Influence of Viscosity Modifiers on Hydrodynamic Friction
Author(s)
Holtzinger, Jennifer
Type
Thesis
Abstract
Polymer additives, named Viscosity Modifiers (VMs), have been added to motor
engine lubricants for more than 50 years, where they are used to increase the viscosity
index of their blends. It is well known that solutions of VMs exhibit shear thinning
under high strain rate conditions as are present in engine journal bearings. In the past,
this shear thinning was regarded as undesirable since it might reduce hydrodynamic
film thickness. However it has been reported that multigrade oils containing VMs
provide lower engine friction than polymer-free oils of comparable viscosity and the
most likely origin of this is a reduction of hydrodynamic friction due to temporary
shear thinning of the polymer solutions.
In this thesis, the role of polymer shear thinning in reducing hydrodynamic friction is
clarified by the experimental work carried out on a range of different polymer types.
This study includes the viscosity measurements over a wide range of shear rate and
also friction and film thickness analyses performed in a soft elastohydrodynamic
lubrication contact in order to avoid piezoviscous effects. A very recent technique
based on laser induced fluorescence technology is used to evaluate the film thickness.
These experimental results are compared with theoretical calculations, which allows
based on the rheological data of each polymer solution, the impact of polymer shear
thinning on hydrodynamic friction to be quantified.
The studied polymer solutions show a decrease in film thickness and in hydrodynamic
friction compared to Newtonian fluids of similar viscosity. This reduction is ascribed
to the temporary shear thinning of polymer blends.
The proposed theoretical models show good agreement with the experimental values.
They appear to be useful tools to quantify the impact of polymer shear thinning on
film thickness and friction.
In addition to this main work, the polymer solutions are analysed under high contact
pressure and the shear stability of some commercials viscosity modifiers are studied. A new method is developed to quantify the permanent viscosity loss of each polymer
solution and this is compared to the industrial Kurt-Orbahn test.
engine lubricants for more than 50 years, where they are used to increase the viscosity
index of their blends. It is well known that solutions of VMs exhibit shear thinning
under high strain rate conditions as are present in engine journal bearings. In the past,
this shear thinning was regarded as undesirable since it might reduce hydrodynamic
film thickness. However it has been reported that multigrade oils containing VMs
provide lower engine friction than polymer-free oils of comparable viscosity and the
most likely origin of this is a reduction of hydrodynamic friction due to temporary
shear thinning of the polymer solutions.
In this thesis, the role of polymer shear thinning in reducing hydrodynamic friction is
clarified by the experimental work carried out on a range of different polymer types.
This study includes the viscosity measurements over a wide range of shear rate and
also friction and film thickness analyses performed in a soft elastohydrodynamic
lubrication contact in order to avoid piezoviscous effects. A very recent technique
based on laser induced fluorescence technology is used to evaluate the film thickness.
These experimental results are compared with theoretical calculations, which allows
based on the rheological data of each polymer solution, the impact of polymer shear
thinning on hydrodynamic friction to be quantified.
The studied polymer solutions show a decrease in film thickness and in hydrodynamic
friction compared to Newtonian fluids of similar viscosity. This reduction is ascribed
to the temporary shear thinning of polymer blends.
The proposed theoretical models show good agreement with the experimental values.
They appear to be useful tools to quantify the impact of polymer shear thinning on
film thickness and friction.
In addition to this main work, the polymer solutions are analysed under high contact
pressure and the shear stability of some commercials viscosity modifiers are studied. A new method is developed to quantify the permanent viscosity loss of each polymer
solution and this is compared to the industrial Kurt-Orbahn test.
Date Issued
2011-12
Date Awarded
2012-10
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Spikes, Hugh
Sponsor
Castrol (Firm)
Publisher Department
Mechanical Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)