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A hybrid DDT enhancement device comprising obstacles of orifice plates and vortex generators is investigated to achieve reliable and repeatable detonations in Pulse Detonation Engines. The vortex generator is capable of yielding homogenous mixing while detonation transition can be achieved by it. The experimental results of deflagration to detonation transition process by a series of designed obstacles are reported. All experiments were carried out using a valveless PDE operated for multiple cycles using stoichiometric ethylene/air mixtures. The results show that initiation of DDT starting within vortex generator can enhance DDT process and achieve a strong overdriven detonation. In addition, during the transition stage, the onset of detonation can occur inside the vortex generator; while it generally takes place after the obstacles terminated. It is realized that effectiveness of the DDT enhancement device depends on the operation frequency. A hybrid obstacle of 0.4m orifice plates connecting 0.5m vortex generator can achieve reliable and repeatable transition within 15 L/D DDT run-up distance. Nomenclature CW= combustion wave L/D = length/diameter L1-L10 = obstacle combinations PW = pressure wave TOF = time of flight V = velocity

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