Measurement and prediction of speeds of sound of fatty acid ethyl esters and ethylic biodiesels Samuel V.D. Freitas a , Ângela Santos b , Maria-Luísa C.J. Moita c , Luis A. Follegatti-Romero d , Telma P.V.B. Dias d , Antonio J.A. Meirelles d , Jean-Luc Daridon e , Álvaro S. Lima f , João A.P. Coutinho a,⇑ a CICECO, Chemistry Department, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal b Departamento de Química e Bioquímica, Centro de Ciências Moleculares e Materiais Faculdade de Ciências da Universidade de Lisboa Campo Grande, Edifício C8, gab. 8.4.34, 1749-016 Lisboa, Portugal c Departamento de Química e Bioquímica, Centro de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal d ExTrAE, Laboratory of Extraction, Applied Thermodynamics and Equilibrium, Department of Food Engineering, Faculty of Food Engineering, University of Campinas, UNICAMP, 13083- 862 Campinas, SP, Brazil e Laboratoire des Fluides Complexes et leurs Réservoirs, Faculté des Sciences et Techniques, UMR 5150, Université de Pau, BP 1155, 64013 Pau Cedex, France f Universidade Tiradentes, Av. Murilo Dantas 300, Farolândia, Aracaju-SE, Brazil highlights " Measurement of speed of sound for several fatty acid ethyl esters was carried. " Speed of sound data for ethylic biodiesels is reported for the first time. " Prediction of speed of sound was carried using the Wada’s group contribution method. " The Wada’s model provides a good description of speed of sound. article info Article history: Received 22 January 2013 Received in revised form 15 February 2013 Accepted 18 February 2013 Available online 5 March 2013 Keywords: Speed of Sound Ethyl esters Biodiesel Wada’s model Mixing rules abstract Speed of sound of fatty esters provides important information about biodiesel injection characteristics and enables the estimation of many other important properties of biodiesels. Nevertheless, the experi- mental speeds of sound of fatty esters are very scant. This work provides new data on speed of sound for nine fatty acid ethyl esters and four ethylic biodiesels, measured at atmospheric pressure and temper- atures ranging from 293.15 to 343.15 K. These new data is used to evaluate the ability of the Wada’s group contribution method to predict the biodiesel speed of sound. It is here shown that this model pro- vides excellent description of the experimental data, with overall average relative deviations (OARDs) of 0.25% for the ethyl esters and between 0.45% and 0.59% for the biodiesels. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Worldwide researchers, fuel industries and policy-makers have placed biofuels at the forefront of renewable energies, through var- ious policies and incentives. Among the biofuels, in Europe the bio- diesel has been playing a key-role in the promotion of energy sustainability, especially for the transport sector. This tendency is expected to keep increasing in the coming years when new feed- stocks for biodiesel production are developed from agricultural residues and non-edible oils. Blends of biodiesel with diesel and ethanol with gasoline are expected to account for 54% of the growth in liquids fuel consumption between 2009 and 2035 [1]. This happens because biodiesel are obtained from vegetable oils, animal fats and greases, and its use as fuel is economically viable, technically compatible and environmentally friendly. Besides being produced from renewable sources, it contributes less to greenhouse gases emissions and can replace petrodiesel totally or partially in conventional diesel engines without modification [2–4]. The aforementioned advantages have fed the academic interest in biodiesel in the last few years. While some works focused on establishing novel approaches to improve the production and puri- fication [5–7] others have oriented their line of research to the 0016-2361/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.fuel.2013.02.041 ⇑ Corresponding author. Tel.: +351 234401507; fax: +351 234370084. E-mail address: jcoutinho@ua.pt (J.A.P. Coutinho). Fuel 108 (2013) 840–845 Contents lists available at SciVerse ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel