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

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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