Soot, formation

There is little known about the limiting parameters for soot (small carbonaceous particles) formation during the combustion of coal. It has been noted that conditions favorable to the formation of soot may prevail if contact with oxygen is delayed. 

Soot formation is commonly observed in the pyrolysis or combustion process of simple hydrocarbons and coals. Soot does great harm to people s health through carcinogenic effects and the presence of soot in air also leads to visibility reduction, globe temperature decrease, and acid deposition. Soot can suspend in the air for up to 1 month and can be delivered by wind to distant places, which causes wide range pollution. Soot suspended in flames is important to combustion systems because it will significantly enhance radiative heat transfer due to its large surface area (Fletcher et al., 1997). 

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The diesel engine operates, inherently by its concept, at variable fuel-air ratio. One easily sees that it is not possible to attain the stoichiometric ratio because the fuel never diffuses in an ideal manner into the air for an average equivalence ratio of 1.00, the combustion chamber will contain zones that are too rich leading to incomplete combustion accompanied by smoke and soot formation. Finally, at full load, the overall equivalence ratio... 

Soot formation Sorbates Sorbent fibers Sorbex systems Sorbex technology Sorbic acid... 

The vapor cloud of evaporated droplets bums like a diffusion flame in the turbulent state rather than as individual droplets. In the core of the spray, where droplets are evaporating, a rich mixture exists and soot formation occurs. Surrounding this core is a rich mixture zone where CO production is high and a flame front exists. Air entrainment completes the combustion, oxidizing CO to CO2 and burning the soot. Soot bumup releases radiant energy and controls flame emissivity. The relatively slow rate of soot burning compared with the rate of oxidation of CO and unbumed hydrocarbons leads to smoke formation. This model of a diffusion-controlled primary flame zone makes it possible to relate fuel chemistry to the behavior of fuels in combustors (7). 

Magnussen, B. F., and B. H. Hjertager. 1976. On the mathematical modelling of turbulent combustion with special emphasis on soot formation and combustion. 16th Symp. (Int.) on Combustion, pp. 719-729. The Combustion Institute, Pittsburgh, PA. 

Russ-bildung, /. soot formation, -braun, n. bister, -brennerei. /. manufacture of lampblack. -dampf, m. sooty vapor. 

At present there is no small-scale test for predicting whether or how fast a fire will spread on a wall made of flammable or semiflammable (fire-retardant) material. The principal elements of the problem include pyrolysis of solids char-layer buildup buoyant, convective, tmbulent-boundary-layer heat transfer soot formation in the flame radiative emission from the sooty flame and the transient natme of the process (char buildup, fuel burnout, preheating of areas not yet ignited). Efforts are needed to develop computer models for these effects and to develop appropriate small-scale tests. 

Schocker, A., Kohse-Hoinghaus, K., and Brockhinke, A., Quantitative determination of combustion intermediates with cavity ring-down spectroscopy Systematic study in propene flames near the soot-formation limit, Appl. Opt., 44, 6660,2005. 

Bockhom, H. (Ed.), Soot Formation in Combustion, Springer-Verlag, Berlin, 1994. 

Frenklach, M., Reaction mechanism of soot formation flames, Phys. Chem. Chem. Phys., 4, 2028, 2002. 

Lll soot images indicating soot formation in the reacting jet and increased concentration downstream from the standing premixed reaction zone. (From Dec, J.E., SAE Trans., 106, 1319, 1997. With permission.)... 

The flame maps shown in Figure 8.3.12 indicate reduction of peak temperatures with the increase in the EGR content, and this translates into tangible decrease in engine-out NO,.. While using EGR is a very effective way of reducing its percentage and thus magnitude of NO t reduction in a practical application is limited by the increased soot formation. 

Generation of Pollutants from Combustion 6.3.1 PAH and Soot Formation... 

Although the aromatic polycyclic hydrocarbons are usually associated with tar and soot formation, in a firing or roasting process, compounds such as fluoranthrene and pyrene have also been found in green... 

Acetylene also plays an important role as intermediate in soot formation in flames, because the reverse of reaction (la) forms singlet methylene,... 

In addition to CN and ON, the smoke point (SP), which is the maximum smoke-free laminar diffusion flame height, has been employed widely to evaluate the tendency of different fuels to form soot. This tool was first applied to kerosenes, later diesel, and then jet engine fuels.19,20 Researchers have tried to relate smoke points of pure compounds to their molecular structure. It was found that the inverse of smoke point, which measures the potential of a fuel to form soot, increases from n-paraffins to iso-paraffins to alkylbenzenes to naphthalenes.21,22 Since smoke points vary with experimental conditions, the concept of a threshold soot index (TSI), which is calculated from the smoke point, molecular weight, and experimental constants, has been used to compare the soot-formation tendencies of different fuel molecules.23... 

Similar to the soot formation in the high temperature range, PM precursor formation at intermediate temperatures is also influenced by the paraffinic molecular structure. It was proposed that the soot formation yield decreases in the order cycloparaffin > 2-branched iso-paraffin > 1-branched iso-paraffin > normal... 

Effer- vescent Atomization 20-340 [87] Combustion Simple, reliable, very good atomization. Low risk of plugging due to large holes. Easy maintenance. Beneficial effects on reducing soot formation exhaust smoke. Cheap. Need for separate supply of atomizing air... 

For the prediction of NOx formation, the extended Zeldovich mechanism described by Heywood[603] was implemented. The soot emission modelis a modified version of previously published models for soot formation and oxidation. Details of the soot emission model have been discussed by Han et al.[604]... 

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