Predicting the temperature dependent density of biodiesel–diesel–bioethanol blends

Abstract

Density is a very important fuel property because it influences production, transportation, and distribution processes as well as all processes that take place in the internal combustion engine. Elaborating models to describe the density of biodiesel–diesel–bioethanol blends with a high content of biofuel facilitates the production of blends that comply with the standard quality requirements for density and the modeling and simulation of injection and combustion processes. For predicting density of rapeseed oil biodiesel–diesel–bioethanol and used cooking oil biodiesel–diesel–bioethanol blends, 2×15 ternary mixtures were prepared, having a maximum amount of biofuel of 30%v/v. The concentration of biodiesel and bioethanol varies between 5% and 25%, in increments of 5%. Their density values were determined in 15 steps in the temperature range of 273.15–343.15K. Based on experimental density values of components and blends, common linear mixing rules were evaluated, obtaining an average relative deviation under 0.125% and a regression coefficient above 0.996. In order to improve accuracy, four new mixing rules with different complexities were elaborated. The temperature dependent density of components was modeled based on experimental density values and constituents composition by linear and polynomial regression, by free version of Rackett equation and by group contribution methods. The elaborated mixing rules were tested for various combinations of component densities, yielding a very good accuracy, with an average deviation of under 0.053%. Taking into account the complexity and accuracy of the elaborated models, recommendations were made regarding their uses according to their concrete applications.