Permittivity of biodiesel-rich blends with fossil diesel fuel: Application to biodiesel content estimation

•Permittivity of biodiesel-rich blends was determined with an uncertainty below 0.3%.•At each composition, permittivity decreases linearly with temperature.•At constant temperature, permittivity increases linearly with biodiesel content.•Biodiesel content is estimated from permittivity and temperature measurements.•The RMS uncertainty of biodiesel content estimation is below 1.5%.

The relative permittivity of biodiesel-rich blends, from pure biodiesel to 50% blends with diesel fossil fuel, were determined at temperatures between 303.0 K and 343.0 K (controlled within ±0.1 K). Measurements were made on biodiesel from soybean in the frequency range from 20 kHz to 2 MHz; the relative measurement uncertainty was below 0.3%.At each composition, experimental values fit very satisfactorily to a linear dependence on temperature. Similarly, at constant temperature, permittivity depends linearly on biodiesel content. From these results, a simple model was proposed to estimate the permittivity of the samples as a function of biodiesel content and temperature. The model parameters were determined from a multiple regression analysis. The RMS uncertainty of the fitting was below 0.7%, for blends with biodiesel concentration ⩾50%. The model was inverted to determine the biodiesel content from permittivity and temperature measurements. The parameters of the inverted model were checked by a multiple regression analysis and the RMS uncertainty of the content determination was below 1.5%.The results presented in this work show that dielectric measurements are a valuable tool for biodiesel content determination in rich-biodiesel blends from vegetable oils with diesel fossil fuel.