interest of 500 to 8000 nm), the incident radiation permeates the particles, and the absorption is proportional to the volume of the particles. In the limit of rjX < < 1, the Rayleigh limit, the monochromatic emissivity e is given by... 

In the elementary reactions of the pyrolysis, the atomic carbon is formed first. Then it transforms into the final product, whether it be soot, graphite, carbon nanofibers, or so forth. Why does the presence of catalysts make it possible to grow carbon nanofibers or nanotubes instead of soot In many cases, this is the so called carbide cycle that is characteristic of the catalytic process of hydrocarbon pyrolysis that is responsible for the growth of the elongated structures but not soot particles. The primary car bon atoms produced by pyrolytic decomposition of the hydrocarbon molecules are dissolved in the metal particle of the active catalyst compo nent to form a nonstoichiometric carbide (the carbon solution in the... 

Effect of Manganese. This metal is relatively effective in reducing smoke from gas turbine combustion systems (8) and furnaces (9). However, under the same experimental conditions as above, no significant effort was ever found with this metal or with iron and nickel. Furthermore, when oxygen was injected into the primary zone of carbon formation with a microprobe, the soot decrease profile did not change when manganese was added to the initial mixture. Hence this metal does not appear to stimulate the oxidation of small soot particles. 

Koylu et al. used extensive TEM studies to derive the mass fractal dimension, Df, of flame-made soot particles from Equation A1 (see the appendix) by extracting the number of primary particles per agglomerate, N, the primary particle size, (ip, and the radius of gyration of the agglomerate, R. The constant fractal prefactor, A, as well as the fractal dimension, Dj, were then determined by regression. 

Fume particles have been measured microscopically and found to have fractal dimensions of 1.3-1.5 (Baron and Willeke, 1993). Soot particles analyzed by Sorenson and Feke (1996) displayed fractal morphology over the range 0.05-400 pm. This range corresponds to agglomerates of 10 to 10 primary particles. These same authors found the relationship between the number of primary particles in an... 

Sources of atmospheric aerosol particles are bulk-to-particle conversion, gas-to-particle conversion, and combustion processes. Bulk-to-particle conversion includes the formation of sea salt, dust, and biogenie partieles. Gas-to-particle formation involves either new particle formation from aerosol precursor gases, or growth of preexisting particles by mass transfer processes between the gas and the partiele phase. Particles derived from gas-to-partiele eonversion processes are also called secondary aerosol particles. Other partieles, sueh as from bulk-to-partiele eonversion processes or combustion particles (soot, fly ash), are called primary aerosol particles. 

Diesel soot particles are almost entirely of respirable size, and consist of an elemental carbon core formed of aggregated primary particles and a variable amount of adsorbed organic sulfur, and metal compounds condensed onto the... 

Oxidative catalytic converters are used to reduce CO and HCs originating from imperfect combustion in engines. At certain temperatures, these converters may also oxidize NO to NO2. Original equipment manufacturer (OEM) particle filters (PFs) employ NO2 to oxidize trapped soot at lower temperatures. However, the excess NO2 may escape from the system as tailpipe emissions. NO2 is very toxic to humans, and it also has impacts on atmospheric ozone-forming chemistry. Alvaraz et al. have stated that the primary NO2 emissions of modern diesel cars are increasing [76]. 

Particulate carbon in the atmosphere exists predominantly in three forms elemental carbon (soot) with attached hydrocarbons organic compounds and carbonates. Carbonaceous urban fine particles are composed mainly of elemental and organic carbon. These particles can be emitted into the air directly in the particulate state or condense rapidly after Introduction into the atmosphere from an emission source (primary aerosol). Alternatively, they can be formed in the atmosphere by chemical reactions involving gaseous pollutant precursors (secondary aerosol). The rates of formation of secondary carbonaceous aerosol and the details of the formation mechanisms are not well understood. However, an even more fundamental controversy exists regarding... 

The air emissions of fossil fuel combustion are dispersed and diluted within the atmosphere, eventually falling or migrating to the surface of the Earth or ocean at various rates. Until recently, most attention was focused on the so-called primary pollutants of fossil fuel combustion that are harmful to human health oxides of sulphur and nitrogen, carbon monoxide, suspended particles (including soot), heavy metals, and products of incomplete combustion. These pollutants are most concentrated in urban or industrialized areas close to large or multiple sources. However, the primary pollutants may interact with each other, and with atmospheric constituents and sunlight, forming secondary pollutants that disperse far beyond the urban-... 

Morphology - The picture in Fig. 11 clearly shows the coating on fullerene soot primary particles. The thickness of the coating could be quantified as being... 

Road transport is an important contributor to primary emissions of PM (soot, wear particles and road dust) and also a source of secondary particles formed by condensation of gaseous species (mainly S- and N-compounds and organics) emitted by the tailpipe and partly also by the wear of brakes and tyres. Thus, PM emissions from road traffic are responsible for an important proportion of the exceedances of the PM10 and PM25 Air Quality Limit Values established by the European legislation for the protection of the human health (2008/50/EC [17]). The daily (50 pg m-3) and annual (40 pg m 3 ) limit values for PM10 (atmospheric particles with mean aerodynamic diameter <10 pm) and the annual limit value for PM2.5 (25 pg m-3) (in force from 2015) concentrations in ambient air are indeed exceeded mostly in the urban areas (Fig. 1 [17]). 

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