Predetonator to Thrust Tube Detonation Transition Studies for Multi-Cycle PDE Applications

Abstract

A series of studies of the phenomena involved in the transition of a detonation from a pre-detonator to a tube of larger cross sectional area, for a geometry in which a significant area change occurs, was investigated. The application of the work is to further the understanding of the conditions that allow establishing a detonation in the thrust tube of a hydrocarbon fueled Pulse Detonation Engine (PDE), using a compact pre-detonator operating with air under dynamic fill conditions. Three sets of experiments were performed to explore the use of overdriven detonation waves to initiate a main chamber detonation and to establish design criteria for compact pre-detonators. The proposed design strategy is as follows. The region containing the pre-detonator obstacles should be long enough to accelerate the deflagration wave up to the C-J deflagration velocity and should terminate at this point. In addition, the distance between the last obstacle and the entrance to the transition section should be chosen so that an overdriven detonation wave enters the transition section. The results obtained support the proposed design strategy, although some intermittency in successful detonation transitioning was noticed when a short pre-detonator was employed. The results also show that generating an overdriven detonation wave in the pre-detonator is a key parameter for obtaining a thrust tube detonation.