Effect of blends of Diesel and Palm-Castor biodiesels on viscosity, cloud point and flash point

Many countries are promoting the use of biodiesel as a direct replacement for, or blend stock component with petroleum based diesel fuel using policy instruments that aim to gradually increase the use of vegetable oil biodiesel-diesel ratio from the current (or inexistent) blend to values among 15-20% by an specific upcoming year. For the particular use of palm oil as biomass raw material in the diesel-palm oil biodiesel (Diesel-POB) blend that goal could bring some difficulties because the high content of saturated fatty acids in POB could confer a problematic high cloud point to the fuel mixtures. On the other hand, the use of castor oil biodiesel in the blends could lower the cloud point value but, simultaneously, increase the viscosity of the diesel-biodiesel blends. In this article there were evaluated three properties (viscosity, cloud point and flash point) of binary mixtures castor oil biodiesel (COB), palm oil biodiesel (POB) and diesel fuel. It was also measured the cloud point for some ternary bends of Diesel/POB/COB. It was found that diesel-castor oil biodiesel (Diesel-COB) blends showed appropriate and approximately the same cloud point temperatures when the biodiesel concentration in those mixtures was under 40% in volume. The use of palm oil biodiesel-castor oil biodiesel (POB-COB) blends to obtain a type of pure biodiesel with both low cloud point and viscosity was not a practical option. Experimental data were also compared with the predictions of different published models for diesel-biodiesel mixtures. The general thermodynamic expressions used for estimation of viscosity and cloud point for liquid mixtures showed lower deviations from experimental values properties predictions from other proposed empirical models. (C) 2012 Elsevier B.V. All rights reserved.