Manufacturers face the challenge of enhancing fuel efficiency, engine performance, and reducing harmful emissions. Novel fuel injection technologies can assist in meeting such demands. This dissertation summarizes the stages in the design, prototyping and experimental analysis of a direct-acting piezoelectric fuel injector concept. In the proposed design, a piezoelectric stack actuator is used to directly control the injection of fuel in order to enhance the injection characteristics by utilizing the fast response time of the actuator. The direct-acting concept was implemented by developing a motion inverter in the form of a disc that reverses the direction of the input and allows the actuator to directly control injections. Tests with input signals similar to those used in diesel engines confirmed the theoretical calculations and verified the prototype’s performance. This design can control the quantity of injected fuel more precisely than currently available commercial injectors.

Manufacturers face the challenge of enhancing fuel efficiency, engine performance, and reducing harmful emissions. Novel fuel injection technologies can assist in meeting such demands. This dissertation summarizes the stages in the design, prototyping and experimental analysis of a direct-acting piezoelectric fuel injector concept. In the proposed design, a piezoelectric stack actuator is used to directly control the injection of fuel in order to enhance the injection characteristics by utilizing the fast response time of the actuator. The direct-acting concept was implemented by developing a motion inverter in the form of a disc that reverses the direction of the input and allows the actuator to directly control injections. Tests with input signals similar to those used in diesel engines confirmed the theoretical calculations and verified the prototype’s performance. This design can control the quantity of injected fuel more precisely than currently available commercial injectors.

Efforts to improve diesel fuel sprays have led to a significant increase in fuel injection pressures and a reduction in nozzle-hole diameters. Under these conditions, the likelihood for the internal nozzle flow to cavitate is increased, which potentially affects spray breakup and atomisation, but also increases the risk of causing cavitation damage to the injector. This thesis describes the study of cavitating flow phenomena in various single and multi-hole optical nozzle geometries. It includes the design and development of a high-pressure optical fuel injector test facility with which the cavitating flows were observed. Experiments were undertaken using real-scale optical diesel injector nozzles at fuel injection pressures up to 2050 bar, observing for the first time the characteristics of the internal nozzle-flow under realistic fuel injection conditions. High-speed video and high resolution photography, using laser illumination sources, were used to capture the cavitating flow in the nozzle-holes and sac volume of the optical nozzles, which contained holes ranging in size from 110 micrometers to 300 micrometers. Geometric cavitation in the nozzle-holes and string cavitation formation in the nozzle-holes and sac volume were both observed using transient and steady-state injection conditions; injecting into gaseous and liquid back pressures up to 150 bar. Results obtained have shown that cavitation strings observed at realistic fuel injection pressures exhibit the same physical characteristics as those observed at lower pressures. The formation of string cavitation was observed in the 300 micrometers multi-hole nozzle geometries, exhibiting a mutual dependence on nozzle flow-rate and the geometry of the nozzle-holes. Pressure changes, caused by localised turbulent perturbations in the sac volume and transient fuel injection characteristics, independently affected the geometric and string cavitation formation in each of the holes. String cavitation formation of was shown to occur when free-stream vapour was entrained into the low pressure core of a sufficiently intense coherent vortex. Hole diameters less than or equal to 160 micrometers were found to suppress string cavitation formation, with this effect a result of the reduced nozzle flow rate and vortex intensity. Using different hole spacing geometries, it was demonstrated that the formation of cavitation strings in a particular geometry became independent of fuel injection and back pressure once a threshold pressure drop across the nozzle had been reached.

New technologies are constantly developing towards the goal of increasing the performance of gas turbine engines while reducing pollutant emissions. The design of the combustion system is vital in the drive to reduce pollutants in order to meet legislative targets. As part of this, the fuel injector is crucial in preparing the fuel for combustion through atomization and correct mixing with the air flow. Thus, it is desirable to develop techniques to allow the analysis of performance in these key criteria and improve the understanding of both fuel injector aerodynamics and fuel atomisation. Particle Image Velocimetry (PIV) allows for spatially resolved velocity data of flow fields to be recorded and therefore enables the inspection of flow behaviour.

No description available.

No description available.

[pt] O desenvolvimento de um motor de quatro tempos, de ignição por centelha, com injeção direta de combustível dentro da câmara de combustão foi uma iniciativa importante para o mercado automobilístico mundial. O potencial termodinâmico deste tipo de motor e sua notória melhoria na economia de combustível têm feito com que a tecnologia seja foco de um grande número de projetos de pesquisa, com o objetivo de entender, desenvolver e aperfeiçoar o sistema de injeção direta de combustível. No entanto, para atender aos novos limites de emissões estabelecidas pela especificação EURO 5, foi necessária uma reavaliação do projeto da geometria do injetor, o que ocasionou no desenvolvimento de um novo componente com um maior número de furos e com uma redução do diâmetro dos mesmos (injetor multifuros). Essa alteração no projeto visa garantir uma melhor pulverização, otimização da relação ar/combustível e, consequentemente, um melhor processo de queima na câmara de combustão, atendendo dessa forma os limites de emissões estabelecidos pela diretriz normativa vigente. Os processos de preparação da mistura, injeção, vaporização e controle do escoamento de ar dentro do cilindro têm sido as principais fontes de publicações de periódicos que estudam o sistema de injeção direta. O presente trabalho, por sua vez, tem por finalidade avaliar a formação de depósitos de compostos inorgânicos nos injetores, provenientes da utilização de combustíveis formulados com diferentes teores de sulfato. O motor utilizado para execução dos testes foi o EP6CDT da PSA Peugeot Citroen. No estudo foram realizados ensaios em bancada de testes e em veículos (estrada e dinamômetro). Outros veículos com a mesma tecnologia, disponíveis no mercado brasileiro, também foram testados. As variáveis avaliadas durante o projeto foram: a composição química de diferentes combustíveis, fator de correção do tempo de injeção (FRA) e a vazão através dos bicos injetores no decorrer dos testes. Os estudos indicaram que a mudança na geometria dos injetores, somada a composição das gasolinas nacionais testadas, originou a formação dos depósitos que será discutida ao longo deste trabalho. / [en] The development of a four-stroke engine, spark ignition, with direct injection of fuel into the combustion chamber was an important initiative for the global automotive market. The thermodynamic potential of this type of engine and its significant improvement in fuel economy have meant this technology as focus of a large number of research projects, with the objective to understand, develop and improve the system of direct fuel injection. However, to meet new emission limits set by Euro 5 specification, it was necessary to reevaluate the geometry design of the injector, which resulted in the development of a new component with a larger number of holes and with a diameter reduction (multi-holes injector). This change in the project aims to ensure a better spray, optimizing air / fuel ratio and, consequently, a better process of combustion inside the combustion chamber, satisfying the emission limits established by the applicable norms. The processes for preparing the mixture, injection, atomization and air flow control inside the cylinder have been the main source of periodic publications that study the direct injection system. Therefore, this paper purpose is to evaluate the formation of inorganic deposits in the injectors using fuels formulated with different amounts of sulfate. The engine used for running the tests was the EP6CDT of PSA Peugeot Citroen. For this study one has performed tests on test bench and in vehicles (road and dynamometer). Other vehicles, with the same technology available in Brazil, were also tested. The variables evaluated during the project were: the chemical composition of different fuels, the correction factor from the injection time (FRA) and flow through the injectors during the tests. This study has indicated that the injector geometry modification, coupled with tested compositions of gasoline, resulted in the formation of deposits that will be discussed throughout this work.

The work presented here pertains to investigations on gas-on-liquid type of impinging injectors with a generic approach with prospective applications in several areas, and at places with particular emphasis on cryogenic or semi-cryogenic liquid propellant rockets. In such rockets, one of the components arrives at the injector in a gaseous phase after passing through the regenerative coolant passages or a preceding combustion stage. Most often, the injectors in such systems are of shear coaxial type. The shear coaxial injectors suffer from several disadvantages like complexity in design, manufacture and quality control. Adoption of impinging jet configuration can alleviate these problems in addition to providing further benefits in terms of cost, robustness in high temperature environment and manifolding. However, there is very little literature on gas-on-liquid injectors either in this context or in any other Even for the simplest form of impinging injectors such as like-on-like doublets, literature provides no conclusive direction at describing a spray from the theoretical models of physical mechanisms. Empirical approach is still the prime mode of obtaining a proper understanding of the phenomena. Steady state spray characterization includes mainly of describing the spatial distribution of liquid mass and drop size distribution as a function of geometric and injection parameters. The parameters that are likely to have an impact on spray characteristics are orifice diameter, ratio of orifice length to diameter, pre-impingement length of individual jets, inter orifice distance, impingement angle, jet velocity and condition of the jet just before impingement. The gas-on- liquid configuration is likely to experience some qualitative changes because of the expansion of the gas jet. The degree to which each one of the above variables influences the drop size and mass distribution having implication to combustion performance forms the core theme of the thesis. A dedicated experimental facility has been built, calibrated and deployed exhaustively. While spray drop size measurement is done largely by a laser diffraction instrument, some of the cases warranted an image processing technique. Two different image processing algorithms are developed in-house for this purpose. The granulometric image processing method developed earlier in the group for cryogenic sprays is modified and its applicability to gas-on-liquid impinging sprays are verified. Another technique based on the Hough transform which is feature extraction technique for extracting quantitative information has also been developed and used for gas-on-liquid impinging injectors. A comparative study of conventional liquid-on-liquid doublet with gas-on-liquid impinging injectors are first made to establish the importance of studying gas-on-liquid impinging injectors. The study identifies the similarities and differences between the two types and highlights the features that make such injectors attractive as replacements to coaxial configuration. Spray structure, drop-size mass distributions are quantified for the purpose of comparison. This is followed by a parametric study of the gas-on-liquid impinging injectors carried out using identified control variables. Though momentum ratio appeared to be a suitable parameter to describe the spray at any given impingement angle, the variations due to impingement angle had to be factored in. It was found that normal gas momentum to liquid mass is an apt parameter to generalize the spray characteristics. It was also found that using identical nozzles for desired mass ratio could lead to rather large deflection of the spray which may not be acceptable in combustion chamber design. One way of overcoming this is to work with unequal orifice sizes for gas and liquid. It was found that using smaller gas orifice for a given liquid orifice resulted in lower SMD (Sauter Mean Diameter of the spray) for constant gas and liquid mass flow rates. This is attributable to the high dynamic pressure of gas in the case of smaller gas orifices for the same mass flow rate. The impinging liquid jets with unequal momentum in the doublet configuration would result in non-uniform mass and mixture ratio distribution within the combustion chamber which may have to operate under varying conditions of mass flow rates and/or mixture ratio. The symmetrical arrangement of triplet configuration can eliminate this problem at the same time generating finely atomized spray and a homogeneous mixture ratio. In view of the scanty literature available in this field, the atomization characteristics of the spray generated by liquid centered triplet jets are examined in detail. It was found that as in the case of gas-on-liquid impinging doublets, normal gas momentum to liquid mass is an ideal parameter in describing the spray. Variants of this configuration are studied recently for many other applications too. As done in the case of doublets, efforts have also been made to compare gas centered triplet to liquid-liquid triplet. It was found that the trend of SMD of gas centered triplet is different from that of liquid-liquid triplets, thus pointing to a different mechanism in play. The SMD in the case of liquid-liquid triplets decreases monotonically with increasing specific normal momentum. It is to be noted that specific normal momentum is an ideal parameter for describing the spray characteristics of liquid-liquid triplets and doublets. In the case of gas centered triplet the SMD first increases and then decreases with specific normal momentum, the inversion point depends on the gas mass flow rate for a constant specific normal momentum. The thesis concludes with a summary of the major observations of spray structures for all the above injector configurations and quantifies the parametric dependencies that would be of use to engineering design

Cette thèse présente la Simulation des Grandes Echelles (LES) de l’injection, de la pulvérisation et de la cavitation dans un injecteur pour les applications liées aux moteurs à combustion interne. Pour la modélisation de l’atomisation, on utilise le modèle ELSA (Eulerian Lagrangian Spray Atomization). Le modèle résout la fraction volumique du combustible liquide ainsi que la densité de surface d’interface liquide-gaz pour décrire le processus complet d’atomisation. Dans cette thèse, l’écoulement à l’intérieur de l’injecteur est également pris en compte pour une étude ultérieure de l’atomisation. L’étude présente l’application du modèle ELSA à un injecteur Diesel typique, à la fois dans le contexte de RANS et de LES.Le modèle est validé à l’aide de données expérimentales disponibles dans Engine Combustion Network (ECN). Le modèle ELSA, qui est normalement conçu pour les interfaces diffuses (non résolues), lorsque l’emplacement exact de l’interface liquide-gaz n’est pas pris en compte, est étendu pour fonctionner avec une formulation de type Volume of Fluid (VOF) de flux à deux phases, où l’interface est explicitement résolu. Le couplage est réalisé à l’aide de critères IRQ (Interface Resolution Quality), qui prennent en compte à la fois la courbure de l’interface et la quantité modélisée de la surface de l’interface. Le modèle ELSA est développé en premier lieu en considérant les deux phases comme incompressibles. L’extension à la phase compressible est également brièvement étudiée dans cette thèse. Il en résulte une formulation ELSA compressible qui prend en compte la densité variable de chaque phase. En collaboration avec l’Imperial College de Londres, la formulation de la fonction de densité de probabilité (PDF) avec les champs stochastiques est également explorée afin d’étudier l’atomisation. Dans les systèmes d’injection de carburant modernes, la pression locale à l’intérieur de l’injecteur tombe souvent en dessous de la pression de saturation en vapeur du carburant, ce qui entraîne une cavitation. La cavitation affecte le flux externe et la formulation du spray. Ainsi, une procédure est nécessaire pour étudier le changement de phase ainsi que la formulation du jet en utilisant une configuration numérique unique et cohérente. Une méthode qui couple le changement de phase à l’intérieur de l’injecteur à la pulvérisation externe du jet est développée dans cette thèse. Ceci est réalisé en utilisant le volume de formulation de fluide où l’interface est considérée entre le liquide et le gaz; le gaz est composé à la fois de vapeur et d’airambiant non condensable. / This thesis presents Large Eddy Simulation (LES) of fuel injection, atomization and cavitation inside the fuel injector for applications related to internal combustion engines. For atomization modeling, Eulerian Lagrangian Spray Atomization (ELSA) model is used. The model solves for volume fraction of liquid fuel as well as liquid-gas interface surface density to describe the complete atomization process. In this thesis, flow inside the injector is also considered for subsequent study of atomization. The study presents the application of ELSA model to a typical diesel injector, both in the context of RANS and LES. The model is validated with the help of experimental data available from Engine Combustion Network (ECN). The ELSA model which is normally designed for diffused (unresolved) interfaces, where the exact location of the liquid-gas interface is not considered, is extended to work with Volume of Fluid (VOF) type formulation of two phase flow, where interface is explicitly resolved. The coupling is achieved with the help of Interface Resolution Quality (IRQ) criteria, that takes into account both the interface curvature and modeled amount of interface surface. ELSA model is developed first considering both phases as incompressible, the extension to compressible phase is also briefly studied in this thesis, resulting in compressible ELSA formulation that takes into account varying density in each phase. In collaboration with Imperial College London, the Probability Density Function (PDF) formulation with Stochastic Fields is also explored to study atomization. In modern fuel injection systems, quite oftenthe local pressure inside the injector falls below the vapor saturation pressure of the fuel, resulting in cavitation. Cavitation effects the external flow and spray formulation. Thus, a procedure is required to study the phase change as well as jet formulation using a single and consistent numerical setup. A method is developed in this thesis that couples the phase change inside the injector to the external jet atomization. This is achieved using the volume of fluid formulation where the interface is considered between liquid and gas; gas consists of both the vapor and non condensible ambient air.