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.

Abstract DEM (Distinct Element Method) models have found numerous applications in a number of engineering disciplines, such as material handling and transport, chemical, industrial, civil, mining and mineral processing. The thesis describes developments using PFC3D (Particle Flow Code in 3D) for simulating rock fragmentation by commercial explosives. Emphasis is on the realistic simulation of explosive detonation in the blasthole as well as the flow of explosive gas from the blasthole, through the fracture network and venting to the atmosphere. Detonation can be initialized at any point along discretized blastholes and proceed up or down the hole according to the Velocity of Detonation of the explosive. Each of the explosive properties (pressure, density, extent of reaction, energy and their time derivatives) is computed according to the conservation equations and the explosive equation of state at any point along the hole. At initiation, the product calculation begins at the sonic locus with input of the detonation product provided by the non-ideal detonation code Vixen-n. The Taylor wave is then computed as a function of the blasthole expansion, which depends on the rock mass response to loading. The explosive gas is treated as a non-steady, compressible fluid and can flow through an arbitrary and evolving fracture network developed in the rock mass as a function of explosive loading. The fracture network (and flow paths) is defined by the coalescence of discrete macro-cracks. The gas has the effect of draining the blasthole and loading the fracture surface by its pressure and drag forces. Fracture intersection with free-surfaces is monitored and venting to the atmosphere is allowed. Validation of the fluid flow scheme is performed by comparing numeric results to analytic solutions for flow in shock tubes. The complete model is demonstrated by simulating stress only models, gas flow models and complete models of field-scale blasts.

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

This study investigated the formulation and characterisation of emulsion explosives. This included the manufacture of more than 120kg of emulsion explosive of which around 105kg was used on the explosive ordnance range in over 350 individual firings. For each emulsion composition, an average of eight firings was undertaken with which to substantiate the explosive performance data. The formulation was varied to determine the effects of water content upon the physical characteristics of the emulsion. These physical effects included thermal conductivity, particle size, viscosity and the explosive performance of the emulsion. In respect of explosive performance, microballoons were added to sensitise the emulsion and the proportions of microballoons added were altered to look at their effect on velocity of detonation, sensitivity and the brisance of the emulsions. Emulsion explosives are commonly referred, in literature, as Type 11 non-ideal explosives. This is due to their non-linear behaviour with respect to the variation of velocity of detonation with density. Traditionally, when an emulsion explosive was commercially manufactured, the water content has been kept at a minimum (12-17%). This was accepted as the way to achieve the best explosive performance, based upon the belief that an emulsion with the highest concentration of active ingredients, ammonium nitrate and oil, would give the best explosive performance. This study examined a wider range of emulsion explosive water contents than has been previously studied, from 12% to 35% water. It was found, during this study, that higher water content emulsions, specifically 25% water, had a marked increase in explosive performance. The highest velocity of detonation recorded was in a 39mm diameter tube, at 25% water content with 3% microballoons, was 5558ms-1. This was some 15% higher than any other VOD recorded in this study. The high velocity of detonation, at 25% water content, was one of a number of physical characteristics in which this water content varied from the other emulsion water contents. This study endeavored to show that emulsion explosives could exhibit two differing types of explosive reaction, thermal explosion and grain burning. This was based on the velocity of detonation and plate dent data, both of which indicated that there was a change in reaction with water content. Emulsion explosives, with a high water and high microballoon content, exhibited a thermal explosion type reaction. They exhibited Type I ideal explosive behaviour, with increasing velocity of detonation with density. Lower water content emulsion explosives, displayed the more commonly expected Type 11 non-ideal behaviour and reacted in a grain burning type detonation.

This thesis is concerned with experimental and computational studies on pulse detonation engine (PDE) that has been envisioned as a new concept engine. These engines use the high pressure generated by detonation wave for propulsion. The cycle efficiency of PDE is either higher in comparison to conventional jet engines or at least has similar high performance with much greater simplicity in terms of components. The first part of the work consists of an experimental study of the performance of PDE under choked flame and partial fill conditions. Detonations used in classical PDEs create conditions of Mach numbers of 4-6 and choked flames create conditions in which flame achieves Mach numbers near-half of detonation wave. While classical concepts on PDE's utilize deflagration-to-detonation transition and are more intensively studied, the working of PDE under choked regime has received inadequate attention in the literature and much remains to be explored. Most of the earlier studies claim transition to detonation as success in the working of the PDE and non-transition as failure. After exploring both these regimes, the current work brings out that impulse obtained from the wave traveling near the choked flame velocity conditions is comparable to detonation regime. This is consistent with the understanding from the literature that CJ detonation may not be the optimum condition for maximum specific impulse. The present study examines the details of working of PDE close to the choked regime for different experimental conditions, in comparison with other aspects of PDEs. The study also examines transmission of fast flames from small diameter pipe into larger ducts. This approach in the smaller pipe for flame acceleration also leading to decrease in the time and length of transition process. The second part of the study aims at elucidating the features of deflagration-to-detonation transition with direct numerical simulation (DNS) accounting for and the choice of full chemistry and DNS is based on two features: (a) the induction time estimation at the conditions of varying high pressure and temperature behind the shock can only be obtained through the use of full chemistry, and (b) the complex effects of fine scale of turbulence that have sometimes been argued to influence the acceleration phase in the DDT cannot be captured otherwise. Turbulence in the early stages causes flame wrinkling and helps flame acceleration process. The study of flame propagation showed that the wrinkling of flame has major effect on the final transition phase as flame accelerates through the channel. Further, flame becomes corrugated prior to transition. This feature was investigated using non-uniform initial conditions. Under these conditions the pressure waves emanating from corrugated flame interact with the shock moving ahead and transition occurs in between the flame and the forward propagating shock wave. The primary contributions of this thesis are: (a) Elucidating the phenomenology of choked flames, demonstrating that under partial fill conditions, the specific impulse can be superior to detonations and hence, allowing for the possibility of choked flames as a more appropriate choice for propulsive purposes instead of full detonations, (b) The use of smaller tube to enhance the flame acceleration and transition to detonation. The comparison with earlier experiments clearly shows the enhancements achieved using this method, and (c) The importance of the interaction between pressure waves emanating from the flame front with the shock wave which leads to formation of hot spots finally transitioning to detonation wave.

This study investigated the formulation and characterisation of emulsion explosives. This included the manufacture of more than 120kg of emulsion explosive of which around 105kg was used on the explosive ordnance range in over 350 individual firings. For each emulsion composition, an average of eight firings was undertaken with which to substantiate the explosive performance data. The formulation was varied to determine the effects of water content upon the physical characteristics of the emulsion. These physical effects included thermal conductivity, particle size, viscosity and the explosive performance of the emulsion. In respect of explosive performance, microballoons were added to sensitise the emulsion and the proportions of microballoons added were altered to look at their effect on velocity of detonation, sensitivity and the brisance of the emulsions. Emulsion explosives are commonly referred, in literature, as Type 11 non-ideal explosives. This is due to their non-linear behaviour with respect to the variation of velocity of detonation with density. Traditionally, when an emulsion explosive was commercially manufactured, the water content has been kept at a minimum (12-17%). This was accepted as the way to achieve the best explosive performance, based upon the belief that an emulsion with the highest concentration of active ingredients, ammonium nitrate and oil, would give the best explosive performance. This study examined a wider range of emulsion explosive water contents than has been previously studied, from 12% to 35% water. It was found, during this study, that higher water content emulsions, specifically 25% water, had a marked increase in explosive performance. The highest velocity of detonation recorded was in a 39mm diameter tube, at 25% water content with 3% microballoons, was 5558ms-1. This was some 15% higher than any other VOD recorded in this study. The high velocity of detonation, at 25% water content, was one of a number of physical characteristics in which this water content varied from the other emulsion water contents. This study endeavored to show that emulsion explosives could exhibit two differing types of explosive reaction, thermal explosion and grain burning. This was based on the velocity of detonation and plate dent data, both of which indicated that there was a change in reaction with water content. Emulsion explosives, with a high water and high microballoon content, exhibited a thermal explosion type reaction. They exhibited Type I ideal explosive behaviour, with increasing velocity of detonation with density. Lower water content emulsion explosives, displayed the more commonly expected Type 11 non-ideal behaviour and reacted in a grain burning type detonation.

Shock waves in reactive media possess very rich dynamics: from formation of cells in multiple dimensions to oscillating shock fronts in one-dimension. Because of the extreme complexity of the equations of combustion theory, most of the current understanding of unstable detonation waves relies on extensive numerical simulations of the reactive compressible Euler/Navier-Stokes equations. Attempts at a simplified theory have been made in the past, most of which are very successful in describing steady detonation waves. In this work we focus on obtaining simplified theories capable of capturing not only the steady, but also the unsteady behavior of detonation waves. The first part of this thesis is focused on qualitative theories of detonation, where ad hoc models are proposed and analyzed. We show that equations as simple as a forced Burgers equation can capture most of the complex phenomena observed in detonations. In the second part of this thesis we focus on rational theories, and derive a weakly nonlinear model of multi-dimensional detonations. We also show, by analysis and numerical simulations, that the asymptotic equations provide good quantitative predictions.

No description available.

Detonation-based combustion systems are desired for propulsion and power systems due to their ability to provide high thermal efficiency and enable supersonic flight. Detonation combustion in hypersonic flows has traditionally been realized using an oblique detonation wave. However, oblique detonation realization and stabilization in combustion systems is challenging. This communication presents an alternative realization of a detonation mode of combustion through a reacting Mach stem. The detonation is experimentally realized in a hypersonic reacting facility, which is optimized for Mach 5 flow at the combustor inlet and includes a 2D-wedge to stabilize hypersonic reactions at high-enthalpy flow conditions. The Mach stem detonation is analyzed with simultaneous 30 kHz schlieren and chemiluminescence imaging, which reveals the coupling between the Mach stem and the reaction. Further confirmation is provided by comparing the Mach number of the reacting Mach stem with the Chapman-Jouguet (CJ) detonation Mach number. It is found that the Mach number of the reacting Mach stem reaches 94% of the CJ detonation Mach number, confirming that the reacting Mach stem realizes a detonation mode of combustion.

A facility was designed to provide high-enthalpy, hypersonic flow to a detonation chamber. Preliminary investigation identified 1300 K and Mach 5 as the total temperature and Mach number require to stabilize an oblique detonation wave inside the detonation chamber. Vitiated-air heating was the preheating method chosen to meet these capabilities. The vitiator facility heats compressed air while still retaining about 50% of the original oxygen content. Schlieren flow visualization and conventional photography was performed at the exit plane of a choke plate, which simulated the throat of a converging-diverging nozzle. A shock diamond formation was observed within the jet exhausting out of the choke hole. This is a clear indication that the facility is capable of producing hypersonic flow. A stoichiometric propane-air mixture was burned inside the combustion chamber. A thermocouple survey measured an average temperature of 1099 K at the exit plane of the mixing chamber; however, the actual temperature is likely higher than this, because cool, ambient air could be seen mixing with the hot, vitiated air near the exit plane. Because the adiabatic flame temperature of propane-air is lower than that of hydrogen-air, if hydrogen is used to vitiate the air, the facility is capable of meeting the 1300-K objective.