This thesis is dealing with testing of two atomizers in combustion of liquid fuels and natural gas. There is a simple analysis of problems, principles and methods of atomizing liquids executed. Problem of pneumatic atomizing liquids is also described in detail. In the next chapters there is a plan and running of testing processed. Overall behavior of the atomizers and flame is evaluated from the outcome measurement and the power characteristics of atomizers and influence of GLR on the quality of combustion are determined. Overall rating of the testing is presented in conclusion this thesis.

Cette thèse est dédiée à l'amélioration des modèles d'atomisation pour les injecteurs automobiles. Le but est de développer et d'évaluer des modèles numériques permettant de capturer le passage de structures liquides en cours d'atomisation depuis les grandes échelles vers les petites échelles de sous-maille dans des configurations complexes. Dans un premier temps, nous mettons en place une procédure de calcul permettant le passage d'une description Eulérienne d'un spray à une procédure Lagrangienne. Afin de ne pas perdre les plus petites structures liquides, celles-ci seront transformées en particules Lagrangienne. Une analyse sur différentes grandeurs physiques, telles que la masse, la quantité de mouvement ou l'énergie cinétique turbulente, lors de cette transformation a été réalisée. L'autre partie de ce travail est consacrée au développement d'un modèle de simulation aux grandes échelles des écoulements diphasiques. La simulation de l'atomisation requiert un traitement spécifique de l'interface. Deux cas limites sont traités dans la littérature : • L'interface peut bien être capturée par le maillage. A ces endroits, une méthode classique de type DNS (Direct Numerical Simulation), comme les méthodes VOF (Volume of Fluid), doit être utilisée. • Lors de la création de plissements inférieurs à la taille de la maille, le maillage ne permet plus de suivre fidèlement l'interface. Il faut alors que le calcul reproduise des résultats d'une méthode LES (Large Eddy Simulation) considérant des structures et des gouttes inférieures à la taille de la maille. Ainsi, la problématique principale consiste à déterminer la configuration dans laquelle se trouve l'interface. La mise en œuvre de ce modèle a permis d'obtenir des résultats dans une configuration proche de l'injection Diesel, qui sont alors comparés à une DNS de référence. / This thesis is dedicated to improve atomization models for automobile injectors. The aim is to develop and evaluate numerical models to capture the liquid structure while they are being atomized from large scales to small sub grid scales in complex configurations. Initially, a calculation procedure is introduced for the transition to an Eulerian description of a spray into a Lagrangian description. In order not to lose the smallest fluid structures, they will be transformed into Lagrangian particles. During this process, an analysis is been performed with various physical parameters such as mass, momentum, or turbulent kinetic energy. The other part of this work is dedicated to the development of a LES (Large Eddy Simulation) for multiphase flow. The simulation of the spray requires a specific treatment of the interface. Two limiting cases are treated in the literature: • The interface may be captured by the mesh. At these locations, a conventional method of DNS (Direct Numerical Simulation) should be used, like the VOF method (Volume of Fluid). • When creating pleating smaller than the size of the mesh, the mesh can no longer match the interface. Then, the calculation must reproduce results from a LES method that take into account structures and drops smaller than the mesh size. Thus, the main problem is to define the configuration of the interface. The development of this model allows to obtain results in a configuration close to the Diesel injection's, which are then compared to a reference DNS.

Although the suspended droplet evaporation and combustion have been studied for decades, fundamental research pertaining to the stochastic phenomena of complex multicomponent mixtures is extremely rare. In this work, an experimental suspended droplet study of Arabian light oil was held to study the frequency of puffing and micro-explosion phenomena during the evaporation/pyrolysis process. The experiments were conducted at three different evaporation temperatures (350 C, 440 C, and 570 C), chosen in accordance with the TGA profle obtained. The suspended droplet experiments were conducted on a furnace with optical access and a gas controlled-preheating system. The droplet size was optically registered at 500 fps by a LaVision Imager Pro HS high-speed camera coupled with a magnification lens Nikon AF-S Micro Nikkor 105 mm. Furthermore, a computer-vision data postprocessing program was developed to identify contours and measure the size of the objects in the frame in order to register the temporal evolution of the droplet size. Additionally, a new approach for characterizing the droplet vaporization of complex multi-component fuels is proposed. This method allowed us to study the continuum (ideal evaporation) and stochastic processes separately, by following the profile of the average normalized square diameter ((D=D0)2) and quantifying the breakup intensity (β) of each stochastic event. Based on the behavior of (D=D0)2, two consecutive stages were identified at every temperature investigated, the swelling and the regression stage. At 350 ◦C and 440 ◦C, the evaporation was finally controlled purely by the diffusion evaporation, whereas at 570 ◦C a pure diffusion stage was not spotted. Instead, a second swelling was registered, where an amorphous carbonaceous structure was formed. Due to the pyrolysis of the heavy hydrocarbons dominated the process. The stochastic events involved during the evaporation were successfully identified and classified in breakup modes depending on their β. Additionally, the effect of the temperature on the breakup events was assessed. Showing that the number of breakup events increased exponentially with temperature.

Powder metallurgy (PM) is a technology used to manufacture near net shape components for an increasing number of applications like automobile components, aircraft components, cutting tools, refractory, household appliances, etc. The general PM process comprises of Powder manufacturing/powder tailoring, Compacting, and Sintering. Based on product’s final requirements, optional secondary operations are performed. PM components for automotive application are experiencing a growth coupled with new challenges.  PM´s capability for producing complex net shaped components with desired properties has enabled it to be an alternative to other traditional manufacturing processes. Average U.S. made vehicle in 2010 contained an estimated 41.6 pounds of PM parts and in Europe, the average per vehicle PM parts in 2010 is estimated 18.5 pounds [3].  New design goals set by OEMs (original equipment manufacturers) demands for complex shaped components with high mechanical properties. Stupendous developments are done in the field of PM component manufacturing and PM raw material manufacturing, endeavoring to cater the technical and economic needs set by OEMs. Based on the application, unique powder characteristics are demanded which are in turn associated with the quality of powders produced.  Powder production for conventional PM application encompasses reduction or atomization followed by annealing. Reduced powders are called sponge iron powders, used for low density (density of PM component) application and atomized powders are used for relatively high density application. Atomization can be further classified into water atomization and gas atomization. Coarse, irregular shapes are the common features of water atomized powders and fine, spherical shapes are the common features of gas atomized powders. Water atomization is one of the prominent methods used in production of powders for conventional PM application. Oxygen content of the powders produced by water atomization plays an important role in determining it’s as sintered properties. In this work, oxide formation during various stages of water atomization and annealing were studied for iron, carbon and manganese alloy system and iron, carbon, chromium, molybdenum and manganese alloy system. Manganese content was varied (0.0%, 0.5%, 1.0%) in the above said two alloy system maintaining the same amount of other alloying constituents for comparison. Total oxygen content and oxide composition formed during processing were studied. Both alloy system showed that total oxygen content increases with increasing manganese content. The composition of oxides includes manganese, chromium and iron for Fe+C+Cr+Mo+Mn alloy system and manganese and iron for Fe+C+Mn alloy system. Key words: Powder metallurgy, Water atomization, Gas atomization, Reduced powders,  Oxygen content, Oxide composition, Annealing, Sintered properties, Iron, Chromium, Molybdenum, Manganese.

Icing on aircraft wings is one of the leading causes of aircraft crashes. It is mainly caused due to accumulation of ice or snow on the wing surface due to impact with supercooled droplets when passing through clouds at high altitudes, causing loss of lift obtained by the wings. It was found that droplet impact characteristics are dependent on droplet size, surface roughness, surface material hydrophobicity, and droplet impact velocity. As a continuation of the study of droplet impact contact characteristics by varying surface roughness and impact velocity, this study focuses on droplets impacting the vibrating surface at frequencies between 2-7 kHz. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. The first set of data is collected by keeping roughness constant and increasing the amplitude of the vibration to observe the critical amplitude at which atomization is initiated. The surface roughness is varied for the second set of experiments. The data is quantified using image processing of the high-speed videos to obtain the rate of ejection for each case. / Master of Science / Icing on aircraft wings is among the leading causes of crashes, which involves small freezing water drops sticking to the wing surface thus reducing the lift. This study is an investigation to experimentally observe how small water droplets interact with surfaces vibrating at high frequencies when impacted. Surface roughness, materials, droplet velocities, and frequency of vibration have been varied and the droplet was captured using high-speed photography to study their effect on the aforementioned interaction. Glass, PET-G. and aluminum having specific roughness were fabricated using laser and chemical etching. Atomization (water drop splitting into smaller droplets and ejecting from the surface) has been observed at different rates for all frequencies. A relation between the amplitude of the vibration and the rate of atomization was found. The effect of varying frequencies and surface roughness has also been documented.

Superhydrophobic (SH) surfaces are characterized by their extraordinary water repellent qualities. When water comes in contact with these surfaces, it beads up and rolls around. This phenomenon is due partially to surface chemistry which promotes weak adhesive forces between liquid and solid. However, micro- and nanoscale surface roughness also plays a crucial role by trapping air beneath the liquid, reducing liquid-solid contact. Many advantages of these surfaces have been identified, including drag reduction and self-cleaning properties, and the body of research regarding them has grown rapidly over the past few decades.This thesis is concerned with water droplets impinging superheated, superhydrophobic surfaces. In these scenarios, boiling is common in the droplet, producing vapor bubbles which burst through the droplet lamella and cause a spray of miniscule water particles known as thermal atomization. The work contained in this thesis uses an image processing technique to quantify trends in thermal atomization intensity during droplet impingement scenarios for a range of surface microstructure configurations, superheat temperatures, and Weber numbers.In one study, droplet impingement on a smooth hydrophobic and three post-patterned SH surfaces of similar solid fraction is considered. In general, as pitch (center-to-center distance between posts) increases, atomization intensity decreases. This is attributed to the enhanced ability for vapor escape beneath the droplet that is present for wider pitch surfaces. Atomization intensity increases with increasing Weber number for each of the surfaces considered. Additionally, the Leidenfrost point is found to increase with increasing Weber number and decreasing pitch.Next, thermal atomization on SH surfaces with two distinct microstructure configurations is considered: square posts (which allow vapor escape between structures) and square holes (which block vapor escape). Tests are done for each configuration with varying microstructure height, and structure spacing and solid fraction are held constant. Comparing the two configurations at each structure height and Weber number, the post-patterned surfaces suppress atomization for a large number of scenarios compared to the hole surfaces, supporting the theory that vapor escape through microstructures suppresses atomization. Microstructure height significantly affects trends in atomization intensity with surface temperature and Weber number. The LFP is seen to decrease with increasing height.

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Engineering applications of unconventional fuels like HFOs require a detailed understanding of the physics associated with their evaporation. The processing of HFOs involves forming a spray; therefore, studying droplets is of particular interest. The work described in this dissertation tackles two of the most obscure aspects associated with HFOs modelling. The first aspect is the identification of a valid chemical description of the structure of the fuel. In particular, the author focused on finding a methodology that allows identifying a discrete surrogate to describe the complex pool of molecules of which the fuels are made. The second part of the work was devoted to understand and model thermally-induced secondary breakup, which is the primary cause of deviation from the "d2" that multi-component droplet experience. The formulation of a surrogate was successfully achieved by developing and implementing a new algorithm that allows building a surrogate from a set of easily accessible physical properties. A new methodology for the post-processing of experimental data was formulated. The methodology consists of studying the evolution of the normalized distance of the interface from the droplet’s centroid instead of its diameter. The new approach allowed the separation between interface deformation and expansion/shrinking. The information was then processed using the dynamic mode decomposition to separate the stochastic contribution associated with secondary atomization and the deterministic contribution of vaporization. Finally, thermally induced secondary atomization was studied using a CFD code appositely developed. The code is based on the geometric Volume of Fluid (VoF) method and consists of a compressible, multi-phase, multi-component solver in which phase change is considered. The novelty in the proposed approach is that the evaporation source term and the surface tension force are evaluated directly from the geometrically reconstructed interface. The code was validated against the exact solution of analytically solvable problems and experimental data. The solver was then used to study HFO secondary breakup and perform a parametric analysis that helped to understand the problem’s physics. A possible application of this framework is the formulation of sub-models to be applied in spray calculations.