Internal structure of a turbulent premixed flame using Rayleigh scattering

The flame-turbulence interaction in a premixed 0.75-equivalence-ratio rod-stabilized propane-air flame was investigated using an instantaneous Rayleigh scattering method. The experimental technique permitted the structure of the flame to be evaluated independently of the flame-front oscillations, thereby providing a means of estimating the effect of flame movement on the measured statistical turbulence characteristics of the flame.The measurements show that the thickness of the instantaneous flame is essentially constant with downstream distance and is of the same order of magnitude as the laminar flame thickness. Flame-front movements are found to be largely responsible for the high values of density fluctuation intensities in the time-averaged flame. The nature of the instantaneous reaction profile and the spatial structure of the flame change with increased distance from the flameholder. Comparison of the experimental density fluctuations with those predicted by the Bray-Moss-Libby model indicates that flame breakup influences the nature of the assumed probability distribution functions in theoretical models.