Flame parameters

As the large-scale computational fluid dynamics (CFD) simulations often invoke simplifying the kinetics as one-step overall reaction, the extraction of such bulk flame parameter as overall activation energy is especially useful when the CFD calculation with detailed chemistry is not feasible. Based on the experimental results, the deduced overall achvation energies of the three equivalence ratios are shown in Figure 4.1.10a. It can be observed that the variation of with is nonmonotonic and peaks near the stoichiometric condition. 

Definitions of flame parameters in channels. D, distance between channel walls effective in flame quenching (quenching distance). D, flame width dead space R, radius of curvature of the flame. 

The cooling effect of the channel walls on flame parameters is effective for narrow channels. This influence is illustrated in Figure 6.1.3, in the form of the dead-space curve. When the walls are <4 mm apart, the dead space becomes rapidly wider. This is accompanied by falling laminar burning velocity and probably lowering of the local reaction temperature. For wider charmels, the propagation velocity w is proportional to the effective flame-front area, which can be readily calculated. On analysis of Figures 6.1.2b and 6.1.3, it is evident that the curvature of the flame is a function of... 

Methane/Air Flame Parameters and Rotational Speeds (a>i) for Which the Tangential and Normal Speeds in an Expanding Flame are Equal... 

Quantitative development of the above model of the ignition process is overwhelmingly complicated. Lewis Von Elbe therefore chose to attempt correlation of experimental minimum ignition energies with some energy functions computed from minimal flame parameters... 

In conclusion of this section it should be noted that the main dimensionless parameters of the problem considered are the ratio of the propagation flame velocity along the channel axis to the normal velocity of flame (parameter e = U/un — 1), and the degree of thermal gas expansion (a = T0/Tb where T0 and Tb are the initial and burned gas temperatures). 

The previous section of fhis chapter has described the flame parameters that must be controlled and optimized to produce a polymer film of the desired level of wettability. The present section is a review of the current state of knowledge of the chemical kinetic mechanism of the reactions between flame reactants and the surface layer of polymer molecules. The discussion begins with a consideration of the flow, impingement, and quenching of the combustion products and reactive intermediates on the cooled surface of the polymer film. The discussion then proceeds to describe a detailed chemical kinetic mechanism for the surface reaction. The resulting mechanism is able to qualitatively account for the influence of the major flame variables on the wettability of fhe polymer surface. Finally, the addition of secondary species, specifically nitrous oxide (N2O), to the primary reactants to alter the thermal and/or chemical behavior of fhe flame is discussed, providing an example of fhe effecfs of flame-chemistry modification. 

Bandaru, R. V., and Turns, S. R. "Turbulent Jet Flames in a Crossflow Effects of Some Jet, Crossflow, and Pilot-Flame Parameters in Emissions." Combustion and Flame 121 (2000) 137-51. 

Previous evidence for the mechanism of formation of CH comes from two experiments. A measurement [6] of spatial profiles in low-pressure C2H2/O2 flames showed the ratio [CH ]/[C2][OH] to be remarkably constant with variation in many different flame parameters. Only the A A state was observed, however. In a more recent study [7] in a low pressure discharge flow at room temperature, emission spatial profiles, measured downstream from mixing of 0 + C2H2, were compared with the results of a computer calculation, varying many discharge parameters. Here it was concluded that CH was produced from the reaction O + C2H, not the reaction C2 + OH deduced from the flame study. The present profiles suggest that neither mechanism is solely responsible for the formation of electronically excited CH. 

C.J. Sun, C.J. Sung, L. He, C.K. Law, Dynamics of weakly stretched flames quantitative description and extraction of global flame parameters. Combust. Flame 118, 108-128 (1999)... 

Data on diffusion flame parameters of hydrogen jet discharges into the surroundings have been summarized as an additional dangerous factor used for the analysis of safe hydrogen transportation. Conditions of spontaneous ignition of both hydrogen and its mixtures with combustible and incombustible additives have been... 

Table 4 Flame Pretreatment/Examples of Flaming Parameters...

Figure 4 shows production rate (g/hr) of Si02 as a function of precursor flow rate (moles/min) for the 6 cm diameter burner. Optimizing the flame parameters, combined with increasing the burner diameter, should lead to higher production rates. 

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