Densities and Kinematic Viscosities in Biodiesel-Diesel Blends at Various Temperatures G. R. Moradi,* B. Karami, and M. Mohadesi Catalyst Research Center, Chemical Engineering Department, Faculty of Engineering, Razi University, Kermanshah, Iran ABSTRACT: In recent years biodiesel fuel has been considered as an alternative fuel for diesel engines. This fuel is made by transesterification of vegetable oils (or animal fat) and alcohols in the presence of a catalyst. Density and viscosity are two important properties that are useful for selecting fuels. In this study the effects of temperature and volume fraction of biodiesel and diesel on the density and kinematic viscosity of blends were investigated. In the previous studies, some correlations have been presented for the prediction of these two properties, but the constants of these correlations differ depending on the type of biodiesel and diesel. In this study two general correlations were presented for estimating density and kinematic viscosity of the blends at several temperatures. These correlations depend on the temperature, volume fraction of biodiesel and diesel, and properties of pure biodiesel and diesel (pure density at 293.15 K and pure kinematic viscosity at 313.15 K). The predicted results showed high accuracy nevertheless to the generality of their constants. ■ INTRODUCTION Reducing sources of fossil fuels and their pollution has been the aim of extensive research performed on alternative energy sources, particularly renewable fuels. Biodiesel is an alternative renewable fuel for diesel fuel, which includes alkyl esters of fatty acids obtained from vegetable oils or animal fats by transesterification reaction. 1-3 Biodiesel has many advantages, which have caused the consideration of this fuel in recent years. It is biodegradable, nontoxic, and renewable. In addition, biodiesel has a higher cetane number and flash point than diesel oil and effectively reduces the release of hydrocarbons and carbon monoxide and suspends particles from combustion. Biodiesel dissolves in diesel oil completely so it can be combined in any percent. Differences between biodiesel and diesel fuels exist (higher density and viscosity, higher cloud point and pour point (in some cases), and lower heat of combustion), but biodiesel can be used pure or mixed with diesel, without modification in diesel equipment directly. 4-6 Viscosity and density are key parameters of fuel for diesel engines. 6 Higher viscous fuels demand more energy from the fuel pump and block the pump elements, 7 also tending to largely form droplets, leading to poor fuel atomization during spraying that affects engine performance and exhaust emission. 7,8 On the other hand density is an important property in that performance parameters such as the cetane number and heating value are correlated against it. 9 Furthermore, an increase in density can affect engine output power because the fuel injection systems measure the fuel by volume, so consequently a greater mass is injected. 10 Several models have been proposed in the literature to predict biodiesel density and viscosity. Freitas et al. 11 evaluated the capability of four models that develops a method for predicting temperature dependence on viscosity of biodiesel based on fatty acid ester composition. The results for several biodiesel systems showed that the average deviation from the experimental data for Ceriani’s 12 model was 8.07 %, for Krisnangkura’s 13 model 7.25 %, for Yuan’s 3 model 5.34 %, and for revised version of Yuan’s model 4.65 % where their parameters were refitted by Pratas et al. 14,15 to the new data reported. Density of Biodiesel. Tat and Van Gerpen 9 measured the specific gravities of soybean oil biodiesel and (75, 50, and 20) % blends with No. 1 and No. 2 diesel fuels from the onset of crystallization temperature to 373.15 K using the standard hydrometer method. The results indicated that biodiesel and its blends demonstrate linear temperature dependency behavior, and they developed eq 1: 9 = + a bT SG (1) where SG is the specific gravity, T is the temperature in K, and a and b are constants that were found to depend on fuel. In some works density was used instead of specific gravity in eq 1. 4,5,16-18 Nita et al. 19 prepared a mixture of rapeseed oil biodiesel-diesel blended at a volume fraction of 0.1 to 0.9 with steps of 0.1 and a measured density at 298.15 K. The experimental data are represented by Kay’s mixing rule, eq 2, with an absolute average deviation of 0.014 %. 19 ρ ρ ρ = + v v m 1 1 2 2 (2) where ρ m is the density of mixture (kg·m -3 ), ρ 1 and ρ 2 are densities of the components 1 and 2 (kg·m -3 ), and ν 1 and ν 2 Received: August 7, 2012 Accepted: November 27, 2012 Published: December 6, 2012 Article pubs.acs.org/jced © 2012 American Chemical Society 99 dx.doi.org/10.1021/je3008843 | J. Chem. Eng. Data 2013, 58, 99-105