V-shaped flames

Instantaneous flame images. Static. Stationary shapes, a-e Images taken at equi-spaced instants during a cycle of excitation. CF, conical flame MF, "M"-shaped flame VF, "V"-shaped flame CSCF, collection of small conical flames. 

V"-shaped flames submitted to convective waves (Figure 5.2.12—CF, MF, and VF). It should be noted that these results obtained for a microphone located in the near-field of the flame still obey the classical relation derived for far-field conditions. 

The so-called turbulent "V-shaped flames" are the flames anchored behind a rod or a catalytic wire in a flow where turbulence is generated by an upstream grid. Trinite et al. [7,40] and Driscoll and Faeth [41] have studied such flames. Instantaneous images of rare beauty have been obtained from which it is very clearly seen that the turbulent flame brush width is continuously increasing downstream of the stabilizing rod, see Figure 7.1.13. 

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.)... 

The agreement between measurements and predictions in Fig. 3.10 was again very good. Slight asymmetries in the flames shapes were due to small differences between the upper and lower wall temperatures, an effect fully accounted for in the model via the boimdary conditions in Eq. (3.31). A notable difference between the fuel-rich and fuel-lean flames is that the former established a connected V-shaped flame, while the latter comprised two separate flame branches near both walls (compare Figs. 3.8 and 3.9 with Fig. 3.10). Flame shapes were dictated by the Lewis number of the deficient reactant Lea < 1 in fuel-lean, and Leo2 > 1 in fuel-rich combustion). Implications of this behavior will be discussed in Section 7. 

P. Goix, P. Paranthoen, and M. Trinite 1990, A tomographic study of measurements in a V-shaped H2-air flame and a Lagrangian interpretation of the turbulent flame brush evolution. Combust. Flame 81 229-241. 

Wagner, J., Kurek, H., Chudnovsky, Y., Malikov, G., and Lisienko, V. "Direct Flame Impingement for the Efficient and Rapid Heating of Ferrous and Nonferrous Shapes."... 

Sulfur bums in air with a bright blue flame to give sulfur dioxide (S02>, a colorless gas with a pungent odor, which condenses to a liquid at 10°C and 1 atm. Sulfur dioxide is a V-shaped molecule, which is a very effective antibacterial agent often used to preserve stored fruit. 

The "M"-flame case shows a different kind of flame interaction illustrated in Figure 5.2.4 (MF). The "M"-shape comprises two reactive sheets separated by fresh reactants. This gives rise to flame-flame interactions between neighboring branches of the "M"-shape [41]. The case presented corresponds to an equivalence ratio O = 1.13, a mixture flow velocity v/v = 1.13 m/s, a modulation level fixed to v = 0.50m/s, and a modulation frequency/= 150 Hz. The description of the flame motion over a cycle of excitation starts as in the flame-plate interaction. A velocity perturbation is generated at... 

Rotating camera images of a CO/O2 flame undergoing the inversion from the hemispherical cap flame to an inverted shape that is now considered a tulip or perhaps more accurately a "two-lip" flame. The flame propagates in a 20.3 cm long closed cylindrical tube of 2.5 cm diameter. (Adapted from EUis, O.C. de C. and Wheeler, R.V., /. Chem. Soc., 2,3215,1928.)... 

All the assumptions of Section 1.3 underlie the formulation. Assumption 1 deserves special mention because buoyancy forces on the hotter, less dense gas in the region of the flame often distort the shape of the flame sheet. A Froude number, Fr = v l(ag) (where g denotes the acceleration of gravity), measures the relative importance of inertial and buoyant forces. If Fr is sufficiently small (for example, Fr Ap/p, where Ap is a representative density difference and p a mean density), then the flame heights are controlled by buoyancy. Correlations of measured flame heights in the form hja Fr , where h is the flame height and < n are available for b 00 under buoyancy-influenced conditions with negligible viscous forces [9]-[ll]. The result of equation (26), namely, hja vajD = Pe, is a Peclet-number (Pe) dependence that cannot be correlated with Fr and that... 

The report of the inquiry [111] criticised the design and fabrication of the alterations made to the original pontoon. The actual cause of the accident was the failure of some tie bars in the detail around the jacking points. The failure was due to brittle fracture which initiated from severe notches such as a small radius curve at the fillet between the spade end and the shank of the tie bar. Weld defects and fatigue cracks were also present in tie bars subsequently recovered from the sea bed. The tie bars had been flame cut to shape and had weld repairs visible to the eye. There had been no post welding heat treatment of the steel. The steel complied with the original specification but tests showed low Charpy V notch impact values. Photo elastic tests indicated a stress concentration factor of 7 at the fillet between the spade end and the shank. The fracture was initiated in the opinion of the inquiry tribunal by the low ambient temperature of around 3°C. 

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