Escuela Superior de Enseñanzas Técnicas

The objective of this research is to analyze the performance of a passive hybrid powerplant control system to be implemented in a lightweight unmanned aerial vehicle capable to ascend up to the high troposphere (10,000 m). The powerplant is based on a high-temperature PEM fuel cell connected in parallel to a set of lithium-polymer batteries and regulated by two power diodes. Test performed in steady state demonstrates that the use of the hybrid system increases the efficiency of the stack by more than 7% because the voltage at the main DC bus is limited by the batteries. The robustness of the passive control system is proved in a long-term test in which random perturbations of ±15% are applied to the average power that would be demanded during the ascent flight. The hybridization of the stack with the batteries eliminates sudden peaks in the current generated by the stack, which are responsible for prompt degradation phenomena that drastically reduce its useful lifetime. The study demonstrates that with the passive hybrid powerplant it is possible to reach the target height with the gas storage system considered in the application, contrary to what happens with the simple power plant.

When fuel cells are used to power mobile applications, such a vehicles, hybridization with batteries is normally required. Depending on the electronic coupling between the energy sources the power plants can have passive or active configurations. Hybrid fuel cell-battery power plants with active power control flow have some advantages. For example, they can decrease the total energy losses, while improving the fuel cell performance, extending its lifetime. Power plants with DC/DC converters show low specific energy ratios, but with a superior energy management. In the present research, the hybrid power plant for an unmanned aquatic surface vehicle (USV) based on a PEM fuel cell and a Li-ion battery is developed. Active (with DC–DC converters) or passive architectures are analyzed by numerical simulations and experimental tests. Good results are obtained for the active power plant, where the peak power demands are managed by the battery pack while the fuel cell power remains constant thanks to the DC-converter control. The study shows that a simple control algorithm (no optimal) can help to extend the USV autonomy above 12 h in calm waters with a specific energy of 85.6 W h kg-1.

Leading edge protection (LEP) coating systems are applied to protect turbine blade edges from rain erosion. The performance of a LEP system is assessed in an accelerated rain erosion test (RET) as a metric for industrial application, but these tests are expensive. Modelling methods are available to predict erosion, based on fundamental material properties, but there is a lack of validation. The Springer model (1976) is analysed in this work to assess it as a tool for using material fundamental properties to predict the time to failure in a rain erosion test. It has been applied, referenced and industry validated with important partial considerations. The method has been applied successfully for erosion damage by wear performance prediction when combined with prior material data from rain erosion test (RET), instead of obtaining it directly from fundamental properties measured separately as Springer proposed. The method also offers accurate predictions when coupled with modified numerical parameters obtained from experimental RET testing data. This research aims to understand the differences between the experimental data used by Springer and the current industry approach to rain erosion testing, and to determine how it may introduce inaccuracies into lifetime predictions of current LEP systems, since they are very different to those tested in the historic modelling validation. In this work, a review of the modelling is presented, allowing for the understanding of key issues of its computational implementation and the required experimental material characterisation. Modelling results are discussed for different original application issues and industry-related LEP configuration cases, offering the reader to interpret the limits of the performance prediction when considering the variation in material fundamental properties involved.

Achieving European climate neutrality by 2050 requires further efforts not only from the industry and society, but also from policymakers. The use of high-efficiency cogeneration facilities will help to reduce both primary energy consumption and CO2 emissions because of the increase in overall efficiency. Fuel cell-based cogeneration technologies are relevant solutions to these points for small- and microscale units. In this research, an innovative and new fuel cell-based cogeneration plant is studied, and its performance is compared with other cogeneration technologies to evaluate the potential reduction degree in energy consumption and CO2 emissions. Four energy consumption profile datasets have been generated from real consumption data of different dwellings located in the Mediterranean coast of Spain to perform numerical simulations in different energy scenarios according to the fuel used in the cogeneration. Results show that the fuel cell-based cogeneration systems reduce primary energy consumption and CO2 emissions in buildings, to a degree that depends on the heat-to-power ratio of the consumer. Primary energy consumption varies from 40% to 90% of the original primary energy consumption, when hydrogen is produced from natural gas reforming process, and from 5% to 40% of the original primary energy consumption if the cogeneration is fueled with hydrogen obtained from renewable energy sources. Similar reduction degrees are achieved in CO2 emissions.

Top coating are usually moulded, painted or sprayed onto the wind blade Leading-Edge surface to prevent rain erosion due to transverse repeated droplet impacts. Wear fatigue failure analysis based on Springer model has been widely referenced and validated to quantitatively predict damage initiation. The model requires liquid, coating and substrate speed of sound measurements as constant input parameters to define analytically the shockwave progression due to their relative vibro-acoustic properties. The modelling assumes a pure elastic material behavior during the impact event. Recent coating technologies applied to prevent erosion are based on viscoelastic materials and develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. In order to analyze the erosion performance by using Springer model, appropriate impedance characterization for such viscoelastic materials is then required and represents the main objective of this work to avoid lack of accuracy. In the first part of this research, it is proposed a modelling methodology that allows one to evaluate the frequency dependent strain-stress behavior of the multilayer coating system under single droplet impingement. The computational tool ponders the operational conditions (impact velocity, droplet size, layer thickness, etc.) with the appropriate variable working frequency range for the speed of sound measurements. The second part of this research defines in a complementary paper, the ultrasonic testing characterization of di erent viscoelastic coatings and the methodology validation. The modelling framework is then used to identify suitable coating and substrate combinations due to their acoustic matching optimization and to analyze the anti-erosion performance of the coating protection system.

En los últimos años, la industria aeronáutica está mostrando un creciente interés en el desarrollo y uso de vehículos aéreos no tripulados (UAV). Los UAV son cada vez más empleados en el sector militar, donde destacan las plataformas destinadas al reconocimiento de terrenos, las comunicaciones y el espionaje. No obstante, también están aumentando las aplicaciones en el sector industrial y civil, en tareas tales como el mantenimiento de grandes infraestructuras, la vigilancia de cultivos y bosques, la protección de parques naturales, el control de fronteras o para realizar mediciones meteorológicas. Propulsar estos dispositivos mediante sistemas eléctricos es preferible por su mayor eficiencia comparada con la de los motores de combustión interna y la práctica ausencia de emisiones contaminantes. La presente tesis se centra en la investigación de una nueva planta de potencia basada en pila de combustible con membrana polimérica (PEMFC), estudiando una solución hibridada con un banco de baterías de litio-polímero comercial que permita a un prototipo de UAV ligero elevar su cota de vuelo hasta la alta troposfera (10.000 m). La tesis se presenta como un compendio de artículos publicados, dividida en tres partes. En la primera, distribuida en seis secciones, se realiza un resumen de todas las investigaciones que han dado lugar a las publicaciones. La segunda contiene el texto adaptado de las publicaciones que conforman la tesis, mientras que en la tercera se incluyen como anexos algunos documentos adicionales, así como la información técnica de la MEA (del inglés Membrane Electrode Assembly) utilizada y los planos de las placas diseñadas para la pila. Para cumplir el objetivo propuesto, durante la tesis se han escrito códigos numéricos específicos que permitieron resolver el problema aerodinámico y realizar un completo análisis energético, obteniendo como resultado la distribución de pesos de los diferentes elementos que conforman el UAV. Las difíciles condiciones de vuelo debidas a la baja presión en la troposfera imponen que la pila de combustible sea de alta temperatura (HT-PEMFC) y cátodo cerrado, ensamblada con membranas de PBI (polibencimidazol) dopadas con ácido fosfórico, lo que permite una temperatura de trabajo de 160ºC. Se ha desarrollado una HT-PEMFC ligera con diseño propio de todos los elementos mecánicos (las placas monopolares, de presión y terminales, el sistema de sellado y el sistema de cierre), excepto los sistemas membranaelectrodo, que son componentes comerciales. Asimismo, se ha resuelto el problema térmico combinando medidas experimentales y simulaciones numéricas con un código propio y se ha diseñado un sistema de refrigeración pasivo con un consumo mínimo de potencia. Los estudios han concluido que la planta de potencia más eficiente y estable es una híbrida formada por la HT-PEMFC y un banco de baterías de litio-polímero. Finalmente, para minimizar el peso total del sistema, se ha propuesto una planta de potencia híbrida con un sistema electrónico de potencia con regulación pasiva. / In recent years, the aeronautical industry has shown growing interest in the development and use of unmanned aerial vehicles (UAVs). UAVs are increasingly used in the military sector for different missions such as reconnaissance, communications and espionage. However, applications in the industrial and civil sectors are also increasing in tasks such as maintenance of large infrastructures, monitoring crops and forests, etc. Propelling these devices with electrical systems is preferable because they are more efficient than internal combustion engines, and are essentially free of pollutant emissions. The present thesis is focused on research with respect to a new power plant (PP) based on a polymer electrolyte membrane fuel cell (PEMFC), considering a hybrid solution with commercial lithium-polymer (LiPo) batteries that allow an existing prototype of light UAV to reach an altitude of 10,000 m. The thesis is presented as a compendium of published articles, structured in three parts. In the first part, divided into six sections, all the research developed to reach the proposed objectives is summarized. The second part encloses the adapted text of the three published papers. Meanwhile, the third part contains some additional documents, the technical information of the membrane electrode assembly (MEA) used (provided by the manufacturer), and the plans of the designed plates that comprise the PEM fuel cell stack. During the research performed, specific numerical codes have been developed to solve the aerodynamic problem and to perform a complete energy analysis. The mass distribution of the different components that make up the UAV have been obtained. With these results, the maximum mass that can be carried on board has been calculated, as well as the mass distribution among the different elements that form the power plant. The very harsh flight conditions due to the low troposphere pressure impose a closed-cathode high-temperature PEM fuel cell (HT-PEMFC). It is formed of PBI polybenzimidazole) membranes doped with phosphoric acid, with a working temperature of 160ºC. At the same time, both hydrogen and oxygen have to be carried on board. In this thesis, all the mechanical elements of the stack (the monopolar, pressure and end plates, the sealing system, and the closing system) have been specifically designed, except the membrane-electrode assemblies, which are commercially available. Besides, the thermal problem has been solved by combining experimental measurements and numerical simulations with a proprietary code. As a result, a passive cooling system with minimum power consumption has been designed. The studies have concluded that the most efficient and stable power plant is a hybrid one, formed by the HT-PEMFC and a bank of lithium-polymer batteries. Finally, in order to minimize the total weight of the system, an HPP with passive power electronics has been considered.