No description available.

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

Orientador: João Andrade de Carvalho Junior / Banca: Ivonete Ávila / Banca: Christian Jeremi Coronado Rodríguez / Resumo: A escassez de combustíveis de origem fóssil tem preocupado setores energéticos e industriais. Outra preocupação eminente são as taxas de emissões de poluentes na atmosfera, causado pelo processo de combustão. Estes processos são responsáveis por grande parte de toda energia primária produzida no mundo. Sendo assim, os bicombustíveis tem sido uma alternativa que atende ambas as preocupações. Neste cenário, a atomização também assume uma importante função dentro da combustão de líquidos. O atomizador tem por objetivo desintegrar o combustível líquido em pequenas gotículas, misturando-se com o oxidante na proporção correta e nas condições adequadas, para produzir um processo de combustão eficiente e estável, reduzindo significativamente as formações de fuligens. O objetivo deste trabalho é realizar um estudo teórico de um atomizador do tipo jato-Y, para atomizar misturas de combustíveis com diferentes proporções de QAV-1 + farnesano, QAV-1 + etanol e farnesano + etanol, analisando experimentalmente as propriedades físico-químicas das misturas de combustíveis e teoricamente as características e a qualidade do spray gerado, fazendo uso da equação de Wigg para calcular o MMD (diâmetro médio de gotas). Através das propriedades físico-químicas das misturas de combustíveis é possível analisar possíveis alternativas de combustíveis que podem apresentar características "drop-in" e substitua parcialmente ou definitivamente o QAV-1 (querosene de aviação) atualmente consumido. Qualitat... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The scarcity of fossil fuels has worried the energetic and industrials sectors. Concern also exists about emissions and their impact on the environment, which are a byproduct of the petroleum combustion processes. These processes account for much of the primary energy produced in the world. However, biofuels have been an alternative that meets both concerns. In this scenario, the atomization also assumes an important function in the combustion of liquids. The atomizer has goal to disintegrate the liquid fuel in small droplets to have the mixture of fuel/oxidant in the suitable ratio, to produce an efficient and stable combustion process, significantly reducing the formation of soot. The objective of this work is perform a theoretical study of one nozzle of the type Y-jet, to atomize binary mix of fuels with different ratio of jet-A1 + farnesane, jet-A1 + ethanol and farnesane + ethanol, experimentally analyzing the physicochemical properties of the mixtures of fuels and theoretically the characteristics and quality of the formed spray, using the Wigg's equation to calculate the MMD (Mass Median Diameter). Through of the physicochemical properties of the mixtures of fuels, it's possible to analyze possible alternatives of fuel that may have "drop-in" characteristics and partially or definitively to replace the currently consumed jet-A1 fuel. Qualitatively the formed spray has the MMD between 30 e 40 µm, however can be varied according with the temperature of work. Furtherm... (Complete abstract click electronic access below) / Mestre

A numerical study of the flow field generated by injection through diamondshaped orifices into a high-speed flow is presented in this document. Jet interaction flows have a wide range of applications in the field of engineering. These applications include the use of jets for fuel injection in scramjets, for reaction control of high-speed aerodynamic bodies and as cooling jets for skins of high-speed vehicles. A necessary requirement in the use of transverse jets for these and other applications is a thorough understanding of the physics of the interaction between the jet and freestream. This interaction generates numerous flow structures that include multiple shocks, vortices, recirculation regions and shear layers. This study involves diamond-shaped orifices that have the advantage of generating weaker or attached interaction shocks as compared to circular injectors. These injectors also negate the effects due to the recirculation region that is formed upstream of the injector. This study was undertaken in order to gain further understanding of the flow features generated by diamond-shaped injectors in a high-speed flow. Numerical simulations were performed using two different levels of turbulence models. Reynolds™ Averaged Navier-Stokes (RANS) simulations were performed using the GASP flow solver while Detached-Eddy Simulation (DES) runs were performed using the Cobalt flow solver. A total of fifteen diamond injector simulations were performed using the RANS model for a 15 half-angle diamond injector. The fifteen simulations spanned over five different injection angles and three jet total pressures. In addition to these, two circular injector simulations were also performed. In addition, low pressure normal injection through diamond and circular orifices simulations were performed using DES. Results obtained from CFD were compared to available experimental data. The resulting flow structure and the turbulent properties of the flow were examined in detail. The normal injection case through the diamond-shaped orifice at the lowest jet total pressure was defined as the baseline case and is presented in detail. In order to study the effect of different components of the vorticity transport equation, an in-house code was used post-process the results from the RANS runs.

No description available.

Les processus physiques qui régissent la pulvérisation de sprays constituent la première étape vers une compréhension globale du comportement de moteurs fusées à ergols stockables. La première partie de ces travaux détermine, au moyen de visualisations et d’analyses granulométriques, les paramètres importants contrôlant la formation de sprays par impact de jets liquides. Des injecteurs dédiés à pulvériser des ergols stockables sont ensuite conçus. L’enjeu de la seconde partie des travaux est d’étudier la combustion de l’éthanol avec le peroxyde d’hydrogène, ergols stockables considérés moins nocifs. L’utilisation de cette association bi-ergols innovante a nécessité d’analyser en détail leur compatibilité à l’allumage, ainsi que leurs performances en combustion sur la gamme de richesses 0,4 – 2,0, à l’aide de diagnostics optiques et physiques spécifiques. Les efficacités de combustion atteignent entre 87 et 98 %, les fluctuations de pression ne dépassent pas 10 %, mais les légères différences obtenues permettent de sélectionner les meilleures configurations d’injection favorisant la combustion ou sa stabilité. / The physical processes involved in spraying are the first step towards a comprehensive understanding of the behavior of rocket engines using storable propellants. The first part of this work identifies, through visualizations and particle sizing, the important parameters driving the formation of spray by impinging liquid jets. Then, injectors dedicated to spray storable green-propellants are designed. The second part of this thesis aims at studying the combustion of ethanol with hydrogen peroxide, which are regarded as green-storable propellants. But the use of this innovative bi-propellant association required a detailed analysis of their ignition compatibility, as well as their combustion performance within the range of 0,4 – 2,0 in overall equivalence ratio. Specific optical and physical diagnostics helped to achieve these goals. Combustion efficiency reached between 87 and 98 %, pressure fluctuations did not exceed 10 %, but the slight differences obtained allowed to select the best injection configurations promoting efficient combustion and stability.

Several modern marine engines use multiple injectors for lower heat losses and higher efficiency. However, the heavy-duty vehicles still apply a single injector per cylinder. This work investigates how multiple injectors can be operated in compression ignition heavy-duty engines along with potential benefits from such concepts. The studies aimed to avoid high boundary gas temperatures by having two injectors at the rim of the bowl, in addition to the standard injector. A longer injector-wall distance reduces the amount of hot gases at the boundaries for reduced convective heat losses. Additional degrees of freedom also follows from an increased number of injectors to simplify combustion control. The thesis included CFD simulations, metal engine experiments, and optical engine diagnostics to investigate the efficiency –and emission benefits for two –and three-injector concepts compared to the single-injector approach. The CFD simulations aimed to set beneficial spray angles and chamber geometries for reduced heat losses and reasonable emission levels with and without swirl at different load conditions. A flat bowl with two injectors reduced the heat losses by 4.2 %-points resulting in a direct efficiency increase of 1.9 %-points at middle-load conditions. Metal engine studies confirmed the simulation results by testing two -and three-injector concepts. The higher three-injector flow rate raised efficiency and diminished heat losses while providing low nitric oxide levels. Thus, three injectors lessen the typical trade-off between efficiency and nitric oxides. The thesis further performed single-injector optical engine experiments to investigate combustion control limitations. The results concluded that high soot levels occur from the multiple injections used to achieve isobaric combustion. These high soot levels followed by injecting into fuel-rich zones, which can be avoided by using multiple injectors. Finally, the thesis provides a multiple injector design suitable for heavy-duty production engines.

Experiments were performed with two different helium injector models at different injector transverse and yaw angles in order to determine the mixing rate and core penetration of the injectant and the flow field total pressure losses. when gaseous injection occurs into a supersonic freestream. Tested in the Virginia Tech supersonic tunnel. with a freestream Mach number of 3.0 and conditions corresponding to a freestream Reynolds number of 5.0 x 107 1m. was a single. sonic. 5X underexpanded, helium jet at a downstream angle of 30° relative to the freestream. This injector was rotated from 0° to _28° to test the effects of injector yaw. The second model was an array of three supersonic, 5X underexpanded helium injectors with an exit Mach number of 1.7 and a transverse angle of 15°. This model was tested in the NASA Langley Mach 6.0, High Reynolds number tunnel, with freestream conditions corresponding to a Reynolds number of 5.4 x 10⁷ /m. The injector array as tested at yaw angles of 0° and -15°. Surface flow visualization showed that significant flow asymmetries were produced by injector yaw. Nanosecond exposure shadowgraph pictures were taken, showing the gaseous injection plume to be unsteady, and further studies demonstrated this unsteadiness was related to shock waves orthogonal to the injectant bow shock, that were generated at a frequency of 30 kHz. The primary data technique used, was a concentration probe which measured the molar concentration of helium in the flow field. Concentration data and other meanflow data was taken at several downstream axial stations and yielded contours of helium concentration, total pressure, Mach number, velocity, and mass flux, as well as the static properties. From these contour plots, the various mixing rates for each case were determined. The injectant mixing rates, expressed as the maximum concentration decay, and mixing distances were found to be unaffected by injector yaw, in the Mach 3.0 experiments, but were adversely affected by injector yaw in the Mach 6.0 experiments. One promising aspect of injector yaw was the that as the yaw angle was increased, lateral motion of the injectant plume became significant, and the turbulent mixing region area increased by approximately 34%. Comparisons of the 15° transverse angled injection into a Mach 6.0 flow to previous experiments with 15° injection into a Mach 3.0 freestream, demonstrated that there is a significant decrease in initial mixing, at Mach 6.0, resulting in a much longer mixing distance. From a parametric computational study of the Mach 6.0 experiments, the effects of adjacent injectors was found to decrease lateral spreading while increasing the vertical penetration of the injectant plume, and marginally increasing the injectant core decay rate. Matching of the computational results to the experimental results was best achieved when using the Baldwin-Lomax turbulence model without the Degani-Schiff modification. / Ph. D.

Decades of research on compression ignition engines have led to a highly efficient combustion cycle in contemporary diesel engines. Nonetheless, the combustion process is being studied perpetually to meet both current and future emission regulations. One of the most influential parameters that impacts the combustion quality, is the fuel spray evolution during injection, and subsequent fuel-air mixture formation inside the engine cylinder. The spray evolution has been investigated to a high level of detail, and the highly complex processes of mixture formation and combustion are well-documented for diesel engines. Most of these investigations are limited to studying either research-grade injectors, or brand new production injectors. Injectors in real-world diesel engines, i.e. normal passenger cars and trucks that are used on a daily basis, are however subject to deposit formation at the tip of the injector nozzle. These deposits have the potential of altering the internal nozzle flow and fuel spray pattern, which in turn degrades combustion quality and increases engine emissions. In the work presented in this thesis the spray evolution of production injectors has been studied over a wide range of injector conditions. Common rail light-duty injectors with a usage history of up to 90 000 miles were acquired from the UK commuter car parc, and several brand new injectors were studied for comparison purposes. It is shown that the spray pattern of the injected fuel changes over the lifetime of the injector. For used injectors a reduced penetration rate was observed in the transient regime of fuel injection, during needle lift. The reduced penetration rate was often accompanied by anomalous radial expansions. Although the magnitude of the effects varied from injector to injector, the highest mileage injectors tended to produce the strongest spray deviations. For several high-mileage injectors the end of injection appeared retarded with respect to new injectors. Expulsions of liquid ligaments and droplets after the end of injection were observed from all injectors, irrespective of the mileage of the injector.

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.