Correlation of Elastohydrodynamic Friction with Molecular Structure of Highly Refined Hydrocarbon Base Oils

Abstract

The molecular compositions of a range of low viscosity hydrocarbon base oils spanning API Groups II to IV have been quantified using 13C NMR and correlated with base oil elastohydrodynamic (EHD) friction. A strong correlation has been found between the proportions of paraffin, linear and branched carbons and EHD friction, with a high proportion of linear and paraffinic carbon atoms contributing to low-EHD friction but branched carbons contributing to high-EHD friction. Correlation equations have been developed to predict EHD friction based on base oil composition. At very high temperature and low pressure, this correlation breaks down as the lubricant in the contact does not reach sufficiently high shear stress for shear thinning to occur. For Group IV polyalphaolefin, the correlation must be extended to account for the very high proportion of linear carbons originating from linear alkene oligomerization. The correlations developed in this study can be used to guide the design of low-EHD friction base oils.

Friction and temperature mapping of environmentally acceptable gear oils

“…These oils are considerably more expensive than mineral oils. They have lower friction [3][4][5] and higher thermal conductivity compared to the mineral oil [6]. Their lower friction coefficient signifies less energy loss in the machine components like gears.…”

“…The model proposed by Bair requires more disposable parameters that are difficult to find for industrial oils. With regard to the contact temperature modeling, Archard model [18] has been commonly used, and it is still implemented in the models [3,19]. In this paper, the Eyring model is used for comparing the rheological properties of the oils, and the Archard model is employed for estimating the contact temperature.…”