A close dielectric spectroscopic analysis of diesel/biodiesel blends and potential dielectric approaches for biodiesel content assessment

Diesel/biodiesel blends have been more and more used as an alternative fuel due to their economic, social and environmental advantages. This is why, in many cases, legislative policies have been or are being implemented to fix a minimal percentage of biodiesel content to be added in diesel fuels. In order to ensure the mandatory use, of course, it is necessary to develop methods able to quantify the amount of biodiesel in such blends. Despite the fact that the methodology based on the Fourier transform mid-infrared spectroscopy is the standard one used to determine the biodiesel content, several other techniques have been, in the last years, proposed as alternative methods to overcome some limitations presented by infrared spectroscopy. In particular, impedance spectroscopy has been proposed as a cheaper alternative technique in this quantification process. Owing to the very high resistivity response from diesel/biodiesel blends, nevertheless, development of dielectric-based biodiesel content sensors has been mainly focussed on measuring the corresponding dielectric constant. By using a sample holder with adequate dimensions, it was possible to carry here out a much complete dielectric spectroscopic study of diesel/biodiesel blends, discussing the results in terms of Debye versus modified-Debye models. The dielectric constant as well as electrical conductivity responses from these blends particularly revealed, at least over the compositional range studied (up to 10 volume% of biodiesel), linear behaviors upon biodiesel content variation, suggesting as well viability of development of resistivity-based biodiesel sensors, with the advantageous possibility of being projected and used even in the direct current mode.