The work herein covers the complete process for development, production and testing of a melt processable pyrotechnic composition, with the goal of using the composition as a printing material in a fused deposition modelling (FDM) type 3D printer. 3D printing is fast becoming an area of interest for energetic materials research. This is due to the role that geometry can play in combustion performance of a composition and 3D printing’s ability to produce a variety of complex designs. Melt processable fluoropolymers were selected as oxidisers. The polymers selected for the study were FK-800® and Dyneon 31508®. Both are co-polymers of vinylidene fluoride (VDF) and chlorotrifluoroethylene (CTFE). Aluminium was the choice fuel in this instance as it had better energetic performance than the alternatives investigated. It was also deemed to be a safer fuel when considering the combustion products. Hazardous combustion products like hydrofluoric and hydrochloric acid could be suppressed by increasing the fuel loading to 30 wt.%, thereby reducing the risks associated with burning the composition. Preliminary differential thermal analysis (DTA) analysis indicated that the compositions would only ignite above 400 °C which was well above the suggested processing temperature of 230 °C as determined from thermogravimetric (TGA) analysis. These thermal analysis techniques indicated that the reactions were most likely a gas-solid reactions due to ignition temperatures being significantly lower than those associated with phase changes occurring in the fuels tested, yet above the decomposition temperatures for the oxidisers. ii Extrusion of the compositions proceeded with addition of LFC-1® liquid fluoroelastomer. This addition was made in order to order to lower the melt viscosity, thereby improving the quality of the filament produced. Compositions were extruded with an aluminium loading of 30 wt.%. Oxidiser and LFC-1® made up the rest of the mass with the LFC-1® contributions being either 7 wt.% or 14 wt.%. Burn rates, temperatures and ignition delays were all influenced by the addition of LFC-1® to the system. FK-800® was found to be a better oxidiser in this instance since its burn rates were consistent especially when compared to erratic nature of the Dyneon 31508® burns. Linear burn rates for the FK-800® increased from 15.9 mm·s−1 to 18.9 mm·s−1 with the increase in LFC-1® loading. Combustion temperature also increased by approximately 180 °C from 794 °C. Printing with the material was achieved only after significant alterations were made to the hot end used. Printing proceeded in a staged, start-stop manner. After each new layer of material was deposited the printer was cleared of material and the hot end was allowed to cool. If this procedure was not followed it led to significant preheating of the material within the feeding section of the extruder. This premature heating caused feeding problems due to softening and swelling of the material within the cold side of the hot end which led to blockages, leading to the conclusion that the composition was not compatible with the off-the-shelf hot end used in this study. Low quality printing could be achieved with both FK-800® and Dyneon 31508® compositions. This would suggest that slight compositional changes paired with the alterations made to the hot end could improve the quality of the prints to an extent that would be comparable to that of more commonplace printing materials. / Dissertation (MEng)--University of Pretoria, 2017. / Chemical Engineering / MEng / Unrestricted

Urolithias, calculus formation in the urinary system, affects 5 – 10% of the population and is a painful and recurrent medical condition. A common approach in the treatment of calculi is the use of laser radiation, a procedure known as laser lithotripsy, however, the technique has not yet been fully optimised. This research examines the experimental parameters relevant to the interactions of the variable microsecond pulsed holmium laser (λ = 2.12 μm, τp = 120 – 800 μs, I ~ 3 MW cm-2) and the Q-switched neodymium laser (λ = 1064 nm, τp = 6 ns, I ~ 90 GW cm-2) with calculi. The laser-calculus interaction was investigated from two perspectives: actions that lead to calculus fragmentation through the formation of shockwave and plasma, and the prospect of material analysis of calculi by laser induced breakdown spectroscopy (LIBS) to reveal elemental composition. This work is expected to contribute to improved scientific understanding and development of laser lithotripsy. The results support the general model of thermal and plasma processes leading to vaporization and pressure pulses. Nd:YAG laser interaction processes were found to be plasma-mediated and shockwave pressure (~ 12 MPa) dependent on plasma and strongly influenced by metal ions. Ho:YAG laser-induced shockwaves (~ 50 MPa) were found to be due to direct vaporisation of water and dependent on laser pulse duration. The characteristics of the pressure pulse waveforms were found to be different, and the efficiency and repeatability of shockwave and the nature of the dependencies for the lasers suggest different bubble dynamics. For the Nd:YAG laser, LIBS has been demonstrated as a potential tool for in situ analysis of calculus composition and has been used for the identification of major and trace quantities of calcium, magnesium, sodium, potassium, strontium, chromium, iron, copper, lead and other elements.

Urolithias, calculus formation in the urinary system, affects 5 – 10% of the population and is a painful and recurrent medical condition. A common approach in the treatment of calculi is the use of laser radiation, a procedure known as laser lithotripsy, however, the technique has not yet been fully optimised. This research examines the experimental parameters relevant to the interactions of the variable microsecond pulsed holmium laser (λ = 2.12 μm, τp = 120 – 800 μs, I ~ 3 MW cm-2) and the Q-switched neodymium laser (λ = 1064 nm, τp = 6 ns, I ~ 90 GW cm-2) with calculi. The laser-calculus interaction was investigated from two perspectives: actions that lead to calculus fragmentation through the formation of shockwave and plasma, and the prospect of material analysis of calculi by laser induced breakdown spectroscopy (LIBS) to reveal elemental composition. This work is expected to contribute to improved scientific understanding and development of laser lithotripsy. The results support the general model of thermal and plasma processes leading to vaporization and pressure pulses. Nd:YAG laser interaction processes were found to be plasma-mediated and shockwave pressure (~ 12 MPa) dependent on plasma and strongly influenced by metal ions. Ho:YAG laser-induced shockwaves (~ 50 MPa) were found to be due to direct vaporisation of water and dependent on laser pulse duration. The characteristics of the pressure pulse waveforms were found to be different, and the efficiency and repeatability of shockwave and the nature of the dependencies for the lasers suggest different bubble dynamics. For the Nd:YAG laser, LIBS has been demonstrated as a potential tool for in situ analysis of calculus composition and has been used for the identification of major and trace quantities of calcium, magnesium, sodium, potassium, strontium, chromium, iron, copper, lead and other elements.

Ce travail porte sur l’étude et la réalisation d’une cellule d’allumage laser pour turbomoteurs. Une étude bibliographique nous a permis d’identifier les caractéristiques nécessaires : des impulsions nanosecondes d’au moins 10mJ. La spécificité de l’application impose de nombreuses contraintes qui ont influencé le choix d’une architecture avec deux étages amplificateurs : un amplificateur fibré suivi d’un amplificateur à base de fibre cristalline. Nous avons développé un code permettant de simuler l’amplification d’une impulsion nanoseconde dans ces milieux et ainsi déterminé les caractéristiques techniquesoptimales de chaque étage amplificateur. Ces résultats ont permis la réalisation d’une chaîne d’allumage et sa caractérisation. Une étude particulière del’amplificateur fibré a permis de maîtriser l’apparition d’effets non-linéaires limitants. Finalement, nous démontrons le potentiel de notre solution laserpar plusieurs campagnes d’allumage sur différents bancs moteurs. / This work deals with the design and the construction of a laser ignitionsystem for turbine engines. A review of the dedicated literature allowed us toidentify the required characteristics : nanosecond pulses with at least 10 mJ ofenergy. Our specific application imposes numerous constraints which directlyinfluenced our choice of two amplifier stages : a fiber amplifier followed by acrystalline-fiber based amplifier. We developped a simulation describing theamplification of nanosecond pulses through these two medias and thus de-termined the optimal technical characteristics of each amplifier stage. Theseresults lead to the realization of an laser ignition system that we completelycharacterised. A specific study of the fiber amplifier allowed us to understandand control the appearance of non-linear limiting phenomena. Eventually, wedemonstrate the capabilities of our solution by several laser-ignition field stu-dies.

<p>The ignition of energetic materials, and specifically solid propellants, is a complex process</p> <p>that must be safe, consistent, and precisely controlled. There is a wide range of applications with</p> <p>specific ignition requirements for solid propellants including inflation of airbags, propulsion</p> <p>systems (including rockets), as well as arm and fire devices. Currently, electrical or percussion</p> <p>pyrotechnic igniters are most the commonly used ignition systems. These systems must be</p> <p>carefully designed to deliver the proper amount of energy to a specified surface area of the</p> <p>propellant. A photon light source (i.e. flash or laser-based, ranging from UV to IR wavelengths)</p> <p>can potentially be used to ignite energetic materials with lower input energy and more precise</p> <p>spatial and temporal control, thereby improving safety and reliability by eliminating electrical</p> <p>systems used in pyrotechnic igniters. In addition, they could be potentially safer from stray</p> <p>electrical charges causing unintentional ignition.</p> <p>The purpose of this work is to further explore the potential of optical ignition for energetic</p> <p>systems and identify ideal materials that can be used for optical ignition. In order to identify</p> <p>optically sensitive materials, we will study ignition energies, ignition delays, flame temperatures,</p> <p>and other combustion characteristics for possible energetic materials. This research addresses a</p> <p>gap in understanding of optical ignition for energetic materials, as finding and integrating materials</p> <p>that are optically sensitive while still being practical can be extremely challenging. These</p> <p>challenges include: (1) a lack of absorptivity to optical wavelengths in the UV to low-IR range,</p> <p>and subsequently, a very high sensitivity to input energy at the absorptive wavelengths that makes</p> <p>sustained ignition difficult, (2) a need for full density materials in practical energetic systems,</p> <p>while optically sensitive materials are exceedingly difficult to ignite as packing density increases</p> <p>due to heat transfer, and (3) the lack of research regarding novel fuels/oxidizers for the specific</p> <p>purpose of optical ignition.</p> <p>Metal/fluoropolymer energetic materials have been of interest to the energetic materials</p> <p>community for many years. Due to fluorine’s excellent oxidizing ability, they can be used in</p> <p>composite materials with metal fuels to produce energetic materials for a wide variety of</p> <p>applications. Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polycarbon</p> <p>13</p> <p>monofluoride (PMF), and terpolymers such as tetrafluoroethylene, hexafluoropropylene, and</p> <p>vinylidene fluoride (THV) have already seen extensive use in applications ranging including</p> <p>protective coatings, strain gauges, and electronics. However, when combined with metals such as</p> <p>lithium, magnesium, aluminum, or titanium, they also present an opportunity for a wide variety of</p> <p>energetic materials. For this study, metal/fluoropolymer composites present a novel opportunity</p> <p>for exploring optical ignition of widely absorptive, full-density energetic materials. This work will</p> <p>characterize the combustion and sensitivity of metal/fluoropolymer composites to provide novel</p> <p>materials for optical ignition of energetics.</p> <p>Specifically, this work will begin with finding a suitable energetic composite that is optically</p> <p>sensitive. Once this material has been identified, research will be done to thoroughly characterize</p> <p>the optically sensitive composite by looking at additive manufacturability, flame temperatures, and</p> <p>ignition sensitivities from various methods and formulations. Once the material has been</p> <p>thoroughly characterized, it will be implemented into solid propellants to test the feasibility of the</p> <p>material in practical energetic systems. Finally, the lessons learned from this work will be applied</p> <p>to novel formulations to identify new optically sensitive energetic composites.</p>

Cette thèse en deux parties porte sur le développement de sources lasers nano et picosecondes et leurs applications. La première partie présente l'étude, et la réalisation d'une chaîne amplificatrice laser nanoseconde pour l'allumage de turbomoteurs. Après avoir présenté les performances et l'évolution de cette chaîne seront présentes les résultats des campagnes d'essais réalisées sur une chambre de combustion sur un banc d'essai à l'ONERA dans des conditions de basses températures et de basses pressions. La deuxième partie de cette thèse traite du développement d'un oscillateur paramétrique optique (OPO) nécessaire pour accorder en longueur d'onde dans l'infrarouge un laser impulsionnel picoseconde ou femtoseconde à haute cadence et forte puissance moyenne. Après avoir présenté la cavité de l'OPO ainsi que ses performances, nous détaillerons la capacité de cet OPO à générer des impulsions femtoseconde comprimées à partir d'impulsions pompe présentant un étirement temporel. / This two-part thesis focuses on the development of nano and picosecond laser sources and their applications. The first part presents the study, and the realization of a nanosecond laser amplifier chain for the ignition of turboshaft engines. After the repport of the performances and the evolution of this amplifier chain will be presented the results of the tests carried out on a combustion chamber on a test bench at ONERA under low temperatures and low pressures conditions. The second part of this thesis deals with the development of an optical parametric oscillator (OPO) in order to tune in the infrared the wavelength of a pulsed picosecond or femtosecond laser at high cadency and high average power. After presenting the OPO cavity and its performance, we will detail the ability of this OPO to generate compressed femtosecond pulses from pump chirped pulses.

<div>This research has been studied a laser-induced spark in flowing gases. The relationship between the minimum ignition energy (MIE), the turbulence intensity, and the flame kernel propagation speed is considered. Plasma emission, produced by the laser-induced spark, and flame kernel generation by the plasma are investigated. The energy balance equation between an ignition energy and energy losses by heat transfer is studied at laminar flows and turbulent flows. Hydrogen and air mixtures were used in a premixed jet burner for ignition experiments. Particle image velocimetry (PIV) examined the velocity and the turbulence intensity under the turbulent flows. The flame kernel development was visualized using Schlieren imaging and infrared images (IR camera). Flame kernel temperatures were measured through Rayleigh scattering and infrared images (IR camera). Plasma evaluations were captured through an intensified CCD camera (ICCD camera). Minimum ignition energies were measured at the laminar flows and the turbulent flows. The MIE decreases with an increase in the turbulence intensity which changed by ignition locations and perforated plates at the constant bulk velocity. Improved mixing rates due to the ignition locations or the geometry of the perforated plates decrease the MIE at the constant bulk velocity. The turbulence intensity increases wrinkles in the flame kernel surface, thus the contact between the flame kernel and reactants increases due to the wrinkles. Therefore, the flame kernel propagation speed increases as the turbulence intensity is higher since the increased reaction by the wrinkles and the contact. Thus, the MIE decreases as the turbulence intensity increases at the constant ignition condition, including bulk velocities and ignition heights, since the high turbulence intensity increases the flame kernel propagation speed. Laser energy differences affect the plasma expansions by the laser absorption. Laser-supported radiation (LSR) wave speeds were measured and calculated using energy balance equations. Velocity does not affect the flame kernel temperature distribution during the early reaction steps because the plasma generates a flame kernel and determines the flame kernel temperature distribution. The MIE increases with increasing the bulk velocity. The energy losses considering convection, conduction, and radiation were calculated using the flame kernel radius, the flame kernel temperature, mixture properties, and the flame speed. The energy balance equation in the ignition of flowing gases is newly written at the laminar flows and the turbulent flows.</div>

L’allumage par claquage laser non résonant des mélanges réactifs considérés à l’état gazeux et au repos est étudié dans ce travail, principalement avec des mélanges n-décane/air (C₁₀H₂₂+N₂+O₂). Ce système est considéré comme étant prometteur dans les différentes stratégies futures concernant les systèmes d’allumages équipant les moteurs à combustion interne. Le plasma d’allumage est généré en focalisant un faisceau laser de haute intensité pendant quelques nanosecondes. Le laser Nd :YAG opère à 1064 nm, il est choisi comme source laser pour l’ensemble des expériences menées en laboratoire afin de montrer l’effet des paramètres physiques, optiques, thermodynamiques (pression) et chimiques (additifs : H₂O, Ar) sur les caractéristiques de l’allumage. Cette étude met en oeuvre une approche statistique sur l’ensemble des expériences en prenant en compte l’ensemble des mesures prises lors de la combustion. Ce manuscrit offre une base de données expérimentale permettant d’appréhender la combustion et la phénoménologie de claquage laser. / Ignition by non-resonant laser breakdown of quiescent reactive mixtures was considered in this experimental study working with gaseous state. In this work, we mainly study the ignition of n-decane / air (C₁₀H₂₂+N₂+O₂) mixtures. This system is considered promising in different future strategies regarding ignitions systems for internal combustion engines. The breakdown is generated by focusing a high intensity laser beam for a few nanoseconds using Nd: YAG laser operating at 1064 nm, it is chosen as the laser source for all experiments conducted here. The experimental plan conducted allows to examine the effect of physical, optical, thermodynamic (pressure) and chemicals (additives: H₂O, Ar) on the characteristics of the laser ignition. This study implements a statistical approach on all the experimental cases taking into account all the measures during breakdown and combustion. This manuscript provides bibliographic basis for understanding combustion and laser breakdown phenomenology.

Les pompiers méditerranéens sont confrontés à des embrasements soudains de la végétation (AFF) dont les mécanismes ne sont pas encore bien compris. La végétation étant l'unique combustible, nous nous sommes penchés sur les gaz qui en proviennent. Nous avons d’abord étudié la dégradation thermique de quatre Composés Organiques Volatils biogéniques (COVb) à l'aide d'une pyrolyse flash et d'un four tubulaire. À partir de cette étude et de la littérature, nous avons choisi un mélange d'étude afin expérimenter ses propriétés de combustion. Nous avons ainsi déterminé l'Énergie Minimale d’Inflammation (EMI) et la vitesse fondamentale de flamme de mélanges d'α-pinène/benzène qui sont respectivement les principaux COV détectés dans les plantes et dans les fumées de feux de forêt. Le dernier chapitre concerne l'étude stationnaire de l'accumulation de gaz dans des vallées à partir d'une maquette de forêt 1/400ème disposée dans une soufflerie. / Mediterranean firefighters cope with powerful accelerations of forest fires (AFF) whose mechanisms are not very well understood. Vegetation is the only fuel of forest fire, then we studied the gases coming from them. First, we studied the thermal degradation of four Biogenic Volatil Organic Compounds (BVOCs) thanks to a flash pyrolysis and a tubular oven. From this study and literature, we chose a representative VOC mixture to study its combustion properties. We determined Minimal Ignition Energy (MIE) and its laminar burning speed of mixtures of α-pinene/benzene that are respectively the main VOC detected in vegetation and forest fire smoke. The last chapter experiment the steady-state gas accumulation above a 1/400 V-shaped forest model.