[ES] La actual crisis climática ha instado a la comunidad investigadora y a los fabricantes a brindar soluciones para hacer que el sector del transporte sea más sostenible. De entre las diversas tecnologías propuestas, la combustión a baja temperatura ha sido objeto de una extensa investigación. La combustión premezclada dual-fuel es uno de los conceptos que abordan el compromiso de NOx-hollín en motores de encendido por compresión manteniendo alta eficiencia térmica. Esta combustión hace uso de dos combustibles con diferentes reactividades para mejorar la controlabilidad de este modo de combustión en un amplio rango de funcionamiento. De manera similar a todos los modos de combustión premezclados, esta combustión es sensible a las condiciones de operación y suele estar sujeta a variabilidad cíclica con gradientes de presión significativos. En consecuencia, se requieren estrategias de control avanzadas para garantizar un funcionamiento seguro y preciso del motor. El control en bucle cerrado es una herramienta eficaz para abordar los desafíos que plantea la combustión premezclada dual-fuel. En este tipo de control, para mantener el funcionamiento deseado, las acciones de control se adaptan y corrigen a partir de una retroalimentación con las señales de salida del motor. Esta tesis presenta estrategias de control basadas en la medición de la señal de presión en el cilindro, aplicadas a motores de combustión premezclada dual-fuel. En ella se resuelven diversos aspectos del funcionamiento del motor mediante el diseño de controladores dedicados, haciéndose especial énfasis en analizar e implementar estas soluciones a los diferentes niveles de estratificación de mezcla considerados en estos motores (es decir, totalmente, altamente y parcialmente premezclada). Inicialmente, se diseñan estrategias de control basadas en el procesamiento de la señal de presión en el cilindro y se seleccionan acciones proporcionales-integrales para asegurar el rendimiento deseado del motor sin exceder las limitaciones mecánicas del motor. También se evalúa la técnica extremum seeking para realizar una supervisión de una combustión eficiente y la reducción de emisiones de NOx. Luego se analiza la resonancia de la presión en el cilindro y se implementa un controlador similar a aquel usado para el control de knock para garantizar el funcionamiento seguro del motor. Finalmente, se utilizan modelos matemáticos para diseñar un modelo orientado a control y un observador que tiene como objetivo combinar las señales medidas en el motor para mejorar las capacidades de predicción y diagnóstico en dicha configuración de motor. Los resultados de este trabajo destacan la importancia de considerar el control en bucle cerrado para abordar las limitaciones encontradas en los modos de combustión premezclada. En particular, el uso de la medición de presión en el cilindro muestra la relevancia y el potencial de esta señal para desarrollar estrategias de control complejas y precisas. / [CA] L'actual crisi climàtica ha instat a la comunitat investigadora i als fabricants a brindar solucions per a fer que el sector del transport siga més sostenible. D'entre les diverses tecnologies proposades, la combustió a baixa temperatura ha sigut objecte d'una extensa investigació. La combustió premesclada dual-fuel és un dels conceptes que aborden el compromís de NOx-sutge en motors d'encesa per compressió mantenint alta eficiència tèrmica. Aquesta combustió fa ús de dos combustibles amb diferents reactivitats per a millorar la controlabilitat d'aquest tipus de combustió en un ampli rang de funcionament. De manera similar a tots els tipus de combustió premesclada, aquesta combustió és sensible a les condicions d'operació i sol estar subjecta a variabilitat cíclica amb gradients de pressió significatius. En conseqüència, es requereixen estratègies de control avançades per a garantir un funcionament segur i precís del motor. El control en bucle tancat és una eina eficaç per a abordar els desafiaments que planteja la combustió premesclada dual-fuel. En aquesta mena de control, per a mantindre el funcionament desitjat, les accions de control s'adapten i corregeixen a partir d'una retroalimentació amb els senyals d'eixida del motor. Aquesta tesi presenta estratègies de control basades en el mesurament del senyal de pressió en el cilindre, aplicades a motors de combustió premesclada dual-fuel. En ella es resolen diversos aspectes del funcionament del motor mitjançant el disseny de controladors dedicats, fent-se especial èmfasi a analitzar i implementar aquestes solucions als diferents nivells d'estratificació de mescla considerats en aquests motors (és a dir, totalment, altament i parcialment premesclada). Inicialment, es dissenyen estratègies de control basades en el processament del senyal de pressió en el cilindre i se seleccionen accions proporcionals-integrals per a assegurar el rendiment desitjat del motor sense excedir les limitacions mecàniques del motor. També s'avalua la tècnica extremum seeking per a realitzar una supervisió d'una combustió eficient i la reducció d'emissions de NOx. Després s'analitza la ressonància de la pressió en el cilindre i s'implementa un controlador similar a aquell usat per al control de knock per a garantir el funcionament segur del motor. Finalment, s'utilitzen models matemàtics per a dissenyar un model orientat a control i un observador que té com a objectiu combinar els senyals mesurats en el motor per a millorar les capacitats de predicció i diagnòstic en aquesta configuració de motor. Els resultats d'aquest treball destaquen la importància de considerar el control en bucle tancat per a abordar les limitacions trobades en la combustió premesclada. En particular, l'ús del mesurament de pressió en el cilindre mostra la rellevància i el potencial d'aquest senyal per a desenvolupar estratègies de control complexes i precises. / [EN] The current climate crisis has urged the research community and manufacturers to provide solutions to make the transportation sector cleaner. Among the various technologies proposed, low temperature combustion has undergone extensive investigation. Premixed dual-fuel combustion is one of the concepts addressing the NOx-soot trade-off in compression ignited engines, while maintaining high thermal efficiency. This combustion makes use of two fuels with different reactivities in order to improve the controllability of this combustion mode over a wide range of operation. Similarly to all premixed combustion modes, this combustion is nevertheless sensitive to the operating conditions and traditionally exhibits cycle-to-cycle variability with significant pressure gradients. Consequently, advanced control strategies to ensure a safe and accurate operation of the engine are required. Feedback control is a powerful approach to address the challenges raised by the premixed dual-fuel combustion. By measuring the output signals from the engine, strategies can be developed to adapt and correct the control actions to maintain the desired operation. This thesis presents control strategies, based on the in-cylinder pressure signal measurement, applied to premixed dual-fuel combustion engines. Various objectives were addressed by designing dedicated controllers, where a special emphasis was made towards analyzing and implementing these solutions to the different levels of mixture stratification considered in these engines (i.e., fully, highly and partially premixed). At first, feedback control strategies based on the in-cylinder pressure signal processing were designed. Proportional-integral actions were selected to ensure the desired engine performance without exceeding the mechanical constraints of the engine. Extremum seeking was evaluated to track efficient combustion phasing and NOx emissions reduction. The in-cylinder pressure resonance was then analyzed and a knock-like controller was implemented to ensure safe operation of the engine. Finally, mathematical models were used to design a control-oriented model and a state observer that aimed to leverage the signals measured in the engine to improve the prediction and diagnostic capabilities in such engine configuration. The results from this work highlighted the importance of considering feedback control to address the limitations encountered in premixed combustion modes. Particularly, the use of the in-cylinder pressure measurement showed the relevance and potential of this signal to develop complex and accurate control strategies. / This thesis was financially supported by the Programa Operativo del Fondo Social Europeo (FSE) de la Comunitat Valenciana 2014-2020 through grant ACIF/2018/141. / Barbier, ARS. (2022). In-Cylinder Pressure-Based Control of Premixed Dual-Fuel Combustion [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/183274

[ES] Reducir las emisiones de gases contaminantes de los motores de combustión interna alternativos (MCIA) es uno de los mayores retos para combatir el calentamiento global. Dado que los motores seguirán siendo utilizados por la industria durante décadas, es necesario desarrollar nuevas tecnologías. En este contexto, la presente tesis doctoral viene motivada por la necesidad de seguir mejorando los motores, tanto desde el punto de vista de la ingeniería técnica como desde el punto de vista social, debido a los efectos de los gases de efecto invernadero. El objetivo principal de esta tesis es desarrollar una metodología de optimización para sistemas de combustión de motores de encendido por compresión (MEC) mediante el acoplamiento de algoritmos de optimización con simulación por ordenador. Con la optimización de los sistemas de combustión es posible aumentar la eficiencia de los motores, reduciendo así el consumo de combustible junto con la reducción de emisiones contaminantes, en particular óxidos de nitrógeno (NOx) y hollín. En el primer paso, se abordan diferentes algoritmos de optimización con el fin de elegir el mejor candidato para esta metodología. A partir de aquí, la primera optimización se centra en un motor de encendido por compresión que funciona con combustible convencional para validar la metodología y también para evaluar el estado actual de evolución de estos motores. Con el objetivo de reducir el consumo de combustible manteniendo los niveles de NOx y hollín por debajo de los valores de un motor real, se inicia el proceso de optimización. Los resultados obtenidos confirman que un nuevo sistema de combustión específico para este motor podría generar una reducción del consumo de combustible manteniendo las emisiones de gases por debajo del valor estipulado. Además, se concluye que los motores MEC que utilizan combustible convencional se encuentran ya en un nivel de eficiencia muy elevado, y es difícil mejorarlos sin utilizar un sistema de postratamiento. Así pues, el segundo bloque de optimización se basa en el uso de motores MEC que funcionan con un combustible alternativo, que en este caso es el OME. El objetivo de este estudio es diseñar un sistema de combustión específico para un motor que utilice este combustible y que ofrezca un rendimiento del mismo orden de magnitud que un motor diésel. En la búsqueda de una mayor eficiencia, las emisiones de NOx son una restricción del sistema de optimización para que el sistema de combustión no emita más gases que un motor real. En este caso, el hollín no se tiene en cuenta debido a que las características del combustible no producen este tipo de contaminante. Los resultados mostraron que un sistema de combustión diseñado específicamente para esta operación podía ofrecer altas eficiencias, incluso la eficiencia obtenida fue alrededor de 2,2 % mayor en comparación con el motor diesel real. Además, fue posible reducir a la mitad las emisiones de NOx cuando el motor funciona con OME. El último bloque de optimización se refiere a una nueva arquitectura de motor que permite eliminar las emisiones de NOx. El modelo de oxicombustión resulta apasionante, ya que se elimina el nitrógeno de la mezcla de admisión y, por tanto, no se generan emisiones que contengan N2. Además, con el uso de este modo de combustión, es posible capturar CO$_{2}$ de los gases de escape, que luego puede venderse en el mercado. Dado que se trata de un tema nuevo y poco investigado, los resultados son prometedores. Demuestran que fue posible obtener un sistema de combustión específico capaz de ofrecer niveles de eficiencia cercanos a los de los motores convencionales. Además, se eliminaron las emisiones de NOx, así como las de hollín. Adicionalmente, este sistema fue capaz de reducir las emisiones de CO y HC a niveles similares a los motores convencionales. Por otra parte, los resultados presentados en esta tesis doctoral proporcionan una base de datos ampliada para explorar el funcionamiento del motor CI. / [CAT] Reduir les emissions de gasos contaminants dels motors de combustió interna alternatius (MCIA) és un dels majors reptes per a combatre el camvi climàtic. Atés que els motors continuaran sent utilitzats per la indústria durant dècades, és necessari desenvolupar noves tecnologies. En aquest context, la present tesi doctoral ve motivada per la necessitat de continuar millorant els motors, tant des del punt de vista de l'enginyeria tècnica com des del punt de vista social, degut a l'efecte dels gasos d'efecte d'hivernacle. L'objectiu principal d'aquesta tesi és desenvolupar una metodologia d'optimització per a sistemes de combustió de motors d'encesa provocada mitjançant l'acoblament d'algorismes d'optimització amb simulació per ordinador. Amb l'optimització dels sistemes de combustió és possible augmentar l'eficiència dels motors, reduint així el consum de combustible, concomitantment amb la reducció d'emissions de gasos, en particular òxids de nitrogen (NOx) i sutge. En el primer pas, s'aborden diferents algorismes d'optimització amb la finalitat d'elegir el millor candidat per a aquesta metodologia. A partir d'ací, la primera optimització se centra en un motor d'encesa per compressió que funciona amb combustible convencional per a validar la metodologia i també per a avaluar l'estat actual d'evolució d'aquests motors. Amb l'objectiu de reduir el consum de combustible mantenint els nivells de NOx i sutge per davall dels valors d'un motor real, s'inicia el procés d'optimització. Els resultats obtinguts confirmen que un nou sistema de combustió específic per a aquest motor podria generar una reducció del consum de combustible mantenint les emissions de gasos per davall del valor estipulat. A més, es conclou que els motors d'encesa per compressió que utilitzen combustible convencional es troben ja en un nivell d'eficiència molt elevat, i és difícil millorar-los sense utilitzar un sistema de posttractament. Així doncs, el segon bloc d'optimització es basa en l'ús de motors d'encesa per compressió que funcionen amb un combustible alternatiu, que en aquest cas és el OME. L'objectiu d'aquest estudi és dissenyar un sistema de combustió específic per a un motor que utilitze aquest combustible i que oferisca un rendiment del mateix ordre de magnitud que un motor dièsel. En la cerca d'una major eficiència, les emissions de NOx són una restricció del sistema d'optimització perquè el sistema de combustió no emeta més gasos que un motor real. En aquest cas, el sutge no es té en compte pel fet que les característiques del combustible no produeixen aquest tipus de contaminant. Els resultats van mostrar que un sistema de combustió dissenyat específicament per a aquesta operació podia oferir altes eficiències, fins i tot l'eficiència obtinguda va ser al voltant de 2,2 % major en comparació amb el motor dièsel real. A més, va ser possible reduir a la meitat les emissions de NOx quan el motor funciona amb OME. L'últim bloc d'optimització es refereix a una nova arquitectura del motor que permet eliminar les emissions de NOx. El model de oxicombustió resulta apassionant, ja que s'elimina el nitrogen de la mescla d'admissió i, per tant, no es generen emissions que continguen N2. A més, amb l'ús d'aquesta manera de combustió, és possible capturar CO$_{2}$ dels gasos de fuita, que després pot vendre's en el mercat. Atés que es tracta d'un tema nou i poc investigat, els resultats són prometedors. Demostren que va ser possible obtindre un sistema de combustió específic capaç d'oferir nivells d'eficiència pròxims als dels motors convencionals. A més, es van eliminar les emissions de NOx, així com les de sutge. Addicionalment, aquest sistema va ser capaç de reduir les emissions de CO i HC a nivells similars als motors convencionals. D'altra banda, els resultats presentats en aquesta tesi doctoral proporcionen una base de dades ampliada per a explorar el funcionament del motor CI. / [EN] Reducing emissions of pollutant gases from internal combustion engines (ICE) is one of the biggest challenges to combat global warming. As the engines will continue to be used by industry for decades, it is necessary to develop new technologies. In this context, the present doctoral thesis was motivated by the need to further improve engines, both from a technical engineering and social point of view, due to the effects of greenhouse gases. The main objective of this thesis is to develop an optimization methodology for compression ignition (CI) engine combustion systems by coupling optimization algorithms with computer simulation. With the optimization of the combustion systems, it is possible to increase the efficiency of the engines, thus reducing fuel consumption, concomitantly with the reduction of gas emissions, in particular nitrogen oxides (NOx) and soot. In the first step, different optimization algorithms are addressed in order to elect the best candidate for this methodology. From this point on, the first optimization is focused on a CI engine operating with conventional fuel in order to validate the methodology and also to evaluate the current state of evolution of these engines. With the goal of reducing fuel consumption while keeping NOx and soot levels below the values of a real engine, the optimization process begins. The results obtained confirm that a new combustion system specifically for this engine could generate a reduction in fuel consumption while keeping gas emissions below the stipulated value. Furthermore, it is concluded that CI engines using conventional fuel are already at a very high-efficiency level, and it is difficult to improve them without the use of an after-treatment system. Thus, the second optimization block is based on the use of CI engines operating on an alternative fuel, which in this case is OME. This study aimed to design a specific combustion system for an engine using this fuel that delivers efficiency on the same order of magnitude as a diesel engine. While searching for better efficiency, the NOx emissions are a restriction of the optimization system so that the combustion system does not emit more gases than a real engine. In this case, soot is not considered due to the characteristics of the fuel not producing this kind of pollutant. The results showed that a combustion system designed specifically for this operation could deliver high efficiencies, including the efficiency obtained was around 2.2 \% higher compared to the real diesel engine. In addition, it was possible to halve the NOx emissions when the engine operates with OME. The last optimization block concerns a new engine architecture that makes it possible to eliminate NOx emissions. The oxy-fuel combustion model is exciting since nitrogen is eliminated from the intake mixture, and thus no emissions containing N2 are generated. Furthermore, with the use of this combustion mode, it is possible to capture CO$_{2}$ from the exhaust gas, which can then be sold to the market. Since this is a new and little-researched topic, the results are promising. They show that it was possible to obtain a specific combustion system capable of delivering efficiency levels close to conventional engines. Furthermore, NOx emissions were eliminated, as well as soot emissions. Additionally, this system was able to reduce CO and HC emissions to levels similar to conventional engines. Moreover, the results presented in this doctoral thesis provide an extended database to explore the CI engine operation. Additionally, this work showed the potential of computational simulation allied with mathematical methods in order to design combustion systems for different applications. / I want to thanks the Universitat Politecnica de Valencia for his predoctoral contract (FPI-2019-S2-20-555), which is included within the framework of Programa de Apoyo para la Investigacion y Desarrollo (PAID). / Spohr Fernandes, C. (2023). Analysis and CFD-Guided optimization of advanced combustion systems in compression-ignited engines [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/193292

The efficient and enhanced mixing of heat and incoming reactants is achieved in modern gas turbine systems by employing swirling flows. This is realized by a low velocity region (internal recirculation zone -IRZ) zone resulting from vortex breakdown phenomenon. Besides, IRZ acts as effective flame holder/stabilization mode. Double concentric swirling jet is employed in plethora of industrial applications such as heat exchange, spray drying and combustion. As such, understanding essential features of vortex breakdown induced IRZ and its acoustic response in swirling flow/flame is important in thermo-acoustic instability studies. The key results of the present experimental investigation are discussed in four parts. In the first part, primary transition (sub-critical states) from a pre-vortex breakdown (Pre-VB) flow reversal to a fully-developed central toroidal recirculation zone (CTRZ) in a non-reacting, double-concentric swirling jet configuration is discussed when the swirl number is varied in the range 0.592 S 0.801. This transition proceeds with the formation of two intermediate, critical flow regimes. First, a partially-penetrated vortex breakdown bubble (VBB) is formed that indicates the first occurrence of an enclosed structure resulting in an opposed flow stagnation region. Second, a metastable transition structure is formed that marks the collapse of inner mixing vortices. In this study, the time-averaged topological changes in the coherent recirculation structures are discussed based on the non-dimensional modified Rossby number (Rom) which appears to describe the spreading of the zone of swirl influence in different flow regimes. The second part describes a secondary transition from an open-bubble type axisymmetric vortex breakdown (sub-critical states) to partially-open bubble mode (super-critical states) through an intermediate, critical regime of conical sheet formation for flow modes Rom ≤ 1 is discussed when the swirl number (S) is increased beyond 0.801. In the third part, amplitude dependent acoustic response of above mentioned sub and supercritical flow states is discussed. It was observed that the global acoustic response of the sub-critical VB states was fundamentally different from their corresponding super-critical modes. In particular, with a stepwise increase in excitation amplitude till a critical value, the sub-critical VB topology moved downstream and radially outward. Beyond a critical magnitude, the VB bubble transited back upstream and finally underwent radial shrinkage at the threshold excitation amplitude. On the other hand, the topology of the super-critical VB state continuously moved downstream and radially outwards and finally widened/fanned-out at threshold amplitude. In the final part, transition in time-averaged flame global flame structure is reported as a function of geometric swirl number. In particular, with a stepwise increase in swirl intensity, primary transition is depicted as a transformation from zero-swirl straight jet flame to lifted flame with blue base and finally to swirling seated flame. Further, a secondary transition is reported which consists of transformation from swirling seated flame to swirling flame with a conical tailpiece and finally to highly-swirled near blowout ultra-lean flame. For this purpose, CH* chemiluminescence imaging and 2D PIV in meridional planes were employed. Three baseline fuel flow rates through the central fuel injection pipe were considered. For each of the fuel flow cases (Ref), six different co-airflow rate settings (Rea) were employed. The geometric swirl number (SG) was increased in steps from zero till blowout for a particular fuel and co-airflow setting. A regime map (SG vs Rea) depicting different regions of flame stabilization were then drawn for each fuel flow case. The secondary transformation is explained on the basis of physical significance of Rom.

O presente trabalho discute a influência da microestrutura dos ferros fundidos, cinzento (FFC) e vermicular (FFV), na ocorrência de metal dobrado (FM) em superfícies brunidas e no comportamento tribológico em ensaio lubrificado do tipo anel sobre cilindro. As amostras de ferro fundido foram extraídas diretamente de um bloco de motor de combustão interna, em regiões de diferentes espessuras. O anel de pistão utilizado foi de aço inoxidável martensítico nitretado com perfil assimétrico e o óleo lubrificante foi o SAE 30 CF monoviscoso. A quantificação de sulcos e de metal dobrado (FM) foi realizada empregando-se uma metodologia baseada na literatura. Para a execução dos ensaios tribológicos foi projetada e construída uma adaptação para a montagem das amostras e controle de temperatura do óleo lubrificante. Um parâmetro para avaliação do desempenho tribológico foi proposto – índice de mérito tribológico (IMT) – que leva em conta coeficiente de atrito (COF) e alterações de topografia. Os ferros fundidos apresentaram microestruturas típicas. Contudo, observaram-se diferenças de morfologia e distribuição da grafita; com maior número de grafitas e menor fração de grafita para os materiais de parede fina. Observou-se FM nos platôs e nos sulcos das superfícies brunidas em todas as amostras. Quantificações mostraram que as larguras dos sulcos foram estatisticamente iguais e com alto percentual de obstrução. A quantificação de FM dos materiais mostrou maiores valores presentes na região do Spk (FMspk) para os FFC's. Os materiais de parede grossa apresentaram maiores valores de % FM dentro do sulco (%FM/Sulco) e este parâmetro teve forte e positiva correlação estatística com a fração de grafita. Evidências, obtidas em avaliações de seções transversais, corroboraram a relação entre FM e grafita. Constatou-se que o FM pode ser formado diretamente sobre a grafita ou, ainda, de forma indireta devido à extrusão desta fase. Ademais, verificou-se que a morfologia e orientação da grafita têm influência na formação do FM. Realizaram-se ensaios preliminares de curta duração de anel sobre cilindro para a avaliação da repetibilidade dos resultados de COF, os quais indicaram menor dispersão para condições com menores frequências e maiores forças normais. Avaliações da dinâmica do ensaio tribológico permitiram apontar relações de redução de COF durante os semi-ciclos de movimento e associá-las à teoria de lubrificação hidrodinâmica. O COF para ensaios de longa duração apresentou comportamento cíclico com transições. Estas transições foram associadas a mecanismos de formação-remoção-formação de tribofilmes de ZDDP. Os ensaios impuseram alterações nos parâmetros de rugosidade (principalmente com alisamento das superfícies) e redução do parâmetro de filme. O IMT evidenciou pouca influência da espessura do material; e melhor desempenho tribológico para os FFV's. A rotina de quantificação de FM mostrou limitação técnica devido ao alisamento da superfície, o que causa mudança na referência de alturas das superfícies brunidas. Ainda assim, verificou-se redução do %FM/Sulco e tendência de desobstrução do sulco. Contatou-se pouca influência do FM no comportamento do COF devido à similaridade dos parâmetros de FM entre os materiais. Contudo, o FM foi associado a um agente de abrasão à três corpos e apresentou forte correlação positiva do parâmetro de FMspk (no início do ensaio) com o parâmetro do IMT relacionado com a alteração de topografia. / The present work discusses the influence of the microstructure of gray cast iron (GCI) and compacted graphite iron (CGI) on the occurrence of folded metal (FM) on honed surfaces and its tribological behavior in ring-on-cylinder test under lubrication. The cast iron samples were taken directly from an internal combustion engine block in regions of different thicknesses. The piston ring used was a nitrided martensitic stainless steel with asymmetrical profile and the lubricant oil was the SAE 30 CF. The quantification of grooves and folded metal (FM) was carried out using a methodology based on the literature. For the execution of the tribological tests an adaptation was designed and built for assembling the samples and for controlling the oil temperature. One parameter to evaluate the tribological performance was proposed - tribological merit index (TMI) - which considers the coefficient of friction (COF) and changes in topography. Each cast iron presented typical microstructures. However, differences in morphology and graphite distribution were observed; the samples from thinner wall presented higher number of graphite and less fraction of graphite. FM was observed on the plateaus and grooves of the honed surfaces in all samples. Quantification showed that the widths of the grooves were statistically similar and with a high percentage of obstruction. GCIs present a higher amount of FM in the Spk region (FMspk).The thicker wall samples presented a higher amount of FM in the grooves (% FM / Groove) and this parameter had a strong and positive statistical correlation with the graphite fraction. Evidences, obtained in cross section evaluations, corroborated the relationship between FM and graphite. It was verified that FM can be formed directly on graphite or indirectly due to the extrusion of this phase. In addition, its morphology and orientation influenced the occurrence of FM. Preliminary short-term tests were performed to evaluate the repeatability of COF results. These tests indicated less dispersion for conditions with lower frequencies and higher normal forces. Evaluations of the dynamics of the tribological test allowed to point out conditions to reduce the COF during the half-cycles of movement and to associate them to the theory of hydrodynamic lubrication. The COF for long-term tests presented cyclical behavior with transitions. These transitions were associated with formation-removal-formation mechanisms of ZDDP tribofilms. The tribological tests imposed changes on the roughness parameters (mainly with smoothness of the surfaces) and reductions on the film parameter. The thickness of samples affected little the TMI; and a better tribological performance of CGIs was detected. The FM quantification routine showed a technical limitation due to surface smoothing, which causes a change in the reference of heights of honed surfaces. Nevertheless, there was a reduction in %FM/Groove and tendency to clear the grooves. There was little influence of FM in COF behavior due to the similarity of FM parameters among the materials. However, FM was associated as a three-body abrasive agent and a strong positive correlation between the FMspk parameter (at the beginning of the test) and the TMI parameter was described.

O presente trabalho discute a influência da microestrutura dos ferros fundidos, cinzento (FFC) e vermicular (FFV), na ocorrência de metal dobrado (FM) em superfícies brunidas e no comportamento tribológico em ensaio lubrificado do tipo anel sobre cilindro. As amostras de ferro fundido foram extraídas diretamente de um bloco de motor de combustão interna, em regiões de diferentes espessuras. O anel de pistão utilizado foi de aço inoxidável martensítico nitretado com perfil assimétrico e o óleo lubrificante foi o SAE 30 CF monoviscoso. A quantificação de sulcos e de metal dobrado (FM) foi realizada empregando-se uma metodologia baseada na literatura. Para a execução dos ensaios tribológicos foi projetada e construída uma adaptação para a montagem das amostras e controle de temperatura do óleo lubrificante. Um parâmetro para avaliação do desempenho tribológico foi proposto – índice de mérito tribológico (IMT) – que leva em conta coeficiente de atrito (COF) e alterações de topografia. Os ferros fundidos apresentaram microestruturas típicas. Contudo, observaram-se diferenças de morfologia e distribuição da grafita; com maior número de grafitas e menor fração de grafita para os materiais de parede fina. Observou-se FM nos platôs e nos sulcos das superfícies brunidas em todas as amostras. Quantificações mostraram que as larguras dos sulcos foram estatisticamente iguais e com alto percentual de obstrução. A quantificação de FM dos materiais mostrou maiores valores presentes na região do Spk (FMspk) para os FFC's. Os materiais de parede grossa apresentaram maiores valores de % FM dentro do sulco (%FM/Sulco) e este parâmetro teve forte e positiva correlação estatística com a fração de grafita. Evidências, obtidas em avaliações de seções transversais, corroboraram a relação entre FM e grafita. Constatou-se que o FM pode ser formado diretamente sobre a grafita ou, ainda, de forma indireta devido à extrusão desta fase. Ademais, verificou-se que a morfologia e orientação da grafita têm influência na formação do FM. Realizaram-se ensaios preliminares de curta duração de anel sobre cilindro para a avaliação da repetibilidade dos resultados de COF, os quais indicaram menor dispersão para condições com menores frequências e maiores forças normais. Avaliações da dinâmica do ensaio tribológico permitiram apontar relações de redução de COF durante os semi-ciclos de movimento e associá-las à teoria de lubrificação hidrodinâmica. O COF para ensaios de longa duração apresentou comportamento cíclico com transições. Estas transições foram associadas a mecanismos de formação-remoção-formação de tribofilmes de ZDDP. Os ensaios impuseram alterações nos parâmetros de rugosidade (principalmente com alisamento das superfícies) e redução do parâmetro de filme. O IMT evidenciou pouca influência da espessura do material; e melhor desempenho tribológico para os FFV's. A rotina de quantificação de FM mostrou limitação técnica devido ao alisamento da superfície, o que causa mudança na referência de alturas das superfícies brunidas. Ainda assim, verificou-se redução do %FM/Sulco e tendência de desobstrução do sulco. Contatou-se pouca influência do FM no comportamento do COF devido à similaridade dos parâmetros de FM entre os materiais. Contudo, o FM foi associado a um agente de abrasão à três corpos e apresentou forte correlação positiva do parâmetro de FMspk (no início do ensaio) com o parâmetro do IMT relacionado com a alteração de topografia. / The present work discusses the influence of the microstructure of gray cast iron (GCI) and compacted graphite iron (CGI) on the occurrence of folded metal (FM) on honed surfaces and its tribological behavior in ring-on-cylinder test under lubrication. The cast iron samples were taken directly from an internal combustion engine block in regions of different thicknesses. The piston ring used was a nitrided martensitic stainless steel with asymmetrical profile and the lubricant oil was the SAE 30 CF. The quantification of grooves and folded metal (FM) was carried out using a methodology based on the literature. For the execution of the tribological tests an adaptation was designed and built for assembling the samples and for controlling the oil temperature. One parameter to evaluate the tribological performance was proposed - tribological merit index (TMI) - which considers the coefficient of friction (COF) and changes in topography. Each cast iron presented typical microstructures. However, differences in morphology and graphite distribution were observed; the samples from thinner wall presented higher number of graphite and less fraction of graphite. FM was observed on the plateaus and grooves of the honed surfaces in all samples. Quantification showed that the widths of the grooves were statistically similar and with a high percentage of obstruction. GCIs present a higher amount of FM in the Spk region (FMspk).The thicker wall samples presented a higher amount of FM in the grooves (% FM / Groove) and this parameter had a strong and positive statistical correlation with the graphite fraction. Evidences, obtained in cross section evaluations, corroborated the relationship between FM and graphite. It was verified that FM can be formed directly on graphite or indirectly due to the extrusion of this phase. In addition, its morphology and orientation influenced the occurrence of FM. Preliminary short-term tests were performed to evaluate the repeatability of COF results. These tests indicated less dispersion for conditions with lower frequencies and higher normal forces. Evaluations of the dynamics of the tribological test allowed to point out conditions to reduce the COF during the half-cycles of movement and to associate them to the theory of hydrodynamic lubrication. The COF for long-term tests presented cyclical behavior with transitions. These transitions were associated with formation-removal-formation mechanisms of ZDDP tribofilms. The tribological tests imposed changes on the roughness parameters (mainly with smoothness of the surfaces) and reductions on the film parameter. The thickness of samples affected little the TMI; and a better tribological performance of CGIs was detected. The FM quantification routine showed a technical limitation due to surface smoothing, which causes a change in the reference of heights of honed surfaces. Nevertheless, there was a reduction in %FM/Groove and tendency to clear the grooves. There was little influence of FM in COF behavior due to the similarity of FM parameters among the materials. However, FM was associated as a three-body abrasive agent and a strong positive correlation between the FMspk parameter (at the beginning of the test) and the TMI parameter was described.

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-21T11:35:55Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-21T11:35:56Z (GMT). No. of bitstreams: 0 / Os projetos de carrocerias veiculares atuais procuram desenvolver estruturas leves, seja para reduzir o consumo de combustível, no caso dos motores de combustão interna, seja para maior autonomia de bateria, no caso dos veículos elétricos e híbridos. Redução no consumo de combustível significa redução na emissão de poluentes. As estruturas precisam ser leves, mas cada vez mais resistentes e rígidas a fim de proporcionar máximo conforto e segurança aos ocupantes. Estas premissas têm levado ao contínuo desenvolvimento dos materiais. No caso dos aços, um dos processos que tem permitido a melhora significativa das propriedades mecânicas é a estampagem a quente. Nos últimos anos, as peças estampadas a quente têm ocupado lugar de destaque na estrutura das carrocerias veiculares por estarem em sintonia com as demandas mencionadas. Há muitas pesquisas em curso para esta tecnologia, seja nos materiais, nos meios de produção, nos revestimentos e em aplicações. O aço mais utilizado neste processo, 22MnB5, também apresenta o chamado efeito bake hardening; a tensão de escoamento é aumentada após tratamento térmico realizado em temperaturas próximas a 200 °C. Neste trabalho, visando à melhoria nas propriedades mecânicas, amostras foram tratadas termicamente na faixa de temperatura supracitada. Após isso, dados obtidos de ensaios mecânicos foram inseridos em programas de simulação de impacto lateral cujo resultado foi a redução na intrusão na célula de sobrevivência. O efeito bake hardening também propiciou um aumento na absorção da energia de impacto em teste estático feito com barras de proteção lateral. O mecanismo metalúrgico envolvido no fenômeno, devido à difusão de intersticiais foi evidenciado no ensaio de atrito interno. / Tese (Doutorado em Tecnologia Nuclear) / IPEN/T / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

Homogeneous Charge Compression Ignition (HCCI) combustion is an alternative combustion mode in which the fuel is homogeneously mixed with air and is auto-ignited by compression. Due to charge homogeneity, this mode is characterized by low equivalence ratios and temperatures giving simultaneously low nitric oxide (NOx) and soot in diesel engines. The conventional problem of NOx-soot trade-off is avoided in this mode due to absence of diffusion combustion. This mode can be employed at part load conditions while maintaining conventional combustion at high load thus minimizing regulatory cycle emissions and reducing cost of after-treatment systems. The present study focuses on achieving this mode in a turbocharged, common rail, direct injection, four-cylinder, heavy duty diesel engine. Specifically, the work involves a combination of three-dimensional CFD simulations and experiments on this engine to assess both traditional and novel strategies related to fuel injection. The first phase of the work involved a quasi-dimensional simulation of the engine to assess potential of achieving HCCI. This was done using a zero-dimensional, single-zone HCCI combustion model with n-heptane skeletal chemistry along with a one-dimensional model of intake and exhaust systems. The feasibility of operation with realistic knock values with high EGR rate of 60% was observed. The second aspect of the work involved three-dimensional CFD simulations of the in-cylinder process with wall film prediction to evaluate injection strategies associated with Early Direct Injection (EDI). The extended Coherent Flame Model-3Zone (ECFM-3Z) was employed for combustion simulation of conventional CI and EDI, and was validated with experimental in-cylinder pressure data from the engine. A new Uniformity Index (UI) parameter was defined to assess charge homogeneity. Results showed significant in-homogeneity and presence of wall film for EDI. Simulations were conducted to assess improvement of charge homogeneity by several strategies; narrow spray cone angle, injection timing, multiple injections, intake air heating, Port Fuel Injection (PFI) as well as combination of PFI and EDI. The maximum UI achieved by EDI was 0.78. The PFI strategy could achieve UI of 0.95; however, up to 50% of fuel remained trapped in the port after valve closure. This indicated that except EDI, none of the above-mentioned strategies could help achieve the benefits of the HCCI mode. The third part of the work involved engine experimentation to assess the EDI strategy. This strategy produced lower soot than that of conventional CI combustion with very short combustion duration, but led to high knock and NOx which is attributed to pool fire burning phenomenon of the wall film, as confirmed by CFD. An Optimized EDI (OptimEDI) strategy was then developed based on results of CFD and Design of Experiments. The Optim EDI consisted of triple injections with split ratio of 41%-45%-14% and advancing the first injection. This strategy gave 20% NOx and soot reduction over the conventional CI mode. Although this strategy gave encouraging results, there was a need for more substantial reduction in emissions without sacrificing efficiency. Hence, a novel concept of utilizing air-assisted Injection (AAI) into the EGR stream was employed, as this implied injecting very small droplets of fuel into the intake which would have sufficient residence time to evaporate before reaching the cylinder, thereby enabling HCCI. The fourth and final part of the work involved engine experimentation with AAI, and combination of OptimEDI with AAI. Results with 20% EGR showed that 5 to 10% of AAI gave further reduction in NOx but not in soot. With experiments involving 48% EGR rate, there was soot reduction of 75% due to combined AAI-EDI. NOx was negligible due to the high EGR rate. Thus, the significant contribution of this work is in proving that combining AAI with EDI as a novel injection strategy leads to substantial NOx and soot reduction.

This thesis aims at automotive starters, their construction, characteristics and problems with starting at low temperatures. There are kinds of starters, function principle, construction, advantages and disadvantages in the first part of thesis. Issues with combustion engine starting and basic technical requirements are also mentioned here; characteristics and importance of starters and combustion engines are also described. Last chapters of this part are dedicated to finite element method and its implication. There are analytical calculations of starter in the second part of thesis. Results are compared with experimental obtained (measured) values and results from RMxprt. Finite element method results are compared, too. Magnetic induction improvement in stator is also suggested.

[ES] El trabajo de investigación presentado en esta tesis es el resultado de varios años dedicados al desarrollo, la implementación y la optimización de dos tecnologías combinadas: un concepto de combustión innovador y una arquitectura de motor de nuevo diseño. Esta investigacion se ha realizado en el marco de una colaboración con Renault SA, como continuación de las actividades realizadas en el proyecto europeo POWERFUL (POWERtrain for FUture Light-duty vehicles) por un lado,y en el marco del proyecto europeo REWARD (Real World Advanced technologies foR Diesel engines), devenido como continuación del proyecto POWERFUL en el marco del programa de investigación Horizonte 2020, por otro lado. Los principales objetivos de estos estudios eran evaluar el potencial del concepto de combustión parcialmente premezclada (PPC) operando con gasolina como combustible en un innovador motor de 2 tiempos de válvulas en culata, y luego diseñar una nueva geometría de motor de 2 tiempos utilizando la arquitectura Uniflujo para superar los principales problemas y limitaciones observados durante la primera etapa, que se pueden resumir principalmente en el rendimiento de barrido (especialmente trabajando en cargas elevadas). La metodología diseñada para este trabajo de investigación sigue un enfoque teórico-experimental. La evaluación del concepto de combustión PPC operando con gasolina se llevó a cabo principalmente con un enfoque experimental con el apoyo del análisis en línea directamente en el banco de ensayo, seguido de un exhaustivo tratamiento posterior de los datos y de un análisis detallado del proceso de combustión utilizando herramientas de diagnóstico. Por el contrario, el desarrollo del nuevo motor Uniflujo de 2 tiempos consistió principalmente en iteraciones sobre modelado 3D-CFD, si bien las actividades experimentales fueron fundamentales para validar las diferentes soluciones propuestas y evaluar su sensibilidad ante diferentes parámetros de interés utilizando una metodología de Diseño de Experimentos (DoE). La primera parte del trabajo se ha dedicado a la comprensión de los procesos termodinámicos involucrados en la combustión operando con el concepto PPC en un motor de 2 tiempos de válvulas en culata utilizando gasolina como combustible, y a evaluar su potencial en términos de emisiones contaminantes, consumo de combustible y ruido. Por último, se ha realizado un trabajo de exploración para ampliar en la medida de lo posible el rango de funcionamiento de este concepto de combustión en esta configuración específica del motor, investigando especialmente el rendimiento en cargas bajas en todo el rango de regímenes de giro del motor, y estableciendo también las principales limitaciones para la operación en cargas altas. La segunda parte de la tesis se ha centrado en el desarrollo y optimización teórica de un motor Uniflujo de 2 tiempos de nuevo diseño, incluyendo su fabricación y validación experimental. El objetivo principal era optimizar, utilizando principalmente simulaciones 3D-CFD, el rendimiento de barrido de esta arquitectura de 2 tiempos mediante el diseño de nuevas geometrías de puertos de admisión, permitiendo un gran control sobre el flujo de aire hacia y a través del cilindro para barrer al máximo los gases quemados y minimizar el cortocircuito de aire fresco hacia el escape. Las soluciones óptimas se evaluaron experimentalmente siguiendo la metodología DoE, antes de comparar finalmente los resultados de rendimiento de barrido con la anterior arquitectura de motor de 2 tiempos con válvulas en culata. / [CA] El treball de recerca presentat en aquesta tesi és el resultat de diversos anys dedicats al desenvolupament, la implementació i l'optimització de dues tecnologies combinades: un concepte de combustió innovador i una arquitectura de motor de nou disseny. Aquesta recerca s'ha realitzat en el marc d'una col·laboració amb Renault SA, com a continuació de les activitats del projecte europeu *POWERFUL (*POWERtrain *for *FUture Light-*duty *vehicles) d'una banda, i en el marc del projecte europeu *REWARD (Real *World *Advanced *technologies *foR Dièsel *engines), es devingut com a continuació del projecte *POWERFUL en el marc del programa d'investigació Horitzó 2020, d'altra banda. Els principals objectius d'aquests estudis eren avaluar el potencial del concepte de combustió parcialment premesclada (PPC) operant amb gasolina com a combustible en un innovador motor de 2 temps de vàlvules en culata, i després dissenyar una nova geometria de motor de 2 temps utilitzant l'arquitectura Uniflux per a superar els principals problemes i limitacions observats durant la primera etapa, que es poden resumir principalment en el rendiment d'escombratge (especialment treballant en càrregues elevades). La metodologia dissenyada per a realitzar aquests treballs de recerca segueix un enfocament tant experimental com teòric. L'avaluació del concepte de combustió PPC operant amb gasolina es va dur a terme principalment amb un enfocament experimental, però sempre amb el suport de l'anàlisi en línia directament en el banc d'assaig, seguit d'un exhaustiu tractament posterior de les dades combinat amb una anàlisi detallada del procés de combustió utilitzant eines de diagnòstic. Per contra, el desenvolupament i el disseny del nou motor Uniflux de 2 temps va consistir principalment en iteracions sobre modelatge 3D-CFD, si bé les activitats experimentals van ser fonamentals per a validar les diferents solucions proposades i avaluar la seua sensibilitat davant una sèrie de paràmetres d'interés utilitzant una metodologia de Disseny d'Experiments (DoE). La primera part del treball s'ha dedicat a la comprensió dels processos termodinàmics involucrats en la combustió operant amb el concepte de combustió PPC en un motor de 2 temps de vàlvules en culata utilitzant gasolina com a combustible, i a avaluar el seu potencial en termes d'emissions contaminants, consum de combustible i també de soroll. Finalment, s'ha fet un treball d'exploració per a ampliar en la mesura que siga possible el rang de funcionament d'aquest concepte de combustió utilitzant eixa configuració específica del motor, investigant especialment el rendiment en càrregues baixes en tot el rang de règims de gir del motor, i establint també les principals limitacions per a l'operació en càrregues altes. La segona part de la tesi s'ha centrat en el desenvolupament i optimització teòrica d'un motor Uniflux de 2 temps de nou disseny, incloent la seua fabricació i validació experimental. L'objectiu principal era optimitzar, utilitzant principalment simulacions 3D-CFD, el rendiment d'escombratge d'aquesta arquitectura de 2 temps mitjançant el disseny de noves geometries de ports d'admissió, permetent un gran control sobre el flux d'aire cap a i a través del cilindre per a escombrar al màxim els gasos cremats i minimitzar el curtcircuit d'aire fresc cap a l'escapament. Les solucions òptimes es van fabricar i van avaluar experimentalment seguint la metodologia DoE, abans de comparar finalment els resultats de rendiment d'escombratge amb l'anterior arquitectura de motor de 2 temps amb vàlvules en culata. / [EN] The research work presented in this thesis is the result of several years dedicated to the development, implementation and optimization of two combined technologies: an innovative combustion concept and a newly designed engine architecture. These investigations have been performed in the framework of a research collaboration with Renault SA following up the activities performed along the European POWERFUL project (POWERtrain for FUture Light-duty vehicles) on the one hand, and in the framework of the European REWARD project (REal World Advanced technologies foR Diesel engines), brought as a continuation of the POWERFUL project in the frame of the Horizon 2020 research program, on the other hand. The main objectives of these studies were to evaluate the potential of the Partially Premixed Combustion (PPC) concept operating with gasoline fuel in an innovative 2-Stroke poppet-valve engine, and then to design a new 2-Stroke engine geometry using the Uniflow architecture to overcome the main problems and limitations observed during the first stage, which can be mainly summarized to the scavenging performance (especially at high loads). The methodology designed for performing these investigation is based on both experimental and theoretical approaches. The evaluation of the gasoline PPC concept was carried out mainly experimentally, but always supported by online analysis directly on the test-bench and followed by a thorough post-processing of the data combined with a detailed analysis of the combustion using combustion diagnostic tools. On the contrary, the development and design of the new 2-Stroke Uniflow engine consisted mainly of 3D-CFD iterations, but experimental testing was crucial to validate the different solutions proposed and evaluate their sensitivity to a set of parameters of interest using a Design of Experiments (DoE) methodology. The first part of the work has been dedicated to the understanding of the thermodynamical processes involved in the combustion in a poppet-valve 2-Stroke engine operating with the gasoline PPC concept, and to evaluate its potential in terms of pollutant emissions, fuel consumption and also noise. Finally, a wide exploration has been performed to extend as much as possible the operating range of this combustion concept using that specific engine configuration, especially investigating the low loads performance throughout the full range of engine speeds, and also laying out the main limitations for high-to-full load operations. The second part of the thesis has been focused on the development and theoretical optimization of a newly designed 2-Stroke Uniflow engine, leading to manufacture and experimental validation. The main objective was to optimize, using mainly 3D-CFD modeling simulations, the scavenging performance of this 2-Stroke architecture by designing new intake ports geometries and to enable a great control over the air flow into and through the cylinder in order to scavenge the burnt gases as much as possible while minimizing the fresh air short-circuit to the exhaust. The optimum solutions were then manufactured and experimentally tested following a DoE methodology, before finally comparing the results of the scavenging performance to the previous 2-Stroke poppet-valve engine architecture. / Thein, KJL. (2021). Evaluation of combustion concepts and scavenging configurations in a 2-Stroke compression-ignition engine for future automotive powerplants [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/164044

[ES] Las nuevas regulaciones en materia de emisiones de efecto invernadero y calidad del aire han conducido la evolución tecnológica de los motores de combustión interna durante los últimos años. Las mejoras en el proceso de la combustión, la sobrealimentación, la gestión térmica, los sistemas de post tratamiento y técnicas como la recirculación de gases de escape, han permitido que los motores de combustión interna de hoy en día sean cada vez más limpios. La adopción en Europa del nuevo ciclo de homologación WLTP, que considera un ciclo de conducción más realista que su predecesor el NEDC, así como la necesidad de evaluar las emisiones contaminantes en diferentes escenarios de temperatura ambiente y de altitud, suponen un desafío para los fabricantes a la hora de diseñar y optimizar sus motores. En este contexto, el modelado unidimensional del motor ofrece la posibilidad de desarrollar y probar diferentes soluciones con la suficiente precisión,a la vez que permite agilizar el proceso de diseño del motor y reducir los costes de éste. El objetivo de esta tesis es el de desarrollar un modelo completo de motor virtual que permita simular condiciones transitorias de régimen de giro y grado de carga, así como diferentes condiciones ambientales de presión y temperatura. Con este modelo de motor se pretende predecir las principales variables termo-fluidodinámicas en diferentes puntos del motor y las emisiones contaminantes liberadas en el escape. Por otra parte, el arranque en frío y el funcionamiento a bajas temperaturas están asociados a un mayor consumo, mayores emisiones de hidrocarburos (HC) y monóxido de carbono (CO), así como mayores emisiones de óxidos de nitrógeno (NOx) debido a la desactivación de los sistemas de recirculación de gases de escape. Para paliar estos efectos adversos, una opción es lograr que el sistema de postratamiento alcance su temperatura de activación lo más pronto posible. En este trabajo se aborda este objetivo mediante dos soluciones. Por un lado, se ha explorado la posibilidad de elevar la temperatura de los gases en el escape mediante un sistema de distribución variable. Con este método se pueden reducir las emisiones de CO y HC en torno a un 40-50 % y las emisiones de NOx hasta un 15 % durante la primera fase del ciclo WLTC, a costa de una penalización en el consumo de combustible. Por otro lado, también se ha estudiado la posibilidad de aislar térmicamente el sistema de escape. En este caso, es posible reducir las emisiones de CO y HC en torno a un 30 % sin mejorar las de NOx. / [CA] Les noves regulacions en matèria d'emissions d'efecte d'hivernacle i qualitat de l'aire han conduït la evolució tecnològica dels motors de combustió interna durant els darrers anys. Les millores en el procés de la combustió, la sobrealimentació, la gestió tèrmica, els sistemes de postractament i tècniques com la recirculació de gasos d'escapament, han permès que els motors de combustió interna d'avui dia siguen cada vegada més nets. L'adopció a Europa del nou cicle d'homologació WLTP, que considera un cicle de conducció més realista que el seu predecessor el NEDC, així com la necessitat d'avaluar les emissions de gasos contaminants en diferents escenaris de temperatura ambient i humitat, suposen un repte per als fabricants a l'hora de dissenyar i optimitzar els seus motors. En aquest context, el modelatge unidimensional del motor ofereix la possibilitat de desenvolupar i provar diferents solucions amb la suficient precisió, al mateix temps que agilitza el procés de disseny del motor i reduïx els costos derivats d'aquest. L'objectiu d'aquesta tesi és el de desenvolupar un model complete de motor virtual que permeta simular condicions transitòries de règim de gir i grau de càrrega, així com diferents condicions ambientals de pressió i temperatura. Amb aquest model de motor es pretén predir les principals variables termo-fluidodinàmiques en diferents punts del motor i les emissions contaminants alliberades en l'escapament. Per altra banda, l'arrancada en fred i el funcionament a baixes temperatures están associats a un major consum, majors emissions d'hidrocarburs (HC) i monòxid de carboni (CO), així com majors emissions d'òxids de nitrògen (NOx) degudes a la desactivació dels sistemes de recirculació de gasos d'escapament. Per a pal·liar aquestos efectes indesitjats, una opció és aconseguir que el sistema de postractament arribe a la seua temperatura d'activació el més prompte possible. En aquest treball, aquest objectiu s'aborda mitjançant dues solucions. Per una banda, s'ha investigat la possibilitat d'augmentar la temperatura dels gasos en l'escapament per mitjà d'un sistema de distribució variable. Amb aquest mètode s'ha aconseguit reduïr les emissions de CO i HC al voltant d'un 40-50 % i les emissions de NOx fins a un 15 % durant la primera fase del cicle WLTC, acosta d'una penalització en el consum de combustible. Per altra banda, també s'ha estudiat la possibilitat d'aïllar tèrmicament el sistema d'escapament. En aquest cas, és possible reduir les emissions de CO i HC vora un 30 % sense millorar les de NOx . / [EN] The new regulations regarding greenhouse emissions and air quality have led the technological progress of the internal combustion engines during the recent years. Improvements in the combustion process, turbocharging, thermal management, after-treatment systems and techniques such as the exhaust gases recirculation, have resulted in cleaner internal combustion engines. The adoption of the new type approval test in Europe, so-called WLTP, which represents a more realistic driving cycle than its forerunner the NEDC, as well as the need to evaluate pollutant emissions at different conditions of ambient temperature and altitude, represent a challenge for manufacturers when it comes to design and optimise their engines. In this context, one-dimensional engine models offer the possibility to develop and test different solutions with enough accuracy, while hastening the engine design process and reducing its costs. The main objective of this thesis is to develop a complete virtual engine model able to simulate transient conditions of engine speed and load, as well as different ambient conditions of pressure and temperature. The engine model is used to predict the main thermo-and fluid dynamic variables at different engine locations and the tailpipe pollutant emissions. Furthermore, engine cold start and its operation at low temperature is associated to a greater fuel consumption, hydrocarbon (HC) and carbon monoxide (CO) emissions; as well as more nitrogen oxide (NOx) emissions due to the deactivation of the exhaust gases recirculation systems. A solution to mitigate these negative effects is to heat up the after-treatment system so as to achieve its activation temperature as soon as possible. In the work presented, this goal is addressed through two different standpoints. On the one hand, variable valve timing systems have been studied as a way to increase the exhaust gases temperature. With this option it is possible to reduce CO and HC emissions by 40-50 % and NOx emissions by 15 % during the first stage of the WLTC cycle, at the expense of a penalty in the fuel consumption. On the other hand, the thermal insulation of the exhaust system has also been studied with the same objective. In this case, it is possible to reduce CO and HC emissions by 30 %, while not improving NOx ones. / The author wishes to acknowledge the financial support received through the FPI S2 2018 1048 grant of Programa de Apoyo para la Investigación y Desarrollo (PAID) of Universitat Politècnica de València. / Auñón García, Á. (2021). Development and validation of a virtual engine model for simulating standard testing cycles [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/168906