The pressure and temperature dependence of volume and viscosity of four Diesel fuels

The relative volumes and the viscosities of four Diesel fuels have been measured experimentally to pressures up to 350 MPa and temperatures to 160 °C. The experimental liquids were an extra low viscosity reference fuel, an ethanol based blend, neat biodiesel and 20% biodiesel. The Tait and Murnaghan equations of state represented the pressure–volume–temperature response equally well. The improved Yasutomi model for supercooling liquids, which accurately represents the temperature and pressure dependence of the viscosity of lubricating oils, did not fit the data well except for neat biodiesel. Surprisingly, the Doolittle free-volume equation was accurate only for the low viscosity reference fuel. The reason for the correlation difficulties may be illuminated by the behavior of the thermodynamic scaling of the viscosities. The Stickel analysis of the normalized Ashurst–Hoover parameter indicates that, for all liquids except the reference fuel, the measured viscosities lie across the transition in the response of viscosity to temperature and pressure. Consequently, only the comprehensive normalized Ashurst–Hoover scaling model successfully fits all data.