Vol.:(0123456789) 1 3 Journal of the Brazilian Society of Mechanical Sciences and Engineering (2020) 42:347 https://doi.org/10.1007/s40430-020-02428-w TECHNICAL PAPER Flash point, kinematic viscosity and refractive index: variations and correlations of biodiesel–diesel blends Dario Alviso 1,2 · Emir Saab 1 · Pascal Clevenot 1,3 · Silvia Daniela Romano 1,4 Received: 3 April 2019 / Accepted: 21 May 2020 © The Brazilian Society of Mechanical Sciences and Engineering 2020 Abstract This paper presents characterization studies of ﬂash point, kinematic viscosity and refractive index for several biodiesel/ diesel blends. Biodiesel is produced from soybean, corn, olive, canola, almond, grape and peanut oils. Regression equations are presented to estimate the kinematic viscosity, refractive index and ﬂash point of the studied biodiesel and their blends with diesel fossil fuel as a function of the blend composition. Moreover, as viscosity and refractive index measurements are simple, fast and require very small volume of samples, a correlation study for the blends is conducted to estimate the ﬂash point from these two properties. It is shown that when kinematic viscosity and refractive index are both used for the estima- tion of the blends ﬂash point, the R 2 values are higher than those found using simple correlations. Keywords Biodiesel · Diesel · Blends · Flash point · Kinematic viscosity · Refractive index 1 Introduction Biodiesel (BD) is a liquid biofuel produced from—new or recycled—animal fats or vegetable oils. This biodegradable fuel is composed of a mixture of fatty acid alkyl esters with dif- ferent degrees of unsaturation. BD is used in compression igni- tion engines in many countries, usually blended up to 20% with petroleum diesel, without major engine modiﬁcations [1–5]. Biodiesel quality is evaluated by means of several phys- icochemical properties usually chosen to characterize each of these fuels from diﬀerent oil origins, such as density, kin- ematic viscosity, ﬂash point, cloud point, cetane number and iodine number, included in the ASTM D 6751 [6] and EN 14214 [7] biodiesel standards. Flash point is the minimum temperature at which a ﬂammable substance, usually a liq- uid, produces enough vapors that when mixed with air would ignite when applying a source of heat at a suﬃciently high temperature [8, 9]. Kinematic viscosity is related to the resist- ance that liquids possess during their ﬂuidity and deformation. Viscosity is a physical property of all ﬂuids, which emerges from collisions between ﬂuid particles that move at diﬀerent speeds, causing resistance to their movement. Concerning biodiesel, it is the most critical property due to its eﬀect on the injection process [10, 11]. Refractive index is a property that allows to evaluate the predominant ester saturation degree [12]. Moreover, refractive index has been used to follow the progress in the conversion of soybean oil to biodiesel [13], to follow the stability of biodiesel in an accelerated oxidation process [14], and in biodiesel combustion studies [15, 16]. Concerning biodiesel physicochemical properties, there are several studies and reviews recently published [17–21]. They include a review of biodiesel properties as well as its composition, speciﬁcations and prediction models [18]; the eﬀects of biodiesel properties on diesel engine performance and exhaust emissions [19]; and reviews on the properties, performance and emission of second-generation [20] and third-generation biodiesel [21]. Diesel fuel (D) is a product that is obtained from the dis- tillation and puriﬁcation of crude oil. This fuel is used in Technical Editor: Roney Leon Thompson, DSc. * Silvia Daniela Romano silviadromano@gmail.com 1 Universidad de Buenos Aires, Facultad de Ingeniería, Grupo de Energías Renovables (GER), Av. Paseo Colón 850, 1063 Buenos Aires, Argentina 2 Laboratorio de Mecánica y Energía, Facultad de Ingeniería, Universidad Nacional de Asunción, Campus Universitario, San Lorenzo, Paraguay 3 Département Mécanique Energétique, Polytech Marseille, Aix Marseille Université, rue Enrico Fermi, 13453 Marseille Cedex 13, France 4 Consejo Nacional de Investigaciones Cientíﬁcas y Técnicas, Godoy Cruz 2290, 1425 Buenos Aires, Argentina