Avaliação da relação entre a energia de ativação e a energia útil para diferentes misturas de etanol e gasolina aplicados a motores de ignição por centelha
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Data
2016-11-29
Autores
Ríos Quiroga, Luis Carlos [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A aplicação do etanol como combustível ou como aditivo misturado à gasolina é muito importante para a maioria dos países que procuram reduzir a dependência dos combustíveis fósseis e mitigar os gases de efeito estufa. O uso cada vez maior de misturas de etanol e gasolina torna cada vez mais relevante o conhecimento de suas propriedades físicas e químicas, de forma a favorecer uma melhor compreensão do efeito do teor de etanol na mistura com a gasolina no desempenho do motor. Esta tese tem por objetivo avaliar se existe, ou não, uma relação entre a energia de ativação da mistura de etanol e gasolina, obtida pelas técnicas de análise térmica, e a energia útil obtida em testes de motor. Foram utilizadas diferentes percentagem de etanol na mistura de etanol-gasolina denominadas por E0 (gasolina pura), E5 (5% v/v etanol), E10, E15, E20, E25, E30, E50 e E75. O estudo cinético foi realizado em um sistema simultâneo TG (termogravimetria) e DTA (análise térmica diferencial) com a metodologia para ensaios não isotérmicos para obter a energia de ativação. Alem de utilizar a análise do sinergismo, entre os componentes das misturas, como ferramenta para avaliar o efeito do teor de etanol na mistura com a gasolina. A energia útil dos combustíveis foi obtida nos testes de dinamômetro no motor monocilíndrico padrão de ciclo Otto com seis taxas de compressão diferentes. Na análise dos dados verificou-se que existe sinergismo nas misturas com teor de etanol entre 5% e 30%. Estas misturas também foram as que apresentaram melhores resultados na potência, para taxas de compressão entre 6:1 a 7:1. Os resultados da análise térmica mostram que as misturas com baixo conteúdo de etanol (até 30%) apresentam maior volatilidade e, possivelmente, esta é característica que melhora a combustão nos motores de ciclo Otto.
The use of ethanol as fuel or as an additive blended with gasoline is very important for most countries which aim to reduce the heavy dependence on fossil fuels and mitigate greenhouse gases emission. An increased use of ethanol and gasoline blends has placed great relevance on acquiring knowledge about their physical and chemical properties. Thus, knowledge of such properties favors a better understanding of the effect of the percentage of ethanol/gasoline blends on engine performance. This thesis aims to assess whether there is or not a relationship between the activation energy of the mixture of ethanol and gasoline, obtained by thermal analysis techniques, and the useful energy obtained in engine tests. They used different percentage of ethanol in the ethanol-gasoline blends denoted by E0 (pure gas), E5 (5% v/v ethanol), E10, E15, E20, E25, E30, E50 and E75. A kinetic study has been conducted through a simultaneous TG (thermogravimetry) and DTA (differential thermal analysis) by following the methodology of non-isothermal tests to obtain the activation energies of the tested mixtures. Was used the synergism analyze, between the components of the mixtures, as a tool to evaluate the effect of ethanol content in the gasoline mixture. The useful energy fuel was obtained by dynamometer tests to Otto cycle single cylinder standard engine with six different compression rates. In the data analysis was found that synergism exists in mixtures with ethanol content between 5% to 30%. These mixtures also showed the best power results for compression ratios of 6:1 to 7:1. The thermal analysis results showed that mixtures with low ethanol content (to 30%) exhibit higher volatility and, possibly, this characteristic improves combustion in Otto cycle engines.
The use of ethanol as fuel or as an additive blended with gasoline is very important for most countries which aim to reduce the heavy dependence on fossil fuels and mitigate greenhouse gases emission. An increased use of ethanol and gasoline blends has placed great relevance on acquiring knowledge about their physical and chemical properties. Thus, knowledge of such properties favors a better understanding of the effect of the percentage of ethanol/gasoline blends on engine performance. This thesis aims to assess whether there is or not a relationship between the activation energy of the mixture of ethanol and gasoline, obtained by thermal analysis techniques, and the useful energy obtained in engine tests. They used different percentage of ethanol in the ethanol-gasoline blends denoted by E0 (pure gas), E5 (5% v/v ethanol), E10, E15, E20, E25, E30, E50 and E75. A kinetic study has been conducted through a simultaneous TG (thermogravimetry) and DTA (differential thermal analysis) by following the methodology of non-isothermal tests to obtain the activation energies of the tested mixtures. Was used the synergism analyze, between the components of the mixtures, as a tool to evaluate the effect of ethanol content in the gasoline mixture. The useful energy fuel was obtained by dynamometer tests to Otto cycle single cylinder standard engine with six different compression rates. In the data analysis was found that synergism exists in mixtures with ethanol content between 5% to 30%. These mixtures also showed the best power results for compression ratios of 6:1 to 7:1. The thermal analysis results showed that mixtures with low ethanol content (to 30%) exhibit higher volatility and, possibly, this characteristic improves combustion in Otto cycle engines.
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Palavras-chave
Análise térmica, Motor padrão, Gasolina, Etanol, Energia de ativação, Energia útil, Thermal analysis, Gasoline, Ethanol, Activation energy, Useful energy