Dissertations / Theses on the topic 'Fuel sprays'

This thesis presents a numerical study of the break-up and atomisation of gasoline fuel sprays injected into atmospheric flow conditions and environments related to combustion chamber conditions. Calculations of the fuel break-up process were achieved by four different models: Taylor Analogy Break-up (TAB), the wave instability theory (WAVE), the Hybrid Sheet-TAB and the Hybrid WAVE-FIPA models. The TAB model relates the break-up process to the droplet oscillations; whereas the WAVE models calculate the fuel break-up from the unstable waves on the droplet surface. The modified version of the TAB model, called the Hybrid Sheet-TAB model delays the start of the break-up further downstream from the nozzle tip. A new hybrid model, the WAVE-FIPA model, divides the spray atomisation processes into a primary stage, where the WAVE model is used, and a secondary stage, which is simulated using experimental correlations to calculate the break-up time for the low Weber number droplets.

The effects of fuel properties on the primary and secondary breakup of the diesel jet have been investigated. Experiments using a long working distance microscope have been carried out to assess the difference in spray formation caused by changes in specific fuel properties. Particular attention was paid to the optimisation of the lighting technique with a range of light sources tested. The use of a diffused laser allowed the acquisition of blur free high quality shadowgraph images. This allowed the visualisation of the processes that lead to the breakup of the fuel jet and velocity measurements at these locations. Images acquired further downstream during the secondary atomization regime allowed drop sizing to be carried out.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999.
"June 1999."
Includes bibliographical references (p. 205-208).
Optimal design of modern direct injection gasoline engines depends heavily on the fuel spray. Most of the studies published regarding these fuel sprays involve cold bench tests or motored optical engines, neglecting the roles of the fuel volatility and temperature. This study, therefore, was designed to describe changes in the spray properties due to fuel volatility and operating conditions using a firing optically-accessible engine. Planar laser-induced fluorescence and planar Mie scattering imaging experiments were performed to show changes in the spray structure, including its radial and axial penetration. Phase-Doppler particle analysis experiments were included to track the droplet diameter and velocity at various points throughout the spray. A computational fluid dynamics model was also used to study the physics leading to the observed changes. The results show that the spray structure changes with not only ambient gas density, which is often measured, but also fuel temperature and volatility. The mean droplet diameter was found to decrease substantially with increasing fuel temperature and decreasing ambient density. Under conditions of low potential for vaporization, the observed trends agree with published correlations for pressure-swirl atomizers. As ambient density decreases and fuel temperature increases, the volatile ends of multi-component fuels evaporate quickly, producing a vapor core along the axis of the spray. Beyond a certain point, evaporation is violent enough to cause additional breakup of the droplets. A fit to this volatility-induced breakup data provides an additional correlation for determining the mean diameter of volatile sprays. Coincident with the volatility-induced breakup trend is an increase in the initial cone angle of the spray. However, the reduced droplet diameter and rapid vapor generation under these superheated conditions result in a narrow spray with increased axial penetration. In the process of performing these experiments, insights were found regarding the operation of these diagnostics in high-density sprays.
by Brad A. VanDerWege.
Ph.D.

Fuel atomization plays a very crucial role in determining the overall efficiency of diesel internal combustion engines. This work focuses on developing fast optical diagnostic tools for the study of the liquid fuel atomization with an aim to characterize the fuel sprays in the near-field of the injector nozzle. At first, classical imaging techniques using continuous illumination with a high-speed camera and an ultra-short pulsed illumination with a high-resolution CCD camera are reviewed. Next, the possibility of supercontinuum (SC) derived illumination is investigated. It was observed that the spray images obtained with such an illumination were almost free from laser speckle, which tremendously improved the clarity of these images. An application of the classical imaging technique to a preliminary study of cavitation inside a transparent injector is presented. In the next part of the thesis optical techniques to reduce the noise originating due to the multiple scattering of light from its interaction with the fuel spray are studied. Optical Kerr effect based time-gate in its primitive crossed-beam configuration is reviewed and a novel approach with collinear overlap of the pump and probe beams for time-resolved imaging of fuel spray with time resolution 1 ps is proposed. Ballistic images of fuel spray in the near-nozzle region with high spatial resolution are obtained. The possibility of using SCderived illumination with the optical time-gate configuration is also discussed. Preliminary time-gated spray images obtained by using SC-derived probe beam for spray illumination in the optical-gate setup shows that laser speckle is substantially reduced maintaining a similar time resolution. The change in the optical polarization properties of the Kerr medium on introduction of the pump pulse are completely characterized by measuring its Mueller matrix (MM). The polarization parameters – depolarization, diattenuation, and retardance are then quantified by decomposing the measured MM using polar decomposition formalism
L’atomisation du carburant joue un rôle très important dans l’efficacité globale du moteur à combustion interne utilisant le Diesel. Ce travail se concentre sur le développement d’outils de diagnostics optiques rapides pour l’étude de l’atomisation du combustible liquide, avec pour but de caractériser les jets de carburant en proche sortie de l’injecteur. Dans un premier temps, les techniques d’imagerie classiques utilisant (i) un éclairage continu avec une caméra à haute vitesse et (ii) un éclairage pulsé ultra-court avec une caméra CCD haute résolution sont examinées. L’utilisation d’un supercontinuum (SC) pour éclairer le jet est testée. On observe alors que les images de spray obtenues avec ce type d’éclairage sont presque exemptes de speckle, ce qui en améliore considérablement la netteté. Une technique d’imagerie classique est ensuite appliquée à l’étude de la cavitation à l’intérieur d’un injecteur transparent et une première approche de ce problème est présentée. Dans la partie suivante de la thèse, la problématique de la réduction du bruit dû à la diffusion multiple de la lumière sur le jet de carburant est posée. Les avantages et les inconvénients d’un montage utilisant une porte optique à effet Kerr avec des faisceaux pompe et sonde non colinéaires sont présentés. Une nouvelle approche avec des faisceaux pompe et sonde colinéaires aboutissant à une résolution temporelle de 1 ps est proposée. Des images balistiques de sprays de carburant en proche sortie d’injecteur ayant une excellente résolution spatiale sont ainsi obtenues. La possibilité d’utiliser un éclairage de type SC avec une porte optique est également discutée. Les images de sprays réalisées par ce montage montrent que l’on réduit le speckle tout en gardant une bonne résolution spatiale. Enfin, les propriétés polarimétriques du milieu Kerr utilisé lorsqu’il est soumis au faisceau pompe sont caractérisées par la mesure de sa matrice de Mueller (MM). Les paramètres de polarisation dépolarisation, diatténuation et retardance sont alors quantifiés par décomposition de la MM mesurée, en utilisant le formalisme de décomposition polaire

This thesis first provided strategic recommendations for the research sponsor, Rolls- Royce plc (RR) and then applied optical diagnostics to measure aero gas turbine fuel spray properties in order to predict Oxides of Nitrogen (NOx) emissions and combustion instability. Analysis of the large civil aero engine sector suggested possible courses of action for RR to protect itself from short-term market volatilities and also prepare for three long term changes in strategic operating context: air traffic growth; tighter United Nations enforced aero engine combustion emissions legislation and entry of civil aviation into the European Union Emissions Trading Scheme. A collaborative game theoretic approach was explored during the pre-competitive, pre-technology, capability acquisition aero engine design phase on unproven future technologies to reduce R&D expenditures, development times and the costs of failure. Lean Prevapourised Premixed combustion demands excellent spray atomisation quality to sustain combustion efficiency, stability and to minimise pollutants. Post development of an improved procedure to calibrate laser signals, methodology to predict NOx and technique to optimise rig operating conditions that minimised fractional discrepancies in two-phase flow behaviour with corresponding engine conditions, this thesis applied quantitative Planar Laser Induced Fluorescence (PLIF) and Laser Sheet Dropsizing (LSD) to measure the fuel placement and dropsize distribution in the near nozzle regions of RR liquid-fuelled hybrid, airblast and pressure-swirl sprays. Measurements were made under non-combusting, low pressure conditions and results were processed to identify fuel injector designs that exhibited low emissions and high stability for the Affordable Near Term Low Emissions (ANTLE) and Instability Control of Low Emission Aero-Engine Combustors (ICLEAC) engine demonstrator programmes. Results also provided validation data and boundary conditions for spray computational codes. Research findings will improve RR core competencies in fuel injection research to accelerate the development and deployment of low emissions aero engine technology.

This thesis focuses on the effect of initial ambient turbulence on the spray characteristics of fuel injected into a constant volume. The investigation is performed experimentally and computationally. The spray axial penetration length and radial penetration width, area and velocity are used as key parameters to characterise the spray in the experimental work together with vapour fuel mass fraction, mean droplet diameters and number of droplets in the computational work. In the experimental study, the liquid fuel (iso-octane) is injected, using a high pressure swirl atomiser, into ambient nitrogen with different prescribed nearly isotropic turbulence levels, characterised by the root mean square (RMS) turbulence velocity. Mie scattering laser sheet and Schlieren techniques are combined with a high speed camera to capture images of the vapour and liquid phases simultaneously as a function of injection pressure and ambient turbulence. These indicate that the latter has a significant influence on tip penetration length, penetration width, cross sectional area and velocity. Increased initial ambient turbulence levels lead to reductions in the penetration length in the axial direction and increases in the penetration width in the radial direction; it is also shown to improve fuel evaporation and mixing. In the computational investigation, the commercial Computational Fluid Dynamics code Fluent is used to explore the effect of the RMS turbulence velocity in a constant volume vessel on the spray characteristics of liquid fuel injected into it. The theoretical results are compared with corresponding experimental data obtained for the case of iso- octane fuel injected into nitrogen; the main features of sprays are successfully predicted. The results show how increased ambient turbulence level in the gas into which fuel is injected influences spray atomisation, break-up and evaporation and leads to reduced vapour penetration length and sauter mean droplet diameter, together with increasing vapour penetration width and number of fuel droplets. Additionally, the effect of injection pressure, ambient density and ambient temperature on spray characteristics is investigated at quiescent and turbulent ambient conditions; in which case increasing the injection pressure leads to increases in both the penetration length and the number of droplets, and a corresponding reduction in the sauter mean diameter.

The concept of gasoline direct injection engines is at the forefront of modern research. Two major concerns with the design are the incomplete evaporation of the injected fuel that leads to increased engine-out emissions and the process of injector fouling caused by the direct exposure of the injector to the flame. The latter also reduces the lifetime of this component and also increases emissions at the same time. These are critical issues for OEMs as emissions legislations around the world demand increasingly stricter thresholds. The research presented is split into two separate parts, to tackle both concerns. First, a series of fuel blends and operating conditions and their effect towards spray shape, droplet size and velocity as well as wall wetting will be investigated in a dedicated injection chamber. In order to quantify the amount of fuel that forms a liquid deposit on the surface a novel measurement technique is presented. The data gathered in these measurements is then used to show trends between the blends investigated and to give suggestions for potential improvements of future engine designs and modified engine operating conditions to reduce the amount of particulate emissions. In the second part of the research a series of injectors that were previously fouled are investigated. The fouling caused a significant increase of particulate emissions in test engines and the focus here is to provide possible explanations for this drift. Additionally, some of the injectors were treated with a detergent fuel which reverted the change in emissions. A comparison of these injectors shall provide information about potential applications of such blends and how they would benefit the longevity of modern engines.

Environmental legislation has pressured fuel and automotive industries to alter their technologies for compliance. Changes made to a fuel to achieve compliance can push specific fuel qualities, such as lubricity, to a level away from that required by the automotive engine, creating a fuel/engine requirement gap. Use of fuel additives offer an economical route to bridge the gap, however, their effects on stages of the diesel combustion process is not yet fully understood owing to measurement difficulty. Greater understanding of additive effects requires precision control of operational test conditions with the ability to apply high fidelity measurement techniques. To enable this a high pressure, high temperature optical facility was developed which allows for the acquisition of large data-sets of spray parameters for a more accurate study of the effect fuel additives have on the diesel combustion process. For facility commissioning, tests on diesel fuel sprays into elevated pressure and temperature environments were carried out, with data obtained from high speed backlight illuminated imaging. Macroscopic spray measurements such as penetration length and spreading areas of the sprays were performed, so that effects of ambient pressure and temperature on these parameters could be identified and discussed. From the tests, injector opening times were a main cause of variability in the observed characteristics which were taken into account in the study. Following commissioning, a systematic study was carried out using combustion improving and detergent additives for the first time, where low and high concentrations were tested. Similar behaviours in penetration lengths for each of the additives tested were seen, however no statistical confidence could be applied to the observation as the penetration lengths of the additised fuels for the tested back pressures, since these values did not shift from the base fuels' measured data by a magnitude greater than the experimental error. Penetrating spray area data variance was large, and changes due to additives were unidentifiable. To further clarify, laser droplet sizing was employed at atmospheric conditions to identify whether additives cause changes in microscopic measurements of the spray. The tests showed no change in the droplets' Sauter Mean Diameters (SMD) were observed due to additives. The study carried out clearly indicates that the additives added in the tested concentrations did not change the statistically determined transient parameters of diesel sprays.

This paper investigated the effects of swirl number and momentum ratio on the atomization and mixing performance of Swirl-Venturi Lean Direct Injection technology. Mie scattering of liquid water, was used to identify the location of water droplets in a cross section of the injector spray. Experiments were performed with three air swirlers with vane angles of 45, 52 and 60 degrees. The swirl number varied from 0.58 to 1.0 and air-to-liquid ratios from 15.8 to 35.6. A transition was observed in the liquid spray distribution for the 52 degree case, which unexpectedly produced twice as much signal than the 45 and 60 degree cases. The main cause of this increased signal may be due to instabilities in the flow when transitioning from low to high swirl states. The results from investigation of swirl number it was found that the spray pattern for is sensitive to swirl intensity. Two flow states were observed for a lower and higher swirl flow as well as a transition state that occurred with the lower swirl state. This work may aid in the specific inquiry of physical mechanisms relating to the effect of flow states on spray distribution. It is found that improved atomization and mixing performance are a result of increase in swirl number.

The introduction of a new imaging approach for simultaneous multi-phase and multi-constituent velocity measurements is the main focus of this research. The proposed approach is based on the use of a single off-the-shelf colour camera which will enable simultaneous imaging of phases/constituents which are colourtagged using fluorescent droplets and multi-wavelength illumination. Highly efficient florescent tracers used to seed the constituents are presented and their visibility in full field imaging experiments is evaluated. A commonly found problem in experimental systems using laser illumination, known as flare, is discussed and the application of the developed fluorescent tracers for its reduction is presented. A strong focus of the imaging approach proposed is its flexibility and simplicity allowing its extension to stereoscopic imaging to obtain simultaneous multi-phase/constituent 3-component measurements with the addition of a second imaging camera. Proof of principle experiments with spatially separated and well mixed flows are presented for which successful phase discrimination is obtained and the uncertainty of the measurements is estimated. The imaging system developed is applied for simultaneous air and fuel velocimetry measurements in a Gasoline Direct Injection spray for which a more detailed understating of the interaction mechanisms is required to generate improved designs. The modified imaging system and experimental setup are presented and previously unavailable simultaneous air/fuel 2 and 3-component velocity fields are presented and analysed.

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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.

Les systèmes liquides produits par les injecteurs mécaniques sont par nature instables. Ceci a pour effet de rompre le système liquide en un spray, c'est à dire en un ensemble de gouttes. Ces gouttes se caractérisent alors par leur dispersion en taille, en vitesse voire en température. Le travail présenté ici ne traite que de la dispersion en taille des particules sphériques. Les phénomènes qui régissent la rupture des systèmes liquides en gouttes restent jusqu'à maintenant mal connus et ne sont pas complètement traités. Les quelques modèles existant ne permettent la prédiction que d'un nombre restreint d'échelles de longueur caractéristiques des instabilités. Le modèle utilisé dans ce travail est la théorie linéaire couplée à un schéma de rupture simplifié et adapté au cas traité. Ceci permet alors le calcul d'une échelle de longueur caractéristique des instabilités présentes et homogène à un diamètre de goutte. L'originalité de notre méthode consiste à proposer une procédure qui couple le résultat de la théorie linéaire au formalisme d'entropie maximum. Ce formalisme permet de calculer la dispersion en taille de goutte la plus vraisemblable tout en respectant l'information réduite issue de la théorie linéaire. La dispersion en taille obtenue est alors représentée sous la forme d'une fonction de densité de probabilité basée sur le volume des gouttes. Cette nouvelle procédure est validée sur trois études expérimentales : les injecteurs d'essence, les injecteurs mécaniques à rotation et les injecteurs ultrasoniques sont traités.

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O motor de combustão interna é a principal fonte de energia de automóveis, sendo de grande importância para o setor de energia no mundo. Com o aparecimento de problemas relacionados com a emissão exagerada de poluentes e gases de efeito estufa, o desenvolvimento de modelos que corretamente descrevem os fenômenos físicos que ocorrem no interior da câmara de combustão de motores tornou-se relevante. Assim, na primeira parte deste trabalho a biblioteca de modelos de fonte aberta de dinâmica de fluidos computacional (CFD) OpenFOAM com módulos desenvolvidos na Universidade de Duisburg-Essen foi utilizada para investigar o efeito do volume das fendas no desenvolvimento da combustão em motores convencionais com ignição por centelha. As simulações de grandes escalas (LES, large eddy simulation) realizadas foram validadas com visualizações de câmeras de alta velocidade obtidas do motor óptico de Duisburg, que mostraram a presença de uma frente luminosa no interior da fenda anular que poderia ser associada a uma chama se propagando. Os resultados apresentados mostraram boa concordância qualitativa com os dados experimentais, o que permitiu concluir que no caso do motor de Duisburg, a chama é realmente capaz de penetrar no volume da fenda. Em seguida, um estudo sobre sprays combustíveis foi realizado, por se tratar de uma tendência muito promissora em motores modernos. Atenção especial foi dada aos fenômenos de conservação de momento, ruptura, evaporação e mistura do caso de teste Spray G da rede de combustão em motores (ECN, engine combustion network). Os processos de ruptura e evaporação foram investigados e simulados, sendo os resultados interpretados de acordo com os modelos utilizados. O comprimento de penetração foi validado com experimentos e uma boa concordância foi atingida. Finalmente, um estudo de sensibilidade da malha foi realizado e seus resultados apresentados e discutidos
The internal combustion engine is the major energy source of automobiles and is of large importance for the energy sector worldwide. As problems related to exaggerated pollutant and greenhouse gases emissions emerged, the development of models to correctly describe the physical phenomena taking place inside the combustion chamber of engines became relevant. Thus, in the first part of this work the open source CFD library OpenFOAM with modules developed at the University of Duisburg-Essen was used to investigate the effect of the crevice volume on the performance of the combustion in port fuel injection spark ignition engines. The LES (large eddy simulation) simulations were validated against high speed flame visualization obtained from the Duisburg optical engine, which showed the presence of a luminous front inside the top land crevice that could be a wrinkled flame. The presented results showed good qualitative agreement with the experimental data, which allowed the conclusion that in the case of the Duisburg engine, the flame indeed penetrates into the crevice volume. Furthermore, a study on fuel sprays was performed, since this is a very promising trend related to modern engines. Special attention was given to the phenomena of momentum exchange, droplet breakup, evaporation and mixture from the test case Spray G provided by the Engine Combustion Network (ECN). The processes of droplet breakup and evaporation were investigated and simulated, being the results interpreted according to the models used. The penetration length was validated against experiments and good agreement was obtained. Finally, a mesh sensitivity study was performed and the results presented and discussed

Orientador: Maurício Araújo Zanardi
Coorientador: José Antônio Perrella Balestieri
Coorientador: Andreas Kempf
Banca: Alex Mendonça Bimbato
Banca: Márcio Teixeura Mendonça
Resumo: O motor de combustão interna é a principal fonte de energia de automóveis, sendo de grande importância para o setor de energia no mundo. Com o aparecimento de problemas relacionados com a emissão exagerada de poluentes e gases de efeito estufa, o desenvolvimento de modelos que corretamente descrevem os fenômenos físicos que ocorrem no interior da câmara de combustão de motores tornou-se relevante. Assim, na primeira parte deste trabalho a biblioteca de modelos de fonte aberta de dinâmica de fluidos computacional (CFD) OpenFOAM com módulos desenvolvidos na Universidade de Duisburg-Essen foi utilizada para investigar o efeito do volume das fendas no desenvolvimento da combustão em motores convencionais com ignição por centelha. As simulações de grandes escalas (LES, large eddy simulation) realizadas foram validadas com visualizações de câmeras de alta velocidade obtidas do motor óptico de Duisburg, que mostraram a presença de uma frente luminosa no interior da fenda anular que poderia ser associada a uma chama se propagando. Os resultados apresentados mostraram boa concordância qualitativa com os dados experimentais, o que permitiu concluir que no caso do motor de Duisburg, a chama é realmente capaz de penetrar no volume da fenda. Em seguida, um estudo sobre sprays combustíveis foi realizado, por se tratar de uma tendência muito promissora em motores modernos. Atenção especial foi dada aos fenômenos de conservação de momento, ruptura, evaporação e mistura do caso de teste "Spray G" da rede de combustão em motores (ECN, engine combustion network). Os processos de ruptura e evaporação foram investigados e simulados, sendo os resultados interpretados de acordo com os modelos utilizados. O comprimento de penetração foi validado com experimentos e uma boa concordância foi atingida. Finalmente, um estudo de sensibilidade da malha foi realizado e seus resultados apresentados e discutidos
Abstract: The internal combustion engine is the major energy source of automobiles and is of large importance for the energy sector worldwide. As problems related to exaggerated pollutant and greenhouse gases emissions emerged, the development of models to correctly describe the physical phenomena taking place inside the combustion chamber of engines became relevant. Thus, in the first part of this work the open source CFD library OpenFOAM with modules developed at the University of Duisburg-Essen was used to investigate the effect of the crevice volume on the performance of the combustion in port fuel injection spark ignition engines. The LES (large eddy simulation) simulations were validated against high speed flame visualization obtained from the Duisburg optical engine, which showed the presence of a luminous front inside the top land crevice that could be a wrinkled flame. The presented results showed good qualitative agreement with the experimental data, which allowed the conclusion that in the case of the Duisburg engine, the flame indeed penetrates into the crevice volume. Furthermore, a study on fuel sprays was performed, since this is a very promising trend related to modern engines. Special attention was given to the phenomena of momentum exchange, droplet breakup, evaporation and mixture from the test case "Spray G" provided by the Engine Combustion Network (ECN). The processes of droplet breakup and evaporation were investigated and simulated, being the results interpreted according to the models used. The penetration length was validated against experiments and good agreement was obtained. Finally, a mesh sensitivity study was performed and the results presented and discussed
Mestre

In modern Internal Combustion (IC) engines, the fuel spray atomization process is known to play a key role in affecting mixture formation, combustion efficiency and soot emissions. Therefore, a thorough understanding of the fuel spray characteristics and atomization process is of great importance. In this study, the fuel spray of modern Gasoline Direct Injection (GDI) engines and diesel engines has been experimentally and numerically studied. At the same time, optimized physical-numerical spray breakup models for the spray simulation have been developed and validated.

As the regulatory limitations of hard-chrome plating surge, the successful application of thermal- sprayed wear/corrosion resistant coatings on complex geometries becomes critical. Thermal spraying is a line-of-sight method and thus, spraying a complex geometry results to changes in the spray angle, the spray distance and the effective gun traverse speed. Although there has been some research on the effects of these kinematic parameters on the coatings, previous work tends to examine the kinematic parameters in isolation, disregarding of any interplay between them. Yet, the effective particle velocity at impingement is dictated both by spray angle and spray distance while the particle temperature is mainly dictated by spray distance. In addition, the heat and mass transfer to the underlying coating are controlled by the gun traverse speed. These facts suggest that significant synergistic effects are expected when the spray kinematic parameters vary simultaneously, as when a complex geometry is sprayed. This work aims at evaluating the systemic effect of the spray kinematic parameters on WC-Co coatings sprayed by HVOF. Various coating properties are comprehensively examined and discussed, exploring the microstructures, phase composition, mechanical qualities and tribological performance. Significant interplay between the spray kinematic parameters is demonstrated in a number of coating properties, yielding non-linear behaviours. The notable beneficial role of small spray angle inclinations at long spray distances, in regards to deposition rate, microstructure, microhardness and wear resistance is demonstrated. Mechanisms of the particle rebounding, superficial oxidation of the coating, metallic tungsten crystallization, tribofilm formation and wear damage progression are proposed, with respect to the spray kinematic parameters. Finally, an attempt to generalize the insights from this work to any given sprayable geometry takes place in a prototype software tool in Matlab.

The spray, combustion and emissions characteristics of diesel and gasoline blends (dieseline) were studied. Experimental results showed that the dieseline fuel spray had tip penetration length similar as diesel. With an increase of the gasoline/diesel blending ratio, the fuel droplets size decreased. When operating with dieseline, the engine's PM emissions were much lower than diesel. With advanced injection timing and large amounts of EGR, both the NOx and PM emissions of dieseline combustion were reduced significantly at part loads. Using split injection strategies gave even more flexibility for the control of mixing strength and combustion phasing. However, the power density of dieseline fuelled PPCI operation was limited. A novel concept, Stoichiometric Dual-fuel Compression Ignition (SDCI) was investigated. The diesel and gasoline were blended internally through direct injection and port fuel injection respectively. Stoichiometric condition was maintained through adjusting the EGR ratio, which thus allows for a three-way-catalyst to handle gaseous emissions. Experimental results showed that the SDCI combustion can achieve better thermal efficiency and lower PM emissions than conventional diesel combustion. Overall, the SDCI concept was proved to be a promising technique for optimising a CI engine's efficiency, emissions and noise without compromise of cost and power density.

[EN] This last few years, the trend in diesel engines has been to use different kinds of fuels to identify their influence and behaviour on the emissions and performance. Among the wide variety of fuels employed are the so called Primary Reference Fuels (PRFs), which represent the behaviour of diesel and gasoline in terms of ignition properties, as they are located at both ends of the octane rating scale and also have very different cetane numbers. One of the disadvantages of using pure gasoline or diesel-gasoline blends in diesel engines is the time needed for the mixture to ignite and to completely burn the fuel. This generally requires working with partial loads or with premixed charges. In order to isolate the fuel effects on the spray processes and to be able to study the characteristic parameters of ignition delay time, lift-off length, vapour and liquid penetration, among others; different experiments under parametric variations of diesel like conditions have been performed. The tests were performed under inert and reactive conditions in a 2-stroke optical engine and a constant-pressure flow (CPF) high-pressure high-temperature vessel using single-hole nozzles, while diverse optical techniques were being employed. To study the influence of the fuel properties, different single-component fuels were employed as well as binary blends and a six-component diesel surrogate, which was also compared to conventional diesel. Additionally, the results have been contrasted with a one-dimensional model in order to further explain the values and trends found. The results presented a strong dependency on the fuel properties for the tests performed under inert and reactive conditions. The difference in physical properties of n-decane and n-hexadecane showed an almost linear reduction of the stabilized liquid penetration down to approximately 60% under some conditions. Additionally, due to the composition of the surrogate fuel, pure n-hexadecane was demonstrated to have almost identical evaporation characteristics, hence proving itself as a good candidate for a single-component surrogate of diesel fuel. In a similar way, the chemical properties of the PRFs n-heptane and iso-octane also proved to be influential on the spray development and radiation emitted. Ignition delay values up to one order of magnitude larger where obtained for both extremes of the blend range, as well as lift-off lengths up to three times longer. The radiation emitted by the soot incandescence presented the highest variations, as some conditions showed a reduction of almost four orders of magnitude among the blend range. Moreover, some cases did not present any radiation corresponding to the soot, and increasing the sensitivity of the camera only caused the chemiluminescence of the OH* radical to be captured. On a different way, the stabilized flame length determined also by the soot radiation did not present much variation as the fuel properties or the air temperature were changed; in fact, the only noticeable differences were caused by the changes in the oxygen composition of the ambient air. In conclusion, the fuel properties proved to have a significant effect on the spray processes. Lighter fuels favoured the evaporation of the spray under a range of conditions, while fuels with lower octane numbers ignited sooner and closer to the spray tip but with more soot luminosity measured.
[ES] Estos últimos años, la tendencia en motores diesel ha sido la de emplear distintos tipos de combustibles para identificar su influencia y comportamiento sobre las emisiones y rendimiento. Dentro de la amplia variedad de combustibles empleados están los llamados combustibles de referencia (PRFs ingl. Primary Reference Fuels), los cuales representan el comportamiento del diesel y la gasolina en lo que respecta a propiedades de encendido, ya que se encuentran en ambos extremos de la escala del número de octano y también poseen números de cetano muy distintos. Una de las desventajas de utilizar gasolina pura o mezclas de diesel-gasolina en motores diesel es el tiempo que toma la mezcla en encender y quemar completamente el combustible. Esto generalmente requiere trabajar con cargas parciales o cargas premezcladas. Para poder aislar los efectos del combustibles sobre los procesos de un chorro y que sea capaz estudiar los parámetros característicos de tiempo de retraso de encendido, longitud de despegue de llama, penetración de líquido y vapor, entre otros, se han realizado distintos experimentos bajo variaciones paramétricas de condiciones de motor diesel. Los ensayos han sido realizados bajo condiciones inertes y reactivas en un motor óptico de dos tiempos y una instalación de alta presión y alta temperatura de flujo continuo a presión constante (CPF ingl. Constant-Pressure Flow) empleando toberas mono-orificio, con aplicación de diversas técnicas ópticas. Para estudiar la influencia de las propiedades de los combustibles se utilizaron distintos mono-componentes, así como mezclas binarias y un sustituto de diesel conformado por seis componentes, el cual fuel comparado con diesel convencional. Adicionalmente, los resultados han sido contrastados con un modelo unidimensional para ayudar a explicar los valores y tendencias encontrados. Los resultados presentaron una fuerte dependencia de las propiedades de los combustibles en los ensayos realizados bajo condiciones inertes y reactivas. La diferencia entre las propiedades físicas del n-decano y n-hexadecano mostraron una reducción casi lineal sobre la longitud líquida estabilizada hasta aproximadamente un 60% bajo ciertas condiciones. Adicionalmente, debido a la composición del combustible de sustitución, el n-hexadecano puro demostró tener características de evaporación prácticamente idénticas, probándose a sí mismo como un buen candidato para ser un sustituto mono-componente del diesel convencional. De una manera similar, las propiedades químicas de los PRFs n-heptano e iso-octano también probaron tener influencia sobre el desarrollo del chorro y radiación emitida. Se obtuvieron valores de tiempo de retraso con diferencias de hasta un orden de magnitud entre ambos extremos del rango de las mezclas, así como longitudes de despegue de llama hasta tres veces más largas. La radiación emitida por la incandescencia del hollín presentó las variaciones más altas, ya que algunas condiciones mostraron reducciones de hasta cuatro órdenes de magnitud dentro del rango de mezclas. Es más, algunos casos no presentaron radiación correspondiente al hollín, e incrementar la sensibilidad de la cámara solo ocasionó que la quimioluminiscencia del radical OH* sea detectada. Por otro lado, la longitud estabilizada de llama calculada mediante la radiación del hollín no presentó mucha variación respecto a las propiedades del combustible o la temperatura del aire. De hecho, la única diferencia apreciable fue causada por los cambios en la composición del oxígeno del aire ambiente. En conclusión, las propiedades de los combustibles demostraron tener un efecto significativo en los procesos de un chorro diesel. Los combustibles más ligeros favorecieron la evaporación del chorro en un rango de condiciones, mientras que combustibles con números de octano más bajos encendieron más pronto y cerca de la tobera pero con mayor luminosidad del hollín medida.
[CAT] En aquests últims anys, la tendència en motors Diesel ha estat la d'emprar diferents tipus de combustibles per a identificar la seva influència i comportament sobre les emissions i rendiment. Dintre de l'àmplia varietat de combustibles emprats estan els anomenats combustibles de referència (PRFs angl. Primary Reference Fuels), els quals representen el comportament del dièsel i la gasolina pel que fa a propietats d'encesa, ja que es troben en ambdós extrems de l'escala del nombre d'octà i també posseeixen nombres de cetà molt diferents. Un dels desavantatges d'utilitzar benzina pura o barreges de Diesel-benzina en motors Diesel és el temps que pren la barreja a encendre i cremar completament el combustible. Això generalment requereix treballar amb càrregues parcials o càrregues premesclades. Per a poder aïllar els efectes del combustibles sobre els processos d'un doll i que sigui capaç estudiar els paràmetres característics de de temps de retard d'encesa, longitud d'enlairament de flama, penetració de líquid i vapor, entre altres, s'han estudiat diferents experiments sota variacions paramètriques de condicions de motor Diesel. Els assajos han estat realitzats sota condicions inertes i reactives en un motor de dos temps i una instal·lació d'alta pressió i alta temperatura de flux continu a pressió constant (CPF angl. Constant-Pressure Flow) emprant toberes mono-orifici, amb aplicació de diverses tècniques òptiques. Per a estudiar la influència de les propietats dels combustibles, van ser utilitzats distints mono-components, així com barreges binàries i un substitut de Diesel conformat per sis components, el qual fuel comparat amb Diesel convencional. Addicionalment, els resultats han estat contrastats amb un model unidimensional per a ajudar a explicar els valors i tendències trobats. Els resultats van presentar una forta dependència de les propietats dels combustibles en els assajos realitzats sota condicions inertes i reactives. La diferència entre les propietats físiques del n-decà i n-hexadecà van mostrar una reducció gairebé lineal sobre la longitud líquida estabilitzada fins a aproximadament un 60% sota certes condicions. Addicionalment, degut a la composició del combustible de substitució, el n-hexadecà pur va demostrar ser tindre característiques d'evaporació pràcticament idèntiques a aquell, demostrant ser un bon candidat per a ser un substitut mono-component del dièsel convencional. D'una manera similar, les propietats químiques dels PRFs n-heptà i iso-octà també provaren tindre influència sobre el desenvolupament del doll i la radiació emesa. Es van obtenir valors de temps de retard amb diferències de fins a un ordre de magnitud entre ambdós extrems del rang de les barreges, així com longituds d'enlairament de flama fins a tres vegades més llargues. La radiació emesa per la incandescència del sutge va presentar les variacions més grans, ja que algunes condicions van mostrar reduccions de fins a quatre ordres de magnitud dintre del rang de barreges. Encara més, alguns casos no van presentar radiació corresponent al sutge, i incrementar la sensibilitat de la càmera solament va ocasionar que la quimioluminiscència del radical OH* sigui detectada. D'altra banda, la longitud estabilitzada de flama calculada mitjançant la radiació del sutge no va presentar molta variació respecte a les propietats del combustible o la temperatura del aire. De fet, la única diferència apreciable va ser causada pels canvis en la composició del oxigen de l'aire ambient. En conclusió, les propietats dels combustibles van demostrar tenir un efecte significatiu en els processos d'un doll dièsel. Els combustibles més lleugers van afavorir l'evaporació del doll en un rang de condicions, mentres que els combustibles amb nombre d'octà més baixos van prendre més aviat i prop de la tovera però amb més lluminositat del sutge mesurat.
Vera-Tudela Fajardo, WM. (2015). An experimental study of the effects of fuel properties on diesel spray processes using blends of single-component fuels [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/58865
TESIS

Orientador: José Antônio Perrella Balestieri
Abstract: Direct injection spark ignition (DISI) engines aim at reducing specific fuel consumption and achieving the strict emission standards in state of the art internal combustion engines. Therefore, in this work the goal is to develop code for simulations of the internal flow in DISI engines, as well as the phenomenon of fuel spray injection into the combustion chamber using a Lagrangian-Eulerian approach for representing the multiphase flow, and Large-eddy Simulations (LES) for modeling the turbulence of the continuum medium by means of the open-source CFD library OpenFOAM. In order to validate the obtained results and the developed models, experimental data from the Darmstadt optical engine, and the non-reactive “Spray G” gasoline injection case, along with the reactive “Spray A” case from the Engine Combustion Network (ECN) will be employed. Finally, a novel open-source solver will be proposed to simulate the Darmstadt optical engine in motored and fired operation under stratified mixture condition, using data compiled by the Darmstadt Engine Workshop (DEW) for validation. Moreover, a deep learning framework is presented to train an artificial neural network (ANN) with the engine LES data generated in this work, in order to make predictions of the small scale turbulence behavior.
Resumo: Motores de ignição a centelha com injeção direta (direct injection spark ignition engines, DISI engines) visam reduzir o consumo específico de combustível e respeitar os restritos níveis de emissão em motores de combustão interna de última geração. Assim, pretende-se com este trabalho desenvolver código para simulação do escoamento interno em motores DISI, assim como os fenômenos de injeção de combustível no interior da câmara de combustão utilizando uma abordagem Lagrangeana-Euleriana para representação do escoamento multifásico e Simulação de Grandes Escalas (Large-eddy simulation, LES) para a modelagem da turbulência no meio contínuo, por intermédio da biblioteca CFD de código aberto OpenFOAM. De modo a validar os resultados e os modelos desenvolvidos, dados experimentais serão utilizados, obtidos do motor óptico de Darmstadt, e do caso de teste de injeção de gasolina não-reativo “Spray G”, juntamente com o caso reativo “Spray A” da Rede de Combustão em Motores (Engine Combustion Network, ECN). Enfim, um novo código aberto será proposto para simular o motor óptico de Darmstadt em condições de escoamento a frio (sem combustão) e com combustão em condição de mistura estratificada, usando dados compilados pelo Workshop do Motor de Darmstadt (Darmstadt Engine Workshop, DEW) para validação. Além disso, uma abordagem de aprendizado profundo (deep learning) será apresentada para treinar uma rede neural artificial (artificial neural network, ANN) com dados de simulação LES de moto... (Resumo completo, clicar acesso eletrônico abaixo)
Doutor

Computational fluid dynamics methodologies have been achieving in the last decades remarkable progresses in predicting the complex physical process in internal combustion engines, which need to be continuously optimised to get the best compromise between fuel economy, emissions and power output/drivability. Among the variety of computational tools developed by researchers to investigate the multi-Phase flow development from high-pressure fuel injection systems for modem diesel and gasoline direct injection engines, the Eulerian-Lagrangian stochastic methodology, which models the air/vapour mixture as continuous phase and the liquid droplets as the dispersed one, has become standard among the developers of commercial or in-house university CFD codes due to its intuitive assumptions and simple implementation. It is generally recognised that this method is specifically suitable for dilute sprays, but it has shortcomings with respect to modelling of the dense sprays present in the crucial region close to the nozzle exit of fuel injection systems. Moreover, the mathematical formulation of the Eulerian-Lagrangian models is intrinsically related to critical numerical issues, like the difficulty of correctly estimating the initial conditions at the nozzle hole exit required by spray modelling calculations and, furthermore, the dependency of the results on the spatial and temporal discretisation schemes used to solve the governing flow equations. To overcome some of these difficulties, a modified Lagrangian methodology has been developed in this study. The interaction between the Eulerian and the Lagrangian phases is not treated on the cell-to-parcel basis, but using spatial distribution functions, which allow for distribution of the spray source terms on a number of cells located within a distance from the droplet centre. The end result is a numerical methodology which can handle numerical grids irrespective of the volume of the Lagrangian phase introduced. These improvements have been found to offer significant advances on Lagrangian spray calculations without the need to switch to Eulerian models in the near nozzle region. Besides these fundamental numerical issues, the present study offers some new insights on the physical processes involved in evaporating sprays under a wide range of operating conditions typical of advanced diesel and gasoline direct injection engines. Attention hag been directed on the topic of liquid droplet vaporisation modelling, which has been addressed by implementing and discussing different models published in the literature. Topics of particular emphasis include phase equilibrium, quasi-steadiness assumption, fuel composition, physical properties correlation, droplet shape and energy and mass transfer in the liquid and gas phases. The models have been implemented and validated against an extensive data base of experimental results for single and multi-component droplets vaporising under suband super-critical surrounding conditions and then implemented in the in-house GFS code, the multi-phase CFD solver developed within the research group over the last decade. A variety of physical sub-models have been assessed against comprehensive experimental data, which include the effect of thermodynamic, operating and physical parameters on the liquid and vapour penetration of diesel sprays. In particular, the effect of liquid atomisation, evaporation, aerodynamic drag, droplet secondary break-up and fuel physical properties has been thoroughly tested. The sensitivity of the predictions on the numerical treatment of the multi-phase interaction has been investigated by identifying and properly modelling the numerical parameters playing the most crucial role in the simulations. Finally the validated code has been used to investigate the flow processes from three high-pressure injection systems for direct injection spark-ignition engines. These have included the pressure swirl atomiser, the multi-hole injector and the outward-opening pintle nozzle. These investigations have enlightened the crucial role of the accurate modelling of the link between the internal nozzle flow prediction and the characteristics of the forming sprays in term of the successive multi-phase flow interaction, as function of the design of the fuel injection system used.

バイオディーゼルは、メタノールと触媒を使用したエステル交換プロセスによって製造されます。バイオディーゼルには、高セタン価、酸化安定性、低排出など、いくつかの利点があります。ただし、バイオディーゼルの高粘度と沸騰温度は、ディーゼルエンジンの噴霧燃焼に影響を与える可能性があります。したがって、高燃料と低沸点燃料を混合することでバイオディーゼルの特性を改善するために、新しい燃料設計法が適用されます。
Biodiesel is one of the promising alternative fuels in the future. Biodiesel is made from the trans-esterification process that uses methanol or alcohol and catalyst. The use of biodiesel in diesel engine has some advantages such as high cetane number, oxidation stability and can reduce some emissions. However, high viscosity, boiling temperatures and surface tension in biodiesel may affect the spray characteristics as compared to diesel oil. To overcome the unbenefited in biodiesel, therefore, the new fuel designed method that high-boiling point fuel is mixed to a low-boiling point fuel is applied in order to improve the properties in biodiesels.
博士(工学)
Doctor of Philosophy in Engineering
同志社大学
Doshisha University

The current pollution policies in all European and American countries are forcing the industry to movetowards a more efficient and environmentally friendly engines. On the other hand, customers requiremaintaining the power and fuel consumption. Lowering mainly nitrous oxides (NOx) and carbon particles(Soot) is therefore a challenging task with a very strong impact on mainly the automotive andaeronautical market.The purpose of the current work is to research the pollution production of automotive diesel enginesand optimize the fuel injection and piston geometry to lower the emissions. The interaction betweenfuel and air as well as the combustion are the two main physical and chemical processes governing thepollutants formation. Converged-CFD will be the CFD tool employed during the analysis of the previousproblems.The fuel-air interaction is related to jet break up, vaporization and turbulence. The strong dependenceon the surrounding flow field of the previous processes require the equations to be solved numericallywithin a CFD code. The fuel is to be placed in a combustion chamber (piston) where the spray will affectthe surrounding flow field and ultimately the combustion process.In order to accurately represent the nature of the processes, the current work is divided into two mainchapters. Spray modelling and Combustion Modelling. The first will help to accurately model the discretephase (fuel spray) and the vapour entrainment. The second chapter, combustion modelling willretrieve the knowledge gain in the first part to accurately represent the fuel injection in the chamber aswell as the combustion process to ultimately model the pollutants emissions.Finally, a piston bowl optimization will be performed using the previous analysed models and give theindustry a measure of the potential improvement by just adjusting the fuel injection or by modifyingthe piston bowl geometry.

Release and combustion of a spray cloud in an atmosphere is a phenomenon encountered in a wide range of applications. For solution of a set of problems which is connected with ecology, theory of combustion and explosion, engine design, fire safety, etc. the knowledge of spray combustion behaviour is required. To investigate the influence of a variety in density and transport coefficients and flame front structure, combustion of pure gas cloud is studied numerically. Combustion of a small-scale spherical pocket of fuel droplets in a calm environment may be considered as a model enabling the transient combustion process to be studied conveniently in one-dimensional geometry. Apart from pure academic interest, such a study provides useful estimations of burning spray cloud characteristics which can be applied for the analysis of more complicated situations. An analytical approach is used to find quasi-steady state distributions of gas temperature and fuel mass fraction for both pure evaporating and burning clouds. This approach is quite fruitful, it gives important qualitative analytical relationships, which help to comprehend the complex process of evaporation or combustion of spray the cloud. Numerical method is used to solve the problem of spray cloud combustion using more common unsteady statement. Two types of ignition are used at the centre or from penphery of cloud. Two types of flames (premixed and diffusion flames) are observed in the numerical simulations. Distributions of all components and temperature are obtained at different moments of time for both types of ignition. The diffusion burning time and total evaporation time are estimated using numerical results.

La législation sur les émissions de polluants des Moteurs à Combustion Interne (ICEs) est de plus en plus contraignante et représente un gros défi pour les constructeurs automobiles. De nouvelles stratégies de combustion telles que la Combustion à Allumage par Compression Homogène (HCCI) et l’exploitation de stratégies d’injections multiples sont des voies prometteuses qui permettent de respecter les normes sur les émissions de NOx et de suies, du fait que la combustion a lieu dans un mélange très dilué et par conséquent à basse température. Ces aspects demandent la création d’outils numériques adaptés à ces nouveaux défis. Cette thèse présente le développement d’un nouveau modèle 0D de combustion Diesel HCCI : le dual Combustion Model (dual - CM). Le modèle dual-CM a été basé sur l’approche PCM-FPI utilisée en Mécanique des Fluides Numérique (CFD) 3D, qui permet de prédire les caractéristiques de l’auto-allumage et du dégagement de chaleur de tous les modes de combustion Diesel. Afin d’adapter l’approche PCM-FPI à un formalisme 0D, il est fondamental de décrire précisément le mélange à l’intérieur du cylindre. Par consequent, des modèles d’évaporation du carburant liquide, de formation de la zone de mélange et de variance de la fraction de mélange, qui permettent d’avoir une description détaillée des proprietés thermochimiques locales du mélange y compris pour des configurations adoptant des stratégies d’injections multiples, sont proposés. Dans une première phase, les résultats du modèle ont été comparés aux résultats du modèle 3D. Ensuite, le modèle dual-CM a été validé sur une grande base de données expérimentales; compte tenu du bon accord avec l’expérience et du temps de calcul réduit, l’approche présentée s’est montrée prometteuse pour des applications de type simulation système. Pour conclure, les limites des hypothèses utilisées dans dual-CM ont été investiguées et des perspectives pour les dévélopements futurs ont été proposées
More and more stringent restrictions concerning the pollutant emissions of Internal Combustion Engines (ICEs) constitute a major challenge for the automotive industry. New combustion strategies such as Homogeneous Charge Compression Ignition (HCCI) and the implementation of complex injection strategies are promising solutions for achieving the imposed emission standards as they permit low NOx and soot emissions, via lean and highly diluted combustions, thus assuring low combustion temperatures. This requires the creation of numerical tools adapted to these new challenges. This Ph.D presents the development of a new 0D Diesel HCCI combustion model : the dual Combustion Model (dual−CM ). The dual-CM is based on the PCM-FPI approach used in 3D CFD, which allows to predict the characteristics of Auto-Ignition and Heat Release for all Diesel combustion modes. In order to adapt the PCM-FPI approach to a 0D formalism, a good description of the in-cylinder mixture is fundamental. Consequently, adapted models for liquid fuel evaporation, mixing zone formation and mixture fraction variance, which allow to have a detailed description of the local thermochemical properties of the mixture even in configurations adopting multiple injection strategies, are proposed. The results of the 0D model are compared in an initial step to the 3D CFD results. Then, the dual-CM is validated against a large experimental database; considering the good agreement with the experiments and low CPU costs, the presented approach is shown to be promising for global engine system simulations. Finally, the limits of the hypotheses made in the dual-CM are investigated and perspectives for future developments are proposed

The continuing tightening of emission regulations has encouraged extensive research into fuel spray vaporising and combustion. This thesis is an investigation into the effect that the cylinder boundaries have upon the quantity and composition of the unburnt hydrocarbons present in the exhaust gas and particulate matter. To determine the cylinder boundaries' effect on the exhaust hydrocarbon content a series of engine tests was completed. The engine used for these experiments was a modem four cylinder turbo charged direct injection diesel engine, operated at five steady state test points. The test consisted of two standard engine builds to determine the accuracy of measurement and to supply a base point for comparison. The second test used standard pistons with modified oil control rings to increase the oil film thickness. The final test used pistons with the top ring moved nearer the top of the piston by 5.5 mm to reduce the top land crevice volume by ?55%.The composition of the particulate soluble organic fraction (SOF) for the test using the low tangential load oil control piston ring was shown to have a greater fuel content than for other tests, showing that adsorption of the fuel in the lubricating oil contributes to the particulate. The reduction of the top ring crevice volume produced similar quantities of particulate SOF but it consisted of generally lighter hydrocarbon species. The effects of these changes were replicated in a mathematical model which calculated the in cylinder values for fuel, soot, temperature and hydrocarbons. The model also simulated the oxidation of hydrocarbons at the cylinder boundary and consisted of 3 primary zones; the combustion chamber, crevice volume and oil film. This research shows that careful design of engine components can influence the quantity and composition of the particulates exhaust gas and allow the reduction of regulated components.

This thesis was initiated by the need to develop a stable low vibration engine with a high power to weight ratio. A new rotary (Wankel) engine was chosen to meet these requirements. A further operating criterion was that the engine was required to use JP8 (aviation fuel). The difficulty created by the use of JP8 is that its combustion temperature is higher than other conventional fuels, and preheating is necessary, especially in the case of cold start. Thus, the question posed was, could a more appropriate and efficient method of fuel delivery be devised? This thesis presents the design and construction of a fluid spray visualisation system for investigating the macroscopic and microscopic characteristics of fuel sprays using low injection pressure up to 10 bar (1 MPa). Laser imaging techniques have been used for data acquisition. The thesis has been divided into several aspects. Firstly, a background study of fluid sprays and fuel injection strategies was carried out. This has centred on the relationship between droplet size and the combustion process. It further investigated what differentiated the fuel delivery approach to Wankle from that to other engines. Secondly, two families of fuel injector were tested and evaluated within the optical engineering laboratory using deionised water (DI) water for safety reasons. The first family involved conventional gasoline injectors with several nozzle arrangements. The second family involved medical nebulisers with several nozzle diameters. The evaluation of the fuel injectors required developing a fluid delivery circuit, and a specific ECU (Electronic Control Unit) for controlling pulse delivery and imaging instrument. The company associated with the project then set up a test cell for performing experiments on JP8 fuel. The initial global visualisation of the jet spray was made using a conventional digital camera. This gave a measurement of the spray angle and penetration length. However, as the study moved to the more precise determination of the fuel spray particulate size, a specialised Nd:YAG laser based diagnostic was created combined with a long range diffraction limited microscope. Microscopic characterisation of the fuel sprays was carried out using a backlight shadowgraph method. The microscopic shadowgraphy method was applied successfully to resolve droplets larger than 4 microns in diameter. The spray development process during an individual fuel injection cycle was investigated, presenting the frequency response effect of electronic fuel injectors (EFI) on the spray characteristics when operating at high injection frequencies (0.25 -­‐ 3.3 kHz). The velocity distribution during the different stages of an injection cycle was investigated using PIV. The influence of the injection pressure on the spray pattern and droplet size was also presented. Novel fluid atomisation systems were investigated for the capability of generating an optimum particulate distribution under low pressure. Finally, it was found that a new electronic medical nebuliser (micro-­‐dispenser) could be used to deliver the fuel supply with the relevant particle size distribution at low flow rate and high injection frequency. However, as yet it has not been possible to apply this approach to the engine; it is hoped that it will yield a more efficient method of cold starting the engine. The characteristics of this atomiser can be applied to provide a controllable fuel supply approach for all rotary engines to improve their fuel efficiency. The second part of this research discusses the droplets-­‐light interaction using Mie scattering for fluid droplets smaller than the microscope visualisation limit (4 microns). Mie scattering theory was implemented into Three-­‐Components Particle Image Velocimetry (3C-­‐ PIV) tests to address a number of problems associated with flow seeding using oil smoke. Mie curves were used to generate the scattering profile of the oil sub-­‐micron droplets, and therefore the scattering efficiency can be calculated at different angles of observation. The results were used in jet flow PIV system for the determination of the optimum position of the two cameras to generate balanced brightness between the images pairs. The brightness balance between images is important for improving the correlation quality in the PIV calculations. The scattering efficiency and the correlation quality were investigated for different seeding materials and using different interrogation window sizes.

The current project represents the first attempt to test the environmental performance of the direct utilisation of purified used cooking oil as a fuel in a heavy goods vehicle under real world driving conditions. The properties of the used cooking oil were different from those of petroleum diesel (PD) standards however, its heat value, carbon footprint reduction potential and low cost were the key incentives driving it’s use as a fuel. The current research was a collaborative project between Convert to Green (C2G), the fuel provider, the United Biscuits Midlands Distribution Centre, the heavy goods vehicle provider and the University of Leeds as the scientific consultant and research executor. The brand of used cooking oil was Convert to Green Ultra-biofuel (C2G UBF) tested on a Mercedes-Benz EURO 5 emissions standard compliant 44 tonne articulate heavy goods vehicle (HGV). The HGV was modified for on-board UBF heating and mixing with PD. UBF was heated by heat recovery from the engine cooling system. The results showed that the UBF/PD blending ratio was 0.845 as a journey average for the entire test series. However, the HGV was recorded to run on 100% UBF at steady high speed on the M1 motorway in the Midlands region of the UK. There were no discernible deficiencies in the HGV’s performance or its traction effort. Nevertheless a slight increase in specific fuel consumption (SFC) was detected for the blended fuel. Engine durability, combustion chamber deposits and maintenance frequency were not affected by the UBF content in the fuel. Although the engine technology was designed to suppress particulate matter (PM) within the combustion process, the use of blended UBF further reduced the tailpipe PM emissions compared to the use of PD. Carbon monoxide emissions decreased when using the blended fuel, while nitrogen oxides, total hydrocarbons and carbon dioxide increased compared to PD emissions. The benefits of UBF utilisation as a fuel lie in the huge carbon savings and reduced PM emissions when compared to the use of PD as well as its use in providing a cost effective fuel supply and waste management technique.

Large eddy simulation of spray combustion in an HSDI engine is carried out in this thesis. The implementation of the code was performed in logical steps that allowed both assessment of the performance of the existing KIVA-LES and later development. The analysis of the liquid annular jet confirmed existence of typical, annular jet exclusive structures like head vortices, stagnation point and recirculation in the inner zone. The influence of the swirl in the ambient domain was found to have profound impact on the development, penetration and radial spreading of the jet. Detailed results were reported in Jagus et al. (2008). The code was further validated by performing an extensive study of large eddy simulation of diesel fuel mixing in an engine environment. The reaction models were switched off in order to isolate the effects of both swirl and the different numerical treatment of LES. Reference RANS simulation was performed and significant differences were found. LES was found to capture much better the influence of the swirl on the liquid and vapour jets, a feature essentially absent in RANS results. Moreover, the predicted penetration of the liquid was much higher for the LES case and more in accordance with experimental measurements. Liquid penetration and subsequent evaporation are very important for prediction of heat release rates and encouraging results formed a good basis to performing a full simulation with models for ignition and combustion employed. The findings were analyzed in the paper by Jagus et al. (2009). Further modifications were introduced into the LES code, among them changes to the combustion model that was originally developed for RANS and calculation of the filter width. A new way of estimating the turbulent timescale (eddy turnover time) assured that the incompatibilities in the numerical treatment were eliminated and benefits of LES maximized. The new combustion model proved to give a very good agreement with experimental data, especially with regard to pressure and accumulated heat release rates. Both qualitative and quantitative results presented a significant improvement with respect to RANS results and old LES formulation. The new LES model was proved to give a very good performance on a spectrum of mesh resolutions. Encouraging results were obtained on a coarse mesh sets therefore proving that the new LES code is able to give good prediction even on mesh sizes more suitable for RANS. Overall, LES was found to be a worthy alternative to the well established RANS methods, surpassing it in many areas, such as liquid penetration prediction, temperature-turbulence coupling and prediction of volume-averaged data. It was also discovered that the improved LES code is capable of producing very good results on under-resolved mesh resolutions, a feature that is especially important in industrial applications and on serial code structure.