Amplification of turbulence level by a flame and turbulent flame velocity

Abstract

In turbulent combustion, the existence of turbulence increnses the flame velocity markedly, while the flame augments the intensity of turbulence. A consideration of this interaction between a flame and the aerodynamics (turbulence) has led to a set of equations from which turbulent flame velocities can be calculated with reasonable accuracy over a wide range of conditions. They consist of the Karlovitz's equation on turbulent flame velocity and an equation expressing the amplifying effect of a flame on the turbulence level, and they were found to fit the various types of flame fairly well from confined turbulent flames to open burner flames like Bunsen or V -shaped flames, regardless of the burner size or the fuel type. The results are: (1) the extent of turbulence amplification depends both on the initial intensity of turbulence and on the difference between the kinetic energies of the gas before and behind the flame front, (2) viscous attenuation of turbulence level because of the high viscosity of the burning gas cannot be ignored, (3) the size of the combustor or burner as well as the scale of turbulence is an important factor affecting the amplifying effect of the flame on turbulence level, and (4) when the burner size or the turbulence scale increases, the extent of turbulence amplification also increases.