Wie vermischen sich Kraftstoff und Luft, wenn ein flüssiger Kraftstoff in einer Umgebung eingespritzt und zerstäubt wird, deren Parameter Druck und Temperatur den kritischen Druck und die kritische Temperatur des Kraftstoffs überschreiten? In dieser Arbeit wurden Experimente basierend auf Raman-spektoskopischen Methoden zur Gemischbildung unter eben solchen Bedingungen durchgeführt. Ziel der Arbeit war der experimentelle Nachweis der Möglichkeit einphasiger Gemischbildung, d.h. des Übergangs von eingespritztem Kraftstoff in das überkritische Regime, und von da Mischung mit der umgebenden initial überkritischen Stickstoffphase ohne Auftreten von Phasengrenzen. Dazu war es nötig, das Zweiphasengebiet der eingesetzten Stoffe exakt zu charakterisieren (die Gas-Flüssig-Gleichgewichte zu messen), und die Temperatur der Flüssigphase zuverlässig während der Gemischbildung zu messen. Mittels eines Mikrokapillar-Aufbaus wurden Daten zu Gas-Flüssig-Gleichgewichten (engl. Vapor-liquid-equilibria, VLE) bei hohen Drücken und Temperaturen erhoben. Dazu wurden unter kontrollierten Bedingungen phasenspezifische Raman-Spektren der Gas- und der Flüssigphase gemessen, aus denen sich in-situ die Gemischzusammensetzung der Phasen ermitteln ließ. Desweiteren wurden Methoden zur Bestimmung der Temperatur der Flüssigphase erarbeitet, sowie eine Methode zur Unterscheidung von Gas- und Flüssiganteil anhand der Raman-Spektren. Die letzten Methoden basieren auf einer Auswertung des Signals der Hydroxyl-Gruppe von Ethanol, welches in der vorliegenden Arbeit als Kraftstoff-Surrogat verwendet wurde. Danach wurden diese Methoden in einer Hochdruck-Hochtemperatur-Einspritzkammer eingesetzt. Hier wurde Kraftstoff unter realistischen Motorbedingungen eingespritzt, und Raman-Spektroskopie zeitlich und örtlich aufgelöst im entstehenden Spray angewandt. Dies erlaubte die Untersuchung der Gemischbildung ohne Beeinträchtigung des Systems, wie etwa durch Zugabe von Marker-Stoffen oder den Einsatz invasiver Messtechniken. Die gewonnenen VLE-Daten stellen eine erhebliche Verbesserung der Datengrundlage in diesem Druck- und Temperaturbereich dar, da Literaturdaten hier rar sind. Der realisierte Mikrokapillar-Aufbau benötigt nur minimale Volumina an Flüssigkeit und Gas, und lässt vielfältige weitere Einsatzmöglichkeiten wie etwa die Messung von VLE-Daten anderer Stoffe oder auch ternärer Gemische, oder die Untersuchung chemischer Reaktionen zu. Gleichgewichte stellen sich aufgrund des hohen Oberflächen-Volumen-Verhältnisses und der insgesamt kurzen Weglängen schnell ein. Die Zuverlässigkeit der gewonnenen Daten konnte durch Vergleich mit den wenigen vorhandenen Literaturdaten gezeigt werden. Bei Vorliegen von Wasserstoffbrückenbindungen konnte die Zuverlässigkeit und Überlegenheit der Raman-Thermometrie basierend auf der „integrated absolute difference spectroscopy“ gezeigt werden, außerdem erlaubt das charakteristische Raman-Signal der Hydroxyl-Gruppe in Wasserstoff-brückenbindung eine Unterscheidung von Gas- und Flüssigphase in überlagerten Spektren. Zum Nachweis der Durchführbarkeit einer solchen Unterscheidung wurde eine Methode entwickelt, um mittels unterschiedlicher Trigger-Signale phasenspezifische Messungen ohne Überlagerung durch eine alternierende Phase durchzuführen. Die gemessenen, örtlich und zeitlich aufgelösten Daten zur Gemischbildung im Spray erlauben die thermodynamische Charakterisierung der Gemischbildung anhand der ermittelten Parameter „globale Gemischzusammensetzung“, „Flüssigphasenanteil“ und „Flüssigphasentemperatur“. Die Ergebnisse zeigten für hohe Umgebungsdrücke und Temperaturen, dass die Flüssigphase Temperaturen jenseits ihrer kritischen Temperatur erreichen kann. Dies lieferte den Nachweis des Auftretens einphasiger Gemischbildung.:I Abbreviations and symbols II Figures III Tables 1. Introduction 2. State of the art 2.1.1. Objective of this thesis 3. Application-oriented fundamentals 3.1. Thermodynamic states 3.1.1. Single-component systems 3.1.2. Multi-compound systems 3.2. Micro-fluidic systems 3.3. Spray break-up 3.4. Raman spectroscopy 3.4.1. Fundamentals 3.4.2. Quantifiability of Raman signals 3.4.3. Liquid fraction determination 3.4.4. Raman thermometry 4. Vapor-Liquid-Equilibra – Experimental setup 4.1. Overview and auxiliary equipment 4.2. Heating system 4.3. Raman probe 4.4. Light guard technique 4.5. Materials and Experiments 5. Vapor-Liquid-Equilibria – Results and discussion 5.1. Data evaluation 5.2. Calibration 5.3. Liquid film correction 5.4. Results ethanol/nitrogen 5.5. Results decane/nitrogen 5.6. Raman thermometry 6. Sprays – Experimental Setup 6.1. Overview and auxiliary equipment 6.2. Calibration setup 6.3. Spray excitation and detection 6.4. Investigated conditions 7. Sprays – Results and discussion 7.1. Data evaluation 7.1.1. Fuel fraction determination 7.1.2. Liquid fraction determination 7.1.3. Liquid temperature determination 7.2. Calibration results 7.3. Spray results 8. Conclusion 9. References / How do fuel and air mix, when liquid fuel is injected and atomized in an environment with parameters pressure and temperature exceeding the respective critical ones of the fuel? In this work, experiments on mixture formation at such conditions based on methods of Raman spectroscopy were performed. Objective of the work was the experimental proof of single-phase mixing, i.e. the transition of injected fuel into the supercritical regime, and therein mixture with the surrounding initially supercritical nitrogen atmosphere without the formation of phase boundaries. To this end, the characterization of the two-phase regime was necessary (i.e. the measurement of the vapor-liquid-equlibria), and the reliable determination of the temperature of the liquid phase during mixture formation. Data on vapor-liquid-equilibria (VLE) were measured in a micro-capillary setup at high temperatures and pressures. To this end, phase-specific Raman spectra of the liquid and the vapor phase were measured at well-controlled conditions, from which the mixture composition of the respective phases was derived in-situ. Furthermore, Methods for the determination of the liquid phase temperature were developed, as well as an approach for the differentiation of the liquid phase signal from the vapor phase signal. The two latter methods exploit the specific signal of the hydroxyl-group of ethanol, which served as a fuel surrogate in this work. In the next step, these methods were applied in a high pressure, high temperature injection chamber. Here, fuel was injected at realistic engine-like conditions, and Raman spectroscopy was applied temporally and spatially resolved across the created spray cone. This approach allowed the Investigation of the mixture formation without affecting the system, compared to e.g. the addition of markers or the use of invasive measurement techniques. The gathered data are a significant addition to the scarce data base available in this pressure and temperature range. The realized micro-capillary setup needs only minimal volume of fluids, and allows various other operational Scenarios like the measurement of VLE data of other components, binary or ternary, or the Investigation of chemical reactions. Equilibria form very fast due to the high surface-to-volume ratio and the short path lenghts. The reliability of the gathered data were shown by comparison with literature. With the presence of hydrogen bonds, the reliability and superiority of the Raman thermometry based on the 'integrated absolute difference spectroscopy' was shown. Furthermore, the characteristic Raman signal of the hydroxyl-group allows for the differentiation of the vapor- and liquid-phase contributions in superimposed spectra from vapor- and liquid-phase. For the proof of feasibility of such a differentiation, a sophisticated method for the phase-specific measurements was developed by exploiting distinctive trigger Signals from the phases, allowing measurements in one phase without cross-talk from the alternating phase. The temporally and spatially resolved data measured during mixture formation in the spray lead to the thermodynamic characterization of the mixture formation with respect to the Parameters 'global mixture composition', 'liquid phase fraction', and 'liquid phase temperature'. The results for high pressures and temperatures inside the chamber show that the liquid or liquid-like phase can reach temperatures exceeding the critical temperature of the fuel. This provides the proof a the existance of single-phase mixing.:I Abbreviations and symbols II Figures III Tables 1. Introduction 2. State of the art 2.1.1. Objective of this thesis 3. Application-oriented fundamentals 3.1. Thermodynamic states 3.1.1. Single-component systems 3.1.2. Multi-compound systems 3.2. Micro-fluidic systems 3.3. Spray break-up 3.4. Raman spectroscopy 3.4.1. Fundamentals 3.4.2. Quantifiability of Raman signals 3.4.3. Liquid fraction determination 3.4.4. Raman thermometry 4. Vapor-Liquid-Equilibra – Experimental setup 4.1. Overview and auxiliary equipment 4.2. Heating system 4.3. Raman probe 4.4. Light guard technique 4.5. Materials and Experiments 5. Vapor-Liquid-Equilibria – Results and discussion 5.1. Data evaluation 5.2. Calibration 5.3. Liquid film correction 5.4. Results ethanol/nitrogen 5.5. Results decane/nitrogen 5.6. Raman thermometry 6. Sprays – Experimental Setup 6.1. Overview and auxiliary equipment 6.2. Calibration setup 6.3. Spray excitation and detection 6.4. Investigated conditions 7. Sprays – Results and discussion 7.1. Data evaluation 7.1.1. Fuel fraction determination 7.1.2. Liquid fraction determination 7.1.3. Liquid temperature determination 7.2. Calibration results 7.3. Spray results 8. Conclusion 9. References

The Ph.D. project compiled in this thesis has focused on the role of the solvent in solid-liquid phase equilibria and in nucleation kinetics. Six organic substances have been selected as model compounds, viz. ortho-, meta- and para-hydroxybenzoic acid, salicylamide, meta- and para-aminobenzoic acid. The different types of crystal phases of these compounds have been explored, and their respective solid-state properties have been determined experimentally. The solubility of these crystal phases has been determined in various solvents between 10 and 50 oC. The kinetics of nucleation has been investigated for salicylamide by measuring the metastable zone width, in five different solvents under different experimental conditions. A total of 15 different crystal phases were identified among the six model compounds. Only one crystal form was found for the ortho-substituted compounds, whereas the meta-isomeric compounds crystallized as two unsolvated polymorphs. The para-substituted isomers crystallized as two unsolvated polymorphs and as several solvates in different solvents. It was discovered that the molar solubility of the different crystal phases was linked to the temperature dependence of solubility. In general, a greater molar solubility corresponds to a smaller temperature dependence of solubility. The generality of this relation for organic compounds was investigated using a test set of 41 organic solutes comprising a total of 115 solubility curves. A semi-empirical solubility model was developed based on how thermodynamic properties relate to concentration and temperature. The model was fitted to the 115 solubility curves and used to predict the temperature dependence of solubility. The model allows for entire solubility curves to be constructed in new solvents based on the melting properties of the solute and the solubility in that solvent at a single temperature. Based on the test set comprising the 115 solubility curves it was also found that the melting temperature of the solute can readily be predicted from solubility data in organic solvents. The activity of the solid phase (or ideal solubility) of four of the investigated crystal phases was determined within a rigorous thermodynamic framework, by combining experimental data at the melting temperature and solubility in different solvents and temperatures. The results show that the assumptions normally used in the literature to determine the activity of the solid phase may give rise to errors up to a factor of 12. An extensive variation in the metastable zone width of salicylamide was obtained during repeated experiments performed under identical experimental conditions. Only small or negligible effects on the onset of nucleation were observed by changing the saturation temperature or increasing the solution volume. The onset of nucleation was instead considerably influenced by different cooling rates and different solvents. A correlation was found between the supersaturation ratio at the average onset of nucleation and the viscosity of the solvent divided by the solubility of the solute. The trends suggest that an increased molecular mobility and a higher concentration of the solute reduce the metastable zone width of salicylamide. / QC 20100831

With this thesis, I present an experimental study focusing on the provision of thermodynamic data of fluids at elevated pressure and temperature conditions. Hereby a microcapillary setup that is equipped with an in situ Raman Spectroscopy unit as well as with a high-speed camera, was further improved within the scientific employment of the author. The setup consists in principle of a fused-silica microcapillary embedded in a heating block, which is furthermore connected to high pressure syringe pumps. Pure compounds and mixtures were studied with the microfluidic setup and different thermodynamic properties were determined. For instance, vapor pressures of Poly(oxymethylene) Dimethyl Ethers (OME3 and OME4), a potential class of renewable diesel fuels, were the first time measured for temperatures exceeding the atmospheric boiling temperature. Hereby the regarded compound is pressurized at constant temperature, from what the vapor pressure is determined optically by detecting bubble or film formation, indicating the transition from vapor to liquid state. The main results of this thesis were however the vapor-liquid equilibria (VLE) of fuel/air-systems that were determined by in situ Raman Spectroscopy, whereby the Stokes-scattered Raman signal can be successfully separated phase-dependently by light barrier technology. A further task was the determination of saturated mixture densities of the validation system ethanol/CO2. With this study, I intend to contribute to the scarce literature data for the studied systems and properties. Therewith I want to help to enhance the understanding of microprocesses such as the evaporation and mixing formation in diesel combustion engines.