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Published January 2007 | Published
Journal Article Open

Toroidal Imploding Detonation Wave Initiator for Pulse Detonation Engines


Imploding toroidal detonation waves were used to initiate detonations in propane–air and ethylene–air mixtures inside of a tube. The imploding wave was generated by an initiator consisting of an array of channels filled with acetylene–oxygen gas and ignited with a single spark. The initiator was designed as a low-drag initiator tube for use with pulse detonation engines. To detonate hydrocarbon–air mixtures, the initiator was overfilled so that some acetylene oxygen spilled into the tube. The overfill amount required to detonate propane air was less than 2% of the volume of the 1-m-long, 76-mm-diam tube. The energy necessary to create an implosion strong enough to detonate propane–air mixtures was estimated to be 13% more than that used by a typical initiator tube, although the initiator was also estimated to use less oxygen. Images and pressure traces show a regular, repeatable imploding wave that generates focal pressures in excess of 6 times the Chapman–Jouguet pressure.Atheoretical analysis of the imploding toroidal wave performed using Whitham's method was found to agree well with experimental data and showed that, unlike imploding cylindrical and spherical geometries, imploding toroids initially experience a period of diffraction before wave focusing occurs. A nonreacting numerical simulation was used to assist in the interpretation of the experimental data.

Additional Information

© 2006 by California Institute of Technology. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Received 17 April 2006; revision received 20 October 2006; accepted for publication 20 October 2006. This work was sponsored by the Office of Naval Research Grants "Pulse Detonation Engines: Initiation, Propagation and Performance" and "Multidisciplinary Study of Pulse Detonation Engine," by General Electric, and by the Department of Defense and Army Research Office through a National Defense Science and Engineering Graduate Fellowship. The authors are grateful for the assistance of M. Grunthaner, J. Haggerty, B. St. John, and F. Pintgen for their assistance with the design and testing of the toroidal initiator and to H. Hornung for his assistance with the numerical simulation. The authors are also grateful to N. Nebeker and P. Nagel at Cordin Scientific Imaging for use of their Model 220 CCD camera.

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