Karlovitz

Karlovitz, B. 1951. Investigation of turbulent flames. /. Chem. Phys. 19 541-547. 

Reference stretch-affected flame speeds as a function of Karlovitz number for various (a) n-heptane/air and (b) iso-octane/air flames, showing how the reference stretch-affected flame speed is extrapolated to zero stretch to obtain the laminar flame speed. The unburned mixture temperature T is 360 K. Solid lines represent linear extrapolation, while dotted lines denote nonlinear extrapolation... 

The concept of turbulent flame stretch was introduced by Karlovitz long ago in [15]. The turbulent Karlovitz number (Ka) can be defined as the ratio of a turbulent strain rate (s) to a characteristic reaction rate (to), which has been commonly used as a key nondimensional parameter to describe the flame propagation rates and flame quenching by turbulence. For turbulence s >/ />, where the dissipation rate e and u, L and v... 

Variations of the maximum Karlovitz number and laminar burning velocities with the equivalence ratio, showing the accessible domain when the maximum/= 170Hz is operated, (a) CH4/air mixtures (b) CH4 diluted with 20-60% N2 (c) CH4 diluted with 20-60% CO2 and (d) combined plots of these maximum-Ka = 170 Hz) lines from (a-c) for comparison. (From Yang, S.I. and Shy, S.S., Proc. Combust. Inst, 29,1841, 2002. 

In any circumstances, it can be expected that and (5x are algebraic functions of turbulence length scale and kinetic energy, as well as chemical and molecular quantities of the mixture. Of course, it is expedient to determine these in terms of relevant dimensionless quantities. The simplest possible formula, in the case of very fast chemistry, i.e., large Damkohler number Da = (Sl li)/ SiU ) and large Reynolds Re = ( Ij)/ (<5l Sl) and Peclet numbers, i.e., small Karlovitz number Ka = sjRej/Da will be Sj/Sl =f(u / Sl), but other ratios are also quite likely to play a role in the general case. 

B. Karlovitz, J.W Denniston, D.IT. Knapschaefer, and RE. Wells 1953, Studies on turbulent flames, Proc. Combust. Inst. 4 613-620. 

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)... 

Two other points about the present state of experimental work should be mentioned. One is that measurements of turbulence scale and intensity are necessarily made in the cold flow the flame may upset the flow field, even generating added turbulence as suggested by Karlovitz (42). The second point is that the flame can never be thought of as burning in a region with constant scale and intensity throughout, not only because of the ordinary decay of turbulent fluctuations, but also because there may be (as in Bunsen... 

Karlovitz, B., Selected Combustion Problems—Fundamentals and Aeronautical... 

Karlovitz B., et al. (1953). A. Flame propagation across velocity gradients. B. Turbulence measurement in flames. Fourth Symposium (International) on Combustion, Williams and Wilkins, Baltimore, p. 613. 

B. Karlovitz, "Combustion Waves in Turbulent Gases, in Combustion Processes, vol. II of High Speed Aerodynamics and Jet Propulsion, B. Lewis, R. N. Pease, and H. S. Taylor, eds., Princeton Princeton University Press, 1956, 312-364. 

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