Análise da influência da temperatura sobre propriedades físico-químicas de amostras de diesel, biodiesel e suas misturas

Abstract

Fuel quality is a major factor affecting the performance of internal combustion engines and it is characterized by a combination of physical and chemical properties. In this study, the influence of temperature on some properties such as density, dynamic viscosity, cloud point and pour point were investigated in different samples of fuels. In addition, measurements involving thermogravimetry and infrared spectroscopy were also performed. Density measurements as a function of temperature or concentration of biodiesel in the sample revealed a linear dependence, indicating that the temperature reduction or increase of the concentration of biodiesel results in a density increase. The rheological study from dynamic viscosity measurements identified the Newtonian fluid behavior for all samples. It was also observed an increase in the dynamic viscosity caused by the increase of the concentration of biodiesel in the sample and also the reducing the temperature. An exponential fit of the Arrhenius type equation was used to analyze the correlation between dynamic viscosity and temperature, allowing to identify a temperature limit, T*, below which this adjustment is lost and the sample solidification process is triggered. A phase diagram as a function of the biodiesel concentration and the temperature T*, the cloud point and poor point was prepared. This diagram shows the temperature ranges in which liquid and/or solid phases can be found, and where the fit between the temperature and dynamic viscosity can be obtained by an exponential equation of Arrhenius type. In addition, calorimetric measurements revealed a higher energy per mass unit for the standard diesel samples, and that this energy decreases linearly with increasing of biodiesel content. Thermal analysis showed different degradation profiles for the samples. Thermograms indicated a shift of the degradation curve at higher temperatures due to the increase in the sulfur content in the samples of standard diesel and also increasing the biodiesel concentration in the samples produced by mixture of diesel and biodiesel. The analysis of liquid samples using infrared radiation allowed the identification of different functional groups present in the samples and to establish, in terms of the intensity of the absorbance characteristic of the carbon-oxygen double bond present in the esters of biodiesel, a relation with the concentration of biodiesel present in the sample. In this sense, through the analysis of different physical and chemical properties of the samples, it was possible to evaluate characteristics and interrelationships of these properties, particularly in respect of temperature variations, which can favor or disfavor the increased biodiesel concentration in blends with diesel. Thus, throughout this study are presented important data and notes related with the theme.