Studies of detonation transition in a gradual area expansion for multi-cycle PDE applications

Abstract

Experimental studies using ethylene/nitrogen/oxygen mixtures were conducted of the transition of a detonation from a pre-detonator to a tube of larger cross sectional area in which a significant area change occurs. The purpose of the work was to further understanding of the processes that allow establishing a detonation in the thrust tube of a hydrocarbon-fueled pulse detonation engine, using a pre-detonator operating only with air under dynamic fill conditions. Two sets of experiments were performed to explore specifically the use of overdriven detonation waves to initiate a thrust tube detonation using compact pre-detonators. Two important results were clear from these studies. The region containing obstacles in the pre-detonator must only be long enough to accelerate the deflagration wave up to the Chapman–Jouguet deflagration velocity and should terminate at this point. In addition, the distance between the last obstacle and the entrance of the transition section should be chosen so that an overdriven detonation wave enters the transition section. Although some intermittency in successful detonation transitioning was noticed for the shortest pre-detonator studied, the results clearly show that efficiently generating an overdriven detonation wave in the pre-detonator is a key parameter for obtaining a thrust tube detonation transition.