Pressure-Viscosity Coefficient of Hydrocarbon Base Oil through Molecular Dynamics Simulations
PZ Liu and HL Yu and N Ren and FE Lockwood and QJ Wang, TRIBOLOGY LETTERS, 60, 34 (2015).
The pressure-viscosity coefficient (the a value), which represents the variation of viscosity as a function of pressure, is an important parameter for elastohydrodynamic lubrication analyses. The properties of hydrocarbons in the C-20-C-40 mass range are of fundamental importance as they are basic constituents of synthetic- and mineral-based lubricant stocks. The conventional acquisition of the a value requires preparation of lubricant samples and experimental testing by means of a high- pressure viscometer. In this paper, we present a method to obtain the a value of a typical base oil (1-Decene trimer) based solely on the molecular dynamics simulations. Non-equilibrium molecular dynamics (NEMD) simulations were performed to calculate the shear viscosity of the lubricant at various temperatures and pressures up to 1 GPa. Elevated temperatures and time-temperature superposition (TTS)-based extrapolations were applied to further extend the ability of the NEMD simulations, and the rotational relaxation time was calculated and used to determine the validity of the NEMD calculations. The a value at 100 degrees C was calculated and compared with experimental results. Effectiveness of the extrapolation was evaluated with a 95 % confidence interval.
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