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Thermal Structure of Flames in Metal Particle Suspensions Michael Soo Department of Mechanical Engineering McGill University Montreal, Quebec December 2016 Supervisors: Professors Jeffrey Bergthorson and David Frost A thesis submitted to McGill University in partial fulfillment of the requirements of the degree of Doctor of Philosophy. © Michael Soo, 2016 Abstract Understanding the combustion behavior of reactive particle suspensions is central to the goal of predicting and tailoring the performance of metalized explosives and propellants. The mass fraction of metal in these energetic compositions can exceed 20%, leading to the metal burning as a dense suspension in the gaseous products of a hydrocarbon fuel matrix. The combustion characteristics in dense particle suspensions are often extrapolated from those measured from isolated, single particles or dilute suspensions. However, these characteristics depend on the temperatures and composition of the gas which are altered during the reaction of the particle suspension. A simple model is explored to demonstrate how particle concentration may affect com- bustion time, reaction regime, and thermal structure in the suspension for a zero-dimensional reactor and for one-dimensional flame propagation. Unlike the majority of models previously developed for particle combustion, no external parameters are imposed, such as particle igni- tion temperature, combustion time, or the assumption of either kinetic- or diffusion-limited particle combustion regimes. Instead, it is demonstrated that these characteristics can be functions of the particle mass concentration, and that the a priori imposition of these char- acteristics from single-particle combustion data may result in erroneous predictions. There are very few experimental techniques developed to determine combustion charac- teristics in dense suspensions. The determination of key parameters such as reaction regime, and burning time in suspension combustion is difficult due to the inability to isolate and observe individual particles. Instead, the particle combustion characteristics must be de- termined from diagnostics on the bulk flame. A flat flame in a suspension of micron-sized aluminum fuel and gaseous oxidizer is stabilized on a counterflow burner to provide a one- dimensional geometry for use with line-of-sight optical diagnostics. An imaging emission spectroscopy and a broadband-laser absorption spectroscopy technique are developed and applied to the flat flame to assess the regime of particle combustion in the flame. These tech- niques provide a method for determining the combustion time of particles in the suspension. i Abr´eg´e Comprendre la combustion de suspensions de particules r´eactives est essentiel pour pr´edir et adapter la performance des explosifs et des propergols m´etallis´es. La fraction massique du m´etal dans ces m´elanges ´energetiques peut exc´eder 20% et ce dernier brˆule ainsi en tant que suspension dense dans les produits gazeux de la matrice d’hydrocarbures du carburant. Les charact´eristiques de ces suspensions denses de particules sont souvent extrapol´eesa ` partir de celles mesur´ees sur des particules isol´ees ou de suspensions dilu´ees. Cependant, ces charact´eristiques d´ependent des temp´eratures et de la composition du gaz qui sont modifi´ees pendant la r´eaction de la suspension des particules. Un mod´ele simple, d´evelopp´e dans cette th´ese, explore et d´emontre comment la con- centration des particules peut affecter le temps de combustion, le r´egime de r´eaction et la structure thermique d’une suspension pour un r´eacteur de dimension z´ero ainsi que dans la propagation d’une flamme unidimensionnelle. A la diff´erence de la plupart des modles de combustion de particules actuels, ce mod´ele n’impose aucun param´etre externe comme la temp´erature d’allumage, le temps de combustion ou la supposition d’un r´egime-limite cin´etique ou de diffusion. Au contraire, les r´esultats d´emontrent que ces charact´eristiques peuvent ˆetre des fonctions de la concentration massique des particules et qu’une imposition a priori de ces charact´eristiques `a partir de la combustion de particules uniques peut r´esulter en pr´edictions erron´ees. Tr`es peu de techniques exp´erimentales permettent la mesure de charact´eristiques de com- bustion des suspensions denses. La d´etermination de param`etres-cl´es tels que le r´egime de r´eaction ou le temps de combustion de la suspension est difficile car pr´esentement, on est incapable d’isoler et d’observer les particules individuellement. Les charact´eristiques de combustion des particules doivent donc ˆetre d´etermin´ees grˆace aux diagnostics de lensem- ble de la flamme. Une flamme plate dans la suspension de micro-particules d’aluminium et d’oxydant gazeux est stabilis´ee sur un brˆuleura ` contre-courant, r´esultant en une g´eometrie unidimensionnelle qui permet une port´ee optique pour les diagnostics. Des techniques de spectrom´etrie de formation d’images d’´emission et de spectrom´etrie d’absorption `a bandes larges ont ´et´ed´evelopp´ees et appliqu´ees sur la flamme plate pour d´eterminer le r´egime de ii combustion des particules dans la flamme. iii Acknowledgments I would like to thank Prof. Jeffrey Bergthorson and Prof. David Frost for their guidance in the completion of the PhD project and for their countless hours editing and critiquing my work. I would also like to thank Dr. Samuel Goroshin whose unique vision and understanding of metal combustion provided inspiration and guidance for the work in this thesis. The technical advice of Prof. Andrew Higgins and Prof. Nick Glumac was invaluable for presentations and in the completion of the diagnostic setups. My colleagues and co-authors, Philippe Julien, Jan Palecka, James Vickery, and Keishi Kumashiro, deserve a special thanks for their comradery and research efforts. I addition- ally owe a debt of gratitude to the rest of the official and unofficial metal flames students for keeping things interesting during my time at McGill and University of Illinois Urbana- Champaign. My thanks also go to my family: Jake, Pip, Sheila, and David. iv Contributions of the Author Section 1.4 of the Introduction: I developed the original analysis of the heterogeneous ignition theory using the steady thermal states presented here. Chapter 2 Publication [1]: Soo, M., Goroshin, S., Bergthorson, J.M., Frost, D.L. Reaction of a particle suspension in a rapidly-heated oxidizing gas. Propellants, Explosives, Pyrotechnics, 2015. 40(4):604-612. I performed the analysis for the understanding of heterogeneous ignition. I wrote the derivation to the governing equations and the assumptions. The coding was completed with assistance from Keishi Kumashiro during a summer undergraduate research project whom I supervised. I performed the analysis of the model and wrote the paper. David Frost, Jeffrey Bergthorson, and Samuel Goroshin provided research guidance and editorial review. Chapter 3 Publication [2]: Soo, M.J., Kumashiro, K., Goroshin, S., Frost, D.L., Bergthorson, J.M. Thermal struc- ture of flames in non-volatile fuel suspensions. Proceedings of the Combustion Institute, 2017. 36(2):2351-2358. I derived the set of governing equations and assumptions. The coding of the model was completed with assistance from Keishi Kumashiro during his undergraduate thesis project. We analyzed the data together. I wrote the paper. David Frost, Jeffrey Bergthorson, and Samuel Goroshin provided research guidance and editorial review. Chapter 4 Publication [3]: Soo, M.J., Goroshin, S., Glumac, N., Kumashiro, K., Vickery, J., Frost, D.L., Bergthor- son, J.M. Emission and laser absorption spectroscopy of flat flames in aluminum suspensions. Combustion and Flame, 2017. 180:230-238. v I developed the diagnostic setup and wrote the spectral processing codes. Experiments were run with help from Keishi Kumashiro and James Vickery. James Vickery wrote the codes to analyze reference burning velocity from the Particle Image Velocimetry technique. I analyzed the data and wrote the paper. David Frost, Jeffrey Bergthorson, Samuel Goroshin, and Nick Glumac provided research guidance and editorial review. vi Appendix D: Laser Absorption Diagnostic [4]: Soo, M., Glumac, N. Ultraviolet absorption spectroscopy in optically dense fireballs using broadband second-harmonic generation of a pulsed modeless dye laser. Applied Spectroscopy, 2014. 68(5):517-24. In the process of constructing the laser absorption setup used for the publication in Chapter 4, I developed a method to extend the visible broadband dye laser technique to produce to broadband, ultraviolet (UV) laser light. I performed the experiments, developed the spectral models, and wrote the paper. Nick Glumac provided research guidance and editorial review. While the publication provides an overview of the diagnostic used in [3] and the novel UV technique may be important for future diagnostic developments, the subject of the paper is considered peripheral to the main body of the thesis. It is, therefore, included as supplemental material. vii List of Figures 1.1 Combustion in condensed-phase fuel suspensions, classified according the fuel volatility. ...................................... 5 1.2 Classifications of combustion mode based on thermodynamics equilibrium cal- culationsfromtheanalysisof[5]......................... 7 1.3Theexpectedmodesofmetalparticlecombustionfrom[5]........... 8 1.4 Thermal structure for the two limiting kinetic and diffusion regimes for het- erogeneous and vapor-phase modes of combustion. A) the kinetic limit, B)

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