The presence of gas in engine liquid cooling systems can have severe consequences for engine efficiency and life. The presence of stagnant, trapped gases will result in cooling system hotspots, causing gallery wall degradation through thermal stresses, fatigue and eventual cracking. The presence of entrained, transient gases in the coolant flow will act to reduce its bulk thermal properties and the performance of the system s coolant pump; critically the liquid flow rate, which will severely affect heat transfer throughout the engine and its ancillaries. The hold-up of gas in the pump s impeller may cause the dynamic seal to run dry, without lubrication or cooling. This poses both an immediate failure threat should the seal overheat and rubber components melt and a long term failure threat from intermittent quench cooling, which causes deposit formation on sealing faces acting to abrade and reduce seal quality. Bubbles in the coolant flow will also act as nucleation sites for cavitation growth. This will reduce the Net Positive Suction Head available (NPSHA) in the coolant flow, exacerbating cavitation and its damaging effects in locations such as the cylinder cooling liners and the pump s impeller. This thesis has analysed the occurrence of trapped gas (air) during the coolant filling process, its behaviour and break-up at engine start, the two-phase character of the coolant flow these processes generate and the effects it has on coolant pump performance. Optical and parametric data has been acquired in each of these studies, providing an understanding of the physical processes occurring, key variables and a means of validating numerical (CFD) code of integral processes. From the fundamental understanding each study has provided design rules, guidelines and validated tools have been developed, helping cooling system designers minimise the occurrence of trapped air during coolant filling, promote its breakup at engine start and to minimise its negative effects in the centrifugal coolant pump. It was concluded that whilst ideally the prevention of cooling system gases should be achieved at source, they are often unavoidable. This is due to the cost implications of finding a cylinder head gasket capable of completely sealing in-cylinder combustion pressures, the regular use of nucleate boiling regimes for engine cooling and the need to design cooling channel geometries to cool engine components and not necessarily to avoid fill entrapped air. Using the provided rules and models, it may be ensured stagnant air is minimised at source and avoided whilst an engine is running. However, to abate the effects of entrained gases in the coolant pump through redesign is undesirable due to the negative effects such changes have on a pump s efficiency and cavitation characteristics. It was concluded that the best solution to entrained gases, unavoidable at source, is to remove them from the coolant flow entirely using phase separation device(s).

Des diagnostics optiques non intrusifs ont été utilisés afin d’investiguer les mécanismes gouvernant l’évaporation de trains de gouttes en interaction ou de sprays. Une technique basée sur la fluorescence induite par laser à deux couleurs (2cLIF) du pyrrométhène 597-8C9 ensemencé en très faible concentration dans le liquide à étudier a été développée pour obtenir la température moyenne de gouttes combustibles mono et bicomposant (alcanes, alcool, cétones) évoluant dans un train de gouttes monodisperse. En parallèle, l’évolution du diamètre des gouttes a été déterminée par interférométrie en diffusion avant. L’évolution temporelle de la température et du diamètre des gouttes en évaporation a été mesurée pour une large gamme de paramètres d’injection et d’interaction. Plusieurs combustibles présentant différentes volatilités ont ainsi été étudiés dans une chambre d’évaporation. Les paramètres caractérisant les transferts de chaleur et de masse représentés par les nombres de Nusselt et de Sherwood, intervenant dans le mécanisme d’évaporation des gouttes en interaction, ont été calculés à partir des données expérimentales, ce qui a permis la caractérisation de l’influence des interactions entre gouttes sur les transferts, en mettant en évidence un effet notable de la volatilité du combustible. Ensuite la technique de 2cLIF a été étendue à la mesure de la température moyenne d’un spray de gouttes binaires composées d’un mélange n-décane / 3-pentanone et injecté dans un écoulement turbulent chauffé. Le développement d’une technique de couplage de la technique LIF avec la granulométrie phase Doppler (PDA) a permis la mesure de températures par classe de taille de goutte / Non intrusive optical diagnostics are used in order to investigate the mechanisms that govern the droplets evaporation. A new technique based on 2-colours laser-induced fluorescence (LIF) of the pyrromethene 597-8C9 was developed to obtain the mean temperature of evaporating bicomponent fuel droplets in a linear monodisperse droplet stream. In parallel size evolution of the droplet was measured thanks to forward scattering methods. Data on evaporating and interacting droplet streaming linearly have been collected for different injection parameters and several monocomponent fuels (alcohol, ketones, alkanes) that exhibit different volatilities and bicomponent fuels (mixture of n-decane and 3-pentanone), in a temperature controlled evaporation chamber. Heat and mass transfers parameters (Nusselt and Sherwood numbers) involved in the evaporation process of interacting droplets are inferred from the experimental data. The result exhibits a strong influence of the volatilities of the fuel on the effect of the interaction on heat and mass transfers. Then the 2-colours LIF technique was extended to measure the mean temperature within a spray made of bicomponent droplets (n-decane / 3-pentanone), injected in a hot air flow where the turbulence and boundary conditions are controlled. By means of a coupling with the PDA (Particle Dynamic Analyser), temperature for each size of droplets was determined

Neste trabalho, foi realizado um estudo experimental detalhado sobre a fase de formação da configuração a campo reverso, no dispositivo denominado T.C.-I da UNICAMP, com a utilização de dignósticos ópticos passivos em plasmas de hélio e hidrogênio. Para cada tipo de gás, os valores do campo de polarização, pré-ionização com temporização do crowbar e pressão de trabalho foram variados para estudar os mecanismos de formação da configuração reversa de campo, através dos diagnósticos da emissão do plasma, complementados com sondas elétricas e magnéticas, externas e internas. Para a obtenção das condições ótimas de operação da máquina, a chave crowbar, construída no próprio Laboratório de Plasma da UNICAMP, demonstrou ser bastante confiável para essa finalidade, pois o tempo entre o final da pré-ionização e o início da descarga principal era um fator importante para uma boa dinâmica de implosão, sem a interferência das oscilações da pré-ionização sobre a fase principal. Nas operações com o plasma de hélio, a melhor pressão de operação do gás foi de 18 mTorr, obtida através das intensidades da linha de HeII (4686 Â), fotodiodos, copo de Faraday e diagnósticos de fluxo excluído. Os valores típicos da densidade e temperatura obtidos foram de 3.2 x 1015cm-3 e 77 eV respectivamente . O raio da separatriz foi de 2.5 cm, durante 1.5us, decaindo rapidamente após a formação da CCR. As medidas espectrais de HeII e OII(4699Â) no plasma de hélio levaram às temperaturas iônicas de 73 a 180 eV, para uma varredura de pressão de 3.8 a 18 mTorr . Em alguns casos, parece provável ter ocorrido efeitos Stark devido a aquecimentos turbulentos atribuídos a campos elétricos microscópicos de 58 kV/cm. Nas operações com hidrogênio , basicamente todos os processos usados para o plasma de hélio foram mantidos. As linhas espectrais analisadas foram Ha, OII, NII, NIII, CIII, CIV e SiIV, tendo sido obtido, a partir das linhas de impurezas, temperaturas iônicas no centro do plasma , mais altas que as do plasma de hélio . Além disso, as temperaturas fornecidas pelas linhas de potencial de ionização mais altos, como o CIII, CIV, SiIV foram maiores que as obtidas com NII ou NIII. Nesta fase, a temperatura e densidades obtidas para a pressão de 3.3 mTorr foram respectivamente 220 eV e 2.9 X1015cm-3. Semelhantemente ao caso do hélio, algumas descargas apresentaram fenômenos prováveis de efeito Stark, tendo sido estimado um campo elétrico microscópico de 21.8 kV/cm . Verificou-se que a influência de sondas magnéticas no interior do plasma é bastante crítica, produzindo uma queda de temperatura de 235 eV para 139 eV na presença da sonda, quando medido com a linha do NIII e de 532 eV para 253 eV quando obtidas com linhas de CIII e SilV. O raio de separatriz estimado para a pressão de operação de 3.3 mTorr foi de 2.2 em com tempo de vida de 3.0 us. Foi ainda observado um novo modo de operação, com a obtenção de modos rotacionais n=4, observados usualmente em pressões de operação mais altas, de 6 a 35 mTorr. / A detailed experimental study of the formation phase in field reversed configuration device T.C.-I at UNICAMP has been carried out for the first time, using passive optical diagnostics on helium and hidrogen gas plasmas. For each type of gas, the values of bias polarization field, pre-ionization with crowbar timing and gas fill pressure have been varied to study field reversed configuration formation mechanism by using plasma emission diagnostics supported by magnetic and electric external and internal multi array probes. For the machine operation condition results, the use of crowbar switch, built at UNICAMP Plasma Laboratory, has shown very reliable operation, where the interval timing between the end of pre-ionization and main discharge phase played important role on good implosion dynamics with no influence of the pre-ionization bank RLC oscillation into the main phase. In the helium plasma operation, the best fill pressure of 18mTorr was obtained using HeII ( 4686Â) spectrum line, photodiode Faraday cup, IMACON, excluded flux diagnostics. The typical density and temperature estimated were 3.2x1015cm-3 e 75 eV respectively. The separatrix radius of 2.5 cm was obtained for 1.5us, decaying soon after the FRC formation. The spectral measurements of HeII, 0II (4699Â) in helium plasma have shown ion temperatures from 73 eV to 180 eV when the pressure is varied from 3.8 to 35 mTorr. In some cases, probable Stark effects due to turbulent heating during implosion also were observed, attributed to 58 kV/cm microscopic electric field. In the hydrogen plasma operation, basically all the process used in helium plasma also were carried out. The spectral line analyzed were Ha\' OII,NII, NIII, eIII, eIV, SiIV, having been obtained temperatures higher than helium plasma in the center of the plasma, using the impurities line. Furthermore, the ion temperatures from higher ionization potential lines (eIII, eIV, SiIV) were higher than temperatures obtained by NII or NIII lines. The average temperature calculated from NII and NIII spectral line was 220 eV and the density for hydrogen plasma was 15 -3 of 2.9 x 10 cm. The influence of internal magnetic probes was very critical, dropping the ion temperature from 235 eV to 139 eV in the presence of probe, when the temperature is calculated through NIII line or from 532 to 253 eV for eIII and SiIV line calculation. Like the helium plasma, in this case also one has been observed a probable Stark effect, attributed to 21.8 kV/cm microscopic electric field. The separatrix radius estimated for fill pressure of 3.3 mTorr was 2.2 cm with the life time of 3.0us interrupted by decaying of external field. We also observed a new plasma mode operation of n=4, usually present at high fill pressure, from 6 mTorr to 35m Torr.

This manuscript has been realized in the frame of SELENE experiment research activities. SELENE is the ac-ronym of Self-rewetting fluids for ENErgy management and consists of a space project aiming to investigate heat and mass transfer phenomena in mono-groove configuration with self-rewetting fluids (SRFs). Self-rewetting fluids are mixture showing an anomalous trend of surface tension with temperature, an inversion of the surface tension slope after certain temperature. As consequence, when the minimum in surface ten-sion is crossed, surface tension gradient at the meniscus interface pulls the liquid towards the warmest region, preventing hot spots. This mechanism is completely spontaneous and has an interesting potential when applied to heat transfer applications as heat pipes (HPs). In HPs heat is removed by the liquid at the warmest region (the evaporator) and transported at the coldest zone (the condenser) by phase change; here, heat is removed by the pipe and dissipated outside through a radiator. To operate correctly, liquid is supplied to the evaporator by capillarity and the liquid vapour is allowed to flow back to condenser from a dedicated pipe region where liquid is not allowed. Vapour condensation releases at the condenser the heat to be dissipated. When SRFs are replacing working fluid in HP applications and temperatures are higher than the characteristic minimum in surface tension, capillary force is assisted by inverse Marangoni flow at the vapour-liquid interface.Since heat pipe performances are related to liquid supplied at the evaporator, in order to compare SRFs and not SRFs working fluids, it is needed to split the contribution of Marangoni and capillary force in the liquid flow. Marangoni effect is related to surface tension gradient that, in a mixture as SRF, is dependent on temperature and local composition at the liquid interface. For all these reasons, SELENE is designed to be the link between scientific research on HPs and heat transfer applications using SRFs. SELENE consists of a mono-groove with trapezoidal section that can be considered as a “clump” of an Inner Grooved Heat Pipe (IGHP) and, in order to split capillary and Marangoni contribution, it is integrated dedicated tools providing the required data in terms of concentration and liquid meniscus shape. Experimental data are used to build a simplified thermo-soluto-fluido dynamic model describing the thermo-mechanic mechanisms between the liquid bulk and the vapour flow. In the manuscript here presented it has been carried on a technology development of the required diag-nostics for the SELENE space project. The diagnostics have been designed to work in microgravity condi-tions even if they are tested on ground. As concentration diagnostic, in the text are proposed several tech-niques and more interest is spent on the adaptation of I-VED (In vivo Embolic Detection) technology meas-uring fluid AC impedance to retrieve composition information; the technology is not yet mature to be inte-grated in SELENE but it presents interesting features to be investigated in microgravity conditions. As me-niscus reconstruction technique it is proposed a new and innovative technology developed in the frame of the presented thesis and it consists of a non-intrusive optical technique aiming to retrieve liquid meniscus shape (and so curvature) from a single visualization window mounted at the top of the SELENE breadboard.An analytical approach aiming to retrieve a simplified mathematical model of the transfer mechanisms is also provided in the text. The analytical analysis clearly shows the relations between the experimental measured data and the velocity profiles in the liquid and vapour regions. In addition, since in SELENE exper-iment the heat conduction across the groove itself is not negligible, in the text it is provided a semi-empirical thermal model based on the Multi Lumped Model (MLM) theory and able to retrieve local heat exchanged information along the pipe length. The model is used to compare experiments with different working fluids at different operational regimes. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Neste trabalho, foi realizado um estudo experimental detalhado sobre a fase de formação da configuração a campo reverso, no dispositivo denominado T.C.-I da UNICAMP, com a utilização de dignósticos ópticos passivos em plasmas de hélio e hidrogênio. Para cada tipo de gás, os valores do campo de polarização, pré-ionização com temporização do crowbar e pressão de trabalho foram variados para estudar os mecanismos de formação da configuração reversa de campo, através dos diagnósticos da emissão do plasma, complementados com sondas elétricas e magnéticas, externas e internas. Para a obtenção das condições ótimas de operação da máquina, a chave crowbar, construída no próprio Laboratório de Plasma da UNICAMP, demonstrou ser bastante confiável para essa finalidade, pois o tempo entre o final da pré-ionização e o início da descarga principal era um fator importante para uma boa dinâmica de implosão, sem a interferência das oscilações da pré-ionização sobre a fase principal. Nas operações com o plasma de hélio, a melhor pressão de operação do gás foi de 18 mTorr, obtida através das intensidades da linha de HeII (4686 Â), fotodiodos, copo de Faraday e diagnósticos de fluxo excluído. Os valores típicos da densidade e temperatura obtidos foram de 3.2 x 1015cm-3 e 77 eV respectivamente . O raio da separatriz foi de 2.5 cm, durante 1.5us, decaindo rapidamente após a formação da CCR. As medidas espectrais de HeII e OII(4699Â) no plasma de hélio levaram às temperaturas iônicas de 73 a 180 eV, para uma varredura de pressão de 3.8 a 18 mTorr . Em alguns casos, parece provável ter ocorrido efeitos Stark devido a aquecimentos turbulentos atribuídos a campos elétricos microscópicos de 58 kV/cm. Nas operações com hidrogênio , basicamente todos os processos usados para o plasma de hélio foram mantidos. As linhas espectrais analisadas foram Ha, OII, NII, NIII, CIII, CIV e SiIV, tendo sido obtido, a partir das linhas de impurezas, temperaturas iônicas no centro do plasma , mais altas que as do plasma de hélio . Além disso, as temperaturas fornecidas pelas linhas de potencial de ionização mais altos, como o CIII, CIV, SiIV foram maiores que as obtidas com NII ou NIII. Nesta fase, a temperatura e densidades obtidas para a pressão de 3.3 mTorr foram respectivamente 220 eV e 2.9 X1015cm-3. Semelhantemente ao caso do hélio, algumas descargas apresentaram fenômenos prováveis de efeito Stark, tendo sido estimado um campo elétrico microscópico de 21.8 kV/cm . Verificou-se que a influência de sondas magnéticas no interior do plasma é bastante crítica, produzindo uma queda de temperatura de 235 eV para 139 eV na presença da sonda, quando medido com a linha do NIII e de 532 eV para 253 eV quando obtidas com linhas de CIII e SilV. O raio de separatriz estimado para a pressão de operação de 3.3 mTorr foi de 2.2 em com tempo de vida de 3.0 us. Foi ainda observado um novo modo de operação, com a obtenção de modos rotacionais n=4, observados usualmente em pressões de operação mais altas, de 6 a 35 mTorr. / A detailed experimental study of the formation phase in field reversed configuration device T.C.-I at UNICAMP has been carried out for the first time, using passive optical diagnostics on helium and hidrogen gas plasmas. For each type of gas, the values of bias polarization field, pre-ionization with crowbar timing and gas fill pressure have been varied to study field reversed configuration formation mechanism by using plasma emission diagnostics supported by magnetic and electric external and internal multi array probes. For the machine operation condition results, the use of crowbar switch, built at UNICAMP Plasma Laboratory, has shown very reliable operation, where the interval timing between the end of pre-ionization and main discharge phase played important role on good implosion dynamics with no influence of the pre-ionization bank RLC oscillation into the main phase. In the helium plasma operation, the best fill pressure of 18mTorr was obtained using HeII ( 4686Â) spectrum line, photodiode Faraday cup, IMACON, excluded flux diagnostics. The typical density and temperature estimated were 3.2x1015cm-3 e 75 eV respectively. The separatrix radius of 2.5 cm was obtained for 1.5us, decaying soon after the FRC formation. The spectral measurements of HeII, 0II (4699Â) in helium plasma have shown ion temperatures from 73 eV to 180 eV when the pressure is varied from 3.8 to 35 mTorr. In some cases, probable Stark effects due to turbulent heating during implosion also were observed, attributed to 58 kV/cm microscopic electric field. In the hydrogen plasma operation, basically all the process used in helium plasma also were carried out. The spectral line analyzed were Ha\' OII,NII, NIII, eIII, eIV, SiIV, having been obtained temperatures higher than helium plasma in the center of the plasma, using the impurities line. Furthermore, the ion temperatures from higher ionization potential lines (eIII, eIV, SiIV) were higher than temperatures obtained by NII or NIII lines. The average temperature calculated from NII and NIII spectral line was 220 eV and the density for hydrogen plasma was 15 -3 of 2.9 x 10 cm. The influence of internal magnetic probes was very critical, dropping the ion temperature from 235 eV to 139 eV in the presence of probe, when the temperature is calculated through NIII line or from 532 to 253 eV for eIII and SiIV line calculation. Like the helium plasma, in this case also one has been observed a probable Stark effect, attributed to 21.8 kV/cm microscopic electric field. The separatrix radius estimated for fill pressure of 3.3 mTorr was 2.2 cm with the life time of 3.0us interrupted by decaying of external field. We also observed a new plasma mode operation of n=4, usually present at high fill pressure, from 6 mTorr to 35m Torr.

[EN] The potential of diesel engines in terms of robustness, efficiency and energy density has made them widely used as power generators and propulsion systems. Specifically, fuel atomization, vaporization and air-fuel mixing, have a fundamental effect on the combustion process, and consequently, a direct impact on pollutant formation, fuel consumption and noise emission. Since the combustion chamber has a limited space respect to the spray penetration, wall impingement is considered to be a common event in direct injection diesel engines, having a relevant influence in the spray evolution and its interaction with both surrounding air and solid walls. This makes of spray-wall interaction an important factor for the combustion process that is still hardly understood. At cold-start conditions, the low in-chamber pressures and temperatures promote the deposition of fuel in the piston wall, which leads to a boost in the formation of unburned hydrocarbons. Additionally, modern design trends such as the increment of rail pressures in injection systems and the progressive reduction of the engine displacement, favor the emergence of spray collision onto the walls. In spite of the evident relevance of the comprehension of this phenomenon and the efforts of engine researchers to reach it, the transient nature of injection process, its small time scales and the complexity of the physical phenomena that take place in the vicinity of the wall, make challenging the direct observation of this spray-wall interaction. Even though computational tools have proven to be priceless in this field of study, the need for reliable experimental data for the development of those predictive models is present. This thesis is aimed to shed light on the fundamental characteristics of spray-wall interaction (SWI) at diesel-like chamber conditions. A flat wall was set at different impingement distances and angles respect to the spray. In this way, two different kinds of experimental investigations on colliding sprays were carried out: A transparent quartz wall was employed into the chamber to, in isolation, analyze the macroscopic characteristics of the spray at both evaporative inert and reactive conditions, which have been observed laterally and through the wall, thanks to the use of a high-pressure and high-temperature vessel with optical accesses. This same test rig was used in the second kind of experiments, where instead of the quartz plate, a stainless steel wall was used to capture the effect of the operating conditions on the heat flux between the wall and the spray during the injection-combustion events and to determine how spray and flame evolution are affected by realistic heat transfer situations. This wall was instrumented to control its initial in-chamber surface temperature and to measure its variation with time by using high-speed thermocouples. Tests at free-jet conditions were also performed in order to provide a solid comparative base for those experiments. / [ES] El potencial de los motores diesel en términos de robustez, eficiencia y la densidad de energía los ha hecho ser ampliamente usados como generadores de energía y sistemas propulsivos. Específicamente, la atomización de combustible, vaporización y mezcla de aire y combustible tienen un efecto fundamental en el proceso de combustión y, en consecuencia, un impacto directo en la formación de emisiones contaminantes, consumo de combustible y generación de ruido. Dado que la cámara de combustión tiene un espacio limitado con respecto la capacidad de penetración del chorro, el impacto de la pared se considera bastante común en motores de inyección directa diésel, que tienen una influencia relevante en la evolución del chorro y su interacción con el aire circundante y las paredes sólidas. Esto hace de interacción chorro-pared, un factor importante para el proceso de combustión que aún es dificilmente comprendido. En condiciones de arranque en frío, las bajas presiones y temperaturas en la cámara promueven la deposición de combustible en la pared del pistón, lo que conduce a un aumento en los niveles de formación de hidrocarburos no quemados. Además, las tendencias modernas de diseño como el incremento de las presiones de rail en los sistemas de inyección y la progresiva reducción en la cilindrada de los motores, favorecen la aparición de colisiones entre chorro y pared. A pesar de la evidente importancia en la comprensión de este fenómeno y los esfuerzos de los investigadores para alcanzarla, la transitoria naturaleza del proceso de inyección, sus pequeñas escalas de temporales y la complejidad de los fenómenos físicos que tienen lugar en las proximidades de la pared, hacen que la observación directa de esta interacción chorro-pared sea un desafío. Aunque las herramientas computacionales han demostrado ser invaluables en este campo de estudio, la necesidad de datos experimentales confiables para el desarrollo de esos modelos predictivos está muy presente. Esta tesis tiene como objetivo arrojar luz sobre las características fundamentales de la interacción chorro-pared (SWI por sus siglas en inglés) en condiciones de cámara similares a las de un motor diesel. Se colocó una pared plana a diferentes distancias de impacto y ángulos con respecto al jet. De esta manera, dos tipos diferentes de investigaciones experimentales sobre chorros en colisión se llevaron a cabo: se empleó una pared de cuarzo transparente en la cámara para, de forma aislada, analizar las características macroscópicas del chorro en condiciones evaporativas inertes y reactivas, que pueden observarse lateralmente y a través de la pared, gracias al uso de una instalación de alta presión y alta temperatura ópticamente accesible. Esta misma instalación se utilizó en el segundo tipo de experimentos en los que se introdujo una pared de acero inoxidable para capturar adicionalmente el efecto de las condiciones de operación en el flujo de calor entre ésta y el chorro durante los eventos de inyección y combustión y para determinar cómo la evolución del chorro y la llama son afectadas por una situación realista de transferencia de calor. Esta pared fue instrumentada para controlar la temperatura inicial de su superficie expuesta a la cámara y medir su variación con el tiempo, utilizando termopares de alta velocidad. Ensayos en condiciones de chorro libre también se realizaron para proporcionar una base comparativa sólida para esos experimentos. / [CA] El potencial dels motors dièsel en termes de robustesa, eficiència i la densitat d'energia els ha fet ser àmpliament usats com a generadors d'energia i sistemes propulsius. Específicament, l'atomització de combustible, vaporització i barreja d'aire i combustible tenen un efecte fonamental en el procés de combustió i, en conseqüència, un impacte directe en la formació d'emissions contaminants, consum de combustible i generació de soroll. Atès que la cambra de combustió té un espai limitat pel que fa la capacitat de penetració de l'raig, l'impacte de la paret es considera bastant comú en motors d'injecció directa dièsel, que tenen una influència rellevant en l'evolució del doll i la seva interacció amb el aire circumdant i les parets sòlides. Això fa d'interacció doll-paret, un factor important per al procés de combustió que encara és difícilment comprès. En condicions d'arrencada en fred, les baixes pressions i temperatures a la cambra promouen la deposició de combustible a la paret del pistó, el que condueix a un augment en els nivells de formació d'hidrocarburs no cremats. A més, les tendències modernes de disseny com l'increment de les pressions de rail en els sistemes d'injecció i la progressiva reducció en la cilindrada dels motors, afavoreixen l'aparició de col·lisions entre el doll i la paret. Tot i l'evident importància en la comprensió d'aquest fenomen i els esforços dels investigadors per aconseguir-la, la transitòria naturalesa de l'procés d'injecció, les seves petites escales de temporals i la complexitat dels fenòmens físics que tenen lloc en les proximitats de la paret , fan que l'observació directa d'aquesta interacció doll-paret siga un desafiament. Tot i que les eines computacionals han demostrat ser invaluables en aquest camp d'estudi, la necessitat de dades experimentals fiables per al desenvolupament d'aquests models predictius està molt present. Aquesta tesi té com a objectiu donar llum sobre les característiques fonamentals de la interacció doll-paret (SWI per les seues sigles en anglès) en condicions de cambra similars a les d'un motor dièsel. Es va col·locar una paret plana a diferents distàncies d'impacte i angles pel que fa al jet. D'aquesta manera, dos tipus diferents d'investigacions experimentals sobre dolls en col·lisió es van dur a terme: es va emprar una paret de quars transparent a la cambra per, de forma aïllada, analitzar les característiques macroscòpiques del doll en condicions evaporació inerts i reactives, que poden observar lateralment i a través de la paret, gràcies a l'ús d'una instal·lació d'alta pressió i alta temperatura òpticament accessible. Aquesta mateixa instal·lació es va utilitzar en el segon tipus d'experiments en els quals es va introduir una paret d'acer inoxidable per capturar addicionalment l'efecte de les condicions d'operació en el flux de calor entre aquesta i el dull durant els esdeveniments d'injecció i combustió i per determinar com l'evolució del doll i la flama són afectades per una situació realista de transferència de calor. Aquesta paret va ser instrumentada per controlar la temperatura inicial de la seua superfície exposada a la càmera i mesurar la seua variació amb el temps, utilitzant termoparells d'alta velocitat. Assajos en condicions de doll lliure també es van realitzar per proporcionar una base comparativa sòlida per a aquests experiments. / Peraza Ávila, JE. (2020). Experimental study of the diesel spray behavior during the jet-wall interaction at high pressure and high temperature conditions [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/149389 / TESIS

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