Extended Operation of Stirling Convertors at NASA Glenn ...

Glenn Research Center at Lewis Field

Extended Operation of Stirling Convertors at NASA Glenn Research Center

International Energy Conversion Engineering Conference August 2, 2011

Salvatore Oriti NASA Glenn Research Center

RPT – Thermal Energy Conversion Branch


Introduction

Advanced Stirling Radioisotope Generator (ASRG) being developed by Lockheed Martin, DOE, Sunpower, NASA GRC • 4 times more efficient than thermoelectric

conversion • Requires ¼ amount of Pu-238 for same electrical

power output • Two Advanced Stirling Convertors (ASCs) operating

up to 850 °C hot-end temperature • 130 We from 2 heat source modules (beginning-of-mission, current best estimate)

ASRG Flight Unit Design Image Courtesy of Lockheed Martin Space Systems

GRC Provides Technical Support for ASC Life and Reliability: • Structural benchmark testing • Vibration testing • High-temperature materials • Magnet life testing • Convertor extended operation

38 free-piston Stirling convertors, 18 ongoing

Piston Position Telemetry

Shunt

PRD

GMV

GPHS

ASC

ACU

Heat Source Support

SDU

AC Power

Analog Telemetry HarnessDC Power

Connector to SV

TLM/Command to SV


Ongoing Stirling Convertor Testing Purpose: • Generate performance data over tens of thousands of hours to observe long-term trends • Support reliability database

Discovery 12 proposed missions : 7 years + 3 years max storage (87,000 hours) Outer planet missions : 17 years (150,000 hours)

Convertors Nominal Operating

Temperatures (Hot/Cold, °C)

Nominal Per-Convertor Power Output

(We)

Convertor Output Voltage (Vrms)

Supplier Date Initiated

Per-Convertor Runtime

(Hrs) As of July 1, 2011

TDC #13 & #14 650/80 65 85 Infinia Jun 2003 60,000 TDC #15 & #16 Mar 2005 49,000 ASC-0 #3 & #4 650/90 75 25

Sunpower

Aug 2007 25,000 ASC-E #2 &# 3

(ASRG-EU) 625/70 65 11 Nov 2008 19,000

ASC-E #1 & #4 650/70 65 11 Dec 2009 10,000 ASC-E2 #1*

850/50 80 15

Mar 2010 6,200 ASC-E2 #2 Feb 2010 2,700

ASC-E2 #3 & #4 Aug 2010 800 ASC-E2 #5 & #6 Aug 2010 4,800

ASC-E2 #7 Nov 2010 2,100 ASC-E2 #8 Jun 2011 20

*ASC-E2 #1 delivery delayed due to heater head manufacturing flaw


Convertor Test Station

ASC-E2

ASC-E2

Cold end fluid plumbing

Circulators Cold-end and alternator

housingtemp control

Test Rack • Operator controls • Data acquisition • Software protection • Hard-wired protection • Automated error notification via email and text messaging • UPS and generator backup

Example ASC-E2 Test Station ASC-E2

Heat Collector Heat Input

Cold-Side Adapter Flange (CSAF) Heat Rejection

Alternator Electricity Output


Test Methodology • 24/7 Operation • Data acquisition:

2-second – All parameters recorded once every two seconds, for transient or 24-hr period evaluation

5-min – Each parameter’s 2-second data averaged over 5-minute period, recorded once per hour, for long-term performance data evaluation

• Maintain constant operating conditions (during extended operation):

• Off-nominal operation included: Performance mapping Operating frequency variation Heat input variation Controller variation Individual temperature variation

Parameter Control Methods

Hot-end temperaturePID control, thermocouple feedback

Constant heat input, heater power feedbackCold-end temperature Circulator with fluid temperature PID control

Alternator housing temperature Auxiliary surface heaters

Fluid heat exchanger

Piston amplitudeAC Bus power supply voltage setpoint

Zener-diode controller DC output setpointASC Controller Unit (ACU, flight method)


0

10

20

30

40

50

60

70

80

90

100

TDC

#14

Pow

er O

utpu

t (W

e)

0 10000 20000 30000 40000 50000 60000 0

10

20

30

40

50

60

70

80

90

100

Hours of Operation

TDC

#13

Pow

er O

utpu

t (W

e)

TDC #13 & #14 Performance Data

1135

9 : C

hang

e C

ircul

ator

Set

tings

1842

4 : L

ow te

mpe

ratu

re C

heck

out

2002

4 : F

ull T

emp.

Ope

ratio

n

2203

9 : N

ew H

eate

r

3288

8 : A

djus

t Pis

ton

Am

plitu

de

4187

9 : R

ack

Cal

ibra

tion

4539

0 : A

djus

t Pis

ton

Am

plitu

de

5163

3 : R

ack

Cal

ibra

tion

5412

4 : N

ew H

eate

r, R

ack

Upg

rade

s

5647

1 : R

ack

Cal

ibra

tion

Technology Demonstration Convertors (TDCs) #13, #14

Regenerator oxidation

• Longest-running convertor pair (60,000 hours each) • Pressure joints welded at 19,000 hours, but helium fill tube remains • Periodic charge pressure adjustments required, manifests as “saw-tooth” output • Zener diode controller hardware drift required adjustment to maintain piston amplitude

Pres

sure

join

ts

wel

ded

Upgraded power measurement

instrumentation


Set

poin

t adj

ustm

ent

1st s

et o

f rac

k im

prov

emen

ts

Set

poin

t adj

ustm

ent

Set

poin

t adj

ustm

ent

2nd

set o

f rac

k im

prov

emen

tsB

egin

AC

U c

ontro

l

Beg

in h

eat i

nput

eff

ect t

est

Res

ume

AC

bus

con

trol

Beg

in o

pera

tion

on c

ards

1 &

332

hou

rs o

f ED

U 2

AC

U c

ontro

l

Rem

oved

J2

conn

ecto

r sav

er

24 h

ours

ope

ratio

n on

car

ds 1

& 2

Rec

alib

ratio

n

Beg

in n

atur

al c

onve

ctio

n te

stE

nd n

atur

al c

onve

ctio

n te

st

Res

ume

oper

atio

n on

car

ds 1

& 2

0

10

20

30

40

50

60

70

80

0

10

20

30

40

50

60

70

80

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

ASC

-E #

3 Po

wer

Out

put (

We)

ASC

-E #

2 Po

wer

Out

put (

We)

Hours of Operation

ASRG EU (ASC-E #2, #3)

• Fully hermetically sealed before delivery (pressure joints and pinched fill tube) • 19,000 hours each (13,000 on Lockheed Martin controller) • Test rack improvements required during initial operation • Tests conducted for Lockheed Martin in support of controller development and flight system development • Good repeatability on ASC controller unit (ACU) with consistent operating conditions

Rack improvements required

Steady

Controller development tests Repeatable

Performance

ASC-E #2 & #3 Performance Data


0

5

10

15

20

25

30

0

5

10

15

20

25

30

0 2000 4000 6000 8000 10000 12000 14000 16000 18000 20000

ASC

-E #

3 Ef

ficie

ncy

(%)

ASC

-E #

2 Ef

ficie

ncy

(%)

Hours of OperationEff iciency = (gross heat input)/(alternator power output)

ASRG EU (ASC-E #2, #3)

• 25% conversion efficiency demonstrated at the system level on flight-like controller • Repeatable and constant conversion efficiency over 19,000 hours of operation

Rack improvements required

Steady

Controller development tests

Repeatable Performance

Efficiency = Alternator output power/Heater power

ASC-E #2 & #3 Performance Data


0 1000 2000 3000 4000 5000 6000 0

10

20

30

40

50

60

70

80

90

100

Hours of Operation

ASC

-E2

#1 P

ower

Out

put (

We)

ASC-E2 #1 Performance Data98

: Sh

utdo

wn/

Res

tart

98 :

Initi

ated

Per

form

ance

Map

ping

296

: Ini

tiate

d Ex

tend

ed O

pera

tion

BO

M L

R

605

: Ini

t Fre

quen

cy S

wee

p

888

: Shu

tdow

n

1143

: R

esta

rt w

ith C

ompa

ct H

eat S

ourc

e13

04 :

Initi

ated

Per

form

ance

Map

ping

1476

: In

itiat

ed E

xt O

pera

tion

BO

M L

R

2629

: O

pera

ting

Poin

t Adj

ustm

ent

3223

: O

pera

ting

Poin

t Adj

ustm

ent

3849

: A

C b

us V

aria

tion

Test

4696

: Sh

utdo

wn/

Res

tart

BO

M L

R

4889

: Sh

utdo

wn/

Res

tart

BO

M L

R

5182

: Sh

utdo

wn/

Res

tart

BO

M L

R53

24 :

Tem

pora

ry A

C lo

ss

5520

: Te

mpo

rary

AC

loss

6097

: N

atur

al F

requ

ency

Tes

t61

93 :

Tran

s B

ack

to B

OM

LR

ASC-E2 #1

• Fully hermetically sealed before delivery (pressure joints and pinched fill tube) • 6,200 hours – majority at 850 °C • Known heater head flaw and helium leakage • AC bus voltage requires adjustment to negate helium leakage

Other tests

Adjustments due to helium leakage

Other tests

Ambient temp disturbance BOM = Beginning of Mission

EOM = End of Mission LR = Low Rejection HR = High Rejection


0

10

20

30

40

50

60

70

80

90

100

ASC

-E2

#6 P

ower

Out

put (

We)

0 1000 2000 3000 4000 5000 0

10

20

30

40

50

60

70

80

90

100

Hours of Operation

ASC

-E2

#5 P

ower

Out

put (

We)

ASC-E2 #5 & #6 Performance Data

855

: Che

ckou

t Com

plet

e, In

itiat

ed P

erf M

ap

1194

: In

itiat

ed E

xten

ded

Ope

ratio

n at

BO

M L

R

1914

: O

pera

ting

Poin

t Adj

ustm

ents

2202

: A

lt H

ousi

ng T

emp

Adj

ustm

ent

2323

: Sh

ut D

own/

Res

tart

EOM

LR

2480

: #5

Hea

t Sou

rce

Failu

re

2665

: Sh

utdo

wn/

Res

tart

EOM

LR

2833

: M

oved

to E

OM

HR

3019

: Se

vera

l Ope

ratin

g Po

int A

djus

tmen

ts

3192

: Sh

utdo

wn/

Res

tart

BO

M H

R

3486

: Sh

utdo

wn/

Res

tart

BO

M H

R

3823

: Te

mpo

rary

AC

loss

4233

: A

djus

ted

to B

OM

LR

ASC-E2 #5, #6

• Fully hermetically sealed before delivery (pressure joints and pinched fill tube) • 4,800 hours – all at 850 °C • Steady when maintaining constant conditions

Perf mapping Checkout testing

Heat source failure

Circulator fluid changes

Repeatable Performance

Circulator fluid changes

Ambient temp disturbance

BOM = Beginning of Mission EOM = End of Mission LR = Low Rejection HR = High Rejection


ASC-E2 #7 & #8 • Slated for durability testing

Stress components to above-nominal levels • Removable alternator housings for inspection

ASC-E2 #7& #8 with removable alternator housings

Heat Collector

Cold-side Adapter Flange (CSAF)

Removable Alternator Housings

Test Description Purpose

Start/Stop Cycling August 2011

Cycle the convertor repeatedly through start/stop cycle to exacerbate any possible wear induced before gas bearings become fully functional

Centrifugal Acceleration

September 2011

Expose operating convertor to 30 g static load using a centrifuge facility to observe response in moving components

Contact Events During Launch

Simulate a limited number of contact events during off-nominal launch by adjusting piston amplitude

Piston Overstroke Simulate a limited number of contact events with desired relative velocities between the piston and displacer with short-term controller disconnection


Conclusion GRC is supporting life and reliability database for free-piston Stirilng conversion via extended convertor operation Ongoing convertor operation: • 18 convertors (4 TDCs from Infinia, 14 ASCs from Sunpower) • 350,000 total convertor hours of operation • 218,000 on Infinia units and 132,000 on Sunpower units

Demonstrating steady convertor performance requires precise maintenance of operating conditions Sources of disruption : • Investigative tests

Varying operating frequency, hot-end temp, cold-end temp • Hot end control method

Constant heat input mode requires more user-adjustment than constant temperature mode Long-term transients in hot end insulation were observed

• Support facility Open-bath circulator fluid concentration drifting Nuisance shutdowns (instrumentation failure, EMI, power outages) Ambient temperature fluctuations due to room HVAC


Acknowledgements

This work was funded through the NASA Science Mission Directorate and the Radioisotope Power Systems Program Office. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the authors and do not necessarily reflect the views of the National Aeronautics and Space Administration.

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