Methane-air flame

Typical velocity gradient values for stoichiometric methane—air flames are at flashback about 400 and at blowoff 2000. Thus, if the mixture is... 

Rahinov, I., Goldman, A., and Cheskis, S., Absorption spectroscopy diagnostics of amidogen in ammonia-doped methane/air flames. Combust. Flame, 145, 105, 2006. 

Scherer, J.J. et al.. Determination of methyl radical concentrations in a methane/air flame by infrared cavity ringdown laser absorption spectroscopy,. Chem. Phys., 107, 6196,1997. 

Flow velocity field determined by PIV. Lean limit flames propagating upward in a standard cylindrical tube in methane/air and propane/ air mixtures, (a) Methane/air—laboratory coordinates, (b) propane/air—laboratory coordinates, (c) methane/air—flame coordinates, and (d) propane/air—flame coordinates. 

Shoshin Y. and Jarosinski ]., On extinction mechanism of lean limit methane-air flame in a standard flammability tube, paper accepted for publication in the 32nd Proceedings of the Combustion Institute, 2009. 

Flame shape images and traces extracted from the high-speed schlieren movie (5000 frames/s) of a stoichiometric methane/air flame going through a tulip inversion while propagating in a square cross-section (38.1 mm on the side) closed tube. 

A lean methane/air flame propagating downward in a tube closed above. The tube is of 51mm diameter, (a) Self-light images of the flame (b) traces of the flame shape at 55 frames/s. (Adapted from Jarosinski, Strehlow, R.A., and Azarbarzin, A., Nineteenth Symposium (International) on Combustion, The Combustion Institute, Pittsburgh, pp. 1549-1555,1982.)... 

A classic self-light stroboscopic image of a premixed flame undergoing a tulip inversion in a closed tube. There is an interval of 4.1 ms between the images of a water vapor saturated CO/Oj flame arranged to have a flame speed comparable with that of a stoichiometric methane/air flame. The tube is 2.5 cm in diameter and 20.3 cm long. (Adapted from Ellis, O.C. de C. and Wheeler, R.V., /. Chem. Soc., 2,3215,1928.)... 

Figure 6.2.5 also shows the effect of RHL, which has an influence on the global quenching of lean methane/ air flames based on the behaviors between N2- and CO2-diluted flames of the same Sl lOcm/s. The larger the RHL is, the smaller is the value of Ka, . For example, Ka, = 26.1 for N2-diluted flames (small RHL), while Ka, = 20.4 for C02-diluted flames (large RHL) when (j> 0.64. It is found that for lean mefhane/air flames of constant Sl, the values of Ka, increased with for both N2- and C02-diluted flames, and fhe difference in the values of Ka, befween these two different diluted flames also increased with (f>, as shown in Figure 6.2.5. On the other hand, the effects of RHL did not have influence on the global quenching of rich methane/air flames, because Ka, 8.4 for both N2- and C02-diluted flames (values of Ka are in a log plof in Figure 6.2.5).

Seshadri, K. and Peters, N., The inner structure of methane-air flames. Combust. Flame 81 96 1990. 

It is also well known that there exist different extinction modes in the presence of radiative heat loss (RHL) from the stretched premixed flame (e.g.. Refs. [8-13]). When RHL is included, the radiative flames can behave differently from the adiabatic ones, both qualitatively and quantitatively. Figure 6.3.1 shows the computed maximum flame temperature as a function of the stretch rate xfor lean counterflow methane/air flames of equivalence ratio (j) = 0.455, with and without RHL. The stretch rate in this case is defined as the negative maximum of the local axial-velocity gradient ahead of the thermal mixing layer. For the lean methane/air flames,... 

Profile comparison of temperature, velocity, major species (CH, Oj, CO, COj, and HjO), and minor species (H, O, and OH) at the extinction state using different outer-flow conditions, for counterflow twin-stoichiometric methane/air flames. For clarity, the symbols do not represent the actual grid distribution employed in the calculation. 

Kee, R.J., Miller, J.A., Evans, G.H., and Dixon-Lewis, G., A computational model of the structure and extinction of strained, opposed flow, premixed methane-air flames, Proc. Combust. Inst., 22, 1479, 1988. 

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

Y.C. Chen, N. Peters, G.A. Schneemarm, N. Wruck, U. Renz, and M.S. Mansour 1996, The detailed flame structure of highly stretched turbulent premixed methane-air flames. Combust. Flame 107 223-244. 

Barlow, R.S., Karpetis, A.N., and Frank, J.H., Scalar profiles and NO formation in laminar opposed-flow partially premixed methane/air flames, Combust. Flame, 127, 2102,2001. 

A number of theoretical (5), (19-23). experimental (24-28) and computational (2), (23), (29-32). studies of premixed flames in a stagnation point flow have appeared recently in the literature. In many of these papers it was found that the Lewis number of the deficient reactant played an important role in the behavior of the flames near extinction. In particular, in the absence of downstream heat loss, it was shown that extinction of strained premixed laminar flames can be accomplished via one of the following two mechanisms. If the Lewis number (the ratio of the thermal diffusivity to the mass diffusivity) of the deficient reactant is greater than a critical value, Lee > 1 then extinction can be achieved by flame stretch alone. In such flames (e.g., rich methane-air and lean propane-air flames) extinction occurs at a finite distance from the plane of symmetry. However, if the Lewis number of the deficient reactant is less than this value (e.g., lean hydrogen-air and lean methane-air flames), then extinction occurs from a combination of flame stretch and incomplete chemical reaction. Based upon these results we anticipate that the Lewis number of hydrogen will play an important role in the extinction process. 

Flame temperature. The hydrogen-air flame is hotter than methane-air flame and cooler than gasoline at stoichiometric conditions (2207°C compared to 1917°C for methane and 2307°C for gasoline). 

Smooke, M. D., Reduced Kinetic Mechanisms and Asymptotic Approximations for Methane-Air Flames Lecture Notes in Physics 384 . Springer-Verlag, New York, 1991. 

Of course, all the appropriate higher-temperature reaction paths for H2 and CO discussed in the previous sections must be included. Again, note that when X is an H atom or OH radical, molecular hydrogen (H2) or water forms from reaction (3.84). As previously stated, the system is not complete because sufficient ethane forms so that its oxidation path must be a consideration. For example, in atmospheric-pressure methane-air flames, Wamatz [24, 25] has estimated that for lean stoichiometric systems about 30% of methyl radicals recombine to form ethane, and for fuel-rich systems the percentage can rise as high as 80%. Essentially, then, there are two parallel oxidation paths in the methane system one via the oxidation of methyl radicals and the other via the oxidation of ethane. Again, it is worthy of note that reaction (3.84) with hydroxyl is faster than reaction (3.44), so that early in the methane system CO accumulates later, when the CO concentration rises, it effectively competes with methane for hydroxyl radicals and the fuel consumption rate is slowed. 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

Following existing convention, oxides of nitrogen (NOj,) are considered here to consist of NO and NO2 since N2O generally is treated separately, and in addition, N2O emissions are small compared with those of NO and NO2. The NO, emission index for methane-air flames then is defined here as... 

In the present analysis, the outer convective-diffusive zones flanking the reaction zone are treated in the Burke-Schumann limit with Lewis numbers unity. Lewis numbers different from unity are taken into account where reactions occur. These Lewis-number approximations are especially accurate for methane-air flames and would be appreciably poorer if hydrogen or higher hydrocarbons are the fuels. To achieve a formulation that is independent of the flame configuration, the mixture fraction is employed as the independent variable. The connection to physical coordinates is made through the so-called scalar dissipation rate. 

Peters, N., and F. A. Williams. 1987. The asymptotic structure of stoichiometric methane-air flames. Combustion Flame 68 185-207. 

Smooke, M. D. 1991. Reduced kinetic mechanisms and asymptotic approximations for methane-air flames. New York Springer-Verlag. 

Yang, B., and K. Seshadri. 1992. Asymptotic analysis of the structure of nonpremixed methane-air flames using reduced chemistry. Combustion Science Technology 88 115-32. 

Seshadri, K., and N. Ilincic. 1995. The asymptotic structure of nonpremixed methane-air flames with oxidizer leakage of order unity. Combustion Flame 101 69-80. 

Driscoll et al. [5] studied NO emission properties of turbulent partially pre-mrxed hydrogen-air and methane-air flames. The emission results for hydrogen-air flames showed that the emission index decreased monotonically with increasing levels of partial premixing because of the reduction in residence time caused by increasing jet velocity. The results for the methane-air flames were more complicated. 

Heberle, N. H., G. P. Smith, D. R. Crosley, J. B. Jeffries, J. A. Muss, and R. W. Dibble. 1995. Laser induced fluorescence measurements in atmospheric pressure partially premixed methane/air flames. Joint Technical Meeting of the Western States, Central States, Mexican Sections of the Combustion Institute and American Flame Research Committee Proceedings. 134-38. 

Nishioka, M., Y. Kondoh, and T. Takeno. 1996. Behavior of key reactions of NO formation in methane-air flames. 26th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 2139-45. 

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