352 r2010 American Chemical Society pubs.acs.org/EF Energy Fuels 2011, 25, 352–358 : DOI:10.1021/ef101299d Published on Web 12/22/2010 Evaluation of Predictive Models for the Viscosity of Biodiesel Samuel V. D. Freitas, † Maria Jorge Pratas, † Roberta Ceriani, ‡  Alvaro S. Lima, § and Jo~ ao A. P. Coutinho* ,† † Centre for Research in Ceramics and Composite Materials (CICECO), Chemistry Department, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal, ‡ Department of Chemical Processes, University of Campinas, 13083-852, Campinas, S~ ao Paulo, Brazil, and § Programa de P os-Graduac - ~ ao em Engenharia de Processos, Universidade Tiradentes, Av. Murilo Dantas 300, Farol ^ andia, Aracaju-SE, Brazil Received September 24, 2010. Revised Manuscript Received November 26, 2010 Viscosity is an important biodiesel parameter, subject to specifications and with an impact on the fuel quality. A model that could predict the value of viscosity of a biodiesel based on the knowledge of its composition would be useful in the optimization of biodiesel production processes and the planning of blending of raw materials and refined products. This work aims at evaluating the predictive capability of several models previously proposed in the literature for the description of the viscosities of biodiesels and their blend with other fuels. The models evaluated here are Ceriani’s, Krisnangkura’s, and Yuan’s models, along with a revised version of Yuan’s model proposed here. The results for several biodiesel systems show that revised Yuan’s model proposed provides the best description of the experimental data with an average deviation of 4.65%, as compared to 5.34% for Yuan’s model, 8.07% for Ceriani’s model, and 7.25% for Krisnangkura’s model. The same conclusions were obtained when applying these models to predict the viscosity of blends of biodiesel with petrodiesel. 1. Introduction Biodiesel refers to a fuel derived from renewable sources that consists of a mixture of methyl or ethyl esters of long- chain fatty acids, which is obtained by transesterification of vegetable oils or other feedstocks largely comprised of tri- acylglycerols with a simple alcohol, such as methanol or ethanol, in the presence of a catalyst. 1,2 It is nonflammable and non-explosive, with a flash point of 423 K compared to 337 K for petrodiesel. 3 As a fuel, it offers many benefits, such as ready availability, portability, renewability, domestic ori- gin, lower sulfur and aromatic content, biodegradability, better ignition quality, inherent lubricity, higher cetane number, positive energy balance, higher density, greater safety, nontoxic character of the exhaust emissions, and cleaner burning. 4-7 It has expanded into the existing markets and infrastruc- tures of gasoline and diesel and has undergone rapid devel- opment and acceptance as an alternative diesel fuel. Its worldwide production exceeded 2500 million tons in 2008. 8 It can be blended with diesel fuel to be used in conventional engines 9 and is able to reduce the carbon dioxide emissions by 78%. 10 Although most commercially available biodiesel is still between 5 and 20% biodiesel blended with petroleum diesel because of the higher prices of feedstocks for biodiesel pro- duction, the tendency of increasing production is expected to continue in the coming decades with the development and growth of nonfood feedstocks. 11 One of the major problems associated with biodiesel is that its viscosity may be higher than that for diesel fuel. A fuel of high viscosity tends to form larger droplets upon injection, leading to poorer atomization during the spray and creating operation problems, such as increased carbon deposits, 12 and may enhance the polymerization reaction, especially for oils of a high degree of unsaturation. 13 It also leads to poor combus- tion and increased exhaust smoke and emissions, beyond the problems in cold weather because of the increase of viscosity with a decreasing temperature. On the other hand, a fuel with low viscosity may not provide sufficient lubrication for the precision fit of fuel injection pumps, resulting in leakage or increased wear. 14 Thus, the kinematic viscosity of biodiesel at 40 °C must be in the range of 3.5-5.0 mm 2 /s according to *To whom correspondence should be addressed: Telephone: þ351- 234401507. Fax: þ351-234370084. E-mail: jcoutinho@ua.pt. (1) Knothe, G.; Steidley, K. R. 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