DOE/NASA/50112-72 NASA TM-100256

Hot Piston Ring Tests

.

David J. Allen Sverdrup Technology, Inc. Middleburg Heights, Ohio 441 30

and

William A. Tomazic National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 441 35

Work performed for U.S. DEPARTMENT OF ENERGY Conservation and Renewable Energy Office of Vehicle and Engine R&D Washington, D.C. 20545 Under Interagency Agreement DE-AI01 -85CE50112 *.

Prepared for Twenty-fifth Automotive Technology Development Contractors’ Coordination Meeting sponsored by the U.S. Department of Energy Dearborn, Michigan, October 26, 1987

https://ntrs.nasa.gov/search.jsp?R=19880005104 2019-03-15T07:52:03+00:00Z

HOT PISTON R I N G TESTS

Dav id J . A l l e n Sverdrup Technology

Lewis Research Center C leve land, Oh io 44135

c and

W i l l i a m A. Tomazic N a t i o n a l Ae ronau t i cs and Space A d m i n i s t r a t i o n

Lewis Research Center C1 eve1 and, Oh io 441 35

SUMMARY

A s p a r t o f t h e DOEINASA Automot ive S t i r l i n g Engine P r o j e c t , t e s t s were made a t NASA Lewis Research Center to determine whether appendix gap losses c o u l d be reduced and S t i r l i n g engine performance increased by i n s t a l l i n g an a d d i t i o n a l p i s t o n r i n g near t h e t o p of each p i s t o n dome. upgraded Mod I Automot ive S t i r l i n g Engine was used for these t e s t s . U n l i k e t h e conven t iona l r i n g s a t t he bo t tom o f t h e p i s t o n , these r i n g s opera ted i n a h i g h tempera ture env i ronment (700 " C ) . Because of t h i s , we c a l l e d them " h o t - r i n g s . " I t was necessary t h a t t hey be made o f a h i g h temperature a l l o y ( S t e l l i t e 68) and t h a t a h i g h temperature s o l i d l u b r i c a n t c o a t i n g (NASA Lewis-developed PS-200) be a p p l i e d t o the c y l i n d e r w a l l s . Engine t e s t s were r u n a t 5, 10, and 15 MPa o p e r a t i n g pressure ove r a range of o p e r a t i n g speeds. T e s t s were r u n bo th w i t h t h e h o t - r i n g s i n p l a c e and w i t h o u t them t o p r o v i d e a b a s e l i n e for comparison. A l though budget and schedule r e s t r i c t i o n s s e v e r e l y l i m i t e d t h e t e s t i n g , t h e minimum da ta t o assess t h e p o t e n t i a l o f bo th t h e h o t - r i n g s and h i g h tempera ture low f r i c t i o n c o a t i n g was ob ta ined .

An MTI-designed a3 0

I w %

Resu l t s i n d i c a t e d a s l i g h t i nc rease i n power and e f f i c i e n c y w i t h t h e ho t - r i n g s ove r t h e b a s e l i n e c o n f i g u r a t i o n . Th is i nc rease was ove r and above t h e f r i c t i o n l o s s i n t r o d u c e d by t h e h o t - r i n g s . Seal leakage measurements showed a s i g n i f i c a n t r e d u c t i o n i n leakage w i t h t h e h o t - r i n g s i n p l a c e . I n a d d l t i o n , cy1 i n d e r w a l l temperature measurements i n d i c a t e d l e s s c y l i n d e r h e a t i n g i n t h e appendix gap area--between t h e lower p i s t o n r i n g s and t h e h o t - r i n g . Approx i - ma te l y 22.4 hours o f r i ng -on -coa t ing o p e r a t i o n were recorded. A f t e r t h e i n i - t i a l b reak - in p e r i o d , wear on b o t h t h e r i n g s and t h e c o a t i n g was low. The PS-ZOO c o a t i n g - seems to o f f e r s i g n i f i c a n t p o t e n t i a h i g h tempera tures .

Both t h e h o t - r i n g and the PS-200 low f r i c t i o n should be pursued f u r t h e r . P o t e n t i a l b e n e f i t s a re S t i r l i n g eng ine , b u t t o the a d i a b a t i c d i e s e l as we

INTRODUCTION

f o r long- te rm o p e r a t i o n a t

c o a t i n g show promise and a p p l i c a b l e n o t o n l y to t h e 1 .

Advanced component techno logy t e s t i n g was done a t NASA Lewis on a Mod I k i n e m a t i c S t i r l i n g engine t h i s p a s t y e a r . gram was i n i t i a t e d i n an a t tempt to reduce the "appendix gap" l osses d e f i n e d a n a l y t i c a l l y for t h e S t i r l i n g engine.

Th is research and development p ro-

The appendix gap i s t h e volume between

t h e c y l i n d e r w a l l and t h e a c t u a l p i s t o n dome i t s e l f as shown i n f i g u r e 1 . T h i s volume i s t h e cross-hatched area. These appendix gap l o s s e s i n t h e o r y r e s u l t i n a decrease i n engine per formance, namely engine brake power and brake e f f i - c i e n c y . A p o s s i b l e way t o reduce t h i s appendix gap loss i s to i n s t a l l an add i - t i o n a l p i s t o n r i n g a t t h e t o p o f t h e p i s t o n dome t o e l i m i n a t e or reduce work ing gas f low i n and o u t o f t h e appendix gap. The conven t iona l p i s t o n c o n f i g u r a t i o n i s shown a t t h e l e f t o f f i g u r e 1 w i t h t h e h o t - r i n g m o d i f i e d v e r s i o n a t t h e r i g h t . ex t remely harsh env i ronment t h a t t h i s r i n g must w i t h s t a n d i n t h i s r e g i o n . o p e r a t i n g tempera ture i n t h i s r e g i o n i s app rox ima te l y 700 "C (1292 " F ) w i t h a hydrogen atmosphere. A h i g h tempera ture meta l a l l o y i s needed t o s u r v i v e under these c o n d i t i o n s . S t e l l i t e 68 was used f o r these t e s t s . Some form o f l u b r i c a - t i o n i s a l s o r e q u i r e d t o a l l o w adequate f r i c t i o n and wear r e s i s t a n c e f o r t h i s h o t - r i n g . A h i g h temperature d r y l u b r i c a n t developed a t NASA Lewis was adapted fo r t h i s purpose.

Th is cannot be done w i t h t h e s tandard Rulon r i n g because o f t h e The

TEST APPARATUS AND PROCEDURES

The engine used f o r t h i s t e s t i n g was a Mod I Automot ive S t i r l i n g Engine w i t h t h e a u x i l i a r i e s , except f o r t h e o i l pump and hydrogen compressor, removed. F i g u r e 2 i s a photograph showing t h e engine i n t h e t e s t c e l l on t h e t e s t s tand. The l i n e s r u n n i n g throughout t h e photo w e r e f o r research i n s t r u m e n t a t i o n .

~

F i g u r e 3 i s a schematic o f t h e englne. The reason fo r i n t r o d u c i n g t h i s schematic i s t o show where t h e m o d i f i e d components a r e l o c a t e d w i t h r e s p e c t t o t h e r e s t o f t h e engine components. M o d i f i e d p i s t o n domes were a t t a c h e d t o t h e s tandard p i s t o n bases and mod i f ied c y l i n d e r heads were i n s t a l l e d i n p l a c e o f t h e o r i g i n a l c y l i n d e r heads.

S p e c i a l M a t e r i a l s Requirements

A s ment ioned p r e v i o u s l y , some form o f d r y h i g h tempera ture l u b r i c a n t was r e q u i r e d to a l l o w o p e r a t i o n o f t h e h o t - r i n g i n t h e h i g h tempera ture c y l i n d e r env i ronment . A m a t e r i a l developed a t NASA Lewis (PS-200) looked p romis ing . PS-200 has a base o f 48 p e r c e n t chrome c a r b i d e and 32 p e r c e n t n i c k e l a l u m i n i d e w i t h 10 pe rcen t ca l c ium and bar ium f l u o r i d e e u t e c t i c , and 10 p e r c e n t s i l v e r . The chrome ca rb ide -n i cke l a lum in ide p rov ides t h e wear r e s i s t a n c e , w h i l e t h e e u t e c t i c - s i l v e r m i x p rov ides t h e h i g h temperature l u b r i c a n t . P in-on-d isk wear and f r i c t i o n t e s t s were made i n b o t h he l i um and hydrogen a t temperatures up t o 760 "C ( r e f s . 1 and 2). Severa l p o t e n t i a l r i n g m a t e r i a l s were t r i e d i n i t i a l l y b e f o r e t h e S t e l l i t e 68 was s e l e c t e d . F i g u r e 4 shows t h e r e s u l t s o f these t e s t s . PS-200 shows a s i g n i f i c a n t r e d u c t i o n i n f r i c t i o n c o e f f i c i e n t ove r t h e chrome carb ide- - f rom 0.6 t o l e s s than 0.2. Wear r a t e s were low. These t e s t s gave us conf idence t h a t we c o u l d r u n t h e h o t - r i n g equipped engine s t a b l y f o r a l o n g enough t i m e t o p r o v i d e t h e d a t a necessary f o r performance comparison.

I

Tes t Hardware

The p i s t o n r i n g c o n f i g u r a t i o n s shown i n f i g u r e 5 were used f o r comparison

T h i s c o n s i s t e d o f an upper and a purposes d u r i n g t h e engine t e s t i n g . s i d e was designed by D r . Roy Howarth o f M T I . l ower h a l f t o t h e p i s t o n dome which a l l o w e d fo r t h e removal or rep lacement o f

The h o t - r i n g c o n f i g u r a t i o n on t h e l e f t

c

t h e a d d i t i o n a l p i s t o n r i n g . The a c t u a l des ign o f t h e h o t - r i n g c o n f i g u r a t i o n i n c l u d e d an upper wave s p r i n g t o keep t h e h o t - r i n g seated a g a i n s t t he lower h a l f o f t he p i s t o n r i n g groove, an expander r i n g beh ind t h e h o t - r i n g to a p p l y u n i f o r m p ressu re a g a i n s t t he c y l i n d e r bore, and t h e h o t - r i n g i t s e l f . Standard s p l i t - s o l i d Rulon r i n g s were used i n t h e conven t iona l p i s t o n r i n g base grooves. Note the v e n t ho les i n t h e p i s t o n base which a l l owed f o r m a n i f o l d i n g o f t h e minimum c y c l e p ressures i n each of t h e f o u r c y l i n d e r s . The c o n f i g u r a t i o n on t h e r i g h t i s a schematic o f the b a s e l i n e p i s t o n dome c o n f i g u r a t i o n employed f o r t h e purpose of comparison. A f i l l e r r i n g was mounted i n p l a c e o f the h o t - r i n g t o a l l o w fo r a u n i f o r m t r a n s i t i o n between t h e upper and lower h a l f o f the p i s - t o n dome.

F i g u r e 6 i s a photograph of the p i s t o n dome i n t h e h o t - r i n g c o n f i g u r a t i o n a f t e r app rox ima te l y 22.4 hours o f t e s t i n g . o r a t i o n a s s o c i a t e d w i t h t h i s h o t - r i n g c o n f i g u r a t i o n than w i t h t h e conven t iona l arrangement. Th i s apparent thermal dam e f fec t w i l l be d iscussed l a t e r .

There i s s i g n i f i c a n t l y l e s s d i s c o l -

F i g u r e 7 i s a photograph of a h i g h tempera ture d r y l u b r i c a n t coated c y l i n - de r . A s you can see, t h e da rke r p o r t i o n of t h e pho to i s where t h e a d d i t i o n a l p i s t o n r i n g rode a l o n g t h e stroke of t h e bore and wore i n t h e c o a t i n g . l i g h t e r p o r t i o n i s t h e o r i g i n a l diamond-ground, f lame sprayed PS-200 c o a t i n g su r face . s p e c i f i c a t i o n s needed to m e e t des ign requ i rements . A c t u a l measurements from i n s p e c t i o n showed t h a t t h e r e was o n l y about 0.0002 i n . wear assoc ia ted due t o the r i ng -on -coa t ing c o n t a c t a f t e r 22.4 hours o f t e s t i n g . The su r face f i n i s h measurement f o r t h e as-ground c o a t i n g was 80 p i n . RMS. A f t e r wear-in, t he su r face f i n i s h was a v e r y smooth 5 p i n . apparent wear was s imp ly r e d u c t i o n of t h e o r i g i n a l sur face a s p e r i t i e s . I t i s n o t c l e a r whether t h e a c t u a l s teady -s ta te wear r a t e s would be acceptab le f o r r e a l engine use. However, o u r purpose was w e l l served.

The

Th is c o a t i n g was flame sprayed and then ground to t h e p a r t i c u l a r

I t would appear t h a t a lmost h a l f t he

f r i c t i o n

I t was necessary to account i n some way for t h e added f r i c t i o n o f t h e ho t - r i n g i n o r d e r t o assess what a c t u a l thermodynamic b e n e f i t may have r e s u l t e d . R ing b e a r i n g pressures were c a l c u l a t e d based on assumed p ressu re d i f f e r e n c e s across the r i n g ove r t h e c y c l e . These were i n t e g r a t e d a l o n g w i t h the p i s t o n speed t o p r o v i d e an average va lue o f PV for each o p e r a t i n g p ressu re and engine speed. The t o t a l r i n g s u r f a c e area was assumed t o be t h e f r i c t i o n b e a r i n g sur- f a c e used i n t h e f r i c t i o n l o s s c a l c u l a t i o n s . F i g u r e 8 shows f r i c t i o n power l o s s i n k w l c v c l e as a f u n c t i o n o f ens ine sDeed. A t t he fu l l - power D o i n t o f 15 MPa work ing p ressu re and h o t - r i n g f r i c t i o n i s approx zero .

The t o t a l work ing gas

4000 rpm; t h e t o t a l engine 1 ma te l y 2 . 5 kW and decreases

RESULTS AND DISCUSSION

eakage p a s t t he p i s t o n r i n g s

s s asso i n e a r l y

was man t o g e t h e r (as mentioned p r e v i o u s l y ) and measured i n an a t t e m p t t o seal i n g e f f e c t i v e n e s s o f t he h o t - r i n g s . Leakage normal l y occurs

i a t e d w i t h the w i t h speed t o

f o l d e d gauge t h e up across t h e

bo t tom r i n g as w e l l as down across t h e t o p r i n g . The h o t - r i n g , o f course, i s in tended to r e s t r i c t o n l y t h e f low from the t o p down. The lower r i n g i s expected t o l e a k s i m i l a r l y i n e i t h e r c o n f i g u r a t i o n . A r e d u c t i o n i n o v e r a l l

3

leakage i m p l i e s a s u b s t a n t i a l l y g r e a t e r r e d u c t i o n i n the flow from t h e t o p o n l y . r i n g c o n f i g u r a t i o n s a t 5 MPa o p e r a t i n g p ressu re . seen. Th is i m p l i e s t h a t t h e h o t - r i n g sea ls v e r y w e l l and does p r e v e n t flow i n

F i g u r e 9 shows a comparison o f t he leakage between the b a s e l i n e and ho t - A s i g n i f i c a n t r e d u c t i o n i s

l and o u t o f the appendix gap. S i m i l a r r e s u l t s were o b t a i n e d a t 10 and 15 MPa.

A f u r t h e r c o r r o b o r a t i o n o f t h e s e a l i n g e f f e c t was o b t a i n e d by measur ing t h e c y l i n d e r e x t e r n a l w a l l tempera tures . F i g u r e 10 shows t y p i c a l r e s u l t s o f these measurements. These d a t a were taken a t 5 MPa and 1000 rpm. The c y l i n d e r schematic shows the thermocouple l o c a t i o n s . Temperatures f o r t h e h o t - r i n g con- f i g u r a t i o n a re c o n s i s t e n t l y lower down the c y l i n d e r i n d i c a t i n g less h o t gas f low i n t o the appendix gap.

I I n o r d e r t o o b t a i n a d i r e c t comparison o f h o t - r i n g performance w i t h t h e s tandard c o n f i g u r a t i o n , t e s t s w e r e r u n a t 5, 10, and 15 MPa over a range o f engine speeds. F i g u r e 1 1 shows brake power as a f u n c t i o n o f engine speeds f o r b o t h c o n f i g u r a t i o n s a t a l l t h r e e o p e r a t i n g p ressu res . U n f o r t u n a t e l y , a mal- f u n c t i o n i n g a i r / f u e l c o n t r o l s y s t e m l i m i t e d t h e maximum f u e l flow a v a i l a b l e and o p e r a t i o n was n o t f e a s i b l e beyond about 3500 rpm a t 10 MPa and 2000 rpm a t 15 MPa. The h o t - r i n g power l e v e l appears t o be s l i g h t l y h i g h e r (as much as 6 p e r c e n t ) a t a l l o p e r a t i n g c o n d i t i o n s . However, we must a l s o cons ide r t h a t t h i s apparent smal l n e t g a i n was ach ieved even though t o t a l r i n g f r i c t i o n was inc reased w i t h the added h o t - r i n g . I f t h i s i s accounted f o r , the apparent thermodynamic g a i n due t o appendix l o s s r e d u c t i o n

We had hoped fo r more.

I a lone was up as much as 11 pe rcen t i n power.

F igu res 12 t o 14 show an e f f i c i e n c y comparison f o r t h e same t e s t s . Again, I as w i t h t h e power, e f f i c i e n c y appears s l i g h t l y h i g h e r f o r a l l o p e r a t i n g cond i -

t i o n s . r e s u l t s as f o r power--maximum apparent thermodynamic ga ins o f 1 1 p e r c e n t or more.

Tak ing t h e added f r i c t i o n i n t o account g i v e s e s s e n t i a l l y t h e same I

I CONCLUDING REMARKS

A l though n o t c o n c l u s i v e , these da ta i n d i c a t e t h a t appendix gap losses a r e r e a l ( i n some form) and may be reduced i f f low i n and o u t o f t h e gap i s reduced. On t h e assumption t h a t t h i s i n i t i a l e f f o r t d i d n o t produce an optimum techn ique t o implement t h i s r e d u c t i o n , more e f f o r t i n t h i s d i r e c t i o n would appear t o be warranted--not o n l y to improve engine per formance, b u t a l s o t o de f ine more c l e a r l y a s i g n i f i c a n t loss mechanism f o r i n p u t to t h e S t i r l i n g engine s i m u l a t i o n . A s i d e b e n e f i t o f t h i s work was the f i r s t use i n a r e a l engine o f a d r y r i n g l u b r i c a n t . t e s t i n g p o s s i b l e , b u t a l s o appears t o o f f e r d e f i n i t e promise f o r p r a c t i c a l engine use. I t may even be a p p l i c a b l e t o t h e a d i a b a t i c d i e s e l where h i g h tem- p e r a t u r e r i n g l u b r i c a t i o n has been a pr ime d e t e r r e n t t o e f f e c t i v e a p p l i c a t i o n .

The PS-200 c o a t i n g n o t o n l y made our l i m i t e d

i REFERENCES

1 . H .E . S l i n e y , " A New Chromium Carbide-Based T r i b o l o g i c a l Coa t ing for Use t o 900 "C w i t h P a r t i c u l a r Reference t o t h e S t i r l i n g Engine,'' Jou rna l o f Vacuum

I I Science and Technology, Vol. 4 , No. 6, Nov.-Dec. 1986, pp. 2629-2632.

1 4

2. C. Della Corte and H . E . Sliney, "Composition Optimization o f Self- Lubricating Chromiuim-Carbide-Based Composite Coatings for Use to 760 "C," ASLE Transactions, Vol. 30, No. 1 , Jan. 1987, pp. 77-83.

7 HOT SPACE - ,

HOLLOW P I STON oom

PISTON BASE > ar CD-87-29786

CONVENTIONAL FIGURE 1. - APPENDIX GAP.

HOT-R ING

5

FIGURE 2. - ENGINE IN TEST CELL.

6

C-84-1870

FIGURE 3. - MOD I AUTOMOTIVE STIRLING ENGINE.

FRICTION OF STELLITE 6B SLIDING ON BONDED CHROMIUM CARBIDE AND ON PS200

k 4 I N HELIUM I N HYDROGEN

.6

I- L

E .4 2

8

E t . 2 2

LL LL

V

L

L L

0 6 B

cR3c2 - 68

PS200 ~

TEWER- ATURE ,

OC

68 6 B __ - cR3c2 PS200

FIGURE 4. - BONDED CHROMIUM CARBIDE AND PS 2 0 0 I N STIRLING ENGINE

CD-87-29788 ATMOSPHERES.

7

FILLER RING-’

MOD I ENGINE PISTON WITH HOT RING

MOD I ENGINE PISTON WITH FILLER RING

FIGURE 5. - PISTON CONFIGURATIONS. CD-87-29787

8

FIGURE 6. - HOT-RING PISTON.

. 6 7

FIGURE 7. - COATED CYLINDER AFTER 22.4 HOURS OF OPERATION WITH HOT-RINGS.

MPA 0 5 0 10 A 15

ENGINE SPEED. RPM

FIGURE 8. - HOT-RING FRICTION LOSS (CALCULATED).

CD-87-29793

9

NOD I STIRLING ENGINE: 5 WA K A N PRESSURE

1 1

m-z- HOT-R I NG 3t -6- BASELINE

I I ,

f : I V w

0 f 4

g 2 -

3 J U

v)

1 1000 2000 3000 4000

1 0

700 r

0" 600

W n

400

ENGINE SPEED. RPM

FIGURE 9. - SEAL LEAKAGE COMPARISON. CD-87-29785

MOD I STIRLING ENGINE: 5 WPA WEAN PRESSURE: 1000 RPM

657 657

BASE- HOT-

604

HOT-

522

BASE- HOT-

WALL T/C -0CATIONS

64

(DIRNSIONS I N MW

470 .. .

BASE- HOT- L INE RING L INE RING L INE RING L INE RING

T 1 T I T2 T2 T 3 13 T4 T4

CYLINDER WALL LOCATION

FIGURE 10. - CYLINDER WALL TEMPERATURE COMPARISON. CL-87-29794

10

MOD I STIRLING ENGINE

40

n W

CT m 10

15 MPA l n YD.

CD-87-29789

MOD I STIRLING ENGINE: 5 MPA MEAN PRESSURE

40 r

ENGINE SPEED. RPM

FIGURE 12. - EFFICIENCY COMPARISON-HOT-RING VERSUS

CD-87-29790 BASEL I NE.

11

MOD I STIRLING ENGINE; 10 MPA MEAN PRESSURE

-&- BASELINE

0 1000 2000 3000 4000 ENGINE SPEED. R P M

FIGURE 13. - EFFICIENCY COMPARISON-HOT-RING VERSUS CD-87-29791 BASEL I NE.

MOD I STIRLING ENGINE; 15 MPA MEAN PRESSURE

: 40r -0- HOT-RING -&- BASELINE

30

:: :: 0 1000 2000 3000 4000

ENGINE SPEED. R P M

!s 20

FIGURE 14. - EFFICIENCY COMPARISON- HOT-RING VERSUS BASEL I NE. CD-87-29792

12

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1. Report No.

Report Documentation Page 2. Government Accession No.

NASA TM-100256 I 4. Title and Subtitle

Hot P i s t o n R ing Tes ts

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7. Author@)

Dav id J . A l l e n and W i l l i a m A. Tomazic

9. Performing Organization Name and Address

N a t i o n a l Ae ronau t i cs and Space A d m i n i s t r a t i o n Lewis Research Center C leve land, Oh io 44135-3191

12. Sponsoring Agency Name and Address

U.S. Department o f Energy O f f i c e o f V e h i c l e and Engine R&D Washington, D.C. 20545

5. Supplementary Notes

3. Recipient's Catalog No.

5. Report Date

December 1987 6. Performing Organization Code

8. Performing Organization Report No.

E-3808 ~

10. Work Unit No.

778-35-1 3 11. Contract or Grant No

13. Type of Report and Period Covered

Techn ica l Memorandum 14. Sponsoring Agency Code

DOE/NASA/50112-72

F i n a l Repor t . Prepared under I n t e r a g e n c y Agreement DE-AI01-85CE50112. Dav id J . A l l e n , Sverdrup Technology, I n c . , M idd lebu rg He igh ts , Oh io and W i l l i a m A. Tomazic, Lewis Research Center . Prepared f o r t h e T w e n t y - f i f t h Automot ive Technology Development C o n t r a c t o r s ' C o o r d i n a t i o n Meet ing , sponsored by t h e U.S. Department o f Enersv. Dearborn, Mich igan, October 26, 1987.

6. Abstract

As p a r t o f the DOE/NASA Automotive S t i r l i n g Engine P ro jec t , t e s t s were made a t NASA Lewis Research Center t o determine whether appendix gap losses could be reduced and S t i r l i n g engine performance increased by i n s t a l l i n g an add i t i ona l p i s ton r i n g near the top o f each p i s t o n dome. An MTI-designed upgraded Mod I Automotive S t i r l i n g Engine was used f o r these tes ts . Un l i ke the conventional r i n g s a t the bottom o f the p i s ton , these r i n g s operated i n a h igh temperature environment (700 " C ) . o f t h i s , we c a l l e d them "hot-r ings." I t was necessary t h a t they be made o f a h igh temperature a l l o y ( S t e l l i t e 68) and t h a t a h igh temperature s o l i d l u b r i c a n t coa t ing (NASA Lewis-developed PS-200) be app l ied t o the cy l i nde r wa l l s . Engine t e s t s were run a t 5, 10, and 15 MPa opera t ing pressure over a range o f opera t ing speeds. Tests were run both w i t h the hot-r ings i n p lace and w i thou t them t o pro- s ide a basel ine f o r comparison. Although budget and schedule r e s t r i c t i o n s severely l i m i t e d the t e s t - i ng , the minimum data t o assess the p o t e n t i a l o f both the hot-r ings and h igh temperature low f r i c t i o n coat ing was obtained. Resul ts ind ica ted a s l i g h t increase i n power and e f f i c i e n c y w i t h the hot-r ings over the basel ine conf igura t ion . the hot-r ings. i n place. I n add i t ion , cy l i nde r wa l l temperature measurements ind ica ted l e s s c y l i n d e r heat ing i n the appendix gap area--between the lower p i s ton r i ngs and the hot-r ing. on-coating operat ion were recorded. the coat ing was low. The PS-200 coat ing seems t o o f f e r s i g n i f i c a n t po ten t i a l f o r long-term operat ion a t h igh temperatures. be pursued f u r t h e r . ad iabat ic d iese l as we l l .

Because

This increase was over and above the f r i c t i o n l o s s introduced by Seal leakage measurements showed a s i g n i f i c a n t reduc t ion i n leakage w i t h the hot-r ings

Approximately 22.4 hours of r ing- A f t e r the i n i t i a l break-in per iod, wear on both the r i ngs and

Poten t ia l bene f i t s are app l i cab le no t on ly t o the S t i r l i n g engine, bu t t o the Both the ho t - r ing and the PS-200 low f r i c t i o n coat ing show promise and should

7. Key Words (Suggested by Author@)) I 18. Distribution Statement

S t i r l i n g engine; Appendix gap; Hot p i s t o n r i n g

U n c l a s s i f i e d - U n l i m i t e d Sub jec t Category 44 DOE Category UC-96

9. Security Classif. (of this report)

Uncl ass i f i ed 20. Security Classif. (of this page)

U n c l a s s i f i e d 21. No of pages

122. Pr&

*For sale by the National Technical Information Service, Springfield, Virginia 221 61 NASA FORM 1626 OCT 86