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World Tribology Congress, Kyoto, 2009
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Tribology and Energy Efficiency
R.I. Taylor1, E. Nagatomi2, S. Doki2 & R.T. Dixon1
1Shell Global Solutions (UK)
2Showa Shell Sekiyu K.K. (ARL), Japan
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Outline of Talk
Economic Importance of Lubricants
Lubricant Properties that Influence Friction
Lubricant Influence on Machine Elements
Real Life Examples of Energy Efficient Lubricants
Future Trends
Conclusions
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Economic Importance of Lubricants
The worldwide lubricants market $50 billion/year
The 1960’s Jost Report estimated that for many countries, around 10% of the Gross National Product (GNP) is spent overcoming friction and wear (for the UK GNP was approx $2250 billion in 2007)
The Jost Report also found that savings of 1.3 to 1.6% of GNP could reasonably be made by application of good tribological principles (use of correct lubricant, energy savings, proactive servicing/maintenance etc)
Nowadays, as well as calculations of financial savings that are achievable, CO2 savings may also be possible
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Economic Importance of Lubricants
An average European car emits around 3 tonnes of CO2 per year (assumes CO2 emissions of 190 g/km and 16,000 km per year)
The benefits of reducing fuel consumption by 5% would be:
Total CO2 savings of almost 4 million tonnes per year for the UK (assumes the 5% saving applies to all cars, and that there are 25 million cars in the UK)
Annual cost savings across UK fleet of almost 2 billion Euros (assumes 5% saving applies to all 25 million cars in UK)
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Economic Importance of Lubricants
For UK, annual electricity consumption (for industrial use) is approx 100 billion kWh For Germany, annual electricity consumption (for industrial use) is approx 200 billion kWh Cost of electricity varies by country but is approx 0.06 Euros/kWh
A 1% reduction in electricity usage would mean, for the UK: Annual savings of 1 billion kWh of electricity Annual cost saving of approx 60 million Euros Annual reduction in CO2 emissions of 430,000 tonnes*
* Assumes official UK Govt figures of 0.43 kg CO2 per kWh
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
Oil Film Thickness/Roughness
Fric
tion
coef
ficie
nt valve train
piston rings skirtplain bearings
boundary mixed fluid-film (HD, EHD)
Viscosity important here
Additives important here
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
In the Hydrodynamic and Elastohydrodynamic lubrication regimes the way in which lubricant viscosity varies with:
Temperature Pressure Shear Rate
will determine the oil film thickness separating the moving surfaces, and the friction loss in the contact
For the elastohydrodynamic lubrication regime, the lubricant pressure-viscosity coefficient, , is important
In the Boundary/Mixed lubrication regimes, the additives in the lubricant will also be important
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
Viscosity varies very greatly with temperature
Example
Mineral oil: Vk100 = 12.5 cSt , Vk40 = 106 cSt, VI 110
Synthetic oil: Vk100 = 12.5 cSt, Vk40 = 82 cSt, VI 150
0.00
25.00
50.00
75.00
100.00
0 20 40 60 80 100
Temperature (C)
Kin
emati
c V
isco
sity
(cS
t)
SAE-10W
SAE-30
SAE-10W/30
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Lubricant Properties That Influence Friction
Viscosity varies greatly with pressure (for pressures > 50 MPa)
*Ref: P.W. Gold et al, Journal of Synthetic Lubrication, Vol 18,, pp 51-79, April 2001
Barus Equation(P) = (0).exp(P)
Graph generated from published data (Aachen University, 2001)*
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Lubricant Properties That Influence Friction
Ref: R.I. Taylor, IMechE Proc Part J, Journal of Engineering Tribology, Vol 213, pp 35-46, 1999
Viscosity variation with shear rate
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
Additive Effects
Two common additives which attach to a surface and affect friction are:
Antiwear aditives – such as ZDTP (Zinc Dialkyldithiophosphate) used in automotive lubricants
Friction modifiers – “slippery” molecules, such as MoS2, boron nitride, esters etc
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
Additive Effects
ZDTP anti-wear additives: ZDTP forms an effective anti-wear film, which is a high friction film It is also a “smart” additive – as contact pressures increase, it becomes harder and better resists the increased pressure
Fluid Lubricant
Alkyl Phosphate precipitates
Partially complexed phosphates
Compacted phosphate matrix
Solid sulphide/oxide layer
Metallic substrate
Low viscosity fluid
High viscosity fluid
Solid
Scuffing resistance
Increasing
resistance to
penetration
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Lubricant Properties That Influence Friction
Additive Effects
Friction Modifiers
Friction modifiers are additives that form easily sheared layers at surfaces (substances such as MoS2, graphite, BN, esters, etc make effective FMs), causing reduced friction in the mixed/boundary lubrication regime
Shown below are typical FMs such as MoDTC (which reacts in the lubricant to form MoS2 at surfaces), and a triglyceride, which would be an organic FM
N - C - S - Mo Mo - S - C - N
S
S
R
RR
RO O
O
CH2 - O - C - R1
CH2 - O - C - R3
CH - O - C - R2
O
O
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Lubricant Properties That Influence Friction Additive Effects
The Mini-Traction Machine is often used to characterise surface active additives
Important to have a “running-in” process
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Lubricant Influence on Machine Elements Bearings
ch min
Low Load High Load
W
RLh
4
3
min
c
LRP
322
5.0
25.075.225.075.175.02
c
WRLP
Radius = R (m)Width = L (m)Angular speed = (rad/s)Viscosity = (mPa.s)Radial clearance = c (m)Load = W (N)P = fricton power loss (W)
Hydrodynamic lubrication: A lower viscosity oil would give lower friction
Ref: R.I. Taylor, SAE 2002-01-3355
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Lubricant Influence on Machine Elements The Piston Assembly
Lubricant viscosity = Linear speed at any particular crank angle = U Load on back of piston ring = W
Minimum oil film thickness = hmin Friction power loss = P (Watts)
W
Uh
min WUP 3
Hydrodynamic lubrication: A lower viscosity oil would give lower friction
Ref: Furuhama et al, JSAE Review, November 1984
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Lubricant Influence on Machine Elements The Piston Assembly
Ref: RI Taylor et al, International Triibology Conference, Yokohama, 1995
Experimental frictionmeasurements
FMEP 0.4
FMEP (kPa)
Peak Force (N)
SAE-10W 37.9 490
SAE-30 51.0 380
SAE-50 64.5 300
Predominantly Hydrodynamic lubrication: A lower viscosity oil gives lower FMEPbut more boundary friction at TDC firing
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Lubricant Influence on Machine Elements The Valve Train
Results below from an M111 cylinder head friction torque test at Shell
Reducing lube viscosity causes increase in friction, but FMs effective
Predicted oil film thickness, Euro 2.0 litre engine, direct acting bucket tappet
Oil Gallery Temperature (°C)
30 40 50 60 70 80
1.5
2.0
2.5
3.0
5W/20: no FM+ FM B + FM B + FM C+ FM C
Camshaft Torque (Nm)
~13%
Onset of
boundary
lubrication
BOUNDARY LUBRICATION
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Real-Life Examples of Energy Efficient Lubricants
Automotive lubricants: Industry standard fuel economy test results - cars
Oil AOil B
Oil ASAE-0W/20
Oil BSAE-0W/30
Reference OilSAE-15W/40
Vk40 (cSt) 40.95 55.69 106.0
Vk100 (cSt) 7.94 10.48 14.5
HTHS (mPa.s) 2.60 3.26 3.90
CCS (mPa.s) 3100 at -30ºC 3380 at -30ºC 3100 at -15ºC
Ref: RI Taylor, IMechE Tribology 2006 Meeting, July 2006, London
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Automotive lubricants: Friction Mean Effective Measurements on motored engine
0
50
100
150
200
0 1000 2000 3000 4000
FMEP
(kP
a)
Engine Speed (rpm)
0W-20 (40°C)
5W-30 (40°C)
0W-20 (100°C)
5W-30 (100°C) 5W-30 0W-20
Vk40 (cSt) 68.85 43.36
Vk100 (cSt) 12.01 8.04
(FMEP) 40-50 kPa whenviscosity changes from 8 to 70 cSt
Evidence of boundary friction
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Automotive lubricants: Importance of Friction Modifiers: Valve train friction
Oil Gallery Temperature (°C)
30 40 50 60 70 80
1.5
2.0
2.5
3.0
5W/20: no FM+ FM B + FM B + FM C+ FM C
Camshaft Torque (Nm)
~13%
Onset of
boundary
lubrication
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: High Viscosity Index Lubricants Fork lift truck tests at low temperature performed in Shell’s Hamburg laboratory.
Equivalent ISO grade hydraulic fluids (ISO 32) but different Viscosity Indices (VI)
Cumulative energy consumption over ten lift cycles. ISO 32 hydraulic fluids
200.0
220.0
240.0
260.0
280.0
300.0
320.0
340.0
360.0
380.0
400.0
-20 -15 -10 -5 0 5 10 20 40
Ambient temperature (°C)
Cu
mu
lative
en
erg
y c
on
su
mp
tio
n (
Wh
) Oil A
Oil B
Oil C
Oil D
Oil E
Name Grade Viscosity Index
Oil A Monograde 104
Oil B Multigrade 149
Oil C Multigrade 175
Oil D Multigrade 183
Oil E Multigrade 306
Ref: RI Taylor, IMechE Tribology 2008 Meeting, July 2008, London
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: Change of Viscosity Grade
In hydraulic circuits, it is often found that the majority of friction losses are in the pipes. The pressure drop in the pipe is directly proportional to the dynamic viscosity of the lubricant
Reducing the lubricant dynamic viscosity will reduce the pressure drop across the pipes, and will require lower pressures to be delivered by the pump – which will result in energy savings
Ref: RI Taylor et al, STLE Annual Meeting, Las Vegas, 2005
motorvalvespipespump pppp
4R
LQppipe
= dynamic viscosity
L = pipe lengthQ = flow rateR = pipe radius+ see talk B2-212 by David Green
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: Change of Viscosity Grade
Effect of changing ISO viscosity grade for hydraulic system Roughly 15% saving in energy in moving from an ISO 46 grade to an
ISO 32 grade, but other aspects of formulation also important (eg VI)
Pump type: Vickers V104C (vane)Speed: 1500 r/minLoad: 140 barsReservoir Temperature: 50°
70
80
90
100
Mineral Synthetic Mineral Synthetic
ISO 46ISO 32
%
Ref: D. Miller, Bao Steel Biannual Conference, Shanghai, Sept 2008
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Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: Benefits of Synthetic Base Fluids
Pressures in many industrial machine elements can be very high (up to GPa in components such as gears, or rolling element bearings)
Lubricant viscosity increases almost exponentially with pressure: = o.exp(P): where is the lubricant pressure-viscosity coefficient,
and P is the pressure Under very high pressure, the lubricant effectively solidifies, and causes
the metal surfaces to deform elastically
Under these conditions, the precise way in which lubricant viscosity varies with temperature and pressure is critical to determining the friction in the contact
In general, synthetic lubricants, based on XHVI™, PAO, PAGs etc will give lower friction than lubricants that use mineral base oils
Ref: RI Taylor et al, STLE Annual Meeting, Las Vegas, 2005
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ISO 220 mineral oils
ISO 220 PAO
ISO 220 PAG
Radicon worm gear efficiencytest at 100ºC
Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: Benefits of Synthetic Base Fluids The data below shows friction coefficients, as measured in a laboratory
tribology rig (the Mini Traction Machine) and power losses as measured in an FZG gearbox test, for a range of mineral and synthetic based gear oils
Significant temperature reductions are also often seen with synthetics
Ref: RI Taylor, IMechE Tribology 2008 Meeting, July 2008, London
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Real-Life Examples of Energy Efficient Lubricants
Industrial Lubricants: Benefits of Synthetic Base Fluids
Even in hydraulic systems, where pressures are only up to 50 MPa, a synthetic base oil with a lower pressure-viscosity lubricant can give benefits
Husky H160 injection moulding machineOil volume = 580 litres
Mineral ISO 46 versus synthetic ISO 46 oils
Mineral ISO 46: 60,000 kWh per yearSynthetic ISO 46: 53,940 kWh per year
Approx 10% electricity saving by changing to the synthetic oil
Ref: A. Guven, Rexroth Bosch Group Energy Efficient Hydraulics Seminar, October 2008
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Future Trends
Other factors that can affect friction in lubricated contacts include:
Increasing use of materials such as DLC Surface texturing Interaction of the lubricant with the fuel Chemical constraints being put on lubricant formulation
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Future Trends
Increasing use of materials such as DLC – for reduced friction Different additives response seen than for steel-steel
Track on the ball
HR0706Steel
HR0706DLC
HR0706Cr DLC
HR0906Cr DLC
Disc:1. Steel2. DLC3. Cr doped DLC
Steel ball
Mini Traction Machine Testing with different disk materials
* H. Renondeau et al, IMechE Journal of Engineering Tribology, 2008
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Future Trends
Increased use of surface texturing – for reduced friction We are investigating this using textured MTM discs
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Future Trends
Fuel-Lubricant Interactions
Increased use of biofuel + deliberate use of increased additive treat rates are impacting on the lubricant
Main responses seen are: (1) potentially higher levels of fuel dilution, and (2) detrimental impact on oxidation stability of lubricant
Both of these effects can impact on friction
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Future Trends
Chemical Constraints on Lubricant Formulation
For lubricants to be compatible with aftertreatment devices, chemical constraints on Sulphated Ash, Phoshorus and Sulphur (SAPS) are being introduced
This is impacting the amount of ZDTP anti-wear additive that can be used, and is leading to the increased use of zero sulphur base oil
+ see talk C2-414 by Kiyoshi Hanyuda
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Conclusions
By optimizing lubricant viscosity, lubricant viscosity-pressure coefficient, and the surface active additives in the formulation, it is possible to design Energy Efficient Lubricants which show real energy savings in the field, in both automotive and industrial applications
These products save energy, and save customers money too We are also carrying out R&D to find out what are the
optimum low SAPS lubricants which will work with DLC coatings, textured surfaces, and which will cope with increased fuel loads
© Shell International Petroleum Company Ltd 2009. All rights reserved.
Acknowledgements
I would like to thank all my co-authors and other colleagues in Lubricants in Shell, particularly:
Simon Dunning, David Green, Selda Gunsel, Ahmed Guven, Dougie Miller, Glyn Roper, Paul Savage, Pete Sant, Keith Selby, Cameron Watson
& former colleagues: Dick Coy, John Bell, Laurence Scales & University contacts: Martin Priest, Peter Jimack
robert.i.taylor@shell.com
Any questions ?
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