Fractal Behavior of Turbulent Premixed Flames Propagating in Combustion Chambers and Turbulence Characteristics of Precombustion Mixture

点击翻译按钮获取中文摘要

The fractal behavior of turbulent premixed flames propagating in a constant volume chamber and in an engine cylinder were investigated with a laser tomography. Methane or propane-air mixture was used. Cross sectional shapes of turbulent flames were observed with a CCD camera and a high speed camera with an image-intensifier. The main results are as follows :(1) The fractal behavior is hardly recognized under the condition of week turbulence, and in the small flame immediately after the ignition. In accordance with flame development, the fractal behavior in flame surface becomes to be recognized, the inner cutoff value epsilon_i decreases and becomes a constant value, and the fractal dimension D_3 increases and becomes a constant value.(2) The outer cutoff value epsilon_<omicron> is nearly equal to the equivalent value of flame radius.(3) The value of epsilon_i/delta varies nearly proportionally with Ka^<-0.5>, where delta is a thickness of preheat zone in laminar flame and Ka is Karlovize number.(4) The ratio of mass burned rate of turbulent flame M_<bT> to that of laminar flame M_<bL> is expressed with an equation, M_<bT>/M_<bL>= [L(epsilon_<omicron>) / (2pir_f)] (epsilon_i/epsilon_<omicron>) ^<2-D_3>, where L (epsilon_<omicron>) is a length of fractal profile of flame. The heat release process of turbulent premixed combustion in a closed combustion chamber are able to simulated by using above equation.(5) In an engine cylinder, the multiple fractal structure of turbulent flame was found.