Karlovitz number

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. 

Keywords Borghi diagram Combustion Chemical reactions Chemical kinetics Damkohler number Flamelets Ignition Karlovitz number Mixing-controlled... 

The classification of flames depends on the mixture characteristics of the fuel and oxidizer, and on the interaction between the flow properties and the chemistry. This classification is done by means of dimensionless quantities, namely, the mrbulent Reynolds number, the turbulent Damkohler number, and the turbulent Karlovitz number, respectively defined by... 

Here diyldt is the flame velocity with respect to the burned gases and it is called a visible velocity 8. The upper index 0 is introduced for a stretch-free flat flame velocity Si in relation to the burned gases. The non-dimensional stretch, called the Karlovitz number, is found from the ratio ... 

Figure 1.1 demonstrates the flame velocity, change in H2 + air mixtures in relation to the Karlovitz number [6]. 

Fig. 1.1 The flame velocity change versus the Karlovitz number in H2 + air mixtures at room temperature and 0.1 MPa pressure...

Karlovitz number (Ka) Denotes the ratio of particle velocity at which they passthrough a flame to the time specified by the flame stretch. 

Fuel mass in a mixture Karlovitz stretch-factor Stretch factor for flame quenching Karlovitz number... 

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