Implementação de modelos atualizados de gás cinza no software FDS para predição do fluxo de calor radiativo em incêndios

Este trabalho tem como objetivo implementar e testar modelos de gás cinza atualizados na rotina de radiação térmica do software Fire Dynamics Simulator (FDS), além da utilização do próprio modelo de gás cinza disponível no software, para a predição do fluxo de calor radiativo. Os modelos de gás cinza estudados foram o modelo padrão do software FDS (aqui denominado como GC1), e os modelos de gás cinza mais atuais: o GC2, no qual o coeficiente de absorção do meio participante é dado por relações polinomiais, e o GC3, sendo este um modelo de gás cinza que baseia o cálculo do coeficiente de absorção no modelo WSGG. Os novos modelos de gás cinza foram implementados no código fonte do software FDS, o qual é um código aberto, e a verificação da implementação foi realizada através da solução numérica do equacionamento utilizando os valores reportados pelo software. Com os novos modelos de gás cinza já corretamente implementados, passou-se então para a simulação computacional dos casos previamente selecionados. Para todos os modelos de gás cinza, foram simulados incêndios em poças, para diferentes combustíveis (etanol, n-heptano e metanol) em diferentes cenários de incêndio, considerando ou não a presença de fuligem no sistema. Os cenários de incêndio eram: (i) totalmente fechado, (ii) totalmente aberto e (iii) com uma condição intermediária, fechado, porém com uma abertura para o meio externo. Um estudo de análise de malha e de diferentes parâmetros, como o estudo da quantidade necessária de ângulos sólidos discretos, foram realizados para correta padronização dos parâmetros. As simulações computacionais foram validadas para o modelo de gás cinza padrão do FDS através da comparação de resultados com aqueles reportados na literatura específica de cada caso. Com os modelos já validados simulou-se novamente cada cenário de incêndio com os diferentes modelos de gás cinza anteriormente implementados. A partir da análise dos resultados obtiveram-se boas concordâncias para os campos de temperatura, frações molares tanto de CO2 quanto de H2O e para as frações volumétricas de fuligem. Os fluxos de calor radiativos foram corretamente preditos para todos os modelos de gás cinza implementados. O modelo GC2 apresentou resultados com desvios médios na faixa de 15%, o modelo de gás cinza baseado no WSGG (GC3) apresentou os melhores resultados, com erros médios inferiores a 10%, enquanto que o modelo padrão do software, GC1, apresentou resultados intermediários.This work aims to implement and test updated gray gas models in the thermal radiation routine of the Fire Dynamics Simulator (FDS) software, as well as the use of the gray gas model available in the software to the prediction of radiative heat flux. The gray gas models studied were the default model of the FDS software (determined GC1), and the most current gray gas models: the GC2, in which the absorption coefficient of the participant medium is given by a polynomial relations, and the GC3, which is a gray gas model that was based on the calculation of the absorption coefficient in the WSGG model. The most recently gray gas models were implemented in the source code, which is an open source, and the verification of the implementation was performed by the numerical solution of the equations from the reported values of the software. With the new gray gas models already implemented, the next step was the computational simulation of the previously selected cases. For all the gray gas models, pool fires were simulated different scenarios of fire for different fuels (ethanol, nheptane and methanol), with and without considering soot presence in the system. The fire scenarios were: (i) fully closed, (ii) fully open and (iii) with an intermediate condition, closed but with an opening to the external environment. A study of a mesh analysis and different parameters, such as the study of the required amount of discrete solid angles, were performed to correct the standard parameters. The computational simulations were verified for the default gray gas model of the FDS by comparing the simulations results with those reported in the specific literature of each case. With the models already verified, each fire scenario was simulated with the different gray gas models previously implemented. From the analysis of the results, good agreements were obtained for the fields of temperature, molar fraction of CO2 and H2O and soot volume fraction. The radiative heat fluxes were correctly predicted for all gray gas models early implemented. The GC2 model present results with average deviation in the range of 15%, the gray gas model based on WSGG (GC3) presented the best results, with average deviation lower than 10%, while the default software model (GC1) presented intermediate results

Development of an Oxy-Fuel Combustion System in a Compression-Ignition Engine for Ultra-Low Emissions Powerplants Using CFD and Evolutionary Algorithms

[EN] This study uses an optimization approach for developing a combustion system in a compression-ignition engine that is able to operate under oxy-fuel conditions, and produces mainly CO2 and H2O as exhaust gases. This is achieved because the combustion concept uses pure oxygen as an oxidizer, instead of air, avoiding the presence of nitrogen. The O-2 for the combustion system can be obtained by using a mixed ionic-electronic conducting membrane (MIEC), which separates the oxygen from the air onboard. The optimization method employed maximizes the energy conversion of the system, reducing pollutant emissions (CxHy, particulate matter, and carbon monoxides) to levels near zero. The methodology follows a novel approach that couples computational fluid dynamics (CFD) and particle swarm optimization (PSO) algorithms to optimize the complete combustion system in terms of engine performance and pollutant generation. The study involves the evaluation of several inputs that govern the combustion system design in order to fulfill the thermo-mechanical constraints. The parameters analyzed are the piston bowl geometry, fuel injector characteristics, air motion, and engine settings variables. Results evince the relevance of the optimization procedure, achieving very low levels of gaseous pollutants (CxHy and CO) in the optimum configuration. The emissions of CO were reduced by more than 10% while maintaining the maximum in-cylinder pressure within the limit imposed for the engine. However, indicated efficiency levels are compromised if they are compared with an equivalent condition operating under conventional diesel combustion.This research work has been supported by Grant PDC2021-120821-I00 funded by MCIN/AEI/10.13039/501100011033 and by EuropeanUnion NextGenerationEU/PRTR. This research was partially supported by Agencia Valenciana de la Innovacio (AVI) through the project "Demostrador de un motor de oxicombustion con captura de CO2" (INNVA1/2021/38).Serrano, J.; Bracho Leon, G.; Gómez-Soriano, J.; Spohr-Fernandes, C. (2022). Development of an Oxy-Fuel Combustion System in a Compression-Ignition Engine for Ultra-Low Emissions Powerplants Using CFD and Evolutionary Algorithms. Applied Sciences. 12(14):1-27. https://doi.org/10.3390/app12147104127121

Combustion Modeling Approach for the Optimization of a Temperature Controlled Reactivity Compression Ignition Engine Fueled with Iso-Octane

[EN] In this study, an innovative Low Temperature Combustion (LTC) system named Temperature Controlled Reactivity Compression Ignition (TCRCI) is presented, and a numerical optimization of the hardware and the operating parameters is proposed. The studied combustion system aims to reduce the complexity of the Reaction Controlled Compression Ignition engine (RCCI), replacing the direct injection of high reactivity fuel with a heated injection of low reactivity fuel. The combustion system at the actual state of development is presented, and its characteristics are discussed. Hence, it is clear that the performances are highly limited by the actual diesel-derived hardware, and a dedicated model must be designed to progress in the development of this technology. A Computational Fluid Dynamics (CFD) model suitable for the simulation of this type of combustion is proposed, and it is validated with the available experimental operating conditions. The Particle Swarm Optimization (PSO) algorithm was integrated with the Computational Fluid Dynamic (CFD) software to optimize the engine combustion system by means of computational simulation. The operating condition considered has a relatively high load with a fixed fuel mass and compression ratio. The parameters to optimize are the piston bowl geometry, injection parameters and the boosting pressure. The achieved system configuration is characterized by a wider piston bowl and injection angle, and it is able to increase the net efficiency of 3% and to significantly reduce CO emissions from 0.407 to 0.136 mg.This research has been supported by Grant UPV-SOLGEN-79674 funded by Universitat Politecnica de Valencia. This research has been supported by Grant CIPROM/2021/061 funded by Generalitat Valenciana. The author C. S. Fernandes thanks the Universitat Politècnica de València for his predoctoral contract (FPI-2019-S2-20-555), which is included within the framework of Programa de Apoyo para la Investigación y Desarrollo (PAID).Pelosin, M.; Novella Rosa, R.; Bracho Leon, G.; Spohr-Fernandes, C.; Lucchini, T.; Marmorini, L.; Zhou, Q. (2022). Combustion Modeling Approach for the Optimization of a Temperature Controlled Reactivity Compression Ignition Engine Fueled with Iso-Octane. Energies. 15(21):1-26. https://doi.org/10.3390/en15218216126152

Estudo numérico de uma aleta elíptica inserida em uma cavidade quadrada com a superfície superior deslizante submetida à convecção mista

This paper aims to evaluate the heat transfer in a square cavity with an elliptical fin located in different positions on the cavity bottom and with different aspect ratios. The optimal geometry was analised using the Constructal Design principle. A two-dimensional, laminar, steady state and incompressible flow was considered. The thermophysics properties were defined for Pr = 0.71 and they are considered constant, except for the specific mass that was determined by the Boussinesq approximation. A Rayleigh number (RaH) of 104 was adopted to define the natural convection, while a Reynolds number (ReH) of 102 was adopted to define the forced convection. The fin position and its dimensions were varied, keeping the ratio of the fin area to cavity area constant (Φ = 0.05). The optimal geometry that maximizes the heat transfer rate was obtained through the Constructal Law. A mesh was created to solve the problem and it was adequately refined to ensure the accuracy of the results. The governing equations of the problem were solved numerically using the software ANSYS/Fluent®. This study shows that the position of the fin which maximizes the average Nusselt number in these conditions is at the point X1 ≈ 0.3 of the lower surface. For the aspect ratio (r) of the fin, it was observed that the minimization of the average Nusselt number occurs for r between 15 and 25. Considering all studied geometries, the optimized one can reach a performance around 50% superior if compared with the worst one, proving the importance of geometric evaluation in this kind of engineering problem, as well as the effectiveness of the Constructal approach.Este trabalho pretende avaliar a transferência de calor em uma cavidade quadrada com uma aleta elíptica localizada em diferentes posições no fundo da cavidade e com diferentes razões de aspecto. A geometria ideal foi analisada usando o princípio do Design Constructal. Foi considerado um escoamento bidimensional, laminar, estacionário e incompressível. As propriedades termo físicas foram definidas para Pr = 0.71 e são consideradas constantes, exceto para a massa específica que foi determinada pela aproximação de Boussinesq. Um número Rayleigh (RaH) de 104 foi adotado para definir a convecção natural, enquanto um número de Reynolds (ReH) de 102 foi adotado para definir a convecção forçada. A posição da aleta e suas dimensões foram variadas, mantendo constante a relação entre a área da aleta e a área da cavidade (Φ = 0,05). A geometria ideal que maximiza a taxa de transferência de calor foi obtida através da Lei Construtal. Uma malha foi criada para resolver o problema e foi adequadamente refinada para garantir a precisão dos resultados. As equações governantes do problema foram resolvidas numericamente usando o software ANSYS / Fluent®. Este estudo mostra que a posição da aleta que maximiza o número de Nusselt médio, nessas condições, está no ponto X1 ≈ 0,3 da superfície inferior. Para a razão de aspecto (r) da aleta, observou-se que a minimização do número médio de Nusselt médio ocorre para r entre 15 e 25. Considerando todas as geometrias estudadas, a otimizada pode atingir um desempenho em torno de 50% superior se comparado com o pior caso, comprovando a importância da avaliação geométrica neste tipo de problema de engenhaaria, bem como a eficácia da abordagem Construtal

Implementação de modelos atualizados de gás cinza no software FDS para predição do fluxo de calor radiativo em incêndios

Este trabalho tem como objetivo implementar e testar modelos de gás cinza atualizados na rotina de radiação térmica do software Fire Dynamics Simulator (FDS), além da utilização do próprio modelo de gás cinza disponível no software, para a predição do fluxo de calor radiativo. Os modelos de gás cinza estudados foram o modelo padrão do software FDS (aqui denominado como GC1), e os modelos de gás cinza mais atuais: o GC2, no qual o coeficiente de absorção do meio participante é dado por relações polinomiais, e o GC3, sendo este um modelo de gás cinza que baseia o cálculo do coeficiente de absorção no modelo WSGG. Os novos modelos de gás cinza foram implementados no código fonte do software FDS, o qual é um código aberto, e a verificação da implementação foi realizada através da solução numérica do equacionamento utilizando os valores reportados pelo software. Com os novos modelos de gás cinza já corretamente implementados, passou-se então para a simulação computacional dos casos previamente selecionados. Para todos os modelos de gás cinza, foram simulados incêndios em poças, para diferentes combustíveis (etanol, n-heptano e metanol) em diferentes cenários de incêndio, considerando ou não a presença de fuligem no sistema. Os cenários de incêndio eram: (i) totalmente fechado, (ii) totalmente aberto e (iii) com uma condição intermediária, fechado, porém com uma abertura para o meio externo. Um estudo de análise de malha e de diferentes parâmetros, como o estudo da quantidade necessária de ângulos sólidos discretos, foram realizados para correta padronização dos parâmetros. As simulações computacionais foram validadas para o modelo de gás cinza padrão do FDS através da comparação de resultados com aqueles reportados na literatura específica de cada caso. Com os modelos já validados simulou-se novamente cada cenário de incêndio com os diferentes modelos de gás cinza anteriormente implementados. A partir da análise dos resultados obtiveram-se boas concordâncias para os campos de temperatura, frações molares tanto de CO2 quanto de H2O e para as frações volumétricas de fuligem. Os fluxos de calor radiativos foram corretamente preditos para todos os modelos de gás cinza implementados. O modelo GC2 apresentou resultados com desvios médios na faixa de 15%, o modelo de gás cinza baseado no WSGG (GC3) apresentou os melhores resultados, com erros médios inferiores a 10%, enquanto que o modelo padrão do software, GC1, apresentou resultados intermediários.This work aims to implement and test updated gray gas models in the thermal radiation routine of the Fire Dynamics Simulator (FDS) software, as well as the use of the gray gas model available in the software to the prediction of radiative heat flux. The gray gas models studied were the default model of the FDS software (determined GC1), and the most current gray gas models: the GC2, in which the absorption coefficient of the participant medium is given by a polynomial relations, and the GC3, which is a gray gas model that was based on the calculation of the absorption coefficient in the WSGG model. The most recently gray gas models were implemented in the source code, which is an open source, and the verification of the implementation was performed by the numerical solution of the equations from the reported values of the software. With the new gray gas models already implemented, the next step was the computational simulation of the previously selected cases. For all the gray gas models, pool fires were simulated different scenarios of fire for different fuels (ethanol, nheptane and methanol), with and without considering soot presence in the system. The fire scenarios were: (i) fully closed, (ii) fully open and (iii) with an intermediate condition, closed but with an opening to the external environment. A study of a mesh analysis and different parameters, such as the study of the required amount of discrete solid angles, were performed to correct the standard parameters. The computational simulations were verified for the default gray gas model of the FDS by comparing the simulations results with those reported in the specific literature of each case. With the models already verified, each fire scenario was simulated with the different gray gas models previously implemented. From the analysis of the results, good agreements were obtained for the fields of temperature, molar fraction of CO2 and H2O and soot volume fraction. The radiative heat fluxes were correctly predicted for all gray gas models early implemented. The GC2 model present results with average deviation in the range of 15%, the gray gas model based on WSGG (GC3) presented the best results, with average deviation lower than 10%, while the default software model (GC1) presented intermediate results

Analysis and CFD-Guided optimization of advanced combustion systems in compression-ignited engines

[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/10251/19329

Metodología para el análisis del sistema de combustión en motores encendidos por compresión utilizando CFD y algoritmos de optimización PSO

[ES] Con el fin de mejorar la eficiencia y reducir el consumo de combustible y las emisiones de los motores, los códigos CFD se utilizan ampliamente en la simulación de motores. Estas herramientas computacionales pueden proporcionar resultados precisos en un tiempo razonable, con una buena concordancia entre los resultados y los costos operativos. Este Trabajo Final de Máster propone una metodología para analizar la influencia de la configuración de la geometría del pistón en el rendimiento de la combustión utilizando CFD. Este trabajo también propone una metodología de optimización que utiliza el particle swarm optimization (PSO) junto con el código CFD. El objetivo es obtener un diseño de sistema de combustión para un motor de encendido por compresión, optimizado con respecto a la reducción del consumo específico de combustible, NOx y emisiones de hollín. Como primer paso, el modelo CFD se configuró para reproducir la presión, la liberación de calor y las emisiones usando datos experimentales como referencia. Con el modelo CFD ya validado, la metodología de optimización se aplica para varias configuraciones. En total, se modificaron 9 parámetros en este trabajo: se utilizan 5 parámetros geométricos para controlar el diseño de la cámara de combustión en función de la forma del bowl; los otros cuatro parámetros son el número de orificios del inyector, el swirl, la presión de inyección y la tasa de EGR. Todas las geometrías generadas se prueban mediante simulación del motor en CFD en el software OpenFOAM y LibICE. Con alrededor de 800 simulaciones, fue posible obtener una configuración del sistema de combustión que proporciona una reducción en el consumo específico de combustible y en las emisiones de NOx y hollín.[EN] In order to improve efficiency and reduce the fuel consumption and emissions of engines, computational fluid dynamics (CFD) codes are widely used in engine simulation since they can provide accurate results in a reasonable time, with good agreement between results and operational cost. This work proposes a methodology to analyze the influence of the bowl geometry configuration on the combustion performance using CFD. This work also proposes an optimization methodology using particle swarm optimization (PSO) coupled with the CFD code. The target is to obtain a combustion system design for a compression-ignited engine, optimized with respect to the reduction of the specific fuel consumption, NOx and soot emissions. As a first step, the CFD model was set up to reproduce the pressure trace, heat release and emissions against experimental data. With the CFD model already validated the optimization methodology is applied for several configurations. In total 9 parameters were modified in this work: 5 geometrical parameters are used to control the design of combustion chamber based on the piston bowl shape; the other four parameters are the injector hole number, swirl number, injection pressure and EGR rate. All the generated geometries are tested by CFD engine simulation in the software OpenFOAM and LibICE. With around 800 simulations it was possible to obtain a combustion system definition that provides a reduction in specific fuel consumption, NOx and soot emissions.Spohr Fernandes, C. (2020). Methodology for analysis of combustion system performance and optimization in compressionignited engines by means of CFD and particle swarm optimization. Universitat Politècnia de València. http://hdl.handle.net/10251/157572TFG

Combustion system optimization for the integration of e-fuels (Oxymethylene Ether) in compression ignition engines

[EN] In this study, a numerical methodology for the optimization of the combustion chamber in compression ignited engines using OME as fuel is presented. The objective is to obtain a dedicated combustion system for an engine that is fueled with this alternative fuel improving the efficiency and reducing the emissions of NOx. This article proposes the integration between the optimization algorithm and CFD codes to evaluate the behavior of an engine fuelled with the low sooting fuel OME. Based on a diesel model validated against experimental data, a further model for OME fuel was implemented for evaluating the performance of the engine. The particle swarm algorithm (PSO) was modified based on the Novelty Search concepts and used as optimization algorithm. Several tools are coupled in order to create each CFD case where all the tools and optimization algorithm are coupled in a routine that automates the entire process. The result is an optimized combustion system that provides an increase of the efficiency (about 2.2%) and a NOx reduction (35.7%) in comparison with the baseline engine with conventional fuel. In addition, a neuronal network was trained with all the results of all simulations performed during the optimization process, studying the influence of each parameter on the emissions and efficiency. From this analysis it was concluded that the EGR rate and injection pressure affects the NOx emissions with a range of variability of 63% and 38% respectively.The work has been partially supported by the Spanish Ministerio de Economia, Industria y Competitividad through Grant No TRA2017-89139-C2-1-R "Desarrollo de modelos de combustion y emisiones HPC para el analisis de sistemas de transporte sostenibles" The author C. S. Fernandes 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)Novella Rosa, R.; Bracho Leon, G.; Gómez-Soriano, J.; Spohr-Fernandes, C.; Lucchini, T. (2021). Combustion system optimization for the integration of e-fuels (Oxymethylene Ether) in compression ignition engines. Fuel. 305:1-12. https://doi.org/10.1016/j.fuel.2021.121580S11230

Estudo numérico de uma aleta elíptica inserida em uma cavidade quadrada com a superfície superior deslizante submetida à convecção mista

This paper aims to evaluate the heat transfer in a square cavity with an elliptical fin located in different positions on the cavity bottom and with different aspect ratios. The optimal geometry was analised using the Constructal Design principle. A two-dimensional, laminar, steady state and incompressible flow was considered. The thermophysics properties were defined for Pr = 0.71 and they are considered constant, except for the specific mass that was determined by the Boussinesq approximation. A Rayleigh number (RaH) of 104 was adopted to define the natural convection, while a Reynolds number (ReH) of 102 was adopted to define the forced convection. The fin position and its dimensions were varied, keeping the ratio of the fin area to cavity area constant (Φ = 0.05). The optimal geometry that maximizes the heat transfer rate was obtained through the Constructal Law. A mesh was created to solve the problem and it was adequately refined to ensure the accuracy of the results. The governing equations of the problem were solved numerically using the software ANSYS/Fluent®. This study shows that the position of the fin which maximizes the average Nusselt number in these conditions is at the point X1 ≈ 0.3 of the lower surface. For the aspect ratio (r) of the fin, it was observed that the minimization of the average Nusselt number occurs for r between 15 and 25. Considering all studied geometries, the optimized one can reach a performance around 50% superior if compared with the worst one, proving the importance of geometric evaluation in this kind of engineering problem, as well as the effectiveness of the Constructal approach.Este trabalho pretende avaliar a transferência de calor em uma cavidade quadrada com uma aleta elíptica localizada em diferentes posições no fundo da cavidade e com diferentes razões de aspecto. A geometria ideal foi analisada usando o princípio do Design Constructal. Foi considerado um escoamento bidimensional, laminar, estacionário e incompressível. As propriedades termo físicas foram definidas para Pr = 0.71 e são consideradas constantes, exceto para a massa específica que foi determinada pela aproximação de Boussinesq. Um número Rayleigh (RaH) de 104 foi adotado para definir a convecção natural, enquanto um número de Reynolds (ReH) de 102 foi adotado para definir a convecção forçada. A posição da aleta e suas dimensões foram variadas, mantendo constante a relação entre a área da aleta e a área da cavidade (Φ = 0,05). A geometria ideal que maximiza a taxa de transferência de calor foi obtida através da Lei Construtal. Uma malha foi criada para resolver o problema e foi adequadamente refinada para garantir a precisão dos resultados. As equações governantes do problema foram resolvidas numericamente usando o software ANSYS / Fluent®. Este estudo mostra que a posição da aleta que maximiza o número de Nusselt médio, nessas condições, está no ponto X1 ≈ 0,3 da superfície inferior. Para a razão de aspecto (r) da aleta, observou-se que a minimização do número médio de Nusselt médio ocorre para r entre 15 e 25. Considerando todas as geometrias estudadas, a otimizada pode atingir um desempenho em torno de 50% superior se comparado com o pior caso, comprovando a importância da avaliação geométrica neste tipo de problema de engenhaaria, bem como a eficácia da abordagem Construtal