Political, environmental and marketing factors mean there is a global requirement to produce vehicles with improved fuel economy and reduced emissions. This thesis shows that the gasoline direct injection (GDI) engine will continue to form a significant portion of the automotive propulsion market in the short to medium term. However, to reach future targets continuous development and optimisation of these engines is essential. The introduction to this thesis discusses the role some of the key aspects of GDI engine design have on overall engine efficiency. The fuel spray is shown to be a key contributor to this, as it is a primary driver in the fuel/air mixing process, and therefore intrinsically linked to the combustion efficiency.

Liquid spray is essential to industries requiring processes such as spray coating, spray drying, spray pyrolysis, or spray cooling. This thesis reports the design, fabrication, and characterization of a thin film deposition system which utilizes a linear multiplexed electrospray (LINES) atomizer. First, a thorough review of the advantages and limitations of prior multiplexed electrospray systems leads to discussion of the design rationale for this work. Next, the line of charge model was extended to prescribe the operating conditions for the experiments and to estimate the spray profile. The spray profile was then simulated using a Lagrangian model and solved using a desktop supercomputer based on Graphics Processing Units (GPUs). The simulation was extended to estimate the droplet number density flux during deposition. Pure ethanol was electrosprayed in the cone-jet mode from a 51-nozzle aluminum LINES atomizer with less than 3% relative standard deviation in the D10 average droplet diameter as characterized using Phase Doppler Interferometry (PDI). Finally a 25-nozzle LINES was integrated into a thin film deposition system with a heated, motion controlled stage, to deposit TiO2 thin films onto silicon wafers from an ethanol based nanoparticle suspension. The resulting deposition pattern was analyzed using SEM, optical profilometry, and macro photography and compared with the numerical simulation results. The LINES tool developed here is a step forward to enabling the power of electrospray for industrial manufacturing applications in clean energy, health care, and electronics

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The first part of this work focuses on control experiments performed on an unstable kerosene-fueled turbulent combustor. Using a phase shift controller and primary fuel modulation stability is successfully gained for a wide band of global equivalence ratios allowing the limitations of the control scheme to be characterized. It is shown that control signal saturation can significantly impact the ability of the control scheme to stabilize the system. Three different regions of controllability are defined based on the degree of saturation. A hysteresis behavior is also found to exist for the controller settings depending on whether stability is being maintained or realized for an unstable system. The second part of this work focuses on the impact that primary fuel modulation has on the fuel spray. Measurements for a simplex nozzle and an air-assist nozzle are taken under both static and dynamic operating conditions with a Phase Doppler Anemometry system. The dynamic modulation is found to significantly impact the spray properties of both nozzles. / Master of Science

La vaporisation explosive, ou flashing, par dépressurisation rapide du C6F14 au travers d'une vanne à boisseau sphérique est analysée expérimentalement sur une grande plage de surchauffe. Les visualisations rapides montrent un jet s’ouvrant très largement en aval, preuve de l'existence d'un fort gradient de pression. Des mesures locales par sonde optique et par vélocimétrie phase Doppler ont permis de caractériser tailles, vitesses, concentration et flux numérique des gouttes en fonction de la surchauffe. La faible influence du degré de surchauffe sur la remontée en pression et sur les tailles et flux de gouttes suggère que le champ de pression s’adapte, et que par conséquent le liquide est soumis à une surchauffe locale bien plus faible que la surchauffe globale imposée. Différents scenarii sont discutés pour expliquer les observations, dont le fait que les tailles de gouttes sont peu sensibles à la surchauffe. Celui basé sur l’existence d’un front d’ébullition est le plus probable. / Depressurization (flashing) experiments through a ball valve were conducted with C6F14 for a large range of superheat. High-speed imaging shows a rapid and wide expansion of the jet, which evidences strong pressure gradients. Local measurements with phase detection optical probes and phase Doppler velocimetry were used to characterize size, speed, concentration and volumetric flux of drops as a function of superheat. The level of superheat has little influence on the vaporized fraction and on drop size and flux: this suggests that due to strong pressure gradients the liquid sees a much weaker level of superheat than the global superheat imposed on the system. Different scenarii are discussed to explain observations, in particular the fact that drop size remains approximately constant independent of the superheat. A scenario based on the existence of a boiling front seems to be the most consistent.

The design and optimisation of a modern gasoline direct injection (GDI) engine requires a thorough understanding of the fuel sprays characteristics and atomisation process.Therefore this thesis presents a detailed optical analysis of atomisation, penetration and interaction of multi-stream GDI sprays under engine relevant pressures and temperatures. The characteristics of the fuel spray in a GDI engine have a great influence on the fuel-air mixing and combustion processes as fuel injectors must provide adequate atomisation for vaporisation of the fuel to take place before combustion is initiated, whilst also avoiding spray impingement on the cylinder walls or piston crown. In this study multi-stream injectors, to be used within GDI engines, are quantified using Laser Doppler Anemometry (LDA) on an atmospheric bench. This process allowed for highly detailed spray analysis of droplet velocities and diameter at precise locations, using a three dimensional traverse, within the injector spray. The aim of the study was to analyse plume interaction between separate plumes of multi-stream injectors. Three multi-stream injectors were subjected to testing; two six-hole injectors and one three-hole injector. The injectors differed by having different distances between the plumes. The effect of fuel type on the liquid break-up and atomisation was investigated using Phase Doppler Anemometry (PDA) and Mie imaging. Mie imaging was also performed to capture images of fuel from a multi-stream injector as it was sprayed into a pressure chamber which was used to recreate the conditions found in an engine likely to cause flash boiling. In total, five variables were investigated: fuel pressure, ambient pressure, ambient temperature, fuel composition and injector geometry. Once processed, the recorded images allowed measurement of spray tip penetration and cone angle. Qualitative data on the change in shape of the spray was also available. The results showed that flash boiling has potential to reduce droplet diameters and improve fuel vaporisation, however, the associated change in spray shape must be taken into account to avoid problems with spray impingement. Keywords: Gasoline Direct Injection, multi-stream injector, atomisation, penetration, cone angle, Mie imaging, Phase Doppler Anemometry, flash boiling.

This diploma thesis deals with matte coatings for 3D scanning purposes. The coatings are made with spray gun which uses a vibrating membrane atomizer and air blow gun. A suspension of titanium dioxide and alcohol is used as a coating material. This thesis describes the effect of the spray gun process parameters on the deposited coatings. These include, for example type of the coating suspension or setup of the blow gun. Phase Doppler Anemometry was used to measure spray characteristics. Deposited coatings were measured with profilometer and scanned with 3D scanner to study their thickness and effect on the results of 3D reconstruction. The result of this work was the coating with thickness below 1 µm with good optical properties for 3D scanning purposes. Standard deviation of the captured point cloud from the reference plane was below 0.0011 mm.

Thermoacoustic instabilities in modern high-performance, low-emission gas turbine engines are often observable as large amplitude pressure oscillations and can result in serious performance and structural degradations. These acoustic oscillations can cause oscillations in combustor through-flows and given the right phase conditions, can also drive unsteady heat release. This coupling has the potential to enhance the amplitude of pressure oscillations. To curb the potential harms caused by the existence of thermoacoustic instabilities, recent efforts have focused on the active suppression and even complete control of these instabilities. Intuitively, development of effective active combustion control methodologies is strongly dependent on the knowledge of the onset and sustenance of thermoacoustic instabilities. Specially, non-premixed spray combustion environment pose additional challenges due to the inherent unstable dynamics of sprays. The understanding of the manner in which the combustor acoustics affect the spray characteristics, which in turn result in heat release oscillation, is therefore, of paramount importance. The experimental investigations and the modeling studies conducted towards achieving this knowledge have been presented in this dissertation. Experimental efforts comprise both reacting and non-reacting flow studies. Reacting flow experiments were conducted on a overall lean direct injection, swirl-stabilized combustor rig. The investigations spanned combustor characterization and stability mapping over the operating regime. All experiments were performed under atmospheric pressure condition, which is considered as an obvious first step towards providing valuable insights into more intense processes in actual gas turbine combustors. The onset of thermoacoustic instability and the transition of the combustor to two unstable regimes were investigated via phase-locked chemiluminescence imaging and measurement and phase-locked acoustic characterization. It was found that the onset of the thermoacoustic instability is a function of the energy gain of the system, while the sustenance of instability is due to the in-phase relationship between combustor acoustics and unsteady heat release driven by acoustic oscillations. The presence of non-linearities in the system between combustor acoustic and heat release and also between combustor acoustics and air through-flow were found to exist. The impact of high amplitude limit-cycle pressure on droplet breakdown under very low mean airflow and the localized effects of forced primary fuel modulations on heat release were also investigated. The non-reacting flow experiments were conducted to study the spray behavior under the presence of an acoustic field. An isothermal acoustic rig was specially fabricated, where the pressure oscillations were generated using an acoustic driver. Phase Doppler Anemometry was used to measure the droplet velocities and sizes under varying acoustic forcing conditions and spray feed pressures. Measurements made at different locations in the spray were related to these variations in mean and unsteady inputs. The droplet velocities were found to show a second order response to acoustic forcing with the cut-off frequency equal to the relaxation time corresponding to mean droplet size. It was also found that under acoustic forcing the droplets migrate radially away from the spray centerline and show oscillatory excursions in their movement. Non-reacting flow experiments were also performed using Time-Resolved Digital Particle Image Velocimetry to characterize modulated sprays. Frequency response of droplet diameters were analyzed in the pulsed spray. These pilot experiments were conducted to assess the capability of the system to measure dynamic data. Modeling efforts were undertaken to gain physical insights of spray dynamics under the influence of acoustic forcing and to explain the experimental findings. The radial migration of droplets and their oscillatory movement were validated. The flame characteristics in the two unstable regimes and the transition between them were explained. It was found that under certain acoustic and mean air-flow condition, bands of high droplet densities were formed which resulted in diffusion type group burning of droplets. It was also shown that very high acoustic amplitudes cause secondary breakup of droplets. / Ph. D.

Human health is significantly influenced by inhaled aerosols. Insight to the aerosol transport and deposition mechanisms is a prerequisite for both, toxicological protection against harmful particles and efficient application of inhaled therapeutic aerosols. The purpose of this doctoral thesis was to gain new knowledge of this topic on the basis of in vitro measurements. Phase-Doppler Anemometry was chosen for aerosol transport measurement, for it allows simultaneous measurement of particle size and velocity. Results were processed by means of statistical methods and frequency analysis. Deposition of spherical aerosol particles was measured by Positron Emission Tomography, while deposition of fibrous aerosol was measured by Phase-Contrast Microscopy combined with automated image analysis. All experiments were performed on physical models created on the basis of the real lung geometry. New knowledge of flow characteristics, transition from laminar to turbulent flow, effect of breathing pattern or particle size on aerosol transport and deposition in human lungs are outcomes of this work. Significant effect of the oral cavity was ascertained due to comparison of aerosol deposition in realistic and semi-realistic model with cylindrical smooth walls. Acquired data not merely extended our knowledge of aerosol behavior in lungs but it can also be used for validation of numerical simulations.

E consenso que o crescente consumo de combustíveis fósseis na geração de potencia tem provocado uma maior degradação do meio ambiente. Para mitigar os efeitos adversos desse consumo, novas fontes e usos sustentáveis de energia são necessários. O uso de etanol na atual geração de motores de combustão interna demanda informações detalhadas sobre os processos de nebulização, evaporação, mistura e combustão das gotas desse combustível. Adicionalmente, novas estratégias de injeção de combustível em MCIs com injeção direta estão em desenvolvimento, como a injeção estraticada. Essa estratégia consiste na injeção de combustível em elevadas frequências durante as etapas de admissão e combustão do ciclo motor. Neste trabalho, técnicas avançadas de diagnostico a laser são utilizadas para analisar a inuência da frequência de injeção de combustível no processo de combustão de sprays pulsados de etanol, em que as chamas resultantes são estabilizadas por um swirler. A técnica de interferometria por efeito Doppler (PDI) foi utilizada para medir o diâmetro e a componente axial da velocidade das gotas. O campo de velocidades do escoamento de ar foi avaliado pela técnica de velocimetria por imagens de partículas (PIV) em duas taxas de aquisição (7,4 Hz e 2.000 Hz) para avaliar tanto valores médios quanto rastrear estruturas coerentes no escoamento. O mesmo sistema PIV foi utilizado para identificar a posição de aglomerados de gotas pela técnica de espalhamento Mie ao longo de eventos individuais de injeção. Já a técnica de uorescência induzida por laser do radical hidroxila (LIF-OH) foi utilizada com taxa de aquisição de 4.700 Hz para rastrear a região com presença deste radical próximo ao queimador utilizado. Imagens da luminescência química espontânea foram obtidas para observar características globais das chamas. O queimador, posicionado em um ambiente aberto, e composto por um dispositivo swirler e um injetor automotivo. As frequências de injeção de 100 Hz, 250 Hz e 400 Hz foram escolhidas para as análises por produzirem chamas com características que variam desde uma chama estável e ancorada ao queimador até o comportamento similar a uma chama suspensa e instável. Etanol anidro líquido foi utilizado como combustível e fornecido ao injetor a pressão e vazão constantes para todos os casos. Os resultados indicaram que a variação na frequência de injeção produziu sprays com diferentes densidades. A menor frequência de injeção produziu um spray com maior densidade, em que as gotas formaram um aglomerado pouco sensível ao escoamento de ar na linha de centro do queimador. Esse aglomerado produz uma chama ancorada ao queimador com formato alongado e estreito. Já a maior frequência de injeção produziu um spray com menor densidade, permitindo que a dinâmica das gotas seja mais susceptível ao escoamento de ar. Essa maior inuência do escoamento de ar promoveu uma maior dispersão espacial das gotas e um processo de combustão com maior susceptibilidade a instabilidades locais do escoamento. Essas instabilidades locais foram associadas a passagem periódica de estruturas coerentes do escoamento de ar através da região de reação das chamas, produzindo uma chama com presença intermitente do radical OH e ausência de emissão de luminescência química espontânea próximo a saída do queimador. / The increase in consumption of petroleum-based fuels promotes environmental degradation and, to mitigate the adverse effects of this consumption, new sustainable sources and uses of energy are required. The use of ethanol as an option to conventional fuels on current generation of engines and gas turbines requires detailed information on atomization, evaporation, mixture and combustion processes of ethanol droplets. In addition, new strategies to fuel injection in ICEs are being developed, such as the stratied fuel injection. In this strategy, fuel is injected in higher injection frequencies along the air intake and combustion phases of the engine cycle. In this work, advanced techniques of laser diagnostic are applied to analyze the inuence of fuel injection frequency on the behavior of the combustion process of pulsed ethanol sprays, in which the resulting ames are stabilized by a swirler. The Phase Doppler Interferometry (PDI) technique is applied to measure both diameter and axial velocity of droplets produced by the injector under different conditions of injection frequency. The velocity eld of the airow is evaluated by the Particle Image Velocimetry (PIV) using two repetition rates (7,4 Hz and 2.000 Hz) to evaluated both mean values and to track coherent structures in the ow. The PIV equipment is also used to evaluate the position of droplet groups by Mie scattering during the individual injection events. A high repetition rate (4.700 Hz) Laser Induced Fluorescence of hydroxyl radical (LIF-OH) system is applied to track the region with presence of OH in a vertical plane near the exit of the burner. Images of spontaneous chemical luminescence are acquired to analyze general aspects of the ames. The burner consists on a swirler and an automotive injector and is positioned in an open space with quiescent air. The analyzed injection frequencies are 100 Hz, 250Hz and 400 Hz, presenting characteristics ranging from a stable anchored ame to a lifted-like unstable ame. Liquid anhydrous ethanol is delivered to the injector with constant pressure and ow rate for all cases. Results show different spray densities produced by the change in the injection frequency. The case with lower injection frequency produced higher spray densities, in which the formation of large groups of droplets prevents the inuence of the recirculating airow on droplet dynamics. This case presented an anchored, elongated, narrow and stable ame. The case with higher injection frequency produced lower spray densities, in which droplet dynamics are more susceptible to the velocities of the airow. This inuence of the airow promotes spatial dispersion of droplets, been more prone to instabilities on the local combustion process. These local instabilities are associated to the inuence of periodic coherent structures of the ow passing through the reaction zone, which leads to the intermittent presence of OH and the absence of spontaneous chemical luminescence near the injection plane of the burner.