A total number of 849 tests were conducted to investigate the transient response of liquid injectors with various geometries including different taper angles, injection angles and orifice lengths. High-speed videos were analyzed to characterize refill times and back-flow distances of nine different injector geometries subjected to a ethylene-oxygen detonation wave. Water was used as the working fluid and experiments were performed at two different vessel pressure settings (60 and 100 psia). Although a minimal difference was found between plain and angled injectors due to having constant orifice diameter geometry, introduction of taper angle resulted in more agile injectors with less sensitivity to ambient and feed pressures. Several attempts were made to normalize refill times and obtain a general trend for transient response of liquid injectors.

The first step in many mining operations is blasting, and the purpose of blasting is to fragment the rock mass in the most efficient way for that mine site and the material end use. Over time, new developments to any industry occur, and design and implementation of traditional techniques have to change as a consequence. Possibly the greatest improvement in blasting in recent years is that of electronic detonators. The improvements related to safety and increased fragmentation have been invaluable. There has been ongoing debate within the explosives industry regarding two possible theories for this. Shorter timing delays that allow interaction between adjacent shock waves or detonation waves, or the increase in accuracy associated with electronic detonators. Results exist on the improved accuracy of electronic detonators over that of electric or non-electric, but data on the relationship between the collision of dynamic stress waves and fragmentation is less understood. Publications stating that the area of greatest fragmentation will occur between points of detonation where shock waves collide exist, but experimental data to prove this fact is lacking. This dissertation looks extensively at the head on collision of shock (in the rock mass) and detonation (in the detonation column) waves with relation to fragmentation through a number of small scale tests in concrete. Timing is a vital tool for this collision to occur and is the variable utilized for the studies. Small scale tests in solid masonry blocks, 15 x 7⅞ x 7⅞ inches in size, investigated shock and detonation wave collisions with instantaneous detonation. Blocks were wrapped in geotextile fabric and a wire mesh to contain the fragments so that in situ tensile crack formations could be analyzed. Detonating cord was used as the explosive with no stemming to maintain the shock pressure but reduce the gas pressure phase of the fragmentation cycle. Model simulations of these blocks in ANSYS Autodyn looked at the stress and pressure wave patterns and corresponding damage contours for a direct comparison with the experimental investigation. Detonation wave collision in a single blast hole was found to positively influence the fragmentation and throw of the material. Mean fragment size decreased compared to tests with no detonation wave collision. Area of greatest throw occurred at the point of detonation collision where a buildup of gas pressure exited the block from one location. Head on collision of shock waves did not positively influence the muck pile. Largest fragments were located at the point of shock collision. The lack of particle velocity with relation to shock collision in previous literature could be attributed to the increased particle size here. Directional particle velocities could actually increase the strength and density of the rock at this location, decreasing the degree of fragmentation rather than increasing it.

The advent of detonation-based propulsion systems represents an opportunity for more sustainable combustion processes and hypersonic travel. In regular detonations, some yet to be resolved instabilities are attributed to the propagation and collision of triple points, formed at the intersection of a Mach stem, an incident shock and a transverse wave. Over time, the tracks observed by these points form a structure made of diamond-shaped cells. Ultimately, The ability to sustain these instabilities plays a key role in the propagation of detonations. The present work unveils the dynamics of gaseous detonations at a sub-cellular level. The experiments are conducted with hydrogen fuel which is of great potential for detonation engine applications. The hydrogen-oxygen mixtures are held at stoichiometry and the nitrogen dilution in oxygen is varied from 30% to 70%. This allows to observe the effects of activation energy through the dilution on the sub-cellular wave dynamics. Measurements of cell sizes and wave velocity are reported through shadowgraph imaging. A new methodology is developed for the simultaneous resolution of the velocity field and cellular structure. The statistical analysis is made possible due to the design of a fully automated detonation facility. The experiments are conducted in a thin channel to minimize gradients in the third direction and confine the detonation cells to a plane. The results in cell sizes are in good agreement with the literature and expand the conditions reported thus far. Local observations of the velocity within the cells are used to explain the regularity of the overall wave speed, found to increase at lower dilution. Lastly, high fidelity simulations are conducted to model the cellular structure in hydrogen-air oblique detonation waves. Similarly to the experiments, the velocity field is extracted along the detonation cells and reveals the effects of wave curvature on triple point dynamics.

Detonation-based propulsion systems are known for their high efficiency and energy release when compared to deflagrative systems, making them an ideal candidate in hypersonic propulsion applications. One such engine is the Oblique Detonation Wave (ODW) engine, which has a similar architecture to traditional scramjets but shortens the combustor and isolator to an anchored ODW after fuel injection. Previous research has focused on using a two-dimensional wedge to induce an ODW while limiting total losses through the combustor. In this configuration, a two-dimensional wedge-based architecture entails a rectangular duct, limiting potential inlet design and increasing overall skin friction. However, an inward-turning axisymmetric ODW wedge architecture, where a two-dimensional wedge is revolved around a central axis, has yet to be examined in detail. The work at present aims to investigate the fundamental physics required to predict the Oblique Shock Wave (OSW) for an inward-turning axisymmetric flow, which is critical for designing a circular ODW engine combustor. Multiple steady simulations of inviscid and ideal air at Mach 4, 6, and 8 were performed over a 1-inch wedge with wedge angles of 16°, 18°, and 20°. The radius of the inlet boundary was also varied between 1, 3, and 5 inches to examine the effect of increasing the blockage ratio. The results showed that the shock angle for an inward-turning axisymmetric flow was up to 8% steeper than the analytical, two-dimensional wedge solution. Additionally, it was found that the OSW diverged further from the two-dimensional solution when the blockage ratio was increased. These findings provide insight into the flow physics that must be considered when designing inward-turning axisymmetric ODW engines.

<p dir="ltr">Tailorable energetics are energetic materials that can be modified to alter their performance and sensitivity. Examples of tailoring energetic materials include additive manufacturing, manufactured hot spots, switchable energetics, and cocrystallization. Developing novel energetic material is a difficult and cost intensive process, because of this, tailoring the performance and sensitivity of existing energetic materials is critical for continued improvement. Additive manufacturing has provided new methods for generating complex geometries of composite materials. Additive manufacturing of composite materials through direct-ink-write (DIW) experiences extrusion limitations due to the high viscosities of highly solids loaded mixtures; the limitations being more severe with smaller syringe tip diameter. A novel printing technique called vibration-assisted printing (VAP) was developed as a method to extend the extrudability limits and extrusion speeds observed with direct-ink-write systems. Printability envelopes were shown in previous work to extend extrudability of monomodal glass bead composites in VAP systems over conventional DIW systems. This study compares the mass flowrates and extrudability limits for bimodal mixtures of glass beads suspended in a hydroxyl-terminated polybutadiene (HTPB) binder for both VAP and DIW printing as a function of volume percent solids loading. The bimodal glass bead mixtures showed a linear response in extrusion rate versus solids loading for both VAP and DIW systems. The VAP system was able to print higher volume loadings than the direct-ink-write system. In addition to extending the extrudability limits, the mass flowrate for the VAP system was significantly higher at all volume loadings tested compared to the DIW. Interestingly, bimodal mixtures were shown to extrude quicker than the monomodal mixtures at all volume loadings and across both printing systems.</p><p><br></p><p dir="ltr">Inhomogeneities within explosives affect the sensitivity and detonation wave shape of energetic materials. The influence of voids on explosive initiation has been well documented; however, the effects that voids between 0.1 mm and 10 mm have on a propagating detonation wave remains largely unexplored. The effect of single cylindrical voids on detonation wave shape and re-initiation was examined here using manufactured voids in a rubberized 1,3,5-trinitro-1,3,5-triazinane (RDX) explosive. Two streak imaging techniques were fielded to investigate void influence. For the first, back-surface streak imaging, the location of the void on the samples was changed and the resulting change in detonation wave shape at the downstream breakout was captured using a streak camera in cut-back experiments. The results from this experiment showed the effects of an initial jet form for short cut-back distances and as shock propagation progressed, the jet formation was absorbed by the unaffected portions of the wave front. The second method, top-surface streak imaging, was used to investigate the re-initiation/downstream propagation of the detonation front and the detonation velocity of the rubberized explosive. These experiments were compared to similar experimental results from machined voids in PBX 9501, a 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX)-based explosive, to investigate the interaction of a detonation wave with a 0.5 mm void for different explosives. The experiments were also compared to simulations using a multi-dimensional and multi-material hydrodynamic code (CTH). These results showed the influence that small features can have on detonation wave shaping and how explosive properties play a key role in that interaction. In addition to air-filled voids, this study examined the effects of 0.5 mm diameter voids filled with different inert metals on the detonation wave shape for an RDX-based rubberized explosive. The metals selected for experiments were 1066 aluminum, brass, copper, and tungsten. Experimental results showed that the extent of detonation wave shaping was closely tied to the density differential between the bulk explosive and metal insert. Simulations were performed using CTH to further analyze material inclusions. Forty-four different filler materials were simulated to isolate the driving factors for wave shaping of the detonation front. The main factors of interest were bulk sound speed, shock impedance, and filler material density. Understanding the influence of material inclusions on detonation performance and wave shape allows for tailoring of detonations as well as characterizing how unintentional defects will alter the explosive.</p><p><br></p><p dir="ltr">Improving the safety of explosive materials through the synthesis of insensitive explosives has been studied extensively. However, little work has focused on creating switchable explosives. A switchable explosive is normally insensitive to detonation, and therefore safe to handle and transport, but can be sensitized when needed to create a functional explosive. Similarly, it may be desired to desensitize an explosive to prevent its function. This study examined the ability to create a switchable RDX-based rubberized explosive using thermally-expandable microspheres (TEMs). The addition of TEMs to the explosive formulation allowed for microstructural changes and potential hot spot locations such as voids to form as the microspheres expanded. Small voids (less than about 10 µm) are more likely to be critical hot spots when shocked, and likewise larger voids are less likely to ignite successfully (sub-critical) when shocked. Consequently, both sensitization and desensitization are possible. The rubberized explosive considered here with unexpanded microspheres was unable to sustain a detonation for the size used, but after specific heating followed by cooling to produce small voids, a detonation was achieved. That is, the TEMs addition to the RDX-based rubberized explosive resulted in an explosive that is detonation insensitive when unheated but becomes a functional explosive after it is sensitized through heating. This paves the way to create insensitive explosive formulations with on-demand switchable detonation function through the incorporation of thermally-expandable microspheres. Desensitization was also demonstrated with specific heating of TEMs in an initially detonable explosive charge. And finally, we also demonstrated that deflagration can be affected by heating TEMs.</p><p><br></p><p dir="ltr">Energetic cocrystallization is a technique that produces a cocrystal that is formed using two known explosives to potentially gain the benefits of one or both without the drawbacks for a particular application. A comparison of cocrystals to a physical mixture of the same coformers can be considered. Cocrystals have unique material properties and crystal structure, whereas a physical mixture is just a mixed combination of the known materials at the same molar ratio. This study used photon Doppler velocimetry (PDV) to compare the particle velocity for 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) and 1-methyl-3,5-dinitro-1,2,4-triazole (MDNT) at a 1:1 molar ratio for both a cocrystal and a physical mixture of the two energetic materials. This cocrystal was previously shown to detonate faster than a physical mixture. However, the PDV results here were not consistent with this result. In addition to measuring output particle velocity with PDV, the cocrystal was characterized to examine phase purity and possible signs of deterioration of the material over time. Evaluating the cocrystal with Fourier-transform infrared spectroscopy (FT-IR), bomb calorimetry, and powder X-ray diffraction (PXRD) allowed for more accurate comparison and greater confidence in the particle velocity measurements obtained in these experiments. The most significant difference in the material characterization results was the difference in enthalpy of formation, as the material tested in this study had a substantially lower enthalpy of formation than previously measured for a CL-20/MDNT cocrystal.</p>

Coal is likely to remain an important energy source for the next several hundred years and hence advances in coal combustion technologies have major practical impact. Detonation combustion of coal initiated by a plasma cartridge driven detonation wave holds promise for improving both system and combustion efficiencies. Both fragmentation and chemical kinetic pathways are qualitatively different in comparison to conventional coal combustion. The present work is a theoretical investigation of fragmentation due to detonation wave. The theoretical simulation starts with simple model and progressively incorporates more realistic analysis such as combined convective and radiative boundary condition. It studies the passing of detonation wave on coal particles suspended in air. Concepts of solid mechanics are used in analysing fragmentation of coal particles. A numerical model is developed which includes stress developed due to both thermal and volatilization effects. Weibull statistical analysis is used to predict the fracture time and fracture location resulting from principal stress induced. It is observed that coal particles fragment within microseconds. Radiation does not have much effect on developed stress. Volatilization does not have much effect on fragmentation for the particle size considered in this work and stress due to thermal effect dominated the fragmentation. Coal size distribution statistics is considered to obtain real regime. Coal is used as mixture of different sized particles in real combustors. Hence it is important to analyse the effect of detonation wave on mixture of coal particles. Results presented in this work from simulation run suggest that plasma assisted detonation initiated technology can fragment coal particles faster. Average fracture time of mixture of coal particles is far less than detonation travel time for the detonation tube considered here. Simulation results suggest that almost 90% of coal particles fragment early. Average fracture time reduces as Mach number increases. Same phenomena can be observed for volatile matter generated at fracture and ow of volatile matter at fracture. Hence it can be concluded that plasma assisted detonation combustion leads to different volatilization and fragmentation pathways.

L’objectif de cette thèse est d’étudier l’initiation directe et la propagation d’une détonation dans un milieu cryogénique diphasique GH2-LOx dans le cadre général des moteurs à onde de détonation pour la propulsion spatiale. Un rappel des bases théoriques sur les processus d’atomisation d’un jet liquide, puis sur la détonation en phase gazeuse, et enfin sur la détonation dans un mélange diphasique, constituent le premier chapitre de la thèse. Le deuxième chapitre présente les dispositifs expérimentaux et les techniques utilisés pour mener à bien les expériences de caractérisation du jet diphasique et d’étude de la détonation. Le troisième chapitre est consacré à l’étude dans un tube en quartz de la granulométrie d’un jet diphasique GHe-LOx non réactif. Une cartographie est ainsi réalisée sur l’ensemble du tube, pour différents débits d’injection. Ces résultats sont corroborés par une étude théorique sur une goutte isolée et par une étude numérique sur le comportement du jet en champ proche de l’injecteur. Le quatrième chapitre présente les résultats de l’étude de la détonation dans un tube en acier d’un mélange réactif GH2-LOx. La détonation est étudiée en fonction de divers paramètres : énergie d’initiation stockée, emplacement du dispositif d’initiation par étincelle, richesse globale du mélange. La célérité et la pression de détonation, ainsi que la structure tridimensionnelle de la détonation, sont les principales informations recueillies pour l’étude du phénomène de détonation en mélange diphasique. Une étude théorique des caractéristiques de la détonation apporte des éclairages supplémentaires sur la détonation à très basse température (100 K). / Within the general framework of detonation engines for space propulsion purpose, this work aims to study direct initiation and propagation of detonation in a cryogenic twophase GH2-LO2 mixture. First chapter is constituted by theoretical basis and state of art on atomization processes in liquid jets, then on gas-phase detonation, and finally on two-phase detonation. Second chapter describes experimental set-up and associate techniques in order to carry out two-phase jet characterization and detonation study. Third chapter is dedicated to the study of droplet size distribution of non reactive two-phase GHe-LO2 jet in a quartz tube. Thus, a droplet size map is constituted through the whole tube, for different helium injection speeds. These results are compared with theoretical study dealing with vaporization and movement of a droplet and with numerical simulations on jet behavior close to the injector. Fourth chapter presents results of a detonation study of a reactive GH2-LO2 two-phase mixture in a semi-open tube. Detonation is studied as a function of following parameters: initiation energy, spark initiation device location along the tube, global equivalence ratio. Velocity, peak pressure and three-dimension structure detonation are the main data collected to study two-phase detonation phenomena. A theoretical study of detonation characteristics brings additional information on detonation at low temperature (100 K).