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Abstract(s)
Nos dias de hoje, com o crescente aumento populacional e melhoria do estilo e qualidade de vida, a procura energética tem crescido. Em consequência, a quantidade de emissões de gases de efeito de estufa tem evoluído ao passo de se tornar uma das maiores preocupações quer a nível ambiental, económico e energético. O setor dos transportes é, atualmente, um dos principais responsáveis por grande parte dessas emissões devido à queima de combustíveis fosseis nos motores. Por esta via, tem emergido a ideia da utilização de combustíveis alternativos, como é o caso do hidrogénio, com o intuito de reduzir grande parte das emissões. No entanto, a utilização do H2 está envolta de algum ceticismo devido à potencial produção de
óxidos de azoto. Assim, este trabalho teve como objetivo principal o estudo da produção de óxidos de azoto num motor de combustão interna que opera segundo um ciclo Otto e cujo combustível é o hidrogénio ou uma mistura que contenha hidrogénio. Como termo de comparação ao ciclo adotado, foram ainda determinadas as produções do monóxido de azoto mediante o ciclo Atkinson. Para modelizar o comportamento do motor durante o seu funcionamento, recorreu-se à aplicação do equilíbrio químico, essencialmente usado para o
processo de queima, e da cinética química, empregue no processo de expansão e aplicada em
conjunto com o mecanismo de Zeldovich estendido, usado para determinar a formação dos óxidos de azoto. Contudo, a aplicação deste modelo não teria sido possível sem recorrer ao cálculo computacional aplicado por via de uma rotina, escrita de acordo com a linguagem de programação Python. De acordo com o modelo, parâmetros como a riqueza da mistura reagente, a razão molar entre os combustíveis e, quando aplicável, a razão de compressão e a relação de expansão foram variados para perceber as diferentes dimensões do problema. Concluiu-se que, a produção de NO é alta no início da expansão, mas tende a congelar após
curto espaço de tempo. Esta grandeza é tanto maior quanto maior for a riqueza da mistura reagente e/ou quanto menor for a razão molar entre os combustíveis. Características em tudo idênticas à temperatura, uma vez que a produção está diretamente dependente desta última. Sobre a concentração concluiu-se que ao logo da expansão, foi diminuindo, em parte, devido à dissociação, mas sobretudo, devido ao aumento do volume disponível. Em suma, obteve-se concentrações menores para o ciclo Atkinson e, por consequência, resultados mais desejáveis, em termos de emissões.
Nowadays, with the increase in population and improvements in lifestyle and quality of life, energy demand has grown. Consequently, the amount of greenhouse gas emissions has become one of the biggest environmental, economic, and energy concerns. The transport sector is currently one of the main sources of these emissions due to the burning of fossil fuels in engines. As a solution, the idea of using alternative fuels, such as hydrogen, has emerged intending to reduce these emissions. However, the use of H2 is met with scepticism due to the potential production of nitrogen oxides. Therefore, the main objective of this study was to investigate the production of nitrogen oxides in an internal combustion engine operating according to the Otto cycle, using hydrogen or hydrogen mixtures as fuel. In comparison, nitrogen monoxide production was also examined using the Atkinson cycle. To model the engine's behaviour during operation, we applied chemical equilibrium primarily for the combustion process and chemical kinetics, in conjunction with the extended Zeldovich mechanism, to determine nitrogen oxides formation. Computational calculations, implemented through a Python script, were essential to facilitate this model. According to the model, parameters such as the fuel mixture richness, molar ratio between fuels, and compression/expansion ratios were varied to understand different aspects of the problem. The results from the Otto cycle study led to the preparation of a scientific article submitted for review by the journal Sustainability. Overall, it was found that NO production is initially high during the expansion phase but tends to stabilize over time. This production rate increases with fuel mixture richness and/or decreases with the molar ratio between fuels, closely correlating with temperature. Concentration-wise, it was observed that NO levels decrease as expansion progresses, partly due to dissociation and primarily due to the increase in available volume. In summary, lower concentrations were achieved with the Atkinson cycle, resulting in more desirable emission outcomes.
Nowadays, with the increase in population and improvements in lifestyle and quality of life, energy demand has grown. Consequently, the amount of greenhouse gas emissions has become one of the biggest environmental, economic, and energy concerns. The transport sector is currently one of the main sources of these emissions due to the burning of fossil fuels in engines. As a solution, the idea of using alternative fuels, such as hydrogen, has emerged intending to reduce these emissions. However, the use of H2 is met with scepticism due to the potential production of nitrogen oxides. Therefore, the main objective of this study was to investigate the production of nitrogen oxides in an internal combustion engine operating according to the Otto cycle, using hydrogen or hydrogen mixtures as fuel. In comparison, nitrogen monoxide production was also examined using the Atkinson cycle. To model the engine's behaviour during operation, we applied chemical equilibrium primarily for the combustion process and chemical kinetics, in conjunction with the extended Zeldovich mechanism, to determine nitrogen oxides formation. Computational calculations, implemented through a Python script, were essential to facilitate this model. According to the model, parameters such as the fuel mixture richness, molar ratio between fuels, and compression/expansion ratios were varied to understand different aspects of the problem. The results from the Otto cycle study led to the preparation of a scientific article submitted for review by the journal Sustainability. Overall, it was found that NO production is initially high during the expansion phase but tends to stabilize over time. This production rate increases with fuel mixture richness and/or decreases with the molar ratio between fuels, closely correlating with temperature. Concentration-wise, it was observed that NO levels decrease as expansion progresses, partly due to dissociation and primarily due to the increase in available volume. In summary, lower concentrations were achieved with the Atkinson cycle, resulting in more desirable emission outcomes.
Description
Keywords
SI Engines Hydrogen Chemical Kinetics Zeldovich Mechanism Nitrogen Oxides Motores SI Hidrogénio Cinética química Mecanismo de Zeldovich Óxidos de azoto