High-Pressure Viscosity of Biodiesel, Diesel, and Biodiesel-Diesel Blends: Experimental Data and Modeling

Abstract

Biodiesel was produced in excess of one billion gallons in the United States last year. It is sold as B100 (neat) and as a variety of blends. It is well known as a renewable fuel that reduces net carbon dioxide production, and other harmful emissions. Because much of the recent experimentation has involved biodiesel simply as a “drop in” fuel, its full, beneficial potential has not been reached. The ability to understand, model and predict important physical property behavior of current and potential fuels can lead to increased diesel engine performance, reduce harmful emissions further, and even improve fuel perception. High-pressure viscosity has been identified as one of the most important fuel properties of diesel fuel due to vehicle injectors creating pressures thousands of times greater than atmospheric. High-pressure viscosity measurements were performed for common biodiesels like those produced from soy and canola oils, but more exotic feedstocks like coconut and jatropha were also tested. Measurements were performed on dozens of fuels for temperatures between 278.15 and 373.15 K and pressures up to 131 MPa. Fuels were found to vary significantly from their ambient viscosities, and some were found to be more than 700 percent of their initial viscosity at the highest pressure tested. Blends were typically found to increase in viscosity with increasing blend fraction of biodiesel, however, this trend was shown to vary at low temperature and high pressure. Possible pressure freezing was found to occur for all biodiesel samples and for several high-percentage biodiesel blends at 283.15 K. Empirical models were developed as functions of temperature, pressure and blend percentage and were typically within the 95% confidence interval of the instrument.