Relative permittivity of bioethanol, gasoline and blends as a function of temperature and composition

Abstract

The dependence of the real part of the relative permittivity of bioethanol, gasoline, and their blends was determined. Measurements were performed in the temperature range between 298 K and 323 K, at a frequency of 100 kHz. Temperature was stabilized within ±0.1K and the uncertainty in the relative permittivity was ±0.01. In all the studied blends, the real part of the relative permittivity decreases as a function of temperature with a very good fit to a linear function. At each temperature, the real part of the relative permittivity increases with the bioethanol content in the sample. The permittivity as a function of blends composition fits very satisfactorily to a fourth - order polynomial. In all cases, the mean square error (ΔRMS) of the permittivity estimation was less than 0.09. Furthermore, for bioethanol concentrations lower than 25%, a second - order polynomial fits with an ΔRMS error below 0.04. At higher bioethanol concentrations, a linear function fits with an ΔRMS error below 0.13. The bioethanol concentration in the blends is estimated from permittivity and temperature measurements, with a mean square error in the estimation of the composition lower than 0.5% in all cases. This work shows that measurements of electrical properties can be very effective in the characterization of gasoline - ethanol blends for laboratory and industrial applications.