h. epstein - shirtbutton-sized gas turbines . the engineering challenges of micro high speed...

8/10/2019 H. Epstein - Shirtbutton-sized Gas Turbines . the Engineering Challenges of Micro High Speed Rotating Machinery

1/23

R E P O R T

DOCUMENTATION

PAGE

Form

Approved

O M B N o.0704-0188

Publ ic reporting burden for this

collection

of nformation s est imated to average hourer response,

ncluding the

t ime

for

reviewing

nstruct ions,

searching

existing

data

source

gathering an d maintaining

th e

data needed, an d completing an d reviewing the collection

of

nformation.

Send

comments

regarding this burden

est imate

or an y other aspect

of

h

coltection

of

nformation ncluding suggestions for reducing

this

burden , to Washington Headquarters Services.

Directorate

for

Information

Operat ions an d Reports, 1215 Jeffers

Davis

Highway

uite

1204'

Arl ington.

VA 22202-4302,

an d

to

the Officeof Management

an dBudget,

PaperworkReduct ionProject(0704-0188),Washington,DC

2 0 5 0 3 .

1 . AGENCYUS EONLYLeaveBlank)

2 . RE P O RT

DA TE

12/4/00

3 .

RE P O RT T YP E ANDDATESC O V E R E D

FINAL

0 1

May

95

-

31

ul

00

4.

TITLE

AND SUBTITLE

Micro

Gas

Turbine

Generators

5 .

FUNDING

N U M B E R S

G r antD AAH0 4 -9 5 -1 -0 0 9 3

6 .

A U T H O R S

A.

Epstein,

.

Breuer,J.Lang,

M.Schmidt,

S.

Senturia,

M.

Spearing,

C.Tan,.Waitz

7 . P E RFO RM I NGORGANIZATION

NAM E ( S)ANDA D D R E S S ( E S )

Massachuset tsInst itute

o f

Techno l ogy

77

Massachuset tsAve.,

31- 264

Cam br idg e ,

M A

0 2 1 3 9

8 . P E RFO RM I NG ORGANIZATION

RE P O RT

N U MB ER

9 .

SP O NSO RI NG

/

MONITORING

AG EN C Y

NAME(S) AND

ADDRE SS( E S)

U.S.

Arm y

Research

Office

P.O.Bo x12211

Research

Triangle

Park,

NC

7709-2211

1 0 . SPONSORING/MONITORING

AG E NCY

R E P O R TNUM BE R

ARO 33888.2-CH-MUR

1 1 . SUP P L E M E NT ARYNOTE S

12a.

^3TR,BUT,O

O6

M|NT

ATEwENTA

Approved for

Publ ic Release

Distr ibut ion

Unlimited

12b. DISTRIBUTIONCO DE

1 3 .

A B S T R A C T

Ma x i mum

20 0

words)

MI T

ha s

developed

th e

technology

fo r

micro-gas

turbine

generators.

hesear emill imeter-to centimeter-size

heat

engines

fabricated with

semiconductor

industry

micromachining

techniques

(MEMS),

ultimately

capable

of

producing10-100

W

of

p o we r

in

es s

than

a

cubic

cent imeter.

Applicat ionsincludecompactpowersources offeringenergy an dpow erdensit iesanorderof

magni tudebetter

thancurrentbattery technology;

propulsionfor small

ai r

vehicles;

an davarietyo f

microb lowers ,

compressors ,

an d

heat

pumps.The

wo rk

w as

d iv ided

nt o8

microscale

disciplinary

areas:

1)

engine

systemsdes ign,

(2 )

turbomachinery fluiddynamics ,

(3)

combust ion,

(4 )

structures,

(5 )

bearings,

(6)

elect romechanics ,

(7)

silicon

fabricationtechnology,

an d

(8)microfabricat iono f

high

temperaturematerials

an d

structures.Advancesinthe

disciplinary

technologies enabledth e

design

an dconstruction

o f

a

proof-of-principle

d em o

engine .

hi s

2 0m msquareby

4m m

thicksimple

cycle

ga s

turbine

is

designed

to

produce

about1 1

gramso f

thrustor 17 wattsof shaft

power.

he design turbine

inlet

temperatureis

1600

K

an d

therotationalspeeds

1.2M

rpm. tth e

conclusionof

thisMURI,th efirstengines

had

beenbuilt

an d

were

justbeginningtesting.

companionmicroturbogenerator isa

fe w

monthsbehind

th e ga s

turbine.

1 4 . S U B J E C TT E R M S

M E M S ,

compact

power ,microturbine,

micromotor,

microcombustion

1 5 . NUM BE ROFP A GE S

2 1

1 6 . PRICECO DE

17 .

ECURITY

CLASSIFICATION

O F

RE P O RT

UNCLASSIFIED

18 .

ECURITY

CLASSIFICATION

OFTHISPAGE

UNCLASSIFIED

19.

ECURITY

CLASSIFICATIONO F

A B S T R A C T

UNCLASSIFIED

20 . LIMITATIONOFABST RACT

UL

NS N7540-01-280-5500

StandardForm2 98

(Rev.

2-89)

Prescribedby ANSIStd.Z39-1298-102

DTicqui

^

LJ AXJ

tL

2 0 0 1 0 1 1 64 3


2/23

GasTurbine

Laboratory

Department

ofAeronauticsandAstronautics

Massachusetts

Institute

of

Technology

Cambridge,

MA

02139

FinalTechnicalProgressReport

on

Grant

#DAAH04-95-1-0093

entitled

MICRO

GAS

TURBINE

GENERATORS

prepared

for

US

Army

Research

Office

P.O.

Box

12211

ResearchTrianglePark,NC7709

ATTN:r.

RichardPaur

CO-INVESTIGATORS:

Dr..

K.S.Breuer

Prof.

A.H.

Epstein

(Principal

Investigator)

Prof.

J.H.

Lang

Prof.

M.A.

Schmidt

Prof.

S.D.

Senturia

Prof.

S.M.

Spearing

D r.

C.S.T an

Prof.I.A.

Waitz

PERIOD

COVERED:

pril1,1996-

July

31 ,

2000

- -_

mM1

^

W

M

.

DISTRIBUTION STATEMENT

A

Approved

fo r

Public Release

December

2000 is tr ibut ionUnl imi ted


3/23

1.0

REPORT

OUTLINE

Thisisthefinaltechnicalprogressreport

on

AROGrant

DAAH04-95-1-0093,

a

five-

year

MultidisciplineUniversityResearchInitiative

(MURI)

program.

ecausetheprogram

has

generated

lengthly

annualtechnicalreports

an da

large

numberof

technicalpublications

an dgraduatetheses

(whichareavailableupon

request)

this

final

technicalreport

is

relatively

brief.

t

consistsof four

sections

in

addition

to

this

one:

(2 )

Ashort

summary

an d

list

of

accomplishments,

(3)

a

listofparticipants,

(4)a

list

of publicationsand

theses,and

(5)

a

technical

paper

which

gives

a

more

detailedoverviewofthetechnology.

2.0SUMMARYANDACCOMPLISHMENTS

Under

this

MURI

support,

M IT has

developed

thetechnologyfo rmicro-gasturbine

generators.

hesearemillimeter-

to

centimeter-sizeheatenginesfabricatedwith

semiconductorindustry

micromachining

techniques.

s

such,

they

are

micro

electrical

an d

mechanical

systems

(MEMS)devices.

hey

also

representthefirstapplication

of

a

new

technical

field

conceivedunder

this

program,

Power

M E M S .

alculations

showthat

these

microdevicesmayultimately

becapableofproducing

10-100

Wofpower

or

10-50

gramsof

thrust

in

lessthan

acubiccentimeter.

pplicationsincludecompact

powersourcesoffering

energyan d

power

densities

an

order

of

magnitude

better

thancurrent

batterytechnology;

propulsionfo rsmallai r

vehicles;

an davarietyof

microblowers,compressors,

and

heat

pumps.

Much

of

this

technology

is

also

applicable

to

M E M S

microrocketengines

(which

are

the

enabling

technology

forverysmall

launchvehicles

and

missiles),

the

technologyof

whichcan

be

considered

derivative

of

this

program.

he

promise

of

Power

M E M S

issufficientthat

DA RPA

an dtheJapanese

governmenthavestartedprograms

in

thisareaandthatPower

M EM S

internationalworkshops

and

meetings

arenow

held.

This

technicalefforthas

been

an

admixture

of

research

and

engineering

design

since

theprojectgoalsaredevice-oriented.

he

work

is

nominally

dividedinto8principal

microscaledisciplinary

areas:

(1)

engine

systems

design,

(2 )

turbomachineryfluiddynamics,

(3)combustion,

(4)

structures,

(5)

bearings,

(6 )electromechanics,(7 )siliconfabrication

technology,

(8 )microfabricationof

hightemperaturematerials

andstructures.

T he

centerpiece

of

this

effort

ha s

been

the

design

and

construction

of

the

world's

first

M E M S

micro-gas

turbine

engine.

ealization

of

such

adevicehas

necessitated

significant

advancesinmany

disciplinary

technologies.

Some

specifictechnical

achievements

include

theestablishment

of

the

enablingbasictechnologyforan ddemonstrationof:

hefirst

M E M S

micro-gasbearing

technology,

with

speeds

above1.4M

rp m

demonstrated.

icro-high-speedturbomachinery,

transoniccentrifugalturbinesan dcompressors.


4/23

he

first

highpower

density

M E M SH

2

an d

hydrocarbonfuelmicrocombustor

technology;

400 wattsofthermalenergyin200

m m

3

hasbeen

demonstrated.

he

firstcooled

silicon

microturbine

airfoils,

which

have

operatedinagastemperatures

above

the

melting

point

of

silicon,

1800

K.

icromotor

performance

OOx

higherthanpreviously

achieved.

dvances

in

the

SO

A

ofhighaspect

ratio

silicon

etching

bya

factor

of 3-5.

he

first

multi-wafer(5-6)precision-aligned(1-2

micron)

silicon

structures.

ackagingfo rveryhigh

temperature

silicon

chips,including

high

pressurefluid

interconnections.

These

advances

in

disciplinary

technology

enabled

the

design

an d

constructionof

a

so-

called"demoengine",asaproof-of-principle.

hi s20

m m

squareby4m mthicksimple

cycle

gas

turbine

is

designedto

produce

about1 1

grams

of

thrust

or

17

watts

of

shaft

power

T he

designturbineinlet

temperature

is

1600

K

an d

therotationalspeed

is

1.2M

rpm.

t

the

conclusionof

this

MURI,

the

first

engines

ha d

beenbuiltan dwerejustbeginningtesting.

companion

microturbogenerator

is

a

few

monthsbehindthe

gas

turbine.

U S A

3

FIRSTSUPEft

US 3

S&- 3

Dem o

Gas

Turbine

Engine

This

success

of

the

technological

advances

made

inthisM U R I

promptedDA RPAto

match

MURIfunding.

iscussionswith

the

Army

suggest

that

further

6.1

an d

6.2

support

m ay

be

available

both

tocontinuethe

basicresearchand

to

beginthetechnologytransitionprocess.IT

ha sinitiated

discussionswithseveralpotentialindustrial

partnersinterested

indeveloping

the

technology

further.


5/23

3.0

CONTRIBUTINGTECHNICAL

PERSONNEL

Name

Faculty:

Prof.

Kenneth

Breuer

Prof.John

Brisson

Prof.

Alan

H.Epstein

Prof.Jeffrey

H.Lang

Prof.

MartinA.

Schmidt

Prof.

Stephen

D .

Senturia

Prof.

MarkS.Spearing

Prof.

IanA.

Waitz

Technical

Staff.

D r.

G.K.Ananthasuresh

(Post

D o c )

D r.

A.

Ayon(Post

Doc)

D r.

Christopher

Cadou

(Post

D o c )

D r.

FredricF.

Ehrich

(Senior

Lecturer)

EricEsteve(Visiting

Eng.)

D r.Anthony

Forte

D r.

GautamGauba

(PostDoc)

D r.Reza

Ghodssi

D r.

YifangGong(PostDoc)

D r.PaulHolke

(Post

Doc)

D r.

Eugene

W .

Huang

(LL

Tech.

Staff)

D r.

Stuart

A.

Jacobson

(Engineer)

D r.

Ravi

Khanna

(ResearchEng.)

D r.

CarolLivermore(Post

Doc)

StevenLukachkoResearchEng.)

D r.

Paul

Maki

(L L

Tech

Staff)

D r.

JamesPaduano(PrincipalEng.)

LarryRetherford,

Jr .

LLTech.Staff)

D r.

Choon

S.

T an(Principal

Eng.)

D r.Steven

Umans

D r.RichardWalker(C.S.Draper

Labs)

Paul

Warren

D r.

WenjingYe(Post

D o c )

Patrick

Yip

(L LTech

Staff)

D r.

Xin

Zhang

(Post

Doc)

Primary

Discipline

Fluids,Instrumentation

Thermal

Systems,

Heat

Transfer

EngineDesign,

Fluids

Electromechanics

(iFab,

Processes

(jFab,Processes

&

Materials

Structures,Materials

Combustion

jiFab

Modeling

uFab,Processes

Fluids,Combustion

RotorDynamics ,

Design

Fluids,

Engines

^Fabrication

Combustion

^Fabrication

Turbomachinery

^Fabrication

Structures

Fluids

^Fabrication

Electromechanics

Combustion

^Fabrication

Controls

Packaging

Turbomachinery

Electromechanics

Gas

Bearings

Electronics

Structures

M AVAvionics

(^Fabrication


6/23

Graduate

Students:

Dye-ZoneChen

Kuo-Shen

Chen

DongwonChoi

Luc

Frechette

T od

Harrison

KashifKhan

Jin-Wook

Lee

Chuang-Chia

Lin

ChunmeiLiu

Kevin

Lohner

AdamLondon

AmitMehra

BrunoMiller

Jose

Miranda

Hyug-SooMoon

Steve

Nagle

DJ.Orr

BaudoinPhilippon

Ed

Piekos

John

Protz

Nicholas

Savoulidis

GregoryShirley

Chris

Spadaccini

ShaunSullivan

DavidTang

Sheng-Yang

Tzeng

Douglas

Walters

Chee

W eiWong

^Fabrication,

Instrumentation

Structures

Structures

&

Materials

Turbomachinery

Systems

Structures,Packaging

Turbomachinery

Combustion

(^Fabrication

Turbomachinery

Structures

&

Materials

Packaging

Turbomachinery

Structures

Electric

Bearings

Structures

&Materials

ElectricMachinery

FluidBearings

Turbomachinery

Fluids

Modelling

Engine

Systems

Bearings

Turbomachinery

Combustion

Fluids,HeatTransfer

Instrumentation

Combustion

Structures

Bearings


7/23

4.0

LIST

OF

PUBLICATIONSANDTHESES

1 .

rinh,T .,Large-ScaleTest

of

Position

Detection

fo r

Microengine

Rotor,"

Technical

Report,

M ay1996.

2.

steve,E.,

"Secondary

Flow

SystemModeling,"TechnicalReport,1996.

3.

aitz,I.A.,

Gauba,G.an d

Tzeng,

Y.-S.,

"Combustorsfo r

Micro-GasTurbineEngines,"

Proc.

of

theInternational MechanicalEngineering

Congress

and

Exposition,

November

1996.

4.

pearing,

S.M .,

Chen,K.S.,

"Micro-GasTurbineEngineMaterialsan dStructures",

presentedat21

s

t

Annual

Cocoa

BeachConferencean dExpositionon

Composite,

Advanced

Ceramics,

Materialsan dStructures,

January

1997.

5.

pstein,

A.

H.,

an d

Senturia,

S.

D .,

"MacroPowerfrom

MicroMachinery",Science,Vol.

276,

M ay

1997,p.1211.

6.

pstein,Senturia,Anathasuresh,

Ayon,

Breuer,

Chen,

Ehrich,

Esteve,Gauba,

Ghodssi,

Groshenry,

Jacobson,

Lang,Lin,Mehra,MurMiranda,

Nagle,

Orr,Piekos,

Schmidt,

Shirley,Spearing,

Tan,

Tzeng,

Waitz,"PowerM E M SndMicroengines,"IEEE

Conference

onSolidStateSensors

and

Actuators,

Chicago,

EL,

June1997.

7.

pstein,Senturia,Al-Midani,

Anathasuresh,

Ayon,

Breuer,

Chen,Ehrich,Esteve,

Frechette,

Gauba,

Ghodssi,

Groshenry,

Jacobson,Kerrebrock,Lang,Lin,London,Lopata,

Mehra,

Mur

Miranda,Nagle,

Orr,Piekos,

Schmidt,

Shirley,

Spearing,

Tan,

Tzeng,Waitz,

"Micro-Heat

Engines,

Gas

Turbines,an d

Rocket

Engines",

AIAA97-1773, 8th

AIAA

Fluid

Dynamics

Conference,

4thAIAAShear

Flow

ControlConference,

Snowmass

Village,CO,

June

29-July

2,1997.

8.iekos,E.S.,

Orr,

DJ.,Jacobson,

S.A.,

Ehrich,F.F.and

Breuer,K.S.,"Designan d

Analysis

of

Microfabricated

High

SpeedGas

Journal

Bearings,"

AIAAPaper

97-1966,

28thAIAA

Fluid

DynamicsConference,

SnowmassVillage,CO,June29-July2,

1997.

9.

aitz,

I.A.,

Gautam,

G.,

Tzeng,

Y.-S.,

"Combustors

fo rMicro-GasTurbineEngines,"

ASMEJournal

ofFluids

Engineering,

Vol.

120,

March

1998.

10.

Mehra,

A.,

an d

Waitz,I.

A.,

"Development

of

a

HydrogenCombustor

for

a

MicrofabricatedGasTurbineEngine",Solid-State

Sensoran d

Actuator

Workshop,Hilton

Head

Island,

SC,

June

1998.

11.

Jacobson,

S.A.,"Aerothermal

Challenges

intheDesignofaMicrofabricatedGas

Turbine

Engine",AIAA98-2545,

29thAIAA

Fluid

Dynamics

Conference,Albuquerque,NM ,

June

1998.

12 .

Ayon,A.A.,

Lin,C.C.,Braff,

R.,Bayt,

R.,

Sawin,

H.H.

an d

Schmidt,

M .,

"Etching

Characteristics

and

Profile

Control

in

a

T im eMultiplexed

Inductively

Coupled

Plasma

Etcher,"

1998

Solid

State

Sensorsand

Actuator

Workshop,Hilton

Head,

SC,

June

1998.

13.

Huang

E.,

"Thermal

DesignTrade

Studies

fo r

ASilicon

Turbojet

Engine ,

(Initial

Report),October

1998.

14.Piekos,E.S.

&

Breuer,

K.S.

"Pseudospectral

Orbit

Simulation

of

Non-IdealGas-

LubricatedJournalBearingsfor

MicrofabricatedTurbomachines,"

PaperNo.

98-Trib-48,

presentedattheTribologyDivis ionof

T he

AmericalSocietyof

MechanicalEngineersfo r

presentationat

the

JointA SME /ST LETribology

Conference,

Toronto,

Canada,

October

1998.

Also,to

appear

inJournal

of

Tribology.


8/23

15.Ayn,A.A.,Ishihara,K.,

Braff,

R. ,

Sawin,H.H.and

Schmidt,

M .,

"Applicationof

the

Footing

Effectin

the

Microfabrication

of

Self-Aligned,Free-StandingStructures,"

45th

InternationalAVS

Symposium,

Baltimore,

M D ,

November1998.

16.Mehra,

A.,

Jacobson,

S.

A.,Tan,C.

S.,

an d

Epstein,

A.

H.,

"AerodynamicDesign

Considerations

forthe

Turbomachinery

of

a

Micro

Gas

Turbine

Engine",

presented

at

the

25*

Nationalan d

s

t

InternationalConference

on

Fluid

Mechanics

andPower,New

Delhi,

India,

December1998.

17.

Chen,K-S,Ayon,

A.

A.,

Lohner,

K.

A.,

Kepets,

M .

A.,Melconian,

T .

K.,

an dSpearing,S.

M .,

"Dependenceof

Silicon

Fracture

Strength

andSurfaceMorphology

onDeepReactive

IonEtchingParameters",presentedatthe

M RS

fallMeeting,Boston,M A,December

1998.

18 .Ayn,A.A.,Ishihara,K .,Braff,R. ,

Sawin,H.H.

andSchmidt,M .,"DeepReactive

Io n

Etching

of

Silicon,"

Invited

Presentation

at

Materials

Research

SocietyFallMeeting,

Boston,

M A,

November

30-December

4,

1998.

19.Mirza,A.R.

an dAyn,A.A.,

"Silicon

WaferBonding:

K eyto

ME MS

High-Volume

Manufacturing,"

SENSORS,

Vol.

5,

No.

12 ,

December

1998,

pp.

24-33.

20.

Chen,K-S,

Ayon,

A.,

and

Spearing,

S.M .,

"SiliconStrengthTestingfo r

Mesoscale

StructuralApplications",MRSProceedings,

Vol.

518,1998,

pp.

123-130.

21.

Lin,C.C.,

Ghodssi,

R. ,Ayon,A.A.,

Chen,D.Z.,Jacobson,

S.,

Breuer,K.S.,Epstein,A.H.

&

Schmidt,

M.A.

"Fabrication

an d

Characterization

ofa

Micro

Turbine/BearingRig",

presentedatM EM S'99,January1999,Orlando,FL .

22.

Mirza,

A.R.

an dAyn,A.A.,"SiliconWafer

Bonding:T heK eyEnablingTechnologyfo r

M E M S

High-VolumeManufacturing,"FutureFab

International,Issue

6,

January1999,

pp.

51-56.

23.Ayn,

A.A.,Braff,

R. ,

Lin,

C.C.,

Sawin,

H.H.

and

Schmidt,

M .,"Characterization

of

a

Time

Multiplexed

Inductively

Coupled

Plasma

Etcher,"

Journal

of

the

Electrochemical

Society,

Vol.

146,

Number

1,

January

1999,

pp .

339-349.

24.

Ayon,A.A.,Ishihara,K,.

Braff,

R.A.,Sawin,H.H.,

Schmidt,

M.A.,

"Microfabricationan d

Testing

of

SuspendedStructuresCompatiblewithSilicon-on-Insulator

Technology",

submitted

to

the

Journal

of

VacuumScienceandTechnology,February1999.

25.

Mirza,

A.

R. ,

Ayon,

A.

A.,

"Advanced

Silicon

Wafer

Bonding,"

Micromachine Devices,

Vol.

4,No.2,

February

1999.

26.Ayon,

A.A.,

Epstein,A:H.,Frechette,

L.,

Nagle,

S.

an d

Schmidt,

M .A.,

"Tailoring

an d

Controlling

Etch

Directionality

in

aDeep

Reactive

Ion

Etching

Tool,"

submitted

to

Transducers'99,

Sendai,

Japan,

June

1999.

27.

Mehra,

A.,

Waitz,I.A.,Schmidt,

M .

A.,

"Combustion

Tests

in theStaticStructure

of

a

6-

Wafer

MicroGasTurbineEngine,"1999SolidStateSensoran d

ActuatorW orkshop,June2-

4,1999.

28.

Mirza,A.R.an dAyon,

A.A.,

"SiliconWafer

Bondingfo r

M E M S

Manufacturing,"

Solid

StateTechnology,Vol.42 ,No.9,

pp.73-78,August

1999.

29.

Mehra,

A.,

Ayon,

A.

A.,

Waitz,I.

A.,

an d

Schmidt,

M.

A.,"Microfabricationof High

Temperature

Silicon

Devices

Using

WaferBonding

and

Deep

Reactive

Io nEtching",


9/23

IEEE/ASME

Journal

ofMicroelectromechanical

Systems,

Vol.

,

No.

2,June

1999,

pp.

152-160.

30.

Ayn,

A.

A.,

Chen,

D.-Z.,

Braff,

R.

A.,Khanna,

R. ,

Sawin,

H.

H.,

Schmidt,M.

A.,

"A

novel

IntegratedProcessUsingFluorocarbon

Films

DepositedwithaDeep

Reactive

Ion

Etching

(DRIE)

Tool,"

Fall

Meeting

of

the

Materials

Research

Society,

Boston,

MA,

November

29

-

December

3,1999.

31.

Chen,K-S,Ayon,A.,andSpearing,S.M .,"Controllingan dTestingthe

FractureStrength

of

Silicon

atthe

Mesoscale",tobe

published

inthe

Journal

of

the

American

Ceramic

Society,

1999.

32 .

Ayn,A.A.,

Braff,

R.A.,

Bayt,

R. ,Sawin,H.H.,Schmidt,M.A.,"Influence

of

Coil

Power

in

the

EtchingCharacteristics

in

a

High

DensityPlasma

Etcher,"

Journal

ofthe

ElectrochemicalSociety,

Vol.

146,

No.

7,

1999.

33.

Epstein,

A.H.,

Jacobson,S.A.,Protz,J.M.,Frechette,

L.G.,"Shirtbutton-Sized

Gas

Turbines:

heEngineering

Challenges

ofMicro

High

Speed

RotatingMachinery,"

Plenary

Lecture,

th

nternational

Symposium

on

Transport

Phenomena

and

Dynamics

of

Rotating

Machinery(ISROMAC-8),

Honolulu,

HI,

March2000.

34.

Epstein,

A.H.,"TheInevitabilityofSmall,"AerospaceAmerica,March2000,pp .30-37.

35.

Ayon

A.A.,

Zhang

X.,

andKhanna

R.,

"Ultra

Deep

AnisotropieSiliconTrenches

Using

Deep

Reactive

Io n

Etching

(DRIE),"

Hilton

Head

Solid-State

Sensor

Actuator

Workshop,

HiltonHeadIsland,SC,

June

4-9,

2000,

pp .

339-342.

36 .

Epstein,A.H.,Jacobson,S.A.,Protz,

Livermore,C,Lang,J. ,Schmidt,M.A.,

"Shirtbutton-

Sized,Micromachined,

GasTurbine

Generators,"

presentedat39

th

Power

Sources

Conference,CherryHill,NJ,June

2000.

37.

Ayon

A.A.,

Protz

J.M.,

Khanna

R,

Zhang

X.,

an d

Epstein

A.H.,

"Application

of

Deep

SiliconEtching

an d

Wafer

Bonding

in

the

MicroManufacturing

of

Turbochargers

an d

Micro-

Air-Vehicles,"the 47

th

International

Symposiumofthe

American

VacuumSociety,Boston,

M A,October

2-6,2000.

38 .

Zhang

X.,

GhodssiR. ,ChenK-S,AyonA.A.,an d

Spearing

S.M.,

"ResidualStress

Characterization

of

ThickPECVD TEOSFilmforPowerM E M SApplications,"HiltonHead

Solid-State

Sensor

Actuator

Workshop,

Hilton

Head

Island,

SC,June4-9,2000,

pp .316-

319.

39.Frechette,

L.G,

Jacobson,S.A.,

Breuer,

K.S.,

Enrich,

F.F.,

Ghodssi,

R. ,Khanna,

R. ,

Wong,

C.W.,

Zhang,

X.,

Schmidt,

M.A.,

an d

Epstein,

A.H.,

"Demonstration

of

a

Microfabricated

High-SpeedTurbine

Supported

on

Gas

Bearings,"

Hilton

Head

Solid-StateSensor

&

Actuator

Workshop,

HiltonHeadIsland,

SC,

June

4-9,2000,

pp .43-47.

40.

Orr,D.J,an dJacobson,S.A.,"High

Order

GalerkinModels

for

Gas

Bearings,"

submitted

to

the

Proceedings

oftheASME/STLE

Tribology

Conference,

paperASME/2000-TRIB-131,

Seattle,WA,

October2000.


10/23

41 .

MehraA.,

Zhang

X.,

Ayon

A.A.,

Waitz

I.A.,an d

Schmidt

MA.,

"A

Through-Wafer

Electrical

InterconnectforMulti-Level

M EM SSevices," JournalofVaccumScience

and

Technology

B,

Vol.18 ,

No.5,

pp .2583-2589,September/October

2000.

42 .

MehraA.,Zhang

X.,

Ayon

A.A.,Waitz

I.A.,SchmidtM.A.,and

Spadaccini

CM.,

"A

6-

Wafer

Combuston

System

for

a

Silicon

Micro

Gas

Turbine

Engine,"

to

appear

in

Journal

of

MicroElectroMechanicalSystems,

December

2000.

43 .

Ayon,

A.A.,"T ime

Multiplexed

Deep

Etching,"

Sensors,

Vol.

16 ,No.

9,

September 2000,

pp.4-73.

44.Ayon,

A.A.,

Bayt,

R.L.,

Breuer,

K.S.,

"Deep

Reactive

Io n

Etching:

Promising

Technology

for

Micro

and Nanosatellites,"submitted toJournalofSmart

MaterialsandStructures:

SpecialIssueon MEMSinSpace,June

2000.

45 .GhodssiR.,

Frechette

L.G.,

Nagle

S.F.,Zhang

X.,

Ayon

A.A.,SenturiaS.D. ,an dSchmidt

M.A.,

"Thick

Buried

Oxide

inSilicon

(TBOS):An

IntegratedFabrication

Technology

for

Multi-Stack

Wafer-Bonded

M EM S

Processes,"

Proceedings

of

the1999

International

Conferenceon Solid-StateSensors

and

Actuators,

Sendai,

Japan,

June

7-10,1999,

pp.

1456-

1459.

46 .

Ghodssi

R,

ZhangX.,

Chen

K-S,

Spearing

S.M.,

an d

Schmidt

M.A.,

"Residual

Stress

Characterization

of

Thick

PECVD

OxideFilmforM EM S

Application,"the46

th

International

Symposiumofthe

American

Vacuum

Society,

Seattle,

WA,

October

25-29,

1999.

47 .

Chen

K-S,Zhang

X .,

an d

Ghodssi

R,"Residual

Stress

an d

Failure

Modeling

of

Thick

PECVD Oxide

Films

forM EM S

Application,"

Proceeding

ofthe

st

jointChina/Taiwan

Symposium

on Microsystem

Technology,Tainan,Taiwan,

M ay

2000,

pp .264-269.

48 .

Chen

K-S,

Zhang

X.,

an d

Spearing

S.M.,

"Processing

of

Thick

Dielectric

Films

for

Power

M EM S:Stressan d

Fracture,"

Materials

Scienceof

Microelectromechanical

System

(MEMS)

DevicesIII,

Materials

Research

SocietySymposium,

Boston,

M A,

November27-

December

1,2000.

49.

Khanna

R,

Zhang

X.,Protz

J.M.,andAyon

A.A.,

"Microfabrication

Protocols

fo r

Multi-

Stack

Projects

Involving

Deep

Reactive

Io n

Etchingand Wafer-Level

Bonding,"

Sensors,

accepted,willbe

published

in

March

issue

of

2001.

50.

Ayon

A.A.,ZhangX.,

an d

Khanna

R,

"AnisotropieSilicon

Trenches30 0um

to500um

DeepEmployingTime

Multiplexed

DeepEtching

(TMDE),"SensorsandActuators,

will

be

published

in

the

special

issue

for the

Hilton

Head

Solid-State

Sensor

&

Actuator

Workshop.

51.Zhang

X.,GhodssiR. ,Chen

K-S,

Ayon

A.A.,an d

SpearingS.M.,"Stress

an d

Fracture

in

ThickTetraethylorthosilicate

(TEOS)

Films,"

Sensors

and

Actuators,

will

be

published

in

the

specialissuefor

the

HiltonHead

Solid-State

Sensor

&

ActuatorWorkshop.

52 .

Savoulides,N.,

Breuer,

K.S.,

Jacobson,

S.,Ehrich,

F.F.,

"Low-OrderModels

fo r

VeryShort

Hybrid

Gas

Bearings,"

ASM E

Paper

2000-TRIB-12,

presented

at the

STLE/ASME

TribologyConference,

Seattle,

W A,

October

2000;also

to

appear

inJ.

ofTribology.


11/23

4.1:

raduateTheses

1 .

roshenry,

C,

"PreliminaryDesignStudyof

a

Micro-GasTurbineEngine,"M.S.

Thesis,

M IT

Departmentof

Aeronautics

an d

Astronautics,

September

1995.

2.ehra,A.,"ComputationalInvestigationan dDesignofLow ReynoldsNumberMicro-

Turbomachinery,"

M.S.

Thesis,

M IT

Department

of

Aeronautics

an d

Astronautics,

June

1997.

3.

ur

Miranda,J.O.,

"Feasibility

of

ElectrostaticBearingsforMicroTurboMachinery,"

M.Eng.

Thesis,M IT

Department

ofElectrical

Engineering

an d

Computer

Science,

December

1997.

4.zeng,Y-S,"A nInvestigation

of

MicrocombustionThermalPhenomena, M.S.Thesis,

M IT

Department

of

Aeronauticsan dAstronautics,June

1997.

5.

hirley,G.,AnExperimental

Investigation

of

a

Low

ReynoldsNumber,High

Mach

NumberCentrifugal

Compressor,"

M.S.Thesis,M IT DepartmentofAeronautics

and

Astronautics,

September1998.

6.

hen,

K-S,

"MaterialsCharacterizationan dStructuralDesignofCeramicMicro

Turbomachinery, Ph.D.Thesis,M IT Departmentof

MechanicalEngineering,February

1999.

7.

in ,C.C.,"Development

of

a

MicrofabricatedTurbine-Driven

Air

Bearing

Rig,"Ph.D.

Thesis,

M IT Department

of

Mechanical

Engineering,

June

1999.

8.ohner,

K.,

"Microfabricated Refractory

CeramicStructures

for

Micro

Turbomachinery,"

M.S.

Thesis,

M IT

Department

ofAeronauticsan d

Astronautics,

June

1999.

9.

hen,D-Z,

"Designan d

Calibration

of

an

InfraredPositionSensor,"M.S.

Thesis,

M IT

Department

of

MechanicalEngineering,

June

1999.

10.Walters,

D .,"CreepCharacterization

of

SingleCrystal

Silicon

in

Support

of

the

M IT

Microengine

Project,"

M.S.

Thesis,

M IT Departmentof

MechanicalEngineering,June

1999.

11.Mehra,A.,"Development

of

a

HighPowerDensityCombustion

Systemfo raSiliconM icro

Gas

TurbineEngine,"Ph.D.Thesis,M IT

Department

of

Aeronauticsan dAstronautics,

February

2000.

12.Orr,D.J.,"Macro-ScaleInvestigationof

HighSpeed

Gas

Bearings

fo r

M E M S

Devices,"

Ph.D.Thesis,

M IT

Departmentof

Aeronauticsan dAstronautics,

February2000.

13.

Piekos,E.,"Numerical

Simulation

of

Gas-LubricatedJournalBearingsfo rMicrofabricated

Machines,"

Ph.D.

Thesis,

M IT Department

of

Aeronautics

an dAstronautics,

February

2000.

14.Savoulides,

N.,

"LowOrderModelsforHybridGas

Bearings,"M.S.Thesis,

M IT

Department

of

Aeronautics

an d

Astronautics,February2000.

15.Liu,C,"DynamicalSystem

Modelingofa

MicroGasTurbineEngine, M SThesis,M IT

Department

of

Aeronautics

an d

Astronautics,

June2000.

16.Lee,Jin-Wook,

"NumericalSimulation

of

a

HydrogenMicrocombustor, M.S.Thesis,


12/23

M IT

Department

of

Aeronautics

an d

Astronautics,M ay

2000.

17.Nagle,S.F.,

"Analysis,

Design

an d

Fabrication

O fAnElectricInductionMicromotorfo r

a

MicroGas-Turbine

Generator",

Ph.D.Thesis,

M IT

Department

ofElectrical

Engineering,

October

2000.

18 .

Frechette,

L.G.,

"Development

of

a

Microfabricated

Silicon

Motor-Driven

Compression

System,"

Ph.D.

Thesis,

M IT

DepartmentofAeronauticsan dAstronautics,

September

2000.

10


13/23

5.0OVERVIEWTECHNICAL PAPER

SHIRTBUTTON-SIZED

GA S

TURBINES:

T HEENGINEERING

CHALLENGESOF

MICRO

HIGH

SPEED

ROTATINGMACHINERY

AlanH.Epstein,Stuart

A.

Jacobson,

Jon

M.Protz,LucG.

Frechette

GasTurbineLaboratory

MassachusettsInstitute

of

Technology

Cambridge,

MA

02139,USA

Fax

617-258-6093,

[email protected]

KEYWORDS: MEMS,

microturbine,microcombustion,

microbearings

ABSTRACT

MIT

sdeveloping

micro-electro-mechanical

ystems

(MEMS)-based

gas

turbine engines,

turbogenerators,

and

rocket

engines.Fabricatedin largenumbers

in parallel

using

semicon-

ductormanufacturing

techniques,

hese

engines-on-a-chip

re

basedon micro-highspeedrotatingmachinerywithpower den-

sities

approaching

those

of theirmore

familiar,

full-sized

breth-

ren.

T he

micro-gas

turbine

is

a

2

cm

diameter

by

3

mm

thick

Si

or

SiC

heat

engine

designed

toproduceabout

10

W

of

electric

poweror0.1

Nof

thrustwhile

consumingabout

15

grams/hr

of

H

2

ater

versions

may

produce

up

to

100

W

using

hydrocar-

bo nfuels.

hi s

paper

gives

an

overview

ofthe

project

and

dis-

cusses

he

challengesaced

inthedesign

an d

manufacture

of

high

speed

microrotating

machinery.

luid,structural,bearing,

and rotordynamics

design

issuesare reviewed.

INTRODUCTION

Highspeed

rotatingmachinery

comesin

manysizes.

n

recent

years

much

emphasis

has

been

placed

on

the

large

end

of

the

business

-0mdiameter

hydroelectric

turbines,

30 0

ton

ground-based

ga sturbinegenerators,

3

m

diameter

aircraft

en-

gines.

hese

machines

are

engineered

to

produce

hundreds

of

megawatts

of

power.

T he

focus

of

this paper

isthe oppositeen d

ofthe

rotating

machine

sizescale,devicesa

few

millimeters

in

diameter

and weighinga gram or

two.

These machinesareabout

one

thousandth

the linearscaleoftheir

largest

brethren an dthus,

since powerlevel

scales

withfluid

mass

flowrate

an dflowrate

scaleswith intakearea,they should produceaboutonemillionth

the

powerlevel,a few

tens

of

watts.

T heinterestinrotatingmachinery

of

thissize

rangeis

fu-

eled by

both

a

technology

pushan da user

pull.

T hetechnology

push

is

the

development

of

micromachining capability based

on

semiconductor

manufacturing

techniques.

This

enables

the

fab-

rication

of

complexsmall

parts

andassemblies

-devices

with

dimensions

in

the1-10,000

micron

size

range

with

micron

an d

evensubmicron

precision.

uc h

parts

are

produced

usingpho-

tolithographydefined

featuresan d

many

can

be

madesimulta-

neously,

holding

ou tthe

promiseof low

production

cost.

uc h

assemblies

re

knownasmicro-electrical-mechanicalystems

(MEMS)

an d

have

been

the

subject

of

thousands

of

publications

overthe lastdecade.arlywork

in

M E M Sfocusedonsensors

an dmanydevicesbased

on

this

echnology

are

inlarge

scale

production

(such

as

pressure

sensorsand

airbag

accelerometers

for

automobiles).

orerecently,workhasbeendoneon

actua-

tors

of

varioussorts.luid

handling

is

receiving

ttentions

well,

for

exampleMEMS

valvesare

commerciallyavailable.

T he

user

pull

is predominatelyone

of

electric

power.There

is

proliferation

ofsmall,

portable

electronics

-

computers,

digi-

talassistants,cell

phones,

GPS

receivers,

etc.

-

which

require

compact

energysupplies.hedemandisfo renergy

supplies

whoseenergy

and

power

density

exceed

that

of

thebest

batter-

ies

available

today.

Also,

the

continuing

advance

in

microelec-

tronics

permits

the

shrinking

of

electronic

subsystems

of

mobile

devices

uc h

as

robots

nd

ai r

vehicles.

hese

mall,

nd

in

some

cases

very

small,

systems

requireincreasing compact

power

an d

propulsion.

Fo rcompactpower

production,

hydrocarbonfuels

burned

inai rhave

20-30

timesthe

energy

density

of

thebestcurrent

lithium

chemistry-based batteries.

Thermalcycles

andhigh

speed

rotating

machinery

offerhigh

powerdensity

compared

to

other

power

productionschemes

and

MEMS

technology is

advancing

rapidly.

ecognizing

thesetrends,

group

at

M IT

began

re-

search

inthe mid1990's

ona

MEMS-based"micro-gas

turbine

generator"capable

of

producing tens

ofwatts

of

electrical power


14/23

from

acubic

centimeter-sized

package

Epstein

an d

Senturia,

1997;

Epstein

et

al

1997).

ince

that

time,relatedeffortshave

been

started

on

a

micromotor-driven

ai r

compressor

and

abi -

propellant,

liquid

rocket

motor

which

utilize

muchof

the

same

technology

as

the

gas

turbine.

he

attractiveness

of

these

de-

vicesispredicatedtoalargepartontheir

high

powerdensity.

T he

power

density

is

function

of

the

designof

the

rotating

machinery.hi s

paperreports

on

this

work

in

progress,

with

emphasison the

rotating

machinery

development.

SYSTEM

DESIGNCONSIDERATIONS

At

length

scalesofa

few millimeters,thermodynamiccon-

siderationsar eno

differentthanfo rmuchlargerdevices.

Thus,

high

power

densityfo ra

simple

Brayton

cycle

requires

high

com-

bustorexit

temperatures

(1400-1800K)

and

pressure

ratiosabove

2 and preferably

above

4.Thisca n

be

seeninthethermodynam-

ic s

ycle

calculation

llustratedinFigure whichshows

ha t

severaltensofwattscan

be

expected

froma

machine

with

a

m m

2

intakearea.

T he

power

density

ofrotatingmachinery,

both

fluid

an d

electric,

scale

with

the

square

of

the

peripheral

speed,

asdoesthestressin the rotor.Thus,

high

power

densityimplies

highly

stressedrotating

structures.

eripheralpeeds

of300-

600m/sare neededtoachieve pressureratiosinthe2:1-5:1per

stage

range,

assuming

centrifugalturbomachinery.This implies

rotorcentrifugal

stresses

on

the order of

hundreds

of

megaPascals.

These

peripheral

speeds

in

rotors

a

few

millimeters

in

diameter

requirerotationalratesonth eorderof

1-3

millionrpm.

hus,

low frictionbearingsare needed.Also, highspeed rotatingma -

chinery

generally

requires

high

precision

manufacturing

to main-

tain

tight

clearanceand

good

balance.For

millimeter-sized m a-

chines

tohave

th e

samefractional

precisionasmeter-sized

de-

vices,

th e

geometric

precision

requirementsare on theorder

of

a

micron.

ABraytoncycle

is

notth eonlychoiceforpowerproduc-

tionfrom

MEMS-based

thermodynamic

cycle.ankine,

Stirling,

an dOtto

cycles

canallbeconsideredcandidates.he

advantages

an d

disadvantages

of

each

differ.

Theprincipal

ad-

vantages

of

the

Brayton

cycle

ar e

simplicity

(only

on emoving

part,

a

rotor,

is

needed),highest

power

density

(duetothe

high

throughflowMach

numberan d

thus

high

mass flow

per

unitarea),

and the availability ofcompressedai r

for

coolingan d

other

uses.

T heprimary

disadvantage

is

ha t

aminimum

component

effi-

ciency

(on

the

order

of

40-50%)mustbemetfo r

the

cycle

to

be

Table

1:

Micro

vs .

MacroMaterial

Properties

1

3

.2 .

c

o

CO

0.8.

u.

o

.6-

'5

4:1

Pressure

Ratio

0.6

1200K

Q.

03 0.4-

Ni-based

Titanium

Macro Micro

Super

Alloys

Alloys

(Micro)

Ceramics

Silicon

Centrifugal

Stress

[V^TpJ

(m/s)

33 0 42 0

42 0

1000

(670)

ThermalStress

2 .7

x

10"

3

1.2

xlO

3

2. 0x10"

3

0.9 x

10"

3

[ctE/a

f/y

]

(1.1

xlO

-3

)

Stiffness

-26 -25

-95

-70

[E/p](MPa/Kgm"

3

)

M ax

Temp(C)

limiting

factor

-1000

(creep)

-300

(strength)

-1500

(oxidation)

-600

(creep)

10

0

0

0

ShaftP o w e rOutpu t(watts)pe rm m

2

Inlet

Area

50

Figure

1:

Simple

cycle

ga s

turbine

performance

with

H2fuel.

self-sustaining;onlythencanne t

power

he

produced.

As thisis

a

first-of-its-kind

effort

thatchallenges

the

capabilities

ofsev-

eral

disciplines,

especially

microfabrication,

simplicity

isa

very

desirable

irtue.

he

Brayton

ycle

eems

most

attractive

in

thisregard.

MechanicsScaling

Thermodynamic considerations

do not

changeas

machines

become

smaller,butmechanicsconsiderationso.tructural

mechanics,

fluid

mechanics,an d

electromechanicsall change

in

a

manner

important

to

machine performance

an ddesign as

length

scaleisdecreased by

a

factorof

order1000.

For

structural

mechanics,

it

is

th echangeinmaterialprop-

ertieswithlengthscalethat

is

mostimportant.

A relatively small

se tofmaterialsar eaccessibletocurrentmicrofabricationtech-

nology.

Themostcommonlyused

by

far

is

Silicon(Si),

while

SiliconCarbide(SiC)an dGallium

Arsinide(GaAs)areusedto

datemainlyin nicheapplications.ormanyof

themetrics

im -

portanttohighspeedrotating

machinery,

Si

an d

Si Caresupe-

riortomost

commonly

usedmetals

such

as

steel,ti tanium,an d

nickel-basedsuperalloys(Spearingan dChen,

1997).

Thisca n

be seenin Table whichcomparesmaterialsin termsof

proper-

tiesimportantforcentrifugalstress,thermalstress,

vibrations,

an d

hot

strength(Figure

2)

(Mehra,

2000).

Materials

such

as

Si

an d

S iC

are not

used

inconventional-sizedrotating

machinery

because

theyarebrittle.Theirusablestrengthisdominatedby

flaws

introduced

inmanufacturing

an dflaw

population

gener-

allyscales with

partvolume.However, thesematerialsare

avail-

able

intheformrequiredfo rsemiconductormanufacture

(thin

wafers)

withanessentiallyperfect,

singlecrystal

structure.

s

such,

they

have

high

usablestrength, values aftermicromachining

above

4

GP a

have

been

eported

Chen

etal

1998),

everal

times higher than

that

ofrotating

machinery

metallic

alloys.

This

higher strengthcan

be used

either to

realize

higher

rotationspeeds

(and

thus

higher

power

densities)

t

constant

geometry,

or

to

simplifythe

geometry

(and

thus

th e

manufacturing)

at

constant

peripheral

speed.

o

date,we haveadoptedth elaterapproach

for

expediency.

n

dditional

materials

consideration

is

ha t

thermal

shock

increaseswith

length

scale.Thus,materials

which

haveveryhightemperaturecapabilitiesbut

ar e

no t

considered

high

temperature

structural

ceramicssuch

as

lumina

or

sap-

phire)

du eto

their

susceptibility

to

thermal

shock,

ar e

viable

at

themillimeterandbelow

ength

scales. Since

these

have

no t


15/23

aW

CO

I1 0

2

10

C VD

Si C

/V\-HastelloyX

;n n

V

nconel

60 0

20 0

SI

1

\

60 000 040 0

Temperature

K )

\

C VD

SiC

25~10

5

-22S5+\


16/23

Starter/

Flame

ue

ue

enerator

Hnlrfpfs

u,Su

r Compressor /

olders

Man

,

d

lnject

Va nes

Blades / **

lnlet

Rotor

Turbine

urbine

xhaust

enterl ine

Nozzleotor

ozzle

f

Rotation

Va nes

Blades

Figure

4:

Baseline

design

microengine

cross-section.

fromhu b

to

tip.

urrent

technology

canyield

a

taper

unifor-

mityof

about

30-50:1

with

eitherapositiveornegativeslope.

The

constraints

onairfoilheights

are the

etch

rate(about3

m i-

crons

perminute)

an d

centrifugal

bending

stresstthe

blade

root.urbomachinesofsimilargeometryhavebeenproduced

with

blade

heights

ofover

40 0

microns.

The

effort

describedherein

has

been

ocussed

on

micrornachinery

which

ar e

producedwithsemiconductor

fabri-

cation

technology

(MEMS).ther

manufacturingtechniques

m ay

be

feasible

as

well,

especially

as

the

device

sizegrows

into

the

centimeter

range.

he

M E M S

approach

w as

chosen

here

because

it

is

intrinsically

highprecision

and

parallel

production,

offering

the promiseofverylow costinlarge

quantity

produc-

tion.

nitial

estimates

suggest

that

th e

cost

per

unit

power

might

ultimately

approach

that

oflargegas

turbine

engines.

GA STURBINE

ENGINE

Considerations

such

as

thosediscussed

above

led

in

1996

tothe

preliminary or "baseline"

gas

turbine

engine

designillus-

trated

in

Figure

4.

he

cm

diameter

engine

is

a

single-spool

arrangement with

a

centrifugal

compressor

an d

radial

inflowtur-

bine,separated

bya

hollowshaft

for

thermalisolation,and

sup-

ported

onai r

bearings.Ata

tip

speed

of

50 0m/s,

the

adiabatic

pressureratio

isabout4:1.

T he

compressor

is

shrouded

an dan

electrostaticstartergeneratorismountedonthetipshroud.T he

combustor

premixes

hydrogen

fuel

an d

ai r

upstream

of

flame

holdersan d

burns

lean

(equivalence

ratio

0.3-0.4)

so

that

th e

combustorexittemperatureis60 0K,withinthetemperature

capabilities

ofan

uncooled

S iC

turbine.

Thedesign philosophy

was

to

use

a high

turbine

inlet

temperature

to

achieve

acceptable

work

perunitai r

flow,

recognizingthatcomponent

efficiencies

wouldberelatively

low

an d

parasitic

losseshigh.Witha4mm

rotordiameter,theunitw assizedtopump

0.15

gram/secof

air

an d

produce

10-20

wattsof

power

at

2 .4

million

rpm.heen -

gine

is

constructed

from

8

wafers,

diffusion-bonded

together.

The

turbine

wafer

wa sassumed to

beSiC.

This

design

served

as

abaselinefo r

the

research

in componenttechnologiesdescribed

inlatersections.

On e

primary

goalofth e

projectis

to

show

that

aMEMS-

based

gas turbine

is

indeed possible,

bydemonstrating

benchtop

operation

ofsuchadevice.

This

impliesthat,for

afirst

demon-

stration,itwould

be

expedientto

trade

engineperformancefo r

simplicity,

especially

fabrication

simplici ty.

y

1998,

th e

req-

uisite

technologies

were

judged

sufficiently

advanced

tobegin

building

such

an

engine

with

th e

exception

of

fabrication tech-

nology

for

SiC.Since Si

rapidlylosesstrength

above 95 0

K,this

becomes

an

upper

limit

to

the

turbine

rotor

temperature.ut

95 0K

is

toolow

acombustorexittemperaturetoclosetheen-

gine

cycle

(i.e.

produce

net

power)

with

th e

component

efficien-

ciesavailable,

so

turbinecooling

is

required.Thesimplest

wa y

to

cool

the

turbine

ina

millimeter-sized

machine

is

toeliminate

the

shaft,an dthus

conductthe

turbineheatto

the compressor,

rejecting

the

heat

to

the

compressorfluid.hi s

has

thegreat

advantageofsimplici tyandthegreatdisadvantageoflowering

the

pressure

ratio

of

the

now non-adiabaticcompressor

from 4:1

to

2: 1

with

a

concomitantdecreasein

cyclepoweroutput

an d

efficiency.ThisexpedientarrangementisreferredtoastheH

2

demo

engine.

t

is

a

gas

generator/turbojet

designed

with

the

objectiveof

demonstrating

th econceptofaM E M Sgasturbine.

It doesno t

contain

electrical

machinery.

The

H

2

demo

enginedesign

is

hown

inFigure5.he

compressor

an d

turbine

rotor

diameters

re

8

m m

and

6

mm

respectively

(sincethe turbinedoesnotextractpowerto

drive

a

generator,

itssize

andthus

its

coolingloadcouldbereduced).

The

compressordischarge

ai r

wraps

around

the

outside

ofthe

combustor

to

cool

the

combustor

walls,capturing

the

waste

heat

an d

so

increasing

the combustorefficiencyand

reducing

the ex -

ternalpackage

temperature.

T herotorissupported

on

a

journal

bearing

on the

periphery

ofthe

turbine

and

by

thrust

bearings

on

the

rotor

centerline.The

peripheral

speed

ofthe

compressor

is

500m/ ssothatth erotationrateis

1.2Mrpm.xternalairis

usedto

start

the

machine.

With

400

microntallairfoils,the unit

is

sizedto

pump

0.36

grams/sec

of

air,

producing

11 rams

of

thrust

or17wattsof

shaft

power.

irst

testsofthis

engine

are

scheduledfo r

2000.

COMPONENT

TECHNOLOGIES

Given

the

overview ofthe system design

requirements

out-

lined

above,the

followingsectionsdiscuss

technical

consider-

ationofthe component

technologies.

For

each

component,the

overriding

designobjective

is

to

devisea

geometry

which

yields

th e

performance

required

by

the

cycle

while

being

consistent

with

near-term

realizablemicrofabricationtechnology.

A

problemcommonto

allofthecomponenttechnologies

is

that

of

instrumentation

an d

testing.

t

device

sizes

of

mi -

Start ing Fuel

.air

in

por t

Com pressor Diffuser

Inlet

\

an e

Combustor

Exhaust

Turbine

1mm

Nozzleguide

vane

Figure

5:

H

demoenginewith

silicon,

cooled

turbine.


17/23

crons

to

hundreds

of

microns,

instrumentation

cannotbe

pur-

chasedan dtheninstalled,ratheritmustbefabricatedintothe

devicefromthe

start.

While

technicallypossible,this

approach

ca neasily

doubleth e

complexity

ofthemicrofabrication,

nd

thesedevices

are

already

on

theedge

ofthestate-of-the-art.T o

expedite

the

development

process

therefore,

whenever

possible

development w as

done

insuperscalerigs,rigslarge

enough

for

conventional

instrumentation.

Bearings

Asinallhighspeedrotatingmachinery,th erotormust be

supported

fo r

all

radial

and

axialloads

seen

inservice.nnor-

ma l

operation

this

load

issimply

theweightoftherotortimes

theaccelerations

imposed

(9

g's

for

aircraftengines).

fa

small

device

isdropped

onahard

floor

from two meters,severalthou-

sand

g's

are impulsively applied.An additional

requirement

for

portableequipment

is

thatth esupport

beindependent

of

device

orientation.he

bearings

an danyassociated

equipment

must

also

be

compatiblewith

the microdevice's

environment,

high

temperature

in

the

case

of

the

gas

urbine

engine.

revious

M E M S

rotating

machines

havebeen

mainly

micromotors

turn-

in g

atsignificantlyowerspeedsha nofinteresthereand

so

couldmake

dowithdryfriction

bearingsoperating

forlimited

periods.

The

higher

speeds

needed

and

longer

lives

desired

for

micro-heatenginesrequirelow frictionbearings.Bothelectro-

magnetic

an d

ai rbearings

have beenconsidered

for

this

applica-

tion.

Electromagneticbearings

can

beimplementedwitheither

magnetic or

electric

fieldsproviding

therotorsupportforce.

Mag-

netic

bearings

have

tw o

disadvantages

fo r

this

application.

First,

magnetic materials

are

no t

compatible withmost

microfabrication

technologies,

limitingdevicefabricationoptions.

econd,Cu -

rie

point

considerations

limit

the

temperatures

twhich

mag-

netic

designscan

operate.ince

these

temperature

ar e

below

those

encountered

in

th e

micro-gas

turbine,

cooling

would

be

required.

Fo r

thesereasons,effortw asfirst concentrated on de-

signsmploying

electric

fields.hese

designs

examined

di d

not

appear

promisingin

that

th eforcesproduced

were

marginal

comparedtothe bearingloads

expected

(Miranda,

1997).

Also,

sinceelectromagnetic bearingsare

unstable,

feedbackstabiliza-

tion

is

needed,adding

tosystem

complexity.

Air

bearings

supporttheir

loadon

thin

ayersofpressur-

ized

air.

f

the

ai r

pressure

is

supplied

from

an

external

source,

the

bearingis

known

as

hydrostatic.ftheai r

ressure

is

de-

rivedfromthe

motion

ofthe rotor,thenthe designishydrody-

namic.

Hybridimplementations combiningaspectsofboth

ap-

proaches

are

also

possible.

Since

the

micromachines

in

question

includeai rcompressors, bothdesignsareapplicable.Eitherap-

proach

ca n

readilysupport

theloads

of

machines

in

this

size

rangeandca nbeused

on

hightemperaturedevices.ll

else

beingthe

same,the

relative

load-bearing capability

ofan

ai r

bear-

ing improvesassizedecreases

since

the surfacearea-to-volume

ratio(andthusthe

inertial

load)scalesinversely

with

size.Ro -

to ran dbearingdynamicsscalingis

more

complex,

however.

T he

simplest journal

bearing

is

a

cylindricalrotor

within

a

close-fittingcircularjournal

Figure

6) .

his

eometrywa s

adopted

firstasthe

easiest

to

microfabricate.

Other,

more

com-

plex

variations

might

include

wave

bearings

an d

foil

bearings.

The

relevant

physicalparametersdeterminingthe

bearingbe-

haviorare the length-to-diameterratio

(L/D)\

the

gap

between

th erotor

nd

journal

atioed

to

he

rotor

radiusc/R);nd

nondimensional

forms

oftheperipheralMach

numberofthe

rotor(a measure

of

compressibility),

th e

Reynolds

number,

an d

themassoftherotor.

ora

bearing

supported

onahydrody-

namic

film,he

oa d

bearing

capability

cales

nverselywith

(c/R)

5

which

tends

todominatethe design

considerations.

Load

bearing

alsoscales

withL/D

(Piekos

et

al.,

1997).

T he

designspace

available

fo rth emicrorotating

machin-

ery isconstrained

by manufacturing capability.

We havechosen

tofabricate

the rotorand journal

structure

atthe

same

time

to

facilitatelo w

cost,

volumemanufacturing.

Themost

important

constraint

is

the

etching

ofverticalsidewalls.

y

pushing

the

limitations

of

published

etching

technology,w ehave

been

able

toachievetaper ratiosofabout30:1

-50:1

on narrow etched

ver-

tical

channels

for

channel

depths

of

300-500

microns

as

shown

inFigure

7

(Lin

et

al.,

1999).

hi s

capability

definesthebear-

ing

lengthwhilethe taperratiodelimitsth ebearing

gap,

c.

T o

A

C

D

Hydrodynamic

pressureforce

Figure6 :Gasbearing

geometry

and nomenclature.

The

gap,

c ,

is

greatly exaggerated

in this

figure.

S-:-;7v,i

Figure7:Narrow trenches can

be

etchedto serveas

journal

bearings.


18/23

Air

Exhaust

Ar

(4)

Instrumentation

Port(4 )

LAYERS

Forward

Foundation

Ar

Inlet

-

Forward

Thrust

Bearing

Turbine

Aft

Thrust

.

Bearing

&Side

Pressurization

Aft

Foundation

Figure 8a:

Explodedviewof five

layers

comprising

the

turbine

bearing

rig.

minimize

gap/radius,the

bearing

should

be

on the

largest

diam-

eter

available,theperipheryof

the

rotor.

he

penalty

fo r

the

high

diameter

is relatively

high

area an dsurface

speed

(thusbear-

in g

drag)

an d

low

UD

(therefore

reduced

stability).

In

the

radial

turbineshowninFigure3,

the journal

bearing

is30 0

microns

long

with

an

UDof0.075,

c/Rof0.01,

an d

peripheral

Mach

number

of

1.

hi s

relativelyshort,

wide-gapped,

highspeed

bearing

is

well

outsideth e

range

ofanalytical

an dexperimental

resultsreportedinthe

gas

bearingliterature.

Stability

is

an

importantconsideration

fo rall

highspeed

rotatingmachines.

When

centered,

hydrodynamicbearings

are

unstable,speciallytlow rotational

speed.

Commonly,uc h

bearings arestabilized

by the

application ofaunidirectional

force

which

pushes

therotor

toward

the

journalwall,

as

measured

by

th e

eccentricity,

the minimumapproachdistanceofthe rotorto

th e

wall

as

a

fractionof th eaverage

gap

(0=

centered,

=wall

strike).At conventional

scale,

the

rotorweight

is

often

thesource

of

this

side

force.

Atmicro

scale,

(1 )

the rotorweightis

negli-

gible,

an d

(2 )

insensitivity

to

orientation

is

desirable,

so

we

have

adopteda

scheme

which

usesdifferential

gas

pressuretoforce

therotor

eccentric.

xtensive

numericalmodeling

of

these

microbearing

flows

have

shown

that

the

rotor

willbe

stableat

eccentricitiesabove0.8-0.9(Piekosan dBreuer,

1998).

For

th e

geometryof

the

turbinein Figure

3,

the

rotor

must

thus

operate

between

1-2 micronsfrom the journalwall(Piekos

et

al.,

1997).

Thisimplies

that

deviations

from

circularity

of

the

journal

an d

rotormustbesmallcomparedto

1micron.

T otestthese

ideas,

tw ogeometricallysimilarturbine-bear-

Thrust-bearing

supplyplenum

Forward

Exhaust

n

J

st

bearing

JSp Af tthrust

f|||| bearing

Pressurizat ion

plenum

Figure

8b :

Five-layermicroturbinebearingrigwith

4

mm

dia

rotor.

in gtest

rigs

have

been

built

and

tested

using

the

samebearing

geometry,

on e

atmicroscale witha4mm diameter

rotor

and the

otheramacroscale

unit

26

times

larger.T hemacroversion

wa s

extensivelyinstrumented for pressure

and

rotormotionmeasure-

ments

(Orr,

999).

T he

microturbine

bearing

test

rig,

hownin

Figure8,consistsoffivestackedlayers,eachfabricatedfroma

single

Si

wafer(Linet

at.,

1999).

T he

center

wafer

is

theradial

inflow turbineofFigure 3,with a4,200micron diameter,300mi -

cronthick

rotor.

he

turbinerotor

is

aparallel-sideddiskwith

bladescantileveredfrom

on e

side.Whilesuchasimpledesignis

viablein

siliconabove

500

m/s,

the

centrifugal

stresses

are

too

high

fo r

metals withouttapering ofthe disk (so the macro version

islimitedto400 m/s).The waferson eithersidecontainthe thrust

bearingsan d plumbing

for

the side

pressurizationneeded

to

oper-

ate

the

rotor

eccentrically.

T he

outside

waferscontain

the

intake,

exhaust,an dvent

holes.

n

this

test

device

the thrust

bearingsare

hydrostatic,

pressurized

by

external

air,

an d

the

journal

bearing

ca noperate

in

eitherhydrodynamicor

hydrostaticmode.Figure 9

isdata

taken

from

an

optical speedsensor

duringhydrostaticbear-

ing operation.

Turbomachinery FluidMechanics

In

many ways

the

fluid

mechanics

of

microturbomachinery

are

similarto

that

of

large

scalemachines,

for

example,

high

t-2.

Twice

synchronous

C D

Q

-3

n

t>

4 -

C D

Q.

W

-5

Ro t

synchro

Bearing

natural

frequency

a r

nous

1

6

a.

o>-7

_l

-B

I/JIMMJW*

JUAJUIA

H

20000

40000

60000

FrequencyHz )

Figure9:

Speeddatafrommicroturbine

at

1. 2Mrpm.


19/23

3

0)

>

Q Z

N

o

z

v

Compressor

Design

Point

.

\


20/23

2 .4

2 .2

2 .0

g

1- 8

o

3

1 6

0

a

1. 4

1. 2

1.0

fflh

-s

Square

Inlet,Experiment

-SmoothIn let,

Experiment

I S ES ,

2DCFD

*

Dawes,

3D

CF D

Fue l

Fue l

ArIn

0. 4

.6

.8

.0.2

CorrectedMassFlow(fractionof

design)

1.4

Figure

12 :

Data

and

simulations

on

a

40 0

m/s

tip

speed

compressoratRe=

20,000.

dence

time

an d

effectively sets theminimum

volume

ofthecom-

bustorfo ragiven

mass

flow.

hemixingtime

ca n

scalewith

device

ize

bu t

the

chemical

reaction

times

ono t

(typically

mixing accountsformore

than90 % ofcombustorresidence

time).

Thus,the combustorvolumeisagreaterfraction of

a

microengine

than

a

large

engine,

by

afactorofabout

40

fo rthe

devices

de -

signed

to

date.

Another

difference

between

large

an d

micro scale

machines

is

the increasedsurfacearea-to-volume ratio

at

small

sizes.

hi s

impliesincreasedheat

loss

frommicrocombustors

but offersmoreareafor catalysts.

T he

design

detailsaredependent

on

th e

fuel

chosen.

ne

design

approach

taken

ha s

been

to

separate

the

fuel-air

mixing

from thechemical

reaction.

This

is

accomplishedby premixing

the

fuelwith

the

compressor

dischargeair

upstream

of

the

com-

bustorflame holders.

This

permitsa

reduction of

the combustor

residencetime

by

a

factor

of

about10

from th e

usual 5-10

msec.

T hedisadvantage

to

this

approach

is

susceptibility

to

flash-

back

fromthe

combustor

intothe

premixzone,which

must

be

avoided.

T oexpedite

the

demonstration

of

a

micro-gas

turbine

engine,hydrogen

wa s

chosenas

theinitialfuelbecauseofits

wide

flammability

limits

an d

fastreaction

time(this

is

the

same

approach

taken

by

vo n

Ohain

when

developing

the

first

jet

en -

ginein

Germany

in the1930s).Specifically,hydrogen willbum

at

equivalence

ratios

aslow as0. 3whichyieldsadiabatic com-

bustion

temperatures

below500K.ydrocarbonfuels

must

be

operated

closer

to stoichiometric

an d

therefore

at

higher

tem-

peratures,

above

2000K.hereduced

heat

load

fromth elow

temperature

combustion,

combined

with

th e

high

thermal

con-

ductivityofsilicon,means

that

silicon

(whichmeltsat1600K)

is

a

viablestructuralmaterialforaH2 combustor(Waitzeted.,

1998;

Mehra

er

a/.,1999a).

Silicon

combustorshave

been

built

which

duplicate

thege -

ometryof the enginesin

Figures

4and 5,withthe

rotating

parts

replacedwith

stationary

swirlvanes

(Mehra

and

Waitz,998).

The combustorvolumesar e66 an d190 m m

3

,respectively(Fig-

ures13

an d

14).

T he

designs

take

advantage

of

microfabrication's

Combustion

Flame

Turbine

Chamber

Holders

Nozzles

Figure

13 :

Microcombustor

which

comprises

the

static

structure

of

th e

demo

engine

ofFigure

S.

ability to

produce

similar

geometric featuressimultaneously.

Fo r

example,

the

largercombustor

ha s

90

fuelinjection

ports,

each

12 0micronsindiameter,

to

promote

uniform

fuel-air

mixing.

T he

smaller combustoroperating

at

a

power

level

of

20 0

watts

is

shownin

Figure

14 along with

a

CF D

simulation

of

the

flowfield.

These

tests

demonstrated

that

conductively-cooled

silicon

tur-

bine

vanescan survive

at

1800

K ga stemperaturesfor5

hrs

with

little

degradation(Figure

15).easurementshave

shown

that

thesemicrocombustorsca nachieve

efficiencies

inthemi d90%

range(Mehraetal.,1999b).

Data

at various

equivalence

ratios

(0 )

are

shown

in

Figure

6.(The

gaps

inthe

inesredu eto

thermocouplesailing

t

high

emperature.)Ignitionhas

ot

proven

a

problem;

a

simple

ho t

wire

ignitorha s

provensuffi-

cient,

even

at

room pressure

(Mehra,

2000).

Hydrocarbons

are more

difficult

to

burn.

nitialtests

show

that theexistingcombustorscanbumethylene

an d

propane,bu t

at

reduced

efficiencies

since

the

residence

times

are

too

short

Figure

14 :

200wattmicrocombustor.


21/23

Figure

15 :

Silicon

turbine

vanes

as

built

and

after

5

hours

in

1800

K

combustor

outflow.

for

complete

combustion.Otherapproaches

being

pursued

here

includea

stoichiometric zone-dilutionschemesimilar

to

con-

ventional

gasturbinecombustors

an dcatalytic combustion.

ElectricalMachinery

Microelectrical

machinery

isrequiredfo r

power

genera-

tion

and

as

a

prime

mover

fo r

a

starter

or

various

pumps

an d

compressors.

here

is

an

extensiveliteratureonmicroelectric

motors,

which

will

no t

be

reviewed

here,

bu t

little

work

ongen-

erators.Therequirements forth edevicesofinterestherediffer

from

previouswork

in

that

th e

power

densities

needed

are

at

least twoordersof

magnitude

abovethosereportedin thelitera-

turetodate.Also,the thermalenvironment

isgenerally harsher.

Integrating

theelectric

machine

within

th e

device(gas

turbine,

compressor,etc.)offerstheadvantageof

mechanical

simplicity

inthat

no

additional bearingsor

structures

are

requiredover

that

neededfo r

the fluid

machine.Also,

there

is

a

supplyof

cooling

fluidavailable.

As

in

the

caseof

electricbearings,

bothelectrostatic

an d

magnetic

machinedesigns

can be

considered

and,

to

first

order,

bothpproachesan

yieldaboutequivalentpowerdensities.

Sincethe

magnetic

machines

ar e

material

property-limited

at

highemperaturend

ecausef

he

hallengesf

microfabricating

magnetic

materials, lectrostatic

commonly

referred

toaselectric)

designswere

first

examined.Powerden-

sity

scales

withelectricfield

strength

(torque),

frequency,

an d

rotational

speed.The

micromachinery

of

interest

hereoperates

at

peripheralvelocities

1-2 ordersof

magnitude

higherthan pre-

viously

reported

micromotors, andso yieldsconcomitantly more

power.

lectric

machines

ma y

be

configured

in

many

ways.

Here

an

inductiondesignw aschosen(Bart

an d

Lang,

1989).

T he

operation

of

anelectricinductionmachineca n

be

un-

derstoodwith

reference

to

Figure

17

(Nagle

an d

Lang,999).

T hemachine

consistsof

tw o

components,

a

rotoran d

a

Stator.

T he

rotor

is

comprised

ofa5-20urn

thick

goodinsulatorcov-

ered

h. epstein - shirtbutton-sized gas turbines . the engineering challenges of micro high speed...

Documents