Methane premixed

Specchia S, Civera A, Saracco G. (2004). In situ combustion synthesis of perovskite catalysts for efficient and clean methane premixed metal burners. Chem Eng Sci. 59, 5091-8. 

Hardee et al. (1978) investigated pure methane and premixed methane-air fireball reactions. They used balloons filled either with 0.1 to 10 kg pure methane, or else with stoichiometric air-methane mixtures. The balloons were cut open just prior to ignition. Integrating heat-flux calorimeters, located either inside the balloons or at their edges, were used to measure the thermal output. 

Bench-Scale Reactor. The bench-scale reactor is 0.81 in. i.d. and 48 in. long. The nominal feed gas rate for this unit is 30 standard cubic feet per hour (scfh) the feed gas is supplied from premixed, high-pressure gas cylinders. Except for reaction temperature, the bench-scale unit is substantially manually operated and controlled. The catalysts used in these studies were standard commercial methanation catalysts ground to a 16-20 mesh size which is compatible with the small reactor diameter. 

Hall, Perchloric Acid Flames. I. Premixed Flames with Methane and Other Fuels , in 10th Symposium (International) on Combustion , The Combustion Inst (196S), 1365... 

Pedersen, T. and Brown, R. C., Simulation of electric field effects in premixed methane flame, Combust. Flame, 94, 433,1994. 

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.)... 

It is presumed that the global-quenching criteria of premixed flames can be characterized by turbulent shaining (effect of Ka), equivalence ratio (effect of 4>), and heat-loss effects. Based on these aforemenhoned data, it is obvious that the lean methane flames (Le < 1) are much more difficult to be quenched globally by turbulence than the rich methane flames (Le > 1). This may be explained by the premixed flame shucture proposed by Peters [13], for which the premixed flame consisted of a chemically inert preheat zone, a chemically reacting inner layer, and an oxidation layer. Rich methane flames have only the inert preheat layer and the inner layer without the oxidation layers, while the lean methane flames have all the three layers. Since the behavior of the inner layer is responsible for the fuel consumption that... 

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,... 

The creation of a steady flame hole was previously carried out by Fiou et al. [36]. In their experiments, a steady-annular premixed edge flame was formed by diluting the inner mixture below the flammability limit, for both methane/air and propane/air mixtures. They found that a stable flame hole was established when the outer mixture composition was near stoichiometry. Their focus, however, was on the premixed flame interaction, rather than on the edge-flame formation, extinction, or propagation. 

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. 

Sankaran, R. and Im, H.G., Dynamic flammability limits of methane-air premixed flames with mixture composition fluctuations, Proc. Combust. Inst., 29, 77, 2002. 

Methane-air Bunsen burner turbulent premixed flame. 

Instantaneous images obtained in a turbulent premixed V-shaped flame configuration, methane and air in stoichiometric proportions. (Reproduced from Kobayashi, H., Tamura, T., Maruta, K., Niioka, T, and Williams, F. A., Proc. Combust. Inst., 26,389,1996. With permission. Figure 2, p. 291, copyright Combustion Institute.)... 

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. 

Figure 2.10 provides a thermodynamic equilibrium molar fraction of the products of CPO of methane as a function of temperature. It is evident that at temperatures above 800°C, hydrogen and CO (in molar ratio of 2 1) are two major products of the reaction. The oxidant (oxygen or air) and the hydrocarbon feedstock (e.g., methane) are premixed in a mixer... 

Bilger, R.W. On reduced mechanisms for methane-air combustion in non-premixed flames, Combustion Flame, 80, 135-149, (1990). 

Unlike premixed flames, which have a very narrow reaction zone, diffusion flames have a wider region over which the composition changes and chemical reactions can take place. Obviously, these changes are principally due to some interdiffusion of reactants and products. Hottel and Hawthorne [5] were the first to make detailed measurements of species distributions in a concentric laminar H2-air diffusion flame. Fig. 6.5 shows the type of results they obtained for a radial distribution at a height corresponding to a cross-section of the overventilated flame depicted in Fig. 6.2. Smyth et al. [2] made very detailed and accurate measurements of temperature and species variation across a Wolfhard-Parker burner in which methane was the fuel. Their results are shown in Figs. 6.6 and 6.7. 

Many detailed reaction mechanisms are available from the Internet. GRI-Mech (www.me.berkeley.edu/gri-mech/) is an optimized detailed chemical reaction mechanism developed for describing methane and natural gas flames and ignition. The last release is GRI-Mech 3.0, which was preceded by versions 1.2 and 2.11. The conditions for which GRI-Mech was optimized are roughly 1000-2500K, lOTorr to lOatm, and equivalence ratios from 0.1 to 5 for premixed systems. 

Within the frame of the present first series of experiments it was almost always oxygen which was injected into supercritical water-methane mixtures. There were several reasons for this first choice. One of these was the desire, to study rich flames and their possible products first. Often the water to methane mole fraction ratio was 0.7 to 0.3. But mixtures down to a methane mole fraction of 0.1 were also used. It was possible, however, to inject oxygen and methane simultaneously into the supercritical water and produce a flame. Not possible was the production of true premixed flames. After a retraction of the thin inner nozzle capillary of the burner (see Fig. 1 b) the two gases could be mixed just below the reaction cell, but the flame reaction proceeded from the nozzle tip in the cell back towards this mixing point immediately. 

James, S., and F. A. Jaberi. 2000. Large-scale simulations of two-dimensional non-premixed methane jet flames. Combustion Flame 123 465-87. 

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... 

Bui-Pham, M., K. Seshadri, and F. A. Williams. 1992. The asymptotic structure of premixed methane-air flames with slow CO oxidation. Combustion Flame 89 343-62. 

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. 

Turns et al. [6] studied turbulent partially premixed flames burning methane, propane, and ethylene with air. The NO emission indices for methane and propane flames first increased and then decreased with increased levels of partial premixing. The NO emission indices for ethylene flames continuously increased at least in the limited range of partial premixing considered in the experiments. The results were qualitatively explained by the opposing effects of flame radiation and residence time on NO emissions. 

The geometry of the present opposed-flow burner is identical to the one designed by Puri and coworkers (see [18] for example). The burner consists of two opposing ducts with 20-millimeter diameter separated by 15 mm. The exhaust is extracted by a vacuum pump though a water-cooled annulus mounted around the bottom duct and a guard co-flow of nitrogen is issued from an annulus around the top duct. Experiments were performed with methane (99% purity) and premixed air introduced from the bottom duct and air admitted from the top duct. The flow rates were monitored using choked orifice meters. 

Gore, J.P., and N. J. Zhan. 1996. NO emission and major species concentrations in partially premixed laminar methane/air co-flow jet flames. Combustion Flame 105 414-27. 

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. 

Tanoff, M. A., M. D. Smooke, R. J. Osborne, T. M. Brown, and R. W. Pitz. 1996. The sensitive structure of partially premixed methane-air vs. air counterflow flames. 26th Symposium (International) on Combustion Proceedings. Pittsburgh, PA The Combustion Institute. 1121-28. 

Tseng, L. K., J.P. Gore, I.K. Puri, and T. Takeno. 1996. Acetylene and ethylene mole fractions in methane/air partially premixed flames. 26th Symposium (Inter-... 

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