Elucidation of Combustion Induced Vortex Breakdown Phenomena

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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