Tribology and Energy Efficiencys04.static-shell.com/.../pdf/tribology-and-energy-efficiency.pdf · Tribology and Energy Efficiency R.I. Taylor1, E. Nagatomi2, ... Journal of Engineering

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


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



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



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)



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


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



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



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



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)*



Ref: R.I. Taylor, IMechE Proc Part J, Journal of Engineering Tribology, Vol 213, pp 35-46, 1999

Viscosity variation with shear rate



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



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



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


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


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


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


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


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


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



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



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



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




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



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



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


ISO 220 mineral oils

ISO 220 PAO

ISO 220 PAG

Radicon worm gear efficiencytest at 100ºC


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




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


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


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


Future Trends

Increased use of surface texturing – for reduced friction We are investigating this using textured MTM discs


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


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


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


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

[email protected]

Any questions ?

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Tribology and Energy Efficiencys04.static-shell.com/.../pdf/tribology-and-energy-efficiency.pdf · Tribology and Energy Efficiency R.I. Taylor1, E. Nagatomi2, ... Journal of Engineering