Studies of the Micro-Structure of Turbulent Flame in Premixed Mixtures

预混火焰中湍流火焰微观结构的研究湍流火焰的微观结构与内燃机的燃烧速度和火焰传播极限密切相关。为了更好地了解湍流火焰的微观结构，对内燃机燃烧过程进行控制并建立其仿真模型也是非常重要的。为了深入了解湍流火焰的微观结构，利用湍流燃烧模型对火焰传播的纹影图像进行了分析。该政权被分为三个阶段。这三个阶段分别是湍流强度较弱的褶皱层流火焰阶段、湍流强度强到足以使许多分布的未燃烧气体孤岛被火焰片包围的分布岛状火焰阶段和过渡阶段。燃烧实验在定容炸弹中进行，其中混合气的特性(层流火焰…较大厚度、层流燃烧速度和氧气浓度)和湍流强度相互独立地变化。得到的纹影图像表明，随着湍流强度的增加，火焰前沿的皱纹增加，光滑区域的尺度减小，皱纹增加的原因是沿燃烧区厚度方向存在的湍流火焰纹影图像的叠加。在解析讨论中，湍流燃烧区被认为是由褶皱层流火焰区和分布岛状火焰区混合而成的，其中每个反应速率由Damkohler数和每个特征反应时间确定。达科勒数是湍流混合的特征时间与化学反应的特征时间之比。这一燃烧流型模型能够解释从褶皱层流火焰阶段到高度分布火焰阶段的湍流火焰结构，这取决于达科勒数和湍流雷诺数。较少

Studies of the Micro-Structure of Turbulent Flame in Premixed MixturesThe micro-structure of turbulent flame has got a large attention in connection with the combustion rate and the flame propagation limit in internal combustion engines. It is important also to control the combustion in internal combustion engines and to make its simulation model by making clear the turbulent flame structure.To gain insight into the micro-structure of turbulent flame, an analysis of the schlieren-images of propagating flame has been made by a turbulent combustion regime model. The regime has been classified into three stages. They are the wrinkled laminar flame stage where the turbulence intensity is weak, the distributed-islands flame stage where the turbulence intensity is strong enough to make many distributed islands of unburned gas surrounded by a flame sheet and the transition stage.Combustion experiments were made in a constant volume bomb, where the characteristics of the mixture ( laminar flam … More e thickness, laminar burning velocity and oxygen concentration) and the turbulence intensity were varied independently with each other. The obtained schlieren-images showed that the wrinkling of the flame front increased and the scale of the smooth area decreased as the turbulence intensity increased.The increased wrinkling has been explained by a superimposition of the schlieren-images of turbulent flamelets existing along the combustion zone thickness. In the analytical discussion, the turbulent combustion zone has been considered to be mixed with the wrinkled laminar flame zone and the distributed-islands flame zone, where each reaction rate has been determined by a Damkohler number and each characteristic reaction time. The Damkohler number is the ratio of the characteristic time of turbulent mixing to that of chemical reaction. This combustion regime model has been shown to be able to explain the turbulent flame structure ranging from the wrinkled laminar flame stage to highly distributed flame stage, depending on both the Damkohler and the turbulent Reynolds numbers. Less