Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Determination of the biodiesel content in diesel/biodiesel blends by using the near-near-infrared thermal lens spectroscopy M. Ventura a , W.B. Deus a , J.R. Silva a , L.H.C. Andrade a , T. Catunda b , S.M. Lima a, ⁎ a Grupo de Espectroscopia Óptica e Fototérmica, Programa de Pós-Graduação em Recursos Naturais, Universidade Estadual de Mato Grosso do Sul, CP 351 Dourados, MS, Brazil b Instituto de Física de São Carlos, Universidade de São Paulo, São Carlos, SP, Brazil GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Near-near infrared Thermal Lens Spectroscopy Diesel/biodiesel blends Thermal diffusivity ABSTRACT A dual-beam mode-mismatched configuration of the Thermal Lens (TL) technique was applied to characterize biodiesel, diesel and diesel/biodiesel blends. The excitation was performed using a tunable laser in the near-near infrared region in order to assess overtones and combination bands of the vibration modes. The thermo-optical properties of the fuels were also determined. The results showed that the biodiesel contents in diesel/biodiesel blends can be monitored with this technique, by excitation the third overtone of the C–H (4ν(C–H)) bond stretching vibration at 916 nm. Both the amplitude of the photothermal signal and thermal diffusivity are im- portant parameters to quantify the biodiesel content in diesel/biodiesel blends. 1. Introduction The use of alternative fuels is growing on the world in the last few years. The biodiesel produced from vegetal or animal fats have being the main substitute for petroleum-derived diesel fuel due to some fac- tors, such as high combustion efficiency, lower sulfur content, excellent lubricity and high cetane number [1,2]. In addition, its economic and environmental advantages can be highlighted [1–3]. Since biodiesel is completely miscible in diesel fuel and have similar properties, the use of diesel/biodiesel blends in different proportions is increasing, mainly in Brazil. Currently, the National Energy Policy Council has approved the addition of 8% (v/v) of biodiesel in diesel oil for commercial use [4]. In this context, it becomes necessary to develop or improve methods able to provide fast and efficient results on the biodiesel content in diesel/ biodiesel blends, in order to control the quality of the commercialized product. http://dx.doi.org/10.1016/j.fuel.2017.10.069 Received 6 September 2017; Accepted 12 October 2017 ⁎ Corresponding author at: Universidade Estadual de Mato Grosso do Sul – UEMS, Programa de Pós-Graduação em Recursos Naturais – PGRN, Grupo de Espectroscopia Óptica e Fototérmica – GEOF, CEP 79804-970 – C.P. 351, Dourados, MS, Brazil. E-mail address: smlima@uems.br (S.M. Lima). Fuel 212 (2018) 309–314 0016-2361/ © 2017 Elsevier Ltd. All rights reserved. MARK