High-Pressure Characterization of Dynamic Viscosity and Derived Properties for Squalane and Two Pentaerythritol Ester Lubricants:  Pentaerythritol Tetra-2-ethylhexanoate and Pentaerythritol Tetranonanoate

The experimental measurements of dynamic viscosity for squalane, pentaerythritol tetra-2-ethylhexanoate (PEB8), and pentaerythritol tetranonanoate (PEC9) have been performed using a Ruska rolling-ball viscometer over the temperature range of 303.15−353.15 K and a pressure range of 0.1−60 MPa. A total of 2016 experimental measurements of the rolling time have been obtained for the determination of 252 dynamic viscosity data. The available literature viscosity data for squalane at high pressures have been compared with the new measurements, and an average deviation of 1.5% has been obtained, which is within the experimental uncertainty (±3%). The higher viscosity values are reached for PEB8, followed by PEC9. For the pentaerythritol esters, it has been observed that the dynamic viscosity increases with the branching degree of the molecule. The relative change in viscosity with temperature is biggest for PEB8 and, consequently, the poorer viscosity index (VI) values and higher temperature coefficients have been obtained for this fluid. The lowest pressure−viscosity coefficient and the highest VI have been obtained for PEC9.