Proceedings of the 9th International Symposium on Experimental and Paper No. 6C-2 Computational Aerothermodynamics of Internal Flows (ISAIF9) 8~11 September 2009, Gyeongju, Korea www.isaif9.org Fig. 1 Erosion of a high-energy arc ignition plug. Practical Methods for Reducing the Deflagration-to-Detonation Transition Length for Pulse Detonation Engines Philip K. Panicker, Frank K. Lu and Donald R. Wilson Aerodynamics Research Center, Mechanical and Aerospace Engineering Department, University of Texas at Arlington, Arlington, TX 76019, USA Abstract Techniques for reducing the deflagration-to-detonation transition (DDT) length are reviewed in this paper. In contrast to previous results from single-shot detonation tube experiments, the present focus is an assessment of the effectiveness and survivability of various DDT devices in an actual engine operating environment. Specific DDT techniques that were considered include Shchelkin spirals, groves, converging-diverging nozzles and orifice plates Keywords: Pulse Detonation Engines, Deflagration-to-Detonation Transition Introduction The impracticality of direct initiation of detonations for pulse detonation engines (PDE), has led to proposals for a combination of techniques to reduce the DDT length to achieve high frequency and reliable detonations. Although the literature on DDT is extensive [1-11] , many of the results are based on single- shot detonation tube experiments. The hostile environment in sustained operation of PDEs poses challenges to the development of a successful DDT technique. Detonations can be directly initiated by using high-energy electric arc ignition; however, severe erosion of the electrodes occurs with sustained operation at high frequency (Fig. 1). A hybrid ignition system using a small pre-detonator, containing an easily detonable primary fuel-oxidizer mixture, can be used to generate a detonation front that has sufficient energy to initiate and sustain detonation in the PDE chamber filled with a less detonable fuel-oxidizer mixture. The complexity in regulating and using two fuel-oxidizer mixtures is significant and this technique may not be suitable for all PDE applications. An alternate approach is to initiate deflagrations via a low-energy ignition that evolve into detonation wave fronts via various DDT enhancing devices. Numerous investigators have shown that these devices can reduce the DDT distance and time significantly. Several non- conventional DDT-enhancing configurations, such as convergent-divergent (C-D) nozzles with different convergent-divergent angles, parallel grooves and helical grooves, were investigated in [9-10] and benchmarked against the well-established Shchelkin spiral. The effectiveness of these devices was characterized in terms of the detonation pressure profiles and time-of-flight (TOF) velocities. Further, durability for sustained operation in a PDE was assessed. Experimental setup Detonation tube The detonation tube used was fabricated from ASME Schedule 80 stainless steel pipe with an inner diameter of 24.3 mm and an outer diameter of 33.4 mm. The tube is made of four detachable sections which have standard high-pressure flanges fully welded to their