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

用激光层析成像技术研究了湍流预混火焰在定容腔室和发动机气缸内的分形行为。使用甲烷或丙烷-空气混合物。用CCD相机和带图像增强器的高速相机观察了湍流火焰的截面形状。主要结果如下：(1)在周湍流条件下，在点火后的小火焰中，分形行为几乎不被识别。随着火焰的发展，火焰表面的分形行为逐渐被识别，内截止值epsilon_i减小并趋于恒定，分形维数D_3增大并趋于恒定。(2)外截止值epsilon_< 0微米>几乎等于火焰半径的等效值。(3) epsilon_i/delta值与Ka^<-0.5>成正比，其中delta为层流火焰预热区厚度，Ka为Karlovize数。(4)湍流火焰M_<bT>与层流火焰M_<bL>的质量燃烧速率之比用方程表示，M_<bT>/M_<bL>= [L(epsilon_<omicron>) / (2pir_f)] (epsilon_i/epsilon_<omicron>) ^<2-D_3>，其中L（epsilon_<omicron>）为火焰分形轮廓的长度。利用上述方程可以模拟封闭燃烧室内紊流预混燃烧的放热过程。(5)在某发动机气缸内，发现了湍流火焰的多重分形结构。

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.