Thesis (M.S. in Astronatical Engineering) Naval Postgraduate School, December 2001. / Thesis Advisor(s): Brophy, Christopher M. ; Sinibaldi, Jose O. "December 2001." Includes bibliographical references (p. 97). Also available in print.

The Transient Inlet Concept (TIC) involves transient aerodynamics and wave interactions with the objective of producing turbulence, compression and flow in ducted engines at low subsonic speeds. This concept relies on the generation and control of multiple detonation waves issuing from different ?stages? along a simple ducted engine, and aims to eliminate the need for compressors at low speeds. Currently, the Zel?dovichvon Neumann-Doering (ZND) steady, one-dimensional detonation is the simplest method of generating the waves issuing from each stage of the TIC device. This thesis focuses on the primary calculation of a full thermochemistry through a ZND detonation from an initially unreacted supersonic state, through a discontinuous shock wave and a subsonic reaction zone, to the final, reacted, equilibrium state. Modeling of the ZND detonation is accomplished using Cantera, an open-source object-oriented code developed at Caltech. The code provides a robust framework for treating thermodynamics, chemical kinetics, and transport processes, as well as numerical solvers for various reacting flow problems. The present work examines the effects of chemical kinetics on the structure of ZND detonation, by using a detailed chemical kinetics mechanism that involves 53 species and 325 simultaneous reactions (Gas Research Institute 3.0). Using a direct integration of the system of inviscid ordinary differential equations for the ZND detonation, I obtain results for the combination of different fuels (hydrogen and methane) and oxidizers (oxygen and air). The detailed thermochemistry results of the calculations are critically examined for use in a future induced-detonation compression system.

Thesis (M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Christopher M. Brophy, Jose O. Sinibaldi. Includes bibliographical references (p. 75-76). Also available online.

This thesis reports on a detailed experimental investigation of near limit ethylene-air detonation phenomena in tubes. The different detonation regimes were determined as a function of ignition energy, composition and stability for a specific tube diameter. The dependence of single head spin detonations on the tube diameter was further investigated. This study has revealed that the different near limit regimes are governed by the acoustic coupling with the tube walls and can be influenced by the energy of the ignition source. The effective source energy and the distance over which this energy will support a detonation phenomenon have been quantified. / It has been shown that the characteristic detonation cell size of the mixture can be obtained by matching the cell length to the spin pitch of the mixture in which the single head spin phenomenon is first observed. In addition, a model for predicting the detonation cell sizes as a function of composition is presented. The detonability limit in a tube has been defined as the composition for onset of spin in this tube. The cell size correlation was effectively used in order to predict the critical tube diameters and minimum ignition energies for unconfined situations.

No description available.

Detonation diffraction has been, and remains, an active area of research. However, detonation diffraction into a confined volume, and specifically the transformation of a planar detonation into a cylindrical detonation, is an area which has received little attention. Experimental work needs to be conducted on detonation diffraction into a confined volume to better understand how the interaction of the diffracted shock wave with a confining wall impacts the detonation diffraction process. Therefore, a facility was constructed to study this problem, and experiments were conducted to determine under what conditions a planar detonation could be successfully transformed into a cylindrical detonation. Four different fuel-oxidizer mixtures, C₂H₂+ 2.5 O₂, C₂H₂+ 4 O₂, C₂H₄+ 3 O₂ and H₂+ 0.5 O₂, were tested in this study using a combination of pressure transducers and soot foil records as diagnostics. Three different regimes of successful transmission; spontaneous re-ignition, continuous reflected re-initiation, and discontinuous reflected re-initiation, were identified. The detonation cell size and the distance from the tube exit to the confining wall, or gap size, were determined to be the most important parameters in the transmission process and a linear correlation for determining whether or not transmission will be successful for a given set of initial conditions was developed for gap sizes between 10 and 35 mm. For gap sizes smaller than 10 mm or gap size larger than 35 mm the linear correlation does not apply. Finally, the results of this study are compared to results on detonation diffraction into a confined volume available in the literature and explanations for any disagreements are given. This study showed that when compared to transmission of a detonation into an unconfined volume, the transmission of a detonation into a confined volume, for the majority of gap sizes, is possible for a wider range of conditions. However, for extremely small gap sizes, when compared to transmission into an unconfined volume, the range of conditions for which successful transmission is possible into a confined volume is actually narrower.

The instability behaviour of detonation waves are studied using Fickett's model with a 2-step reaction model with separately controlled induction and reaction zones. This model acts as a simplified toy-model to the reactive Euler equations allowing for more clarity of the detonation phenomenon. We numerically simulate a 1D self-supported detonation and investigate the pulsating instability behaviour. We are able to clarify the governing mechanism behind the pulsations through a characteristic analysis describing the coupling that takes place between the amplification of the compressions waves and the alteration to the induction timing. We examine the acceleration phase of the pulsations and determine an analytical solution to describe the strength of the amplification. Fickett's model is as well shown to reproduce the same period doubling bifurcation with increasing sensitivity of the induction rate, and route to chaos as seen in the full reactive Euler equations.

The instability behaviour of detonation waves are studied using Fickett's model with a 2-step reaction model with separately controlled induction and reaction zones. This model acts as a simplified toy-model to the reactive Euler equations allowing for more clarity of the detonation phenomenon. We numerically simulate a 1D self-supported detonation and investigate the pulsating instability behaviour. We are able to clarify the governing mechanism behind the pulsations through a characteristic analysis describing the coupling that takes place between the amplification of the compressions waves and the alteration to the induction timing. We examine the acceleration phase of the pulsations and determine an analytical solution to describe the strength of the amplification. Fickett's model is as well shown to reproduce the same period doubling bifurcation with increasing sensitivity of the induction rate, and route to chaos as seen in the full reactive Euler equations.

No description available.

No description available.