Shear thinning and hydrodynamic friction of viscosity modifier-containing oils. Part II: impact of shear thinning on journal bearing friction
File(s)
Published version
Author(s)
Marx, Nigel
Fernández, Luis
Barceló, Francisco
Spikes, HA
Type
Journal Article
Abstract
In a companion paper, the temporary shear thinning behaviour of a series of viscosity-modifier (VM)-containing blends was studied over a wide shear rate and temperature range [Marx et al. in Tribol Lett, https://doi.org/10.1007/s11249-018-1039-5]. It was found that for almost all VMs the resulting data could be collapsed on a single viscosity versus reduced strain rate curve using time–temperature superposition. This made it possible to derive a single equation to describe the viscosity–shear rate behaviour for each VM blend. In the current paper, these shear thinning equations are used in a Reynolds-based hydrodynamic lubrication model to explore and compare the impact of different VMs on the film thickness and friction of a lubricated, isothermal journal bearing. It is found that VMs reduce friction and especially power loss markedly at high shaft speeds, while still contributing to increased hydrodynamic film thickness at low speeds. The model indicates that VMs can contribute to reducing friction in two separate ways. One is via shear thinning. This occurs especially at high bearing speeds when shear rates are large and can result in a 50% friction reduction compared to the equivalent isoviscous oil at low temperatures for the blends studied. The second is via their impact on viscosity index, which means that for a set viscosity at high temperature the low-shear-rate (and thus the high shear rate) viscosity of a high-VI oil, and consequently its hydrodynamic friction, will be lower at low temperatures than that of a low-VI oil. The identification and quantification of these two alternative ways to reduce friction should assist in the design of new, fuel-efficient VMs.
Date Issued
2018-06-21
Date Acceptance
2018-06-11
Citation
Tribology Letters, 2018, 66
ISSN
1023-8883
Publisher
Springer Verlag
Journal / Book Title
Tribology Letters
Volume
66
Copyright Statement
© The Author(s) 2018. Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.
License URL
Identifier
https://link.springer.com/article/10.1007/s11249-018-1040-z
Publication Status
Published
Article Number
91
Date Publish Online
2018-06-21