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Vegetable oils can be considered as an alternative or emergency fuel for diesel engine. However, vegetable oils result in operational and durability problems for the long-term operation because of being much more viscous than diesel fuel. To eliminate this drawback, blending of vegetable oils with diesel fuel or alcohol is one of the most widely used techniques. In the existing literature, many studies are available on the measurement and prediction of density and viscosity of binary blends (especially biodiesel (BD)-diesel fuel (DF) blends), although, there is still the lack of comprehensive studies in which reliable density and viscosity data are presented, new regression models are proposed and compared with other regression models for waste cooking oil (WCO)-DF binary blends. Therefore, in the present study, (1) WCO was blended with DF on the volume basis of 2, 4, 6, 8, 10, 15 and 20 %, (2) the measurements of viscosities and densities of the binary blends were performed at various temperatures (278.15–343.15 K) in accordance with DIN 53015 and ISO 4787 standards, respectively, (3) the variations of viscosity and density values of binary blends vs. temperature were evaluated, (4) the new rational and exponential models as a function of temperature were fitted to the experimental data measured by the authors and Baroutian et al. (regarded as typically different data), and finally (5) the models were also compared to Yoon et al. and linear models, previously proposed by other authors, in order to investigate their reliability. According to results, (i) the best correlation was obtained by the rational model with the lowest maximum relative errors of 2.9679 % and 3.2725 % for the viscosity data measured by the authors (WCO-DF blends) and Baroutian et al. (palm oil (PO)-DF blends), and (ii) for the density data of WCO-DF and PO-DF binary blends, the best correlation was obtained using the exponential model giving the lowest maximum relative errors of 0.0470 % and 0.0581 %, respectively.

Nowadays, biodiesel is drawing attention as a renewable and clean alternative to fossil diesel fuel because of numerous advantages such as higher flash point, cetane number and density. However, the high viscosity of biodiesel is one of the critical shortcomings and it causes poor atomization, decrease in engine performance and increase in exhaust emissions. To overcome this shortcoming, in this study, the effects of main transesterification reaction variables on the viscosities of produced safflower oil methyl and ethyl esters (biodiesel) were investigated as a full factorial experimental design, and optimum parametric values giving the lowest viscosity were determined. Density and viscosity were measured according to ISO 4787 and DIN 53015 standards. Sodium ethoxide (C2H5ONa) was utilized as a catalyst, and 90 and 120 minutes of reaction duration were kept constant for methanolysis and ethanolysis reactions. According to the results, the optimal reaction parameters were determined as: 0.75 % catalyst concentration, 8:1 alcohol to oil molar ratio and 56 °C reaction temperature for methanolysis; 1.00 % catalyst concentration, 12:1 alcohol to oil molar ratio and 70 °C reaction temperature for ethanolysis. Based on the reaction parameters, the methyl and ethyl esters were produced with the lowest viscosities of 3.989 mm2/s and 4.393 mm2/s, respectively. In the light of results obtained in this study, similar studies on production of biodiesels from different oils and alcohols can be performed.

Nowadays, biodiesel and vegetable oils have received increasing attention as renewable clean alternative fuels to fossil diesel fuel because of decreasing petroleum reserves and increasing environmental concerns. However, the straight use of biodiesel and vegetable oils in pure form results in several operational and durability problems in diesel engines because of their higher viscosity than fossil diesel fuel. One of the most used methods for solving the high viscosity problem is to blend them with fossil diesel fuel or alcohol. The reliable viscosity and density data of various biodiesel-diesel-alcohol ternary blends or biodiesel-diesel binary blends are plentifully available in existing literature, however, there is still the scarcity of dependable measurement values on different biodiesel-diesel-vegetable oil ternary blends at various temperatures. Therefore, in this study, waste cooking oil biodiesel (ethyl ester) was produced, and it was blended with fossil diesel fuel and waste cooking oil at different volume ratios to prepare ternary blends. Viscosities and densities of the ternary blends were determined at different temperatures according to DIN 53015 and ISO 4787 standards, respectively. The variation in viscosity with respect to temperature and oil fraction and the change of density vs. temperature were evaluated, rational and exponential models were proposed for these variations, and these models were tested against the density and viscosity data measured by the authors, Nogueira et al. and Baroutian et al. by comparing them to Gupta et al. model, linear model, Cragoe model and ANN (artificial neural networks) previously recommended in existing literature.