Predicting the kinematic viscosity of FAMEs and biodiesel: Empirical models

Three correlations are proposed to predict the kinematic viscosity of fatty acid methyl esters (FAMEs) in a wide temperature range. One correlation is derived for saturated species from C6:0 to C24:0 while two complementary correlations are used for unsaturated species, from C14:1 to C22:1, including C18:2 and C18:3. The correlation for saturated FAMEs was derived from 247 viscosity experimental points taken from the literature, giving an average absolute deviation (AAD) of 1.33%. In the case of unsaturated species, 154 experimental data points reported in the literature were considered, obtaining an AAD of 2.88%. The predictive capacity of the proposed correlations was tested by calculating the viscosity of 31 pure biodiesels (193 data points) and four binary biodiesel blends (150 data points) whose compositions and viscosities at different temperatures were gathered from the literature. A global AAD of 5.33% was obtained for pure biodiesels while the global AAD for biodiesel blends was 7.58%. These results were compared to the AADs obtained for other different six models previously reported in the literature and applied to the same data bank. The comparison showed that the lowest AADs for both data sets (pure biodiesel and biodiesel blends) were obtained with the correlations of this work.