Flame calculation

Dj = Equivalent vent diameter to be used in flame calculation, in meters... 

Scatter plots of temperature atx/d = 15 in turbulent Cl-14/air jet flames with Reynolds numbers of 13,400 (Flame C) and 44,800 (Flame F). The stoichiometric mixture fraction is = 0.351. The line shows the results of a laminar counterflow-flame calculation with a strain parameter of a = 100 s and is included as a visual guide. (From Barlow, R.S. and Frank, J.H., Proc. Combust. Inst, 27,1087,1998. With permission.)... 

FlameMaster v3.3 A C+ + Computer Program for OD Combustion and ID Laminar Flame Calculations. FlameMaster was developed by H. Pitsch. The code includes homogeneous reactor or plug flow reactors, steady counter-flow diffusion flames with potential flow or plug flow boundary conditions, freely propagating premixed flames, and the steady and unsteady flamelet equations. More information can be obtained from http //www.stanford.edu/group/pitsch/Downloads.htm. 

The rates Wj, Wij, and Woj in a turbulent flame are assumed to be similar to those in a laminar flame. Thus, prior turbulent flame calculations, Wj, Wij, and Woj, are tabulated in the form of look-up tables. 

Use laminar premixed free-flame calculations with a detailed reaction mechanism for hydrocarbon oxidation (e.g., GRI-Mech (GRIM30. mec)) to estimate the lean flammability limit for this gas composition in air, assuming that the mixture is flammable if the predicted flame speed is equal to or above 5 cm/s. For comparison, the lean flammability limits for methane and ethane are fuel-air equivalence ratios of 0.46 and 0.50, respectively. 

Use GRI-Mech (GRIM30. mec) and a laminar premixed flame code to simulate a stoichiometric, burner-stabilized methane-air flame at a pressure of 20 Torr and an unbumed gas velocity of 1 m/s. Evaluate the contribution to NO formation by the N2O mechanism and prompt NO, respectively, by removing the initiation steps in these mechanisms and repeat the flame calculations. 

Figure 10. Density ration across flame front used in V-flame calculations...

A list of substances which have been used or considered to support decomposition flames is shown in Table I. Almost all of these substances have been studied at one time or another to provide fundamental information for the evaluation of the theory of flame propagation. As previously mentioned, the ozone decomposition has proved most useful as the basis of a flame which is amenable to both theoretical and experimental study. The NO decomposition flame provided a situation where a clear-cut prediction was made possible by flame theory (P2). On the basis of a flame calculation it was predicted that a strong preheat would permit the stabilization of this flame at a measurable flame velocity, since it was known that a flame would not propagate into the gas at room temperature. Subsequent experimental work confirmed the prediction by stabilizing a flame with approximately the predicted value. This places a great deal of... 

Figure 2. Space and time scales in the gedanken flame calculation. A naive direct solution of the problem could take 3000 years of computer time. The calculation should be possible in 100 sec.

The soot temperature was found to exceed the gas temperature as measured by thermocouples in the absence of droplet injection but decayed at a similar rate. This is attributed to bulk heating effects associated with the localized burning of vaporized material. A detailed diffusion flame calculation for a cylindrical source of reactants and relative velocity on the same order as these experimental data, indicate that this bulk heating effect is reasonable. 

Both diffusional flame calculations and detailed spatial mapping indicate that the nondispersed injection mode produces a vapor cloud that is characterized by diffusionally controlled combustion and bulk heating while subjecting the droplets to near isothermal conditions. The soot produced in this cloud is strongly influenced by bulk diffusion limitations and as such represents a bulk soot formation extreme. It was found that fuel changes had little effect on the overall soot yield due to this diffusion control. Lower gas temperatures and richer conditions were found to favor soot formation under bulk sooting conditions, probably due to a decrease in the oxidation rate of the soot. 

U. Maas and S.B. Pope, Laminar Flame Calculations Using Simplified Chemical Kinetics Based on Intrinsic Low-Dimensional Manifolds, 25th Symp. (Int.) Comb. (1994) pp. 1349-1356. 

Fig. 9 The time evolution of CH4 and CO concentration and temperature in an adiabatic flame calculated using the GRE-Mech kinetic mechanism. The flame temperature in this example is 1263°C, but this design allows for much higher flame temperatures, if needed. (From Ref l) (View this art in color at www.dekker.com.)...

Our approach to the fuel nitrogen conversion to NO problem has been to examine the kinetics of NH as a model compound using detailed flame calculations with modelable flame experiments. 

Dasch, C.J. Blint, R.B. "An Improved Spalding-Stephenson Transformation for One Dimensional Flame Calculations", accepted for publication in Combust. Sci. Tech. and Western States Section Fall Meeting, The Combustion Institute, Paper WSS/CI 82-89, 1982. 

ISO 5659-2 [108] determines the optical density of smoke generated and measured in a single test chamber. The test cabinet and smoke tneasuring equipment is that of the earlier NBS test defined as ASTM E662 and BS 6401. This ISO test uses a horizontal fire model in which the standard test specimen (75 mm square) is supported on a load cell. The specimen is exposed to radiant heat from a conical radiator positioned above the specimen holder see Fig. 19. Although a range of heat flux values can be used, the standard specifies that tests should be carried out at 25 kW.nr with and without a pilot ignition flame, at 50 kW m without a pilot flame. Calculation of results is by the method defined in the earlier tests. 

For 2D and 3D dynamic simulations such on-line reduction are very computationally costly. A less CPU time intensive approach is to pre-define the combustion domains or zones in which a certain sub-set of the detailed mechanism is used. This is often used for diffusion flame calculations where the domains can be defined by the fuel rich and the fuel lean zones. Hence, schemes that find the smallest chemical sub-set locally in time or space have been proposed e.g. by Schwer et al. (Schwer et al., 2003)). Here each computational cell was assigned a certain sub-mechanism based on a set of physical criteria such as temperature, pressure, species concentrations etc. For highly turbulent flames where these criteria can change rapidly and steeply from cell to cell, this method can be demanding. A single criterion was therefore proposed by Lovas et al. (Lovas et al., 2010), where the sub-mechanism was chosen based on mixture fraction alone. This approach will act as example of implementation of adaptive... 

The overpressure generated in front of a spherical flame calculated with various models is shown in Fig. 12. 

Various calculations of reacting flows, such as perfectly stirred reactors [12], laminar flames [13,14], turbulent flames [15,16], and hypersonic flows [17] have verified the approach presented above. Due to space limitation we shall only present one example, namely a premixed laminar flat flame calculation [13]. It provides a nice, simple test case for the verification of the model. The specific example is a syngas (40 Vol. % CO, 30 Vol. % H2, 30 Vol. % N2)-air system at p = 1 bar, and with a temperature of 290 K in the unburnt gas. The fuel/air ratio is 6/10. The influence of simplified transport models is described elsewhere [13]. Here, for the sake of simplicity, only systems with equal diffusivity shall be considered. In this case a three-dimensional manifold with enthalpy and two reaction progress variables as parameters has been calculated, i.e. the chemistry has been simpli-... 

Comparisons of cpu-times needed for laminar flame calculations show that the computational demand is reduced considerably if simplified chemical kinetics is used. Even for the CO-H2-N2-N2 system consisting of 13 chemical species, we observe a speed-up factor of 10 if simplified chemistry with 2 reaction progress variables is used. The reason is that not only the number of equations to be... 

U. Riedel, D. Schmidt, U. Maas, J. Warnatz, Laminar Flame Calculations Based on Automatically Simplified Chemical Kinetics Proc. Eurotherm Seminar 35, Compact Fired Heating Systems, Leuven, Belgium (1994). 

Fig. 5.13 Example of scatter plot showing the response in the mole fraction of pollutant nitrogen oxide (NO) to a change in A-factor of a rate coefficient expression contained in the chemical model for a flame calculation. Reproduced from Ziehn and Tomlin (2008b) with permission from Wiley...

Maas, U., Pope, S.B. Laminar flame calculations using simplified chemical kinetics based on intrinsic low-dimensional manifolds. Proc. Combust. Inst. 25, 1349-1356 (1994)... 

The code FlameMaster (FlameMaster) is another alternative to the CHEMKIN simulation codes. It is a free computer program for OD combustion and ID laminar flame calculations with local sensitivity analysis. FlameMaster can carry out homogeneous reactor and perfectly stirred reactor calculations, and is able to simulate freely propagating premixed flames and steady counterflow diffusion flames with potential flow or plug flow boundary conditions. 

Many investigators use a flat flame model for their calculations. The best known flat flame calculation algorithm PREMIX [58] has been developed by SANDIA. A characteristic feature of this simulation is that the laminar flame velocity is found as a stationary problem solution. 

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