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Abstract(s)
O presente trabalho aborda a combustão de hidrogénio juntamente com metano e as suas emissões de óxidos de azoto. O principal objetivo passa por desenvolver um modelo matemático que permita calcular as emissões de óxidos de azoto provenientes desta combustão, que se formam no decorrer da expansão de um motor com ciclo Otto. A revisão bibliográfica apresenta: os motores de combustão, dando ênfase aos motores de combustão de ciclo Otto; caraterísticas e propriedades do hidrogénio como combustível, incluindo os motores de combustão interna a hidrogénio; óxidos de azoto e o mecanismo para o cálculo dos mesmos; conceito de cinética química. Quanto aos métodos utilizados, são apresentados o método do equilíbrio químico que é utilizado para determinar quantidades de todos os constituintes, temperaturas e pressões, resultantes da combustão de hidrogénio e metano com o ar, bem como o método da cinética química que tem como princípio o método anterior e que vai ser a base do método de cálculo elaborado para calcular as quantidades das emissões geradas pela combustão de hidrogénio e metano que se formam no decorrer da expansão. Após a obtenção de resultados é possível concluir que as melhores condições para efetuar esta combustão são: a utilização de 10% de metano em massa relativamente ao hidrogénio, um excesso de ar de 100% e uma taxa de compressão de valor 10. Com estas condições referidas é possível obter os valores mais baixos em termos de concentração de óxidos de azoto nos fumos da combustão, bem como retirar o melhor rendimento térmico possível do motor.
This work deals with the combustion of hydrogen together with methane and its nitrogen oxide emissions. The main objective is to develop a mathematical model to calculate the emissions of nitrogen oxides from this combustion, which are formed during the expansion of an Otto cycle engine. The literature review presents: combustion engines, with emphasis on Otto cycle combustion engines; characteristics and properties of hydrogen as a fuel, including hydrogen internal combustion engines; nitrogen oxides and the mechanism for calculating them; the concept of chemical kinetics. As for the methods used, the chemical equilibrium method is presented, which is used to determine the quantities of all the constituents, temperatures and pressures resulting from the combustion of hydrogen and methane with air, as well as the chemical kinetics method, which is based on the previous method and will form the basis of the calculation method designed to calculate the quantities of emissions generated by the combustion of hydrogen and methane that are formed during expansion. After obtaining the results, it is possible to conclude that the best conditions for carrying out this combustion are: the use of 10% methane by mass in relation to hydrogen, 100% excess air and a compression ratio of 10. With these conditions, it is possible to obtain the lowest values in terms of the concentration of nitrogen oxides in the combustion fumes, as well as obtaining the best possible thermal efficiency from the engine.
This work deals with the combustion of hydrogen together with methane and its nitrogen oxide emissions. The main objective is to develop a mathematical model to calculate the emissions of nitrogen oxides from this combustion, which are formed during the expansion of an Otto cycle engine. The literature review presents: combustion engines, with emphasis on Otto cycle combustion engines; characteristics and properties of hydrogen as a fuel, including hydrogen internal combustion engines; nitrogen oxides and the mechanism for calculating them; the concept of chemical kinetics. As for the methods used, the chemical equilibrium method is presented, which is used to determine the quantities of all the constituents, temperatures and pressures resulting from the combustion of hydrogen and methane with air, as well as the chemical kinetics method, which is based on the previous method and will form the basis of the calculation method designed to calculate the quantities of emissions generated by the combustion of hydrogen and methane that are formed during expansion. After obtaining the results, it is possible to conclude that the best conditions for carrying out this combustion are: the use of 10% methane by mass in relation to hydrogen, 100% excess air and a compression ratio of 10. With these conditions, it is possible to obtain the lowest values in terms of the concentration of nitrogen oxides in the combustion fumes, as well as obtaining the best possible thermal efficiency from the engine.
Description
Keywords
Hidrogénio Metano Ciclo Otto Óxidos de Azoto Cinética Química Hydrogen Methane Otto Cycle Nitrogen Oxides Chemical Kinetics