Self-replenishing, Self-repairing Solid Lubrication Technology for Fuel Cells

Emmanuel Y.A. Wornyoh and C. Fred Higgs III

Particle Flow and Tribology LaboratoryMechanical Engineering

Dowd/ICES SeminarOctober 21, 2005

Outline of Presentation

Need for new compressor technology in fuel cells

Oil-free, self-replenishing lubrication

Proposed Research: Developing oil-free,

self-replenishing lubrication for compressor

Mobile Fuel Cell (FC) Power Systems

Benefits of Fuel Cell Compressors:

Increased fuel efficiency

Increased power density

Reduced stack size

Reduced cost

Compressed Air

Compressor** Fuel Cell*

Fuel Cell Automobile*

*Daimler-Chrysler**http://www.mechanology.com

Needs of Fuel Cell Compressors:

More powerful positive-pressures

Extreme rotational speeds (~160 mph)

Oil-free lubrication

Lubrication Mechanism for Fuel Cell Compressor

Motivation Energy efficiency

Replacing oil lubricants with powder lubricants

Freeing depleting global oil supplies

Environmental concerns Testing “green”

lubricants

Tribological Advantages Stability, sustainability in

extreme environments (-100 oC to ~800 oC)

++

U

Bearing

Shaft

h

Lube

++

U

Bearing

Shaft

h

Lube

ShaftBearing

Fuel Cell Compressor (Courtesy Mechanology,LLC)

Journal Bearing

Problem StatementNeed for a novel lubrication system for fuel cell

compressorsOil-free lubrication to avoid fuel cell stacks contaminationLubrication must be adequate at extreme speeds (~160mph)

and high loads

Proposed MethodDesign and construction of tribometerConduct experimentsDevelopment of the powder lubrication (CVFC) model

Predicts tribological parameters (e.g., friction and wear)

Film Transfer Experiments: Pellet-On Disk with Slider

•Higgs III, C.F., Ph.D Thesis, Rensselaer Polytechnic Institute, 2001

•Kaur, Higgs, and Heshmat, STLE Tribology Transactions, 2001

Measurables

1) Pad friction

2) Pellet friction

3) Pellet Wear

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

0 . 0 0 E + 0 0

5 . 0 0 E - 1 2

1 . 0 0 E - 1 1

1 . 5 0 E - 1 1

2 . 0 0 E - 1 1

2 . 5 0 E - 1 1

Wea

r Fa

ctor

,

S a m p le B

S a m p le C

0

0 . 0 5

0 . 1

0 . 1 5

Fri

ctio

n C

oeffi

cien

t, s

S a m p l e B

S a m p l e C

C o n t a c t P r e s s u r e , P c ( k P a )

1 0 2 0 . 1 4 9 . 6

1 0 2 0 . 1 4 9 . 6

C o n t a c t P r e s s u r e , P c ( k P a )

( a )

( b )

Contact Pressure Pc (psi)

Contact Pressure Pc (psi)

Past Powder Results: Friction and wear versus slider contact pressure

Dep

osit

ion

rate

(cm

3 cm

-1k

g-1)

Fri

ctio

n co

effi

cien

t

Proposed Research

Experimentation

Modeling

Pellet holder

Slider

Disk

Drive system

Experimentation: Pellet-On Disk with Slider Tribometer

Measurables:

1) Pad friction

2) Pellet friction

3) Pellet wear

Pellet holder

Slider

Disk

Drive system

Experimentation: Pellet-On Disk with Slider Tribometer(in construction)

Tribometer (Photograph)

(Boric acid powder )

Control Volume Fractional Coverage (CVFC) Model

XVFKXVKXVFkdt

dXhA

h

hVFK

h

hVFK

h

hVFk

dt

dhA

seseppp

sespeppp

)1(

)1(

max

maxmaxmax

RateOutput

FilmPowder -

RateInput

FilmPowder

Rate Storage

FilmPowder

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

TiC Disk

Lubricant Film

Journal Bearing

V

Pellet-on Disk:Deposits solid lubricant (by wearing)

Slider Pad

Slider Pad:Supports bearing load

MoS2 pellet

Fp

Fs

Wornyoh, E.Y.A., & Higgs, C.F., III, Proceedings of World Tribology Congress III, 2005

Conservation Law

Solving the CVFC Model

)exp(1

)()(

t

KKFKF

KFtX

peppess

pp

VKKFKF

Ah

peppess )(max

)( peppess

ppss KKFKF

KFX

Time Constant

Solution = Fractional Coverage

Steady State Fractional Coverage

Adopting the Linear Rule of Mixtures

pdrypp

sdryss

XX

XX

,lub,

,lub,

Dickrell, P.L., Sawyer, W.G., and Erdemir, A., Journal of Tribology, 2004

Pellet coefficient of friction

Slider coefficient of friction

Current and Proposed Research

Construction of tribometer

Pellet-on-disk with slider experiments

Powder lubrication modeling

Acknowledgements

The Dowd/ICES PhD fund at CMU

The Pennsylvania Infrastructure for Technological

Innovation (PITA)

Mechanical Engineering Machine Shop

Members of the Particle Flow & Tribology Laboratory