Elucidation of Combustion Induced Vortex Breakdown Phenomena

利用PIV系统和带有像增强器的高速摄像机，对燃烧诱导的涡流破裂现象进行了实验研究。以可燃混合物的涡环为研究对象，分别在露天和密闭容器中进行了实验研究。在密闭容器中研究了初始压力高达0.3 Mpa的情况。在露天实验中，已经证实，随着涡环最大切向速度的增加，火焰直径减小，当火焰直径小于涡环核心直径时，通常与最大切向速度相同的火焰速度变得低于最大切向速度。在封闭的容器中，火焰成功地沿着涡核传播，压力在比没有涡环的情况下更早达到最大值的时间更早到达。进一步证明了在压力升高的情况下，火焰仍然可以在强烈作用于燃气的浮力的作用下沿涡旋轴传播，燃烧时间被一个气动因素，即最大切向速度所缩短和控制。这些结果表明，燃烧诱导的涡流破裂现象有可能提高火花点燃式内燃机的输出功率，也可以通过让火焰沿涡核平稳传播来抑制爆震的发生。

Using a PIV system and a high-speed video camera with an image intensifier, combustion induced vortex breakdown phenomena have been experimentally investigated. Vortex rings of combustible mixtures were used for this study, and the experiments were conducted in an open air and also in closed vessels. The initial pressures up to 0.3 MPa were investigated in the closed vessel. In the open air experiments, it has been confirmed that with increasing the maximum tangential velocity of the vortex ring, the flame diameter is decreased, and the flame speed, which is usually the same as the maximum tangential velocity, becomes lower than the maximum tangential velocity if the flame diameter becomes less than the core diameter of the vortex ring. In a closed vessel, the flame successfully travels along the vortex core, and the pressure reaches its maximum at a time more earlier than the time at which it reaches without a vortex ring. It is further demonstrated that under elevated pressures, the flame can still propagate along the vortex axis against buoyancy force, which strongly acts on the burned gas, and it is turned out that the combustion time is reduced and controlled by an aerodynamic factor, i.e., the maximum tangential velocity. These results suggests the potential of the combustion induced vortex breakdown phenomena for increasing output of spark-ignited combustion engines, and also for suppressing the occurrence of knocking by letting the flame smoothly propagate along the vortex core