Transient Plasma Ignition for Delay Reduction in Pulse Detonation Engines

Abstract

This presentation reviews testing and evaluation at four laboratories of transient plasma for pulse detonation engine (PDE) ignition, and presents data showing significant reductions in times required for detonation. The aerospace community has ongoing interests in the development of propulsion technologies based on pulse detonating engines (PDE), and work is underway to determine whether this is a feasible technology. The PDE provides impulse through fuel detonation, and potential advantages include efficient operation at both subsonic and supersonic speeds. In theory a PDE can efficiently operate from Mach 0 to more than Mach 4 [1,2]. In order to achieve almost continuous thrust firing rates of 100 Hz or more are needed. Critical to achieving high repetition rates are minimal delay to detonation times. In work supported by the Office of Naval Research and the Air Force Office of Scientific Research, transient plasma ignition (TPI) has consistently shown substantial reductions in ignition delay time for various fuels [3,4,5]. Experiments have been conducted at the University of Southern California and in collaboration with researchers at the Naval Postgraduate School, Wright Patterson Air Force Research Laboratory, Stanford University, the University of Cincinnati, and California Institute of Technology [6]. In these studies it was observed that TPI significantly reduces delay times in both static and flowing systems. Transient plasma ignition is attractive as an ignition source for PDEs because it produces reductions in ignition delay times, can reduce Deflagration to Detonation Transition (DDT) times, and has been shown to provide the capability to ignite under leaner conditions. This allows for high repetition rates, high altitude operation, and reduced NO, emissions [7,8]. The geometry of the discharge area is such that ignition is achieved with a high degree of spatial uniformity over a large volume relative to traditional spark ignition. The short timescale of the pulse ( < 100 ns) prevents formation of an arc, and a voluminous array of streamers is used for ignition. It is possible that energetic electrons in the highly non-equilibrated electron energy distribution of the streamers cause dissociation of hydrocarbon chain molecules, producing active radicals throughout the ignition volume [9]. A further advantage of TPI is that a smaller fraction of the electrical energy goes into thermal heating of the mixture. These effects allow for large numbers of active species to be generated throughout the volume.