Surface flame

The atmospheric transmissivity, t, greatly affects the radiation transmission by absorption and scattering by the separating atmosphere. Absorption may be as high as 20-40%. Pietersen and Huerta (1985) give a correlation that accounts for humidity (equation 9.1-31), where t = atmospheric transmissivity, = water partial pressure (Pascals), X = distance from flame surface to target (m). 

The introduction of obstacles results in some flame acceleration, especially for the more reactive fuels. This effect is especially strong if the flame surface is distorted by the presence of obstacles over its entire surface, such as were present in the experiments of Dorge et al. (1976) and Harrison and Eyre (1986, 1987). The more reactive the fuel, the more effect obstacles seem to have on flame acceleration (Harris and Wickens 1989). 

The volume-source method is not only useful in a spherical approach, but can also be used in more arbitrary geometries, where it is possible to express the volume source strength in a product of burning velocity and flame surface area ... 

This concept can be generalized for more arbitrarily shaped clouds, provided that a reasonable estimate can be made of combustion process development in terms of burning velocity and flame surface area. According to Strehlow (1981), a conservative estimate of source strength is made by... 

The flame-surface area dependent on time is approximated by a plane cross-section moving at burning speed through the stationary cloud. 

Radiation heat flux is strongly time dependent, because both the flame surface area and the distance between the flame and intercepting surfaces vary during the eourse of a flash fire. The path of this curve ean be approximated by calculating the radiation heat flux at a sufficient number of discrete points in time. 

Calculate the view factor using the equation given in Appendix A for a vertical plane surface emitter, or else read the view factor from Table A-2 of Appendix A for the appropriate X and fi. This results in F = 0.062 for each portion of the flame surface, and implies a total view factor of... 

In contrast to the lean propane flame, the burning intensity of the lean limit methane flame increases for the leading point. Preferential diffusion supplies the tip of this flame with an additional amoxmt of the deficient methane. Combustion of leaner mixture leads to some extension of the flammability limits. This is accompanied by reduced laminar burning velocity, increased flame surface area (compare surface of limit methane... 

A flame edge can be defined as the boundary between the burning and the nonbuming states along the tangential direction on a flame surface, which could exist in both premixed and nonpremixed flames [1,2]. The base of a nozzle-attached flame, either premixed or nonpremixed systems, is a typical example. 

Based on the flame-hole dynamics [59], dynamic evolutions of flame holes were simulated to yield the statistical chance to determine the reacting or quenched flame surface under the randomly fluctuating 2D strain-rate field. The flame-hole d5mamics have also been applied to turbulent flame stabilization by considering the realistic turbulence effects by introducing fluctuating 2D strain-rate field [22] and adopting the level-set method [60]. 

Considering the case of premixed flames, it is noted by Thomas and Williams [26] that sound radiation can be related to the rate of change of the flame surface area by assuming that the burning velocity is constant. Similarly, Ref. [35] and later Ref. [36] indicate that in the wrinkled flame regime, the rate of chemical conversion is directly linked to the flame surface area A(t). For a mixture of fresh reactants at a constant equivalence ratio, the pressure field is directly linked to the instantaneous flame surface ... 

Note <3>, equivalence ratio modulation frequency SPL, sound pressure level A, mean flame surface area fluctuation of flame area v, mean velocity at the burner outlet and v, imposed velocity... 

As mutual flame annihilation is believed to control and limit flame surface area in turbulent combustion, the previous results suggest that this mechanism could also be a source of intense noise radiation in turbulent combustors. 

Time traces OH light intensity I, flame surface area A, pressure fluctuahons p, and computed pressure fluctuations kdA/dt. Circles indicate extracted flame surface areas A in cm (S and A are used indifferently to designate the flame surface). Black circles marked a, b, c, d correspond to flame patterns presented in images from Figure 5.2.3. 

The steady states of such systems result from nonlinear hydrodynamic interactions with the gas flow field. For the convex flame, the flame surface area F can be determined from the relation fSl = b zv, where Sl is the laminar burning velocity, the cross-section area of the channel, and w is the propagation velocity at the leading point. 

Localized extinction of the flame surface can readily occur in the turbulent combustion devices, where wrinkled flames interact with turbulent eddies and gas... 

An individual isothermal surface can be traced with the help of laser tomography, also known as laser sheet imaging, where a laser sheet and oil droplets are combined to visualize the instantaneous flame surface in a plane. This technique is ideal when wrinkling of an isoline is of interest besides, typically it shows the area occupied by the combustion products if the instantaneous flame thickness is small, such as a black area in... 

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