2014 STLE Annual Meeting & Exhibition
May 18-21, 2014
Disney’s Contemporary Resort
Lake Buena Vista, Florida, USA
Friction Characteristics of Polyalkylene Glycol Based Engine
Oil Formulations
CATEGORY
Engine and Drive Train
AUTHORS AND INSTITUTIONS
A. Gangopadhyay, D.G. McWatt, and L.D. Elie, Ford Motor Company, Dearborn, MI
J. B. Cuthbert, E. D. Hock, and K. Sinha*, Dow Chemical Company, Midland, MI
* Currently at Chevron Oronite Company
INTRODUCTION
Mineral based engine oil formulations have been used for several decades and served the
industry well with incremental performance improvements including fuel economy. Over the
past twenty years engine oil derived fuel economy improved substantially through improvements
in base oils and additive technology. However, further improvement appears challenging while
maintaining durability and other performance requirements.
Polyalkylene glycols (PAG) are being explored recently as base oil for engine oil formulations.
Polyalkylene glycol base fluids have outstanding overall load-carrying capacity, film strength
and anti-wear properties (1). These base stocks also have low friction coefficients. Their
excellent property profile enables formulated lubricants using polyalkylene glycols as base
stocks to reduce the need for the extreme pressure-anti wear (EP/AW) additives, viscosity index
(VI) improvers and dispersants that are traditionally used in hydrocarbon based oils (API Groups
I-IV). Polyalkylene Glycol-based (PAG) lubricants are used extensively in industrial lubricants
today including compressor lubricants, metal working fluids, turbine oils, refrigeration lubricants
and many other applications.
Merryweather et al. (2) explored friction behavior of PAG oils in a laboratory reciprocating rig
using sections of a piston ring and a liner at different temperatures and under certain conditions
reported lower friction coefficients compared to mineral base engine oil formulations. Motored
valvetrain tests also showed significant friction reduction of glycol based oils at 120C (3).
The objective of this paper is to investigate friction reduction potential of PAG oils at various
temperatures initially at engine component systems; valvetrain, and power cylinder and later on
a motored engine.
Polyalkylene Glycol Formulations
Table 1 shows various PAG oil formulations and their physical properties. The PAG oils were
formulated from the reaction of ethylene and/or propylene oxide with alcohol and they could be
either capped or uncapped. The viscosity index of PAG oils is significantly higher than typical
engine oil formulations (about 150) which offer a flatter viscosity-temperature relationship. The
kinematic viscosities of PAG oils are also lower than mineral based engine oils. All PAG oils
were formulated with one additive package consisting of antioxidant, antiwear, corrosion
inhibitors and an acid scavenger.
Table 1. Physical properties of PAG oils investigated
Friction Evaluations
Valvetrain Friction - The friction
reduction potential of PAG
engine oil formulations was
evaluated using a motored
direct acting mechanical bucket
valvetrain rig where a single
camshaft was driven by an
electric motor through a flywheel
and a set of couplings. An inline torque meter measured the
average torque. Engine oil was
heated externally in a sump and
then pumped into the engine
inlet from where it flowed
through the original channels to
lubricate the cam and tappet
contact interface. The engine oil
temperature was maintained at
40C, 80C, and 100C. Figure 1 Figure 1. Valvetrain friction of PAG oils at 100C oil temperature.
shows friction torque as a
function of camshaft speed at 100C oil temperature. All PAG oil formulations showed significant
friction reduction compared to the GF-5 SAE 5W-20 oil but the extent of friction reduction varied
by PAG oil formulations. The degree of friction reduction was higher at lower camshaft speed
because the lubrication regime was more boundary than hydrodynamic. Similar results were
obtained at other oil temperatures.
Piston Ring Friction Force – The friction
force between the cylinder liner and
piston ring and piston skirt was
measured using a motored single
cylinder engine.
Friction force was
measured as a function of crank angle at
different engine speeds and at various
oil temperatures using the “floating liner”
principle. Current production cast iron
liner and ring pack were used. Figure 2
shows typical friction force which is the
average of piston ring upstroke and
downstroke. All PAG oil formulations
shows substantial friction reduction
compared to GF-5 SAE 5W-20 oil and a
small difference was observed between Figure 2. Piston ring friction force for various PAG oil
PAG oils.
formulations compared to GF-5 SAE 5W-20 oil.
Motored Engine Friction – The torque to
turn the crankshaft in a production I-4
engine was measured as a function of
engine speed at various engine oil
temperatures. Results on Figure 3 shows
PAG oils reduced friction compared to GF5 SAE 5W-20 oil at 100C oil temperature.
The friction reduction was higher at lower
engine speeds and all PAG oils shows
similar friction characteristics.
SUMMARY
Polyalkylene glycol based engine oils were
formulated from ethylene and/or propylene
oxide feed stock.
Friction reduction
potential was evaluated at motored Figure 3. Motored engine friction with PAG oil
valvetrain and power cylinder systems and formulations.
then on an engine. Significant friction
reduction was observed at engine component levels which translated into substantial friction
reduction in engine tests. These are encouraging results but additional evaluations are
necessary for durability and other performance characteristics.
REFERENCES
1. J. Thoen, D. Zweifel, and M. Woydt, "Potential for polyalkylene glycols in automotive engine oil
applications", Conference: Engine oil circulation system of internal combustion engines, May
2009, Zwickau, Germany.
2. S. Merryweather, D. Zweifel, and M. Woydt, “Fuel economy though engine oils based on
polyalkylene glycols”, Proc. 18th Int. Coll. Tribology, TAE Esslingen, 2012, Editor W. Bartz.
3. F. Gili, A. Igartua, R. Luther, and M. Woydt, “The Impact of Biofuels on Engine Oil´s
Performance”, Proc. 17th Int. Coll. Tribology, TAE Esslingen, 2010, Editor W. Bartz.