STABILIZING MECHANISM OF DIFFUSION FLAME FORMED IN AN AXISYMMETRIC IMPINGING JET

点击翻译按钮获取中文摘要

Characteristics of edge flames that dominate the stabilizing mechanisms of diffusion flames have been studied experimentally by using the novel burner system that utilized an axisymmetric impinging jet. The burner consisted of a round nozzle that issued air, and porous disk that was embedded in the impinging plate for fuel ejection. Then, by closing a part of the porous plate with a solid disk, the edge flame could be formed as a hole in the counter diffusion flame. When the solid disk diameter di was smaller than the nozzle diameter D, the edge flame was established in the stagnation region of the impinging jet. For di>D, the edge flame was established in the axisymmetric wall jet. The each conclusion for stagnation flow and wall jet is as follows.1. For di<D, the 4e flame shows qualitatively the same blowoff character as a pure diffusion flame, that is, the edge flame has the critical stagnation velocity gradient beyond which the flame can never be stabilized. It means that the blowoff of the diffusion flame with a hole in the stagnation flow is due to the chemical limitation on the reaction rate in the edge flame zone. Moreover the critical value of the blowoff decreases as the hole diameter is increased.2. For di>D, the edge flame turns into a triple flame that is edge flame with premixed flame, and finally triple flame blows out with increasing the air flow velocity. In the transition process, the amount of heat release in the edge flame zone gains. Moreover the determinant factor for flame position changes from the thermal interaction between the edge flame and the solid wall to the fluid dynamical balance between the burning velocity of triple flame and the flammable mixture velocity in that process.