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The following paper presents a one-dimensional numerical model for simulating transient thermohydraulic pipe flow based on the Method of Characteristics. In addition to mass and momentum conservation, the proposed scheme also guarantees compliance with the laws of thermodynamics by solving the energy equation. The model covers transient changes in fluid properties due to pressure changes, heat transfer and dissipation. The presented methodology also allows the computation of the transient temperature distribution in the pipe wall through an additional ordinary finite difference scheme. The numerical procedure is implemented in the commercial simulation software DSHplus. The capability of the code is examined by comparing the simulation results with theoretical solutions and experimental data.

The Marine Corps Systems Command documented mission requirements that cannot be met by current rebreathers. They need to extend dive times without compromising the stealth and compact design of existing devices. This can be accomplished by reducing the fresh gas flow rate. The current flow rate is adequate to support a diver in heavy work. However, the diver will be utilizing a Diver Propulsion Device (DPD) during a large portion of the mission in question. The assumption, then, is that this portion of the mission will not require "hard work". Thus, a new fresh gas flow rate can be established which is sufficient to sustain a Marine diver using a DPD but is conservative enough to extend the duration of the dive. This experiment was designed for manned testing of the rebreathers in such a way to establish the average oxygen consumption rate for divers using a DPD. Marine divers were fitted with a Divex Shadow Excursion (DSE) rebreather modified with a Draeger C8A PO2 monitor coupled with a Delta P VR3 dive computer. The DSE is a semiclosed-circuit underwater breathing apparatus that provides a constant flow of mixed gas containing oxygen and nitrogen or helium to the diver. The partial pressure of oxygen (PO2) and diver depth were monitored and recorded at ten-second intervals. The Navy Experimental Diving Unit has developed and tested a computational algorithm that uses the PO2 and depth to compute the oxygen consumption rate. Two techniques were employed to estimate the error in this approach: curve fitting and propagation of error. These methods are detailed and the results are presented. They show that the fresh gas flow rate can be safely reduced while the diver is utilizing the DPD, which consequently, will substantially increase the dive time allowed by the device.

Fuel direct injection represents one of the key turning points in the development of the Diesel engines. The appeal of this solution has been growing thanks to the parallel advancement in the technology of the injection hardware and in the knowledge of the physics involved in the spray formation and combustion. In the present thesis, the effect of partial needle lift and injection rate shaping has been investigated experimentally using a multi-orifice Diesel injector. Injection rate shaping is one of the most attractive alternatives to multiple injection strategies but its implementation has been for long time impeded by technological limitations. A novel direct-acting injector prototype made it possible to carry out the present research: this injector features a mechanical coupling between the nozzle needle and the piezo-stack actuator, allowing a fully flexible control on the nozzle needle movement and enabling partial needle lift as well as the implementation of alternative injection rate shapes typologies. Different optical diagnostics were applied to study the spray development and combustion in a novel continuous flow test chamber that allows an accurate control on a wide range of thermodynamic conditions (up to 1000K and 15MPa). In addition, hydraulic characterization tests were carried out to analyze the fuel flow through the injector nozzle. Partial needle lift has been found to affect the injection event, reducing the mass flow rate (as expected) but also causing a reduction in the effective orifice area and an increase on the spreading angle. Moreover, at this condition, higher hole-to-hole dispersion and flow instabilities were detected. Needle vibrations caused by the needle interactions with fuel flow and by the onset of cavitation in the needle seat are likely the causes of this behavior. Injection rate shaping has a substantial impact on the premixed phase of the combustion and on the location where the ignition takes place. Furthermore, the results proved that the modifications in the internal flow caused by the partial needle lift are reflected on the ignition timing. On the other hand, the analysis of the experimental data through a 1D spray model revealed that an increasing mass flow rate (e.g. ramp or boot injection rate profiles) causes an increase in the fuelair equivalence ratio at the lift-off length and a consequent higher soot formation during the diffusive phase of the combustion. Finally, the wide range of boundary conditions tested in all the experiments served to draw general conclusions about the physics involved in the injection/combustion event and, in some cases, to obtain statistical correlations. / Bardi, M. (2014). PARTIAL NEEDLE LIFT AND INJECTION RATE SHAPE EFFECT ON THE FORMATION AND COMBUSTION OF THE DIESEL SPRAY [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37374

Le biodiesel est un carburant très intéressant car du fait de son caractère renouvelable il augmente la sécurité énergétique et est plus respectueux de l'environnement. De plus il a un indice de cétane plus élevé et une plus faible teneur en soufre et en aromatique que le Diesel pur. Les principaux inconvénients de biodiesel sont sa viscosité élevée, sa faible teneur en énergie, un point trouble et le point d'écoulement plus élevé, une émission d'oxyde d'azote (NOx) plus élevée lors de sa combustion et un coût élevé. Cependant, de nombreux pays peuvent produire leur propre biodiesel et assurer des mélanges d’une teneur entre 2 et 20% de biodiesel avec du carburant diesel. Les nouvelles normes Euro VI impliquent des problèmes liés au démarrage à froid. Pour approfondir notre compréhension de ces mélanges, il est nécessaire de tester un plus large éventail de carburants de 10 à 50% de biodiesel jusqu’à -8°C pour pallier le manque d’information dans la littérature. La présente thèse porte sur une étude expérimentale sur l'influence des propriétés physiques et chimiques des mélanges de carburants Biodiesel/Diesel sur l'injection : taux et répartition des sprays dans des conditions de non évaporation. L'originalité de l'approche concerne la définition d'une matrice de carburant (un total de neuf combustibles) dont les propriétés sont modifiées via le pourcentage de biodiesel ou la température. En outre tous les stades de l'injection diesel sont considérés. Des expériences ont été menées en enceinte contrôlée en température. L'analyse se concentre principalement sur la phase quasi-stationnaire de l'événement d'injection et les résultats expérimentaux sont disponibles pour calibrer des modèles physiques et de nouvelles corrélations empiriques sont proposées. / Biodiesel is a very interesting fuel because it is renewable, thus increasing energy security, it is environmentally friendly, and it has a higher cetane number and a lower sulfur and aromatic content than pure Diesel. The main disadvantages of biodiesel are its higher viscosity, lower energy content, higher cloud point and pour point, higher nitrogen oxide (NOx) emissions, lower power and high cost. However, many countries can produce their own biodiesel and blends with diesel fuel of 2–20%. The new Euro VI standards involve problems related to cold-start. To further our understanding of these mixtures, it is necessary to test a larger range of fuels with a biodiesel fraction of 10 to 50%, and under cold temperatures, no information is available in the literature, however, on the injection rate and spray penetration of Diesel–Biodiesel blends in cold conditions. The present thesis focuses on an experimental study of the Influence of physical and chemical properties of biodiesel, Diesel and their blended fuels on injection and spray for Diesel engine application. The originality of the approach concerns the definition of a fuel matrix (a total of 9 fuels) for which properties are varied by varying the percentage of biodiesel and the temperature. Moreover all the stages of Diesel injection are considered. Experiments were conducted in dedicated temperature-controlled vessels. The analysis focuses mainly on the quasi-stationary phase of the injection event and experimental results are scaled to physics-based models and new empirical correlations are proposed.

The following paper presents a one-dimensional numerical model for simulating transient thermohydraulic pipe flow based on the Method of Characteristics. In addition to mass and momentum conservation, the proposed scheme also guarantees compliance with the laws of thermodynamics by solving the energy equation. The model covers transient changes in fluid properties due to pressure changes, heat transfer and dissipation. The presented methodology also allows the computation of the transient temperature distribution in the pipe wall through an additional ordinary finite difference scheme. The numerical procedure is implemented in the commercial simulation software DSHplus. The capability of the code is examined by comparing the simulation results with theoretical solutions and experimental data.

The diploma thesis focuses on the optimization of technological parameters of plastic injection molding and the study of the influence of technological parameters on the quality of molded test specimens’ type 1A. The quality of molded parts for 3 types of polypropylene (PP) with different melt flow rate (Mosten GB 002, Mosten GB 218, Mosten MA 230) and 1 type of polystyrene (PS) (Krasten PS GP 154) was evaluated in terms of dimensional stability and weight. The contribution of software for modeling the plastic injection molding process was evaluated in this work. SOLIDWORKS Plastics software was used to optimize technological parameters. The construction of the bodies, mold and cooling system was constructed, and test bodies were produced on the basis of parameters obtained from the simulation of the injection molding process. Their quality parameters were compared with a 3D model and for each of the studied materials the optimal technological parameters were selected in terms of quality and the degree of influence of individual injection parameters on the quality of moldings was evaluated. The accordance of the results of the theoretical simulation with the real experiment was proved and a computational module independent of the optimized quality parameters, generally suitable for optimizing the quality parameters of the injected parts, was developed.

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