Soot emission model

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]... 

The fraction of black-body radiation actually emitted by flames is called emissivity. Emissivity is determined first by adsorption of radiation by combustion products (including soot) in flames and second by radiation wavelength. These factors make emissivity modeling complicated. By assuming that a fire radiates as a gray body, in other words, that extinction coefficients of the radiation adsorption are independent of the wavelength, a fire s emissivity can be written as... 

Farmer, R. C. Edelman, R. B. Wong, E. "Modeling Soot Emissions in Combustion Systems" Particulate Carbon Formation During Combustion, 1980, GM Research Symposium. 

Westbrook, C.K., Pitz, W.J., Curran, H.J. Chemical kinetic modeling study of the effects of oxygenated hydrocarbons on soot emissions from diesel engines. J. Phys. Chem. A 110, 6912-6922 (2006)... 

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). 

The fundamentals of thermal radiation modeling are treated in Chapter 3. The value for emissive power can be computed from flame temperature and emissivity. Emissivity is primarily determined by the presence of nonluminous soot within the flame. The only value for flash-fire emissive power ever published in the open literature is that observed in the Maplin Sands experiments reported by Blackmore... 

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. 

Human exposure to complex mixtures of polycyclic aromatic hydrocarbons (PAH) occurs through inhalation of tobacco smoke and polluted indoor or outdoor air, through ingestion of certain foods and polluted water, and by dermal contact with soots, tars, and oils CO. Methylated PAH are always components of these mixtures and in some cases, as in tobacco smoke and in emissions from certain fuel processes, their concentrations can be in the same range as some unsubstituted PAH. The estimated emission of methylated PAH from mobile sources in the U.S. in 1979 was approximately 1700 metric tons (2). The occurrence of methylated and unsubstituted PAH has been recently reviewed (1, 2). In addition to their environmental occurrence, methylated PAH are among the most important model compounds in experimental carcinogenesis. 7,12-Dimethylbenz[a]anthracene, one of... 

In this section, the physical model used to describe the flow-through monolith reactor is outlined. Such a reactor is common to all the emissions control strategies discussed in this chapter, apart from soot filters. 

Soot formation and oxidation In fires, soot is usually the dominant emitter and absorber of radiation. The modeling of soot formation and oxidation processes is therefore important for the accurate prediction of radiant emissions. Detailed models that solve for soot number density and mass fraction have been developed over the years, and implemented also in fire CFD models such as SOFIE [64], and more recently in [65] and [66], In post-flame conditions, the problem is mostly following of the soot produced in the flame zone. Currently, FDS can only follow this passive soot, but engineering models for soot formation and oxidation that rely on the laminar smoke point height have been postulated [67-69], Unfortunately, the soot formation and oxidation processes are sensitive to the temperature and the same problems appear as in detailed combustion modeling. 

At the same time calculations on the modified MEIS are possible without additional kinetic models and do not require extra experimental data for calculations, which makes it possible to use less initial information and obviously reduces the time and labor spent for computing experiment. Furthermore, there arise principally new possibilities for the analysis of methods to mitigate emissions from pulverized-coal boilers, since at separate modeling of different mechanisms of NO formation the measures taken can result in different consequences for each in terms of efficiency. Consideration of kinetic constraints in MEIS will substantially expand the sphere of their application to study other methods of coal combustion (fluidized bed, fixed bed, etc.) and to model processes of forming other pollutants such as polyaromatic hydrocarbons, CO, soot, etc. 

Quasiglobal kinetics models, which have previously been shown to represent lean and stoichiometric combustion of a variety of hydrocarbon fuels, have been extended to represent lean and rich combustion of toluene and iso-octane. The model predicts the thermal state of the flow and emissions of CO, soot, and N0X. The thermal state of the flow and the stable species were shown to be accurately predicted for jet-stirred combustor experiments. For rich combustion, hydrocarbon intermediates and soot are additional combustion products. The global reactions and rates were developed to represent near-adiabatic jet-stirred combustor data and were then verified by comparison to the near iso-thermal jet-stirred combustor data. N0X emissions behavior was investigated with the quasiglobal kinetics model to represent rich combustion... 

With respect to combustion, the research focus will be on improvement of the models regarding tars and their effect on emissions of CO. soot and unburned hydrocarbons (UHC). Part of that research will be the testing of a combustor integrated in an entire 500 kWth small scale gas turbine set-up. 

Natural convection provides poor mixing of air with fuel gases and can result in incomplete combustion, soot and emissions in open wood stoves. A chimney can supply 1 mm water pressure per meter of height. Addition of a chimney for cooking can greatly improve wood combustion in closed models, but also adds complication and requires wasting heat to operate. 

In technical furnaces the radiation from soot, coal and ash particles has to be considered as well as the gas radiation. Then the scattering of radiation by the suspended particles becomes important, alongside absorption and emission. P. Biermann and D. Vortmeyer [5.67], as well as H.-G. Brummel and E. Kakaras [5.68] have developed models for this. A summary can be found in [5.69] and in [5.37], p. 652-673. The calculations of heat transport in furnaces has been dealt with by W. Richter and K. Corner [5.70] as well as H.C. Hottel and A.F. Sarohm [5.48],... 

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