Assessment on the use of biodiesel in cold weather: pour point determination using a piezoelectric quartz crystal

Abstract

In order to use biodiesel safely, as an alternative fuel for diesel engines, without fear of cold weather, the pour point of the blends needs to be estimated. This paper is aimed to propose an alternative and easy to use methodology, based on a piezoelectric quartz crystal, to determine the pour point of biodiesels and blended fuels. Impedance and phase of impedance vs. frequency of the piezoelectric quartz crystal change significantly during cooling of biodiesel and biodiesel blended fuels and allows to confirm the role of ethanol as a cold flow improver for biodiesel. Pour point is readily determined by finding the minimum series or parallel frequencies of a barred piezoelectric quartz crystal in contact with the biodiesel blended fuel along cooling. This new methodology only needs the measurement of series frequency, which can be accomplished with high precision by connecting a frequencymeter to a home made oscillator that drives the piezoelectric quartz crystal. Although inexpensive, this new methodology is no more based on visual inspection as the ASTM D97 method, and allows data to be acquired more frequently than the 3 °C intervals recommended by the time consuming standard methodology. In the new proposed methodology, data is acquired while the fuel is at the controlled temperature, which is not possible with the ASTM method, where the test jar needs to be removed from the thermostatic bath for visual inspection. Pour points of biodiesel blends with a commercial diesel fuel determined by this new methodology were compared with the ones obtained by the official ASTM methodology. For samples with pour points ranging from 2.3 °C (pure biodiesel) to −15.0 °C (pure commercial fuel diesel), median pour point values obtained for replicate measurements performed by the two methodologies were not statistically different (α = 0.05), although the results obtained by the new methodology were more precise.