No description available.

No description available.

Thesis (M.S. in Engineering Science (Mechanical))--Naval Postgraduate School, December 2003. / Thesis advisor(s): Chris M. Brophy, Garth V. Hobson. Includes bibliographical references (p. 103). Also available online.

The results of five experimental investigations on the initiation, propagation and transmission of detonation have shown that the wave behavior depends on the relative rates of gasdynamic expansion and chemical energy release occurring within the cellular detonation front. The former rate is controlled by the "boundary conditions" defined by the physical system, while the latter rate depends on the chemical and physical properties of the combustible mixture. The fractional increase (xi) in the area of the post-shock "stream tube", evaluated over a chemical kinetic distance equal to the cell length, has been identified as a parameter which satisfactorily characterizes the competition between these two rate processes. For (xi) less than about 20%, the chemical processes survive the gasdynamic expansion and self-sustained propagation is possible. However, under these "supercritical" conditions, the wave propagates with a velocity deficit which appears to be a universal and theoretically predictable function of (xi). / For (xi) greater than 20%, the shock/reaction zone coupling breaks down, resulting in failure of the wave. The "critical" conditions for the propagation of detonation waves subjects to a wide range of expansion inducing mechanisms, including viscous boundary layers, compressible boundary gases and yielding walls, are all found to be consistent with the 20% criterion. However, the criterion becomes inapplicable as the cell size approaches the characteristic transverse dimension of the geometry. / In the case of direct initiation or transmission of detonation from one geometry to another, the critical conditions are shown to be linked to the requirement for the diverging wave to exceed some minimum radius of curvature. Such radius is geometry dependent and satisfies the stream tube criterion. The role of the "initial conditions" in this type of problem is to guarantee survival of the wave until it achieves the minimum radius for which shock/reaction zone coupling, and hence self-substance, are possible.

The phenomenon of photochemical initiation of gaseous detonation waves has been experimentally and theoretically investigated. In the experiments, the flash photolysis technique has been employed and the initiation phenomenon has been directly observed through schlieren photography, while in the theoretical phase, the non-steady reacting flow-field of a photochemically ignited gas mixture has been numerically analyzed. The results conclusively show that the direct detonation initiation can be generated by an intense ultra-violet radiation, and it is shown that the initiation mechanism is mainly attributed to the rapid shock wave amplification occurring in a non-uniformly photo-dissociating gas mixture. It was found that the shock wave amplification is due to the coherent energy release from the non-uniformly reacting gas mixture to the shock wave and that the induction time gradient field generated by the flash photolysis plays an important role in the shock amplification process. / Further insight into the fundamental mechanisms of shock wave amplification has been obtained by considering a relatively simple theoretical model. This model illustrates the important role of the induction time gradient field in the shock wave amplification. Finally the concept of shock wave amplification in an induction time gradient field has been further extended to include the problem of transition to detonation in a non-uniformly preheated mixture.

Thesis (Ph. D.)--University of Washington, 1993. / Vita. Includes bibliographical references (leaves [97]-101).

No description available.

Elimination or reduction of auxiliary oxygen use in Pulse Detonation Engines (PDEs) is necessary if the technology is to compete with existing Ramjet systems. This thesis investigated a Transient Plasma Ignition (TPI) system and found that the technology can at least reduce and may be able to completely remove the auxiliary oxygen requirement of current PDE systems. TPI was tested and compared with a traditional capacitive discharge spark plug system in a dynamic flow, ethylene/air mixture combustor. Ignition delay time, Deflagration-to-Detonation transition (DDT) distance and time, detonation wave speed and fire success rate performance were analyzed for various mass flow rates and stoichiometric ratios. A transient plasma dualelectrode concept was also employed and analyzed. Results show that TPI is more effective and reliable than the spark plug ignition with considerable improvements to DDT performance. The TPI dual-electrode concept was proven to be the most effective configuration with average reductions in DDT distance and time of 17% and 41% respectively when compared to the capacitive discharge spark plug system configuration.

Thesis (Ph. D.)--University of Washington, 1990. / Vita. Includes bibliographical references (leaves [100]-105).

Approved for public release, distribution is unlimited / Operational characteristics of a valveless pulse detonation engine system were characterized by experimental measurements of thrust, fuel flow, and internal gas dynamics. The multi-cycle detonation experiments were performed on an axis-symmetric engine geometry operating on an ethylene/air mixtures. The detonation diffraction process from a small 'initiator' combustor to a larger diameter main combustor in a continuous airflow configuration was evaluated during multi-cycle operation of a pulse detonation engine and was found to be very successful at initiating combustion of the secondary fuel/air mixture at high frequencies. The configuration was used to demonstrate the benefit of generating an overdriven detonation condition near the diffraction plane for enhanced transmission of the larger combustor. Results have shown that the addition of optical sensors, such as tunable diode lasers, to provide fuel profile data are invaluable for providing high fidelity performance results. The performance results demonstrated the ability of the valveless pulse detonation engine to run at efficiencies similar to valved pulse detonation engine geometries and may be a low cost alternative to conventional air-breathing propulsion systems. / Funded By: N00014OWR20226. / Lieutenant, United States Navy