Combustion detailed modelling

Frenklach, M. and Warnatz, J., Detailed modeling of PAH profiles in a sooting low-pressure acetylene flame. Combust. Sci. Tech., 51,265,1987. 

Heimerl, J. M., and T. P. Coffee. 1980. The detailed modeling of premixed, laminar steady-state flames. 1. Ozone. Combustion Flame 39 301-15. 

The measurements of temperature and species concentrations profiles in premixed, laminar flames play a key role in the development of detailed models of hydrocarbon combustion. Systematic comparisons are given here between a recent laminar methane-air flame model and laser measurements of temperature and species concentrations. These results are obtained by both laser Raman spectroscopy and laser fluorescence. These laser probes provide nonintrusive measurements of combustion species for combustion processes that require high spatial resolution. The measurements reported here demonstrate that the comparison between a model and the measured concentrations of CH, O2,... 

Errors and confusion in modelling arise because the complex set of coupled, nonlinear, partial differential equations are not usually an exact representation of the physical system. As examples, first consider the input parameters, such as chemical rate constants or diffusion coefficients. These input quantities, used as submodels in the detailed model, must be derived from more fundamental theories, models or experiments. They are usually not known to any appreciable accuracy and often their values are simply guesses. Or consider the geometry used in a calculation. It is often one or two dimensions less than needed to completely describe the real system. Multidimensional effects which may be important are either crudely approximated or ignored. This lack of exact correspondence between the model adopted and the actual physical system constitutes the basic problem of detailed modelling. This problem, which must be overcome in order to accurately model transient combustion systems, can be analyzed in terms of the multiple time scales, multiple space scales, geometric complexity, and physical complexity of the systems to be modelled. 

Oran, E. S and Boris, J. P., Detailed Modelling of Combustion Processes, to appear in Prog, in Energy and Comb. Sci, 1980. 

The form of EBU expression is mainly based on dimensional arguments. The ratio k/ is the turbulent time scale. If the turbulence intensity is high, so is the fuel consumption. For the prediction of secondary species, such as CO, HC1, and soot, more advanced models using flamelets [37] have been used. The flamelets (and state relations) can be determined either experimentally [39] or computationally, using detailed models for combustion chemistry [40] that incorporate strain rate effects. 

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. 

E. Oran and J. Boris, detailed Modeling of Combustion Systems" NRL Memorandum Report 4371, November 1980. 

Radical decompositions are unimolecular reactions and show complex temperature and pressure dependence. Section 2.4.l(i) introduces the framework (the Lindemann mechanism) with which unimolecular reactions can be understood. Models of unimolecular reactions are vital to provide rate data under conditions where no experimental data exist and also to interpret and compare experimental results. We briefly examine one empirical method of modelling unimolecular reactions which is based on the Lindemann mechanism. We shall return to more detailed models which provide more physically realistic parameters (but may be unrealistically large for incorporation into combustion models) in Section 2.4.3. 

As a third step, the global model for hydrocarbon combustion was extended with a detailed model of 21 elementary steps for moist CO combustion, resulting in a quasi-global model similar to that of Edelman and Fortune. This model [202] predicted the species profiles as well. A similar model was almost simultaneously proposed by Duterque et al. [206] for five fuels. 

The inclusion of reactions to represent the low-temperature chemistry in a detailed model for n-butane oxidation at high pressures, that is appropriate to temperatures down to about 600 K began in 1986 [225]. At the present time, models which include around 500 species and more than 2000 reversible reactions to represent alkane isomers up to heptane, are in use [219] and still larger schemes are under development [220]. Progress in the validation and application of these models, and kinetic representations for propane and propene oxidation, are discussed in the next subsection. Modelling of the low-temperature combustion of ethene has also been undertaken more recently [20]. 

The application of the basic ideas to real combustion systems is then taken up in Chapters 6 and 7. In Chapter 6, experimental and modelling studies are described which link the mechanistic observations of Chapter 1 to combustion characteristics of fuels studied under laboratory conditions. The experimental emphasis is initially on global combustion phenomena - ignition and oscillatory cool-flames - for a range of hydrocarbons. Section 6.5 then addresses the distribution of products in hydrocarbon oxidation this discussion differs from that in Chapter 1 where the conditions were optimized to allow the investigation of specific reactions. The focus is now on studies of oxidation products over a range of isothermal and non-isothermal conditions, the interpretation of the results in terms of elementary reactions and the use of the experimental data as a detailed test of combustion models. The chapter provides an overview of the success of detailed models in describing combustion phenomena and combustion... 

Peters B. (1995) A detailed model for devolatilization and combustion of waste material in packed beds. 3" European Conference on industrial Furnaces and Boilers. Porto, 86-104. 

Oran, E.S. and Boris, J.P. (1982), Detailed modeling of combustion systems. Prog. Energy Combust. Sci., 1, 1-72. 

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