Fractal Analysis of Turbulent Premixed Flames in a Closed Combustion Chamber

The cross-sectional images of turbulent premixed flames of methane-air mixture in a closed combustion chamber were investigated using laser tomography method. The swirling flow was generated in the combustion chamber, and the mean velocity and turbulence intensity were measured with LDA. The fractal analysis was done to determine the degree of wrinkling the flame front. Fractal dimension, inner cutoff scale and outer cutoff scale were obtained by ensemble averaging of data from several images. Consequently, the fractal dimension increases, and the inner cutoff scale decreases a little and approches a constant value during the flame propagation. The fractal dimension increases with increasing the ratio of turbulence intensity to laminar burning velocity under the condition of the same pressure. The inner cutoff scale is expressed as the function of Karlovitz number, and the outer cutoff scale is equal to the equivalent flame radius.