[ES] En los últimos años, el interés por el desarrollo de motores de aviación limpios y eficientes se ha incrementado debido al impacto perjudicial sobre la salud y el medio ambiente ocasionado por los sistemas de combustión convencionales. En este contexto, la comunidad científica ha ido centrando cada vez más sus esfuerzos en el estudio de la combustión turbulenta y la generación de emisiones contaminantes como las partículas de hollín. Con los recientes avances en lo que respecta a potencia de cálculo, las simulaciones de alta fidelidad emergen como una valiosa alternativa para reproducir y analizar estos fenómenos. En concreto, las simulaciones basadas en el modelado de la turbulencia LES son consideradas como una de las herramientas numéricas más prometedoras a la hora de profundizar en la comprensión sobre los complejos procesos dinámicos que caracterizan el flujo reactivo turbulento y predecir emisiones de hollín en aplicaciones aeronáuticas. En el presente trabajo, se estudia y analiza la combustión turbulenta y producción de hollín en aplicaciones de turbina de gas mediante LES de alta fidelidad. El modelado de la combustión se aborda a través de un método flexible de química tabulada basado en el concepto flamelet, el cual es capaz de representar fenómenos químicos complejos con un coste computacional asequible. Además, se emplea una aproximación Euleriana-Lagrangiana para la descripción de la fase gaseosa y las gotas, de forma que se represente correctamente el flujo reactivo multifásico. Para la predicción de hollín en simulaciones computacionalmente eficientes, se emplea un novedoso enfoque de modelado basada en el método seccional y acoplada al modelo de combustión de química tabulada. Esta estrategia de modelado numérica es utilizada en este trabajo para analizar el proceso de combustión y evaluar sus capacidades para predecir hollín y las características de la llama en quemadores de turbina de gas representativos. En primer lugar, se estudia la combustión de flujo bifásico en una llama atmosférica sin torbellinador con inyección líquida de combustible. Este quemador presenta una estructura doble del frente reactivo y las simulaciones numéricas son capaces de capturar adecuadamente los fenómenos de extinción local que tienen lugar en la zona interna de la llama debido a la interacción de las gotas y la turbulencia con el frente reactivo. Posteriormente, se investiga la combustión y producción de hollín en un quemador presurizado con torbellinador que incluye aire secundario de dilución en el interior de la cámara de combustión. La validación del flujo reactivo y hollín se lleva a cabo tanto en la configuración del quemador con aire secundario como sin el mismo, mostrando unas excelentes capacidades predictivas en ambos casos. La presente estrategia de modelado reproduce de forma precisa el complejo patrón de flujo, la estructura de la llama y la dinámica de generación de hollín, además de que es capaz de proporcionar diferentes distribuciones de tamaño de partícula dependiendo de las variaciones en los procesos de formación y oxidación del hollín. En resumen, los diferentes casos prácticos estudiados permiten consolidar y validar la metodología computacional seguida en la presente tesis. La estrategia de modelado basada en química tabulada propuesta demuestra ser lo suficientemente válida y adecuada para reproducir los complejos fenómenos de la combustión y la formación de hollín, en vista de la consistencia del análisis, las precisas predicciones y la concordancia satisfactoria con las medidas experimentales. / [CA] En els últims anys, l'interés pel desenvolupament de motors d'aviació nets i eficients s'ha incrementat a causa de l'impacte perjudicial sobre la salut i el medi ambient ocasionat pels sistemes de combustió convencionals. En aquest context, la comunitat científica ha anat centrant cada vegada més els seus esforços en l'estudi de la combustió turbulenta i la generació d'emissions contaminants com les partícules de sutge. Amb els recents avanços pel que fa a potència de càlcul, les simulacions d'alta fidelitat emergeixen com una valuosa alternativa per a reproduir i analitzar aquests fenòmens. En concret, les simulacions basades en el modelatge de la turbulència LES són considerades com una de les eines numèriques més prometedores a l'hora d'aprofundir en la comprensió sobre els complexos processos dinàmics que caracteritzen el flux reactiu turbulent i predir emissions de sutge en aplicacions aeronàutiques. En el present treball, s'estudia i analitza la combustió turbulenta i la producció de sutge en aplicacions de turbina de gas mitjançant LES d'alta fidelitat. El modelatge de la combustió s'aborda a través d'un mètode flexible de química tabulada basat en el concepte flamelet, el qual és capaç de representar fenòmens químics complexos amb un cost computacional assequible. A més, s'empra una aproximació Euleriana-Lagrangiana per a la descripció de la fase gasosa i les gotes, de manera que es represente correctament el flux reactiu multifàsic. Per a la predicció de sutge en simulacions computacionalment eficients, s'empra un nou plantejament de modelatge basat en el mètode seccional i acoblat al model de combustió de química tabulada. Aquesta estratègia de modelatge numèrica és utilitzada en aquest treball per a analitzar el procés de combustió en cremadors de turbina de gas representatius, i avaluar les seues capacitats per a predir sutge i les característiques de la flama. En primer lloc, s'estudia la combustió de flux bifàsic en una flama atmosfèrica sense remolinador amb injecció líquida de combustible. Aquest cremador presenta una estructura doble del front reactiu i les simulacions numèriques són capaces de capturar adequadament els fenòmens d'extinció local que tenen lloc en la zona interna de la flama a causa de la interacció de les gotes i la turbulència amb el front reactiu. Posteriorment, s'investiga la combustió i producció de sutge en un cremador pressuritzat amb remolinador que inclou aire secundari de dilució a l'interior de la cambra de combustió. La validació del flux reactiu i sutge es duu a terme tant en la configuració del cremador amb aire secundari com sense aquest, mostrant unes estupendes capacitats predictives en tots dos casos. La present estratègia de modelatge reprodueix de manera precisa el complex patró de flux, l'estructura de la flama i la dinàmica de generació de sutge, a més de que és capaç de proporcionar diferents distribucions de grandària de partícula depenent de les variacions en els processos de formació i oxidació del sutge. En resum, els diferents casos pràctics estudiats permeten consolidar i validar la metodologia computacional seguida en la present tesi. L'estratègia de modelatge basada en química tabulada proposada demostra ser prou vàlida i adequada per a reproduir els complexos fenòmens de la combustió i la formació de sutge, en vista de la consistència de l'anàlisi, les precises prediccions i la concordança satisfactòria amb les mesures experimentals. / [EN] In recent years, interest in the development of efficient and clean aviation powerplants has increased due to the detrimental impact on health and the environment caused by conventional combustion systems. In this context, the research community has increasingly focused its efforts on the study of turbulent combustion and the generation of pollutant emissions such as soot particulates. With recent advances in computational power, high-fidelity simulations emerge as a valuable alternative to reproduce and analyze these phenomena. Specifically, Large Eddy Simulations (LES) are considered as one of the most promising numerical tools to provide further insight into the complex dynamic processes that characterize reactive turbulent flows and predict soot emissions in aeronautical applications. In the present work, turbulent combustion and soot production is studied and analyzed in gas turbine engine applications by means of high-fidelity LES. Combustion modelling is addressed by a flexible tabulated chemistry method based on the flamelet concept, which is able to represent complex chemical phenomena with an affordable computational cost. In addition, an Eulerian- Lagrangian description is employed for the gas phase and droplets in order to correctly represent the multiphase flow in spray flames. A recently developed approach based on the sectional method and coupled to the tabulated chemistry framework is considered for soot prediction in computationally efficient simulations. This numerical modelling framework is used in this work to analyze the combustion process and evaluate its capabilities to predict soot and flame characteristics in representative gas turbine burners. First, an atmospheric non-swirled spray flame is studied in terms of two-phase flow combustion. This burner shows a double reaction front structure and local extinction occurs in the inner layer due to both droplet-flame and turbulence-flame interactions, which is properly characterized by LES. Subsequently, combustion and soot production is investigated in a pressurized swirled model combustor which includes secondary dilution jets inside the combustion chamber. The assessment of the reacting flow field and soot is addressed for burner configurations with and without secondary air, showing excellent predictive capabilities in both cases. The present modelling approach accurately reproduce the complex swirled flow field, flame structure and soot dynamics and is able to provide different particle size distributions depending on the variations of the soot formation and oxidation processes. In summary, the different practical cases studied allow to consolidate and validate the computational methodology followed in the present thesis. The proposed tabulated modelling strategy is sufficiently valid and suitable for reproducing complex combustion and soot formation phenomena, in view of the consistency of the analysis, the accurate predictions and the satisfactory agreement with the experimental measurements. / El desarrollo de la presente tesis ha sido posible gracias a una ayuda para la Formación de Profesorado Universitario (FPU 18/03065) perteneciente al Subprograma Estatal de Formación del Ministerio de Ciencia, Innovación y Universidades de España. Además, el trabajo desarrollado está enmarcado en el proyecto ESTiMatE (Emissions SooT ModEl), que ha sido financiado por el consorcio Clean Sky 2 bajo el programa de investigación e innovación Horizonte 2020 de la Unión Europea (acuerdo No. 821418). Las actividades de simulación numérica han sido posibles gracias a la Red Española de Supercomputación y al Centro de Supercomputación de Barcelona por los recursos computacionales proporcionados en MareNostrum, además del grupo PRACE por conceder el acceso a HAWK (GCS, HLRS, Alemania) a través del proyecto SootAero. / Olmeda Ramiro, I. (2023). Assessment of Detailed Combustion and Soot Models for High-Fidelity Aero-Engine Simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/202284

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

This study performed detailed measurements on and around scaled up conducting and adiabatic airfoils with and without film cooling. The conducting vane was a matched Bi airfoil, which accurately scaled the convective heat transfer and conduction through the solid, in order to produce non-dimensional surface temperatures and thermal boundary layers that were representative of an actual engine. Measurements made on all vane models included surface temperature measurements and thermal profiles above the walls. Separate measurements on non-film cooled and film cooled conducting models allowed for the individual contributions of the internal convective cooling and external film cooling to the overall cooling scheme to be quantified. Surface temperature and thermal field measurements above the wall were also performed on a film cooled adiabatic model. For the conducting model with internal cooling only, strong streamwise temperature variations were seen. The surface temperature variations were highly dependent on the local external and internal heat transfer coefficients. Spanwise temperature variations also existed, but were modest in comparison to streamwise variations. Comparing the thermal fields above the film cooled adiabatic and conducting walls allowed for the assumption that the conducting wall would not significantly affect the thermal field in the film cooling jet to be tested. Near the edge of the film cooling jet the developing thermal boundary layer had a clear effect on the overlying gas temperature, suggesting that the common assumption that the adiabatic wall temperature is the appropriate driving temperature for heat transfer to a film cooled wall was invalid. On the jet centerline thermal boundary layer effects were less influential, due to the development of a new, thin boundary layer. This suggested that the adiabatic wall temperature as driving temperature for heat transfer was a reasonable assumption on the jet centerline for most cases tested. As film cooling momentum flux ratio increase, thermal boundary layer effects became more influential on the jet centerline. Additionally, the high resolution surface temperature measurements and thermal field measurements above the wall presented in the current study represent a significant improvement in the data available for validation of computational simulations of conducting turbine airfoils. / text

In modern, low emission, gas turbine combustion systems the amount of air available for cooling of the flame tube liner is limited. This has led to the development of more complex cooling systems such as cooling tiles i.e. a double skin system, as opposed to the use of more conventional cooling slots i.e. a single skin system. An isothennal experimental facility has been constructed which can incorporate 10 times full size single and double skin (cooling tile) test specimens. The specimens can be tested with or without effusion cooling and measurements have been made to characterise the flow through each cooling system along with the velocity field and cooling effectiveness distributions that subsequently develop along the length of each test section. The velocity field of the coolant film has been defined using pneumatic probes, hot-wire anemometry and PIV instrumentation, whilst gas tracing technique is used to indicate (i) the adiabatic film cooling effectiveness and (ii) mixing of the coolant film with the mainstream flow. Tests have been undertaken both with a datum low turbulence mainstream flow passing over the test section, along with various configurations in which large magnitudes and scales of turbulence were present in the mainstream flow. These high turbulence test cases simulate some of the flow conditions found within a gas turbine combustor. Results are presented relating to a variety of operating conditions for both types of cooling system. The nominal operating condition for the double skin system was at a coolant to mainstream blowing ratio of approximately 1.0. At this condition, mixing of the mainstream and coolant film was relatively small with low mainstream turbulence. However, at high mainstream turbulence levels there was rapid penetration of the mainstream flow into the coolant film. This break up of the coolant film leads to a significant reduction in the cooling effectiveness. In addition to the time-averaged characteristics, the time dependent behaviour of the .:coolantfilm was. also investigated. In particular, unsteadiness associated with large scale structures in the mainstream flow was observed within the coolant film and adjacent to the tile surface. Relative to a double skin system the single skin geometry requires a higher coolant flow rate that, along with other geometrical changes, results in typically higher coolant to mainstream velocity ratios. At low mainstream turbulence levels this difference in velocity between the coolant and mainstream promotes the generation of turbulence and mixing between the streams so leading to some reduction in cooling effectiveness. However, this higher momentum coolant fluid is more resistant to high mainstream turbulence levels and scales so that the coolant film break up is not as significant under these conditions as that observed for the double skin system. For all the configurations tested the use of effusion cooling helped restore the coolant film along the rear of the test section. For the same total coolant flow, the minimum value of cooling effectiveness observed along the test section was increased relative to the no effusion case. In addition the effectiveness of the effusion patch depends on the amount of coolant injected and the axial location of the patch. The overall experimental data suggested the importance of the initial cooling film conditions together with better understanding of the possible mechanisms that results in the rapid cooling film break-up, such as high turbulence mainstream flow and scales, and this will lead to a more effective cooling system design. This experimental data is also thought to be ideal for the validation of numerical predictions.

Der integrierte Gas-Dampf (GiD-) Prozess mit Wasserrückgewinnung ist ein flexibler Kraft-Wärme-Kopplungsprozess, der die gleichzeitige Bereitstellung von Strom und Wärme teilweise entkoppeln kann. Der effiziente und sparsame Einsatz von fossilen Brennstoffen ist aus ökonomischer wie auch ökologischer Sicht geboten. Die Kraft-Wärme-Kopplung (KWK), die gleichzeitige Erzeugung von Strom und Wärme, ist eine Möglichkeit dafür. Allerdings erfordert die KWK auch eine gleichzeitige Abnahme von Strom und Wärme beziehungsweise deren Speicherung. Sowohl Strom als auch Prozessdampf lassen sich nur aufwendig und damit relativ teuer speichern, weshalb Alternativen gefragt sind. Der GiD-Prozess besteht aus einer Gasturbine mit nachgeschaltetem Abhitzedampfkessel. Die Gasturbine verfügt als Besonderheit über eine Dampfinjektion, die vor, nach oder direkt in die Brennkammer erfolgen kann. Der Abhitzekessel hat zusätzliche Wärmeübertragerflächen um das Abgas bis unter den Taupunkt abzukühlen. Somit kann ein Teil des injizierten Dampfes aus dem Abgas zurückgewonnen und wiederverwendet werden. Der in die Gasturbine injizierte Dampf führt dieser weitere Energie zu. Diese kann entweder zur Leistungssteigerung der Anlage oder zur Reduzierung des fossilen Brennstoffbedarfes genutzt werden. Die erste Option der Leistungssteigerung ist auch als Cheng-Prozess bekannt. Diese Arbeit widmet sich der weniger untersuchten zweiten Möglichkeit der Brennstoffreduzierung. Beim Vergleich des GiD-Prozesses mit verschiedenen anderen Kraftwerks-Prozessen zeigt sich, dass dieser besonders gut für industrielle Anlagen mit Prozessdampfbedarf und einer elektrischen Leistung kleiner 20 MW el geeignet ist. Im Rahmen dieser Arbeit wurde der GiD-Prozess mittels einer Versuchsanlage auf Basis einer Industriegasturbine mit 650 kW el untersucht. Die Arbeit dokumentiert verschiedene Versuchsfahrten und Untersuchungen an dieser Anlage. Die Injektion von Dampf reduziert die Schadstoffemissionen in den zulässigen Bereich und kann sehr flexibel zu einer Steigerung des Anlagenwirkungsgrades von bis zu zwei Prozent führen. Dabei wird der Dampf sehr gleichmäßig in die Versuchsanlage eingebracht, so dass keine signifikanten Änderungen der Abgastemperaturverteilung erkennbar sind. Die Überhitzung des Dampfes kann zu einer weiteren Steigerung des Anlagenwirkungsgrades führen. Die Rückgewinnung des eingebrachten Dampfes ist mit den entsprechenden Wärmeübertragern möglich. Das zurückgewonnene Wasser ist durch die Stickoxide des Abgases verunreinigt und muss entsprechend aufbereitet werden.

Les réglementations toujours plus drastiques sur les émissions de polluants ont conduit au développement de systèmes de combustion opérant en régimes pauvres qui sont malheureusement sujet aux instabilités thermo acoustiques. La capacité de la Simulation aux Grandes Echelles (SGE) à simuler des turbines à gaz industrielles complexes de grande puissance est mise en évidence au cours de ce travail de thèse. Tout d’abord, la SGE est appliquée à un brûleur académique et validée par comparaison à des mesures effectuées à l’Université de Berlin ainsi qu’à des simulations SGE effectuées avec OpenFOAM chez Siemens. Afin de déterminer la stabilité de ce bruleur le couplage entre l’acoustique et la combustion est modélisé par l’approche de type fonction de transfert de flamme (FTF). Suite à ces calcules et l’évaluation de la FTF les fluctuations du nombre de swirl sont identifiées comme un paramètre à même de modifier cette réponse de flamme. Après cette première étape de validation, une turbine à gaz industrielle est simulée en SGE pour deux géométries différentes du brûleur et pour deux points de fonctionnement. La FTF issue de ces calculs est peu influencée par les deux points de fonctionnement. A l’inverse, des légères modifications de la géométrie du swirler modifient les caractéristiques de la FTF montrant que plusieurs mécanismes sont en jeu. Ces mécanismes sont identifiés comme étant la vitesse d’entrée, les fluctuations de swirl et les fluctuations de fraction de mélange. Cette dernière est causée par: 1) la pulsation du débit de carburant injecté et 2) la trajectoire fluctuante des jets de carburant. Bien que le swirler soit conçu pour fournir un mélange le plus homogène possible, d’importantes hétérogénéités de mélange à l’entrée de la chambre de combustion sont présentes. Les perturbations de mélange se combinent avec les fluctuations de vitesse (et donc avec les fluctuations de swirl) aboutissant à des résultats de FTF différents. Un modèle étendu pour la FTF reliant le dégagement de chaleur à la vitesse d’entrée et à la fluctuation de fraction de mélange (modèle MISO) se révèle être une bonne solution pour ces systèmes complexes. Une analyse non linéaire montre en outre que l’amplitude de forçage conduit non seulement à une saturation de la flamme, mais aussi à un changement de la réponse de flamme. La saturation de la flamme n’est vérifiée que pour la FTF globale et le gain augmente localement avec une amplitude croissante. Pour ce système on notera enfin que la flamme linéaire, comme la flamme non linéaire, ne sont pas compactes: certaines zones pourtant situées l’une à coté de l’autre, ont des différences significatives de délai de FTF, montrant que certaines parties de la flamme amortissent l’excitation alors que d’autres l’amplifient. / Modern pollutant regulation have led to a trend towards lean combustion systems which are prone to thermo-acoustic instabilities. The ability of Large Eddy Simulation (LES) to handle complex industrial heavy-duty gas turbines is evidenced during this thesis work. First, LES is applied to an academic single burner in order to validate the modeling against measurements performed at TU Berlin and against OpenFoam LES simulations done at Siemens. The coupling between acoustic and combustion is modeled with the Flame Transfer Function (FTF) approach and swirl number fluctuations are identified changing the FTF amplitude response of the flame. Then, an industrial gas turbine is analyzed for two different burner geometries and operating conditions. The FTF is only slightly influenced for the two operating points but slight modifications of the swirler geometry do modify the characteristics of the FTF showing that a simple model taking only into account the flight time is not appropriate and additional mechanisms are at play. Those mechanisms are identified being the inlet velocity, the swirl and the inlet mixture fraction fluctuations. The latter is caused by two mechanisms: 1) the pulsating injected fuel flow rate and 2) the fluctuating trajectory of the fuel jets. Although the diagonal swirler is designed to provide good mixing, effects of mixing heterogeneities at the combustion chamber inlet occur. Mixture perturbations phase with velocity (and hence with swirl) fluctuations and combine with them to lead to different FTF results. Another FTF approach linking heat release to inlet velocity and mixture fraction fluctuation (MISO model) shows further to be a good solution for complex systems. A nonlinear analysis shows that the forcing amplitude not only leads to a saturation of the flame but also to changes of the delay response. Flame saturation is only true for the global FTF and the gain increases locally with increasing forcing amplitude. Both, the linear and the nonlinear flames, are not compact: flame regions located right next to each other exhibited significant differences in delay meaning that at the same instant certain parts of the flame damp the excitation while others feed it.

A thermal tip clearance control system provides a robust and flexible means of manipulating the closure between the casing and the rotating blade tips in a jet engine, reducing undesirable tip leakage flows. This may be achieved using an impingement cooling scheme on the external casing of the engine in conjunction with careful thermal management of internal over-tip seal segment cavity. For a reduction in thrust specific fuel consumption, the mass flow rate of air used for cooling must be minimised, be at as low a pressure as possible and delivered through a light weight structure surrounding the rotating components in the turbine. This thesis first characterises the effectiveness of a range of external impingement cooling arrangements in typical engine casing closure system. The effects of jet-to-jet pitch, number of jets, inline and staggered alignment of jets, arrays of jets on flange, on an engine representative casing geometry are assessed through comparison of the convective heat transfer coefficient distributions in a series of numerical studies. A baseline case is validated experimentally. The validation data allowed the suitability of different turbulence closure models to be assessed using a commercial RANS solver. Importantly for each configuration the thermal contraction of an idealised engine casing is predicted using thermo-mechanical finite element models, at a series of operating conditions representing engine idle to maximum take-off conditions. Cooling is provided by manifolds attached to the outside of the engine. The assembly tolerance of these components leads to variation in the standoff distance between the manifold and the casing. For cooling arrangements with promising performance, the study is extended to characterise the variation in closure with standoff distance. It is shown that where a sparse array of non-interacting jets is used the system can be made tolerant of large build misalignments. The casing geometry itself contributes to the thermal response of the system, and, in an additional study, the effect of casing thickness and circumferential thermal control flanges are investigated. Restriction of the passage of heat into the flanges was seen to be dramatically change their effectiveness and slight necking of the flanges at their root was shown to improve the performance disproportionally. High temperature secondary air flowing past the internal face of the engine casing tends to heat the casing, causing it to grow. Experimental and numerical characterisation of a heat transfer within a typical over-tip segment cavity heat transfer is presented in this thesis for the first time. A simplified modelling strategy is proposed for casing and a means to reduce the casing heat pickup by up to 25 % was identified. The overall validity of the modelling approach used is difficult to validate in the engine environment, however limited data from a test engine temperature survey became available during the course of the research. By modelling this engine tip clearance control system it was shown that good agreement to the temperature distribution in the engine casing could be achieved where full surface external heat transfer coefficient boundary conditions were available.

<p>U okviru istraživačkog rada formiran je matematički model za simulaciju<br />procesa transformacije energije u postrojenju gasne turbine pri<br />sagorevanju gasova srednje ili niže toplotne moći. Data je analiza procesa<br />kosagorevanja gasa iz gasifikacije kukuruznog oklaska i prirodnog gasa u<br />postrojenju gasne turbine, za tri različite konfiguracije postrojenja.<br />Analiza je rađena na primeru osnovnog Joule-ovog ciklusa sa vazduhom<br />hlađenim lopaticama.</p> / <p>This paper presents mathematical model for simulation of energy<br />transformation process in gas turbine facility with combustion of medium<br />and low calorific gases. The basis of the mathematical model is the<br />M&uuml;ller&rsquo;s method. Analysis of co-firing the corn cob gas and natural gas for<br />different gas turbine facility configurations is presented. The basic Joule<br />cycle with blade cooling was analyzed.</p>

Coatings are frequently applied on gas turbine components inorder to restrict surface degradation such as corrosion andoxidation of the structural material or to thermally insulatethe structural material against the hot environment, therebyincreasing the efficiency of the turbine. However, in order toobtain accurate lifetime expectancies and performance of thecoatings system it is necessary to have a reliableunderstanding of the mechanical properties and failuremechanisms of the coatings. In this thesis, mechanical and fracture behaviour have beenstudied for a NiAl coating applied by a pack cementationprocess, an air-plasma sprayed NiCoCrAlY bondcoat, a vacuumplasma-sprayed NiCrAlY bondcoat and an air plasma-sprayed ZrO2+ 6-8 % Y2O3topcoat. The mechanical tests were carried out ata temperature interval between room temperature and 860oC.Small punch tests and spherical indentation were the testmethods applied for this purpose, in which existing bending andindentation theory were adopted for interpretation of the testresults. Efforts were made to validate the test methods toensure their relevance for coating property measurements. Itwas found that the combination of these two methods givescapability to predict the temperature dependence of severalrelevant mechanical properties of gas turbine coatings, forexample the hardness, elastic modulus, yield strength, fracturestrength, flow stress-strain behaviour and ductility.Furthermore, the plasma-sprayed coatings were tested in bothas-coated and heat-treated condition, which revealedsignificant difference in properties. Microstructuralexamination of the bondcoats showed that oxidation with loss ofaluminium plays an important role in the coating degradationand for the property changes in the coatings. Keywords:small punch test, miniaturised disc bendingtests, spherical indentation, coatings, NiAl, APS-NiCoCrAlY,VPS-NiCrAlY, mechanical properties

Catalytic combustion is an environmentally benign technologywhich has recently reached the stage of commercialization.Palladium is the catalyst of choice when considering gasturbines fuelled with natural gas because of its superioractivity for methane oxidation. Several fundamental issues arestill open and their understanding would result in animprovement of the technology. Hence, the work presented inthis thesis aims at the identification of some of theparameters which govern the combustion activity ofpalladium-based catalysts. The first part of this work gives a background to catalyticcombustion and a brief comparison with other existingtechnologies. Paper I reviews some of the issues related tomaterial development and combustor design. The second part of this thesis consists of an experimentalinvestigation on palladium-based catalysts. The influence ofthe preparation method onthe properties of these catalystmaterials is investigated in Paper II. Paper III examines theactivity of the following catalysts: Pd/Al2O3, Pd/Ba-Al2O3 andPd/La-Al2O3. Specific attention is given to the metal-supportinteraction which strongly affects the combustion activity ofpalladium. The effect of doping of the support by addition ofcerium is reported in Paper IV. Finally, the deactivation of combustion catalysts isconsidered. The various deactivation processes which may affecthigh temperature combustion catalysts are reviewed in Paper V.Paper VI focuses on the poisoning of supported palladiumcatalysts by sulphur species. Palladium exhibits a higherresistance to sulphur poisoning than transition metals.Nevertheless, the nature of the support material plays animportant role and may entail a severe loss of activity whensulphur is present in the fuel-air mixture entering thecombustion chamber. <b>Keywords</b>: catalytic combustion, gas turbine, methane,palladium, alumina, barium, lanthanum, oxidation, preparation,temperature-programmed oxidation (TPO), decomposition,reoxidation, X-ray photoelectron spectroscopy (XPS),metal-support interaction, deactivation, sulphur, poisoning.The cover illustration is a TEM picture of a 100 nm palladiumparticle supported on alumina