Diffusion flames definition

The emission index in general is defined as the mass of pollutant emitted per unit mass of fuel consumed. In quasi-steady diffusion flames, this is the ratio of the mass flux of pollutant out of the flame to the mass rate of consumption of fuel per unit flame area. Depending on the application, it may be more desirable to consider only the flux of pollutant to the air or the sum of the pollutant flux to both air and fuel. The latter definition is selected here, and a pollutant balance for the flame then enables the emission index to be expressed as the ratio of the mass rate of production of pollutant per unit area to the mass rate of consumption of fuel per unit area. In terms of the mass rate of production of species i per unit volume cDj, the mixture fraction, and the magnitude of its gradient VZ, the mass rate of production of species i per unit area is... 

Even within our restricted definition, so many diffusion-flame problems exist that we do not have enough space to consider them all. Therefore, we shall merely illustrate the analytical procedure by means of three examples (Sections 3.1-3.3). The problem of droplet burning (Section... 

Distributions like those in Figure 10.4, for example, indicate that Yp or T differs from Yp(Z) or T(Z), respectively. If mixing were complete in the sense that all probability-density functions were delta functions and fluctuations vanished, then differences like T — T Z) would be zero. That this situation is not achieved in turbulent diffusion flames has been described qualitatively by the term unmixedness [7]. Although different quantitative definitions of unmixedness have been employed by different authors, in one way or another they all are measures of quantities such as Yp — Yp(Z) or T — T(Z). The unmixedness is readily calculable from P(Z), given any specific definition (see Bilger s contribution to [27]). 

CA 42, 5229(1948)(Theory of propagation of flame. States conditions in an expl chem reaction necesssry for propagation of the flame at a const rate. Calcs this rate for a definite relationship between diffusion and heat conductance. Evaluates the effect of chain reactions on the propagation of the flame) 4) B. Karlovitz, JChemPhys 19, 541-46(1951) Sc CA 45, 9341 (1951)(Theory of turbulent flames) 5) G. Klein, Phil-TransRoySocLondon 249, 389—415 (1957)... 

Colwell, Wachi, and Greene41 examined the C2F4-Oa flame. Both diffusion and premixed flames were investigated. Flame temperatures were between 1900 and 2300°K. The products in the effluent gas of premixed flames were C02, CO, and CF4. From the emission at 2400-3200 A, it was found that CF2 was a principal species in the flame. Less definite spectroscopic evidence was also found for CF. The bright blue continuum was probably due to the reaction... 

The flame is not, however, a discontinuity. There are definite gradients of temperature and composition because of conduction of heat and diffusion of reaction products into the fresh gas. The temperature gradients have been studied by three techniques direct measurement with very fine thermocouples (24, 25, 43) refraction of a narrow slit of light (11, 16) and tracing the path of a stroboscopically lighted dust particle and computing temperature from its direction and velocity (l, 27). 

The diffusion flux is proportional to Si grad p, in order to bring the resulting expression in line with the ordinary definition of the diffusion coefficient D relating to the isothermic case, we write for a planar flame... 

Nin, Y.-S., Vervisch, L., Tao, P.D. An optimization-based approach to detailed chemistry tabnlatimi antomated progress variable definition. Combust. Flame 160, 776-785 (2013) Octme, R., Astaiita, G. Lumping nonlinear kinetics in porous catalysts diffusion-reaction lumping strategy. AIChE J. 39. 288-293 (1993)... 

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