GPU-3 Stirling Engine

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DOEINAW51040-31
NASA TM-82646
High-Power Baseline and Motoring Test
Results for the GPU-3 Stirling Engine
(UASI-Td-82646) H1Gt i - f CLEP EASELI NE A Y C 181-J20€7
I OTOEXYG TBST i i Ei i di . TS kQh TiiE GP Q- 3 Sl ' I BLl YG
EYGI UE Fi nal Report (NASA) 37 y
uC Ao3/H: A01 CSCL 13P Uncias
G3/LI5 27361
Lanny G. Thierne
Nationzl Aeronautics and Space Administration
Lewis Research Center
June 1981
Prepared for
U.S. DEPARTMENT OF ENERGY
Consenration and Renewable Energy
Qffice of Vehicle and Engine R&D
OOUNASAlS1m1
NASA TM-02646
High-Power Baseline a d Motoring Test
Results for the GPU-3 Stirling Engine
Lanny G. Thieme
National Aeronautics and Space Administration
Lewis Research Center
Cleveland, Ohio 441 35
June 1981
Work performed for
U.S. DEPARTMENT OF ENERGY
Conservation and Renewable Energy
Office of Vehicle acd Engine R&D
Washington, D.C. 20545
Under Interagency Agreement DE-A101-77CS51040
I n support of t he Department of tnergy' s St i r l i ng Engine Highwiry
Vehicle Systems proqran, t he NASA Lewis Research Center has i nst al l ed a
7.S-kilowatt (10-hp) GPU-3 St i r l i ng engine wi t h a not ori ng dynlvaoaeter t o
continue t o obt ai n data f o r val i dat i ng S t i r i i ng-cycl e caeputer si sul at i ons
and t o prepare f o r f ut ur e c w n e n t testi ng. The engine was or i gi nal l y
b u i l t by General Motors Research Laboratori es f o r t he U.S. Arqy i n 1%5 as
par t c f a 3-ki l owatt engine-generator set.
Base 1 i ce t est s were run t o map t he engine over a range o f #an
c~r essi on- space pressures of 2.8 t o 6.9 peqapascals (400 t o 1000 psi ) and
engine Spef?dS of lW0 t o 3500 rpta wi t h both helium and hjdrogen as t he work-
i ng f l ui d. A l l t est s were run at a heater-tube gas terperaturc o f 677' C
(1250. F). Naxirura power obtained wi t h hydrogen was 6-82 ki l owat t s
(9.14 hp) at 6.9 megapascals (1000 psi ) and 3W rpa. The power
wi t h helium was 4.26 ki i owat t s (5.71 hp) a t 6.9 megapascals (1000 psi ) and
2500 rpm. Tne highest brake tnernal ef f i ci enci es obtained were 26.4 percent
f or hyarogen and 21.3 percent f o r heliwa. These both occurred a t 6.9-
megapasca 1 (1000-psi ) mean crnressi on-space pressure and 1500-rp engine
speed.
Tne engine output was low a t hi gh speeds as corapared wi t h t hat f or t ne
previous l y reportea l ottpouer base i i ne t est s t hat used t he a l t er nat cr and
resi stance load bank i nstead of t he dynwroraeter. It i s f e l t t hat chi s r&
duced power wds caused by degradation of heat exchanger effecti veness as a
r esul t of contamination by r ust and c i l . However, ef f i ci ency was hi gher
tnan i n the previous t est s because cf tne i nst al l at i on of a noncontaminated
preneater t hat reduced combustion system losses.
Indi cated power r esul t s were obtained as a functi on o f man
compression-space pressure and engine speed f o r both he1 i m and hydrogen.
The maximum i ndi cated power measurea was 8.6 ki l owat t s (11.3 Lw) f o r
hyarogen .
Hotori ng t est s were ther: run t o ai d i n determining ~nechanical losses.
Tests were completed over a range of mean conpression-space pressures ma
engine speeds f or both hel i um and hydrogen as the ni r ki ng f l ui d. The re-
sui t s were compared wi t h tne r esul t s nf an energy-balance metnod f o r f i ndi ng
inecnanical losses. The energy balance yi el ds a l i near var i at i on of echani -
cal losses w i t h engine Speed, but the motoring r esul t s snow a higher-order
var i at i on wi t n speed. Tne two met9oas gi ve r esul t s t nat are about the same
at low speeds out di t f er si gni f i cant l y a t ni gh speeds.
I NTROOUCTION
This work was done i n support of the U.S. Department of Energy (W€)
St i r l i ng Engine Highway Veni cl e Systems program. The NASA Lewis ResedrCh
Center, through interagency agreement 0EAIC;l-77CS51040 w i t n DOE, i s respon-
si ol e f or manag,lment of the pr oj ect under the program di r ect i on of the DOE
Off i ce of Vehic i e and Engine R&D, Conservation and Renewable Energy.
As par t of t hi s ef f or t Lewis i s operati ng a 7.5-kilowatt (10-hp),
si ngl e-cyl i nder, rhombic-orive St i r l i ng englce. Tho engine was or i gi nal l y
b u i l t by General Motors Research Laboratori es f or t he U.S. Army i n 1965 as
gart ot a 3-ki l owatt engine-generator set t hat was designated the GPU-3
(Grouna ?ewer Uni t 3) .
The S3U-3 St i r l i ng engine r est prograta a t Lewis has t hree obj ecti ves:
(1) To obt ai n dnd publ i sh det ai l ed engine performance data
( Z j To val i date, document, and publ i sh a NASA Lewis St i r l i ng- cycl e
canpu t er mode l
( 3) To provi de a t est bed f or eval uati ng new caraponent concepts t hat
evolve from supporting St i r l i ng engine technology act i vi t i es
Af t er i t was converted t o a research confi gurati on, t he engine was t est ed
w i t h tne or i gi nal al t er nat or and a resi stance load bank t o aosorb the engine
output. These t est r esul t s are reported i n reference 1. However, t he al t er -
nator ana load bank were not capable of absorbing tne f u l l engine output
power. Thus fol l owi ng c ~ l e t i o n o f these tests, t he al t er nat or was removed
and the engine was i nst al l ed wi th a motoring dynamometer. i h i s allowed t est -
i ng at t ne f u l l engine output as wel l as running mt or i ng t est s t o ai d i n
oet eni ni ng mechanical losses.
Thi s paper presents the r esul t s o f bot h t he high-pcwer basel i ne t est s and
t.ne mt or i ng tests. Curves of engine output and brake speci f i c f uel cons*
t i on as functi ons of engine speed and mean compression-space pressure are
given f or tne nish-power t est s f or both helium and hydrogen as the working
f l ui a. These t j s t s were r un a t a constant heater-tube gas temperature.
Indi catea power r esul t s are show as oetermined by three methods: by an
energy balance, by usi ng pressure-volume diagrams, and by s~llaning brake power
and mecnanical losc,es determined from motoring resul t s.
f o r t he mt or i nq t est s the cooler-regenerator cart ri ages were removed, and
a specl al di spl acer was used t o l i m i t f l ow through the neat-exchanger ci r -
cui t . The motcring power r esul t s are presented as a f unct i on of engine speed
and mean coapression-space pressure. i ndi cated gas work was al so measured and
used t c correct the motoring power t o ar r i ve a t an i ndi cat i on of the wchani -
cal losses. Comparison i s then maoo t o energy-balance inetnads f o r determining
t w ~necnanical losses.
At'3ARATUS AND 39OiEOURE - HIGH-POWER 3ASEL INE TESTS
i ngl ne Descri pti on and dackground
Tne SPU-3 St i r l i ng engine and dynamometer t est bed are shown i n f i gur e 1.
The engine as testea i 5 a combination c i par t s taken from two i dent i cal GPU-3
unl t s. The f i r s t of these was obtained from t ne U.S. Prmy Hooi t i t y Equipment
Aesearcn an6 Oe~elopnlent i snt er (NRK) at f o r t Bsl voi r, Vi rgi ni a; the second
was ootainea tnrough a loan frm tne Smithsonian I nst i t ut i or ?. These uni t s
were originally 3-k:iowatt engine-generator sets o u i l t by General Motors
Research Laboratori es i n 1965 f or the U.S. Army. They were completely sel f -
contained ans capabie of operati ng w i t h a var i et y of f uel s over a broad range
o f ambient conditions. The uni t s were designed t o use hydrogen as tne working
f l ui d. The 3311-3 engine 1s d si ngl e-cyl i nder, ai spl acer engine wi t h a rhombic
dr i ve and sl i di ng r od seals. I t i s capable of producing a maximun engine out-
put of approxinately 7.5 ~ i l o wa t t s (10 hp) wi th hydrogen working f l u i d at
b.9 megapdscals (1000 psi ) mean compression-space pressure. The pi st on swept
vlllume i s 120 cubic centimeters (7.3 i n3).
The engine obtained from For t Bel voi r was i n i t i a l l y t or n down and restored
t o operating condi ti on. It was then tested ds par t of tne or i gi nal 6PU-3 with
onl y those charl;es t hat were i~ecessary t o make the uni t operable. Tests were
run w i t h both nydrogen dno helium as the working f l u i d at various pressures
ano at the design heater-tube gas tenrgerature o f 677' C (1250' f ) and an
engine speed of 3000 rpm. C q a r i sons were made wi t h data taken by t ne A r q
i n 1966. These r esul t s and a descri pt i on of the or i gi nal W&3 engine cOq0-
nents and systems are gi ven i n reference 2.
The f ol l owi ng changes were then made t o convert ttte engine t o a research
confi gurati on. The engi nedr i ven accessories were reiaoved (except f or t he o i l
system) wi t h ai r, water, fuel , and working f l u i d suppl i ed from t he f a c i l i t y
support systems. The or i gi nal cont r ol system was replaced wi t h manual con-
t r ol s. Where necessary, new part s were made. i ncl udi ng new cwl er-regenerator
cartri dges. Extensive i nstrumentati on was added t o obt ai n an eneqy balance,
engine t eqxr at ur e pr of i l es, conduction losses, working-space as t m r a t u r e s
and dynamic pressures, and a measuresent o f i ndi cated power. ! i nal l y, d i m
si onal and vol~rrse raeasurewents were completed as were steady-state flow t est s
on t ne vari ous heat exchangers.
Baseline t est s were r un t o map t he engine over a range o f heater-tube gas
teaperatures, mean conpression-space pressures, and engine speeds wi t h both
nelium and hydrogen as the working f l ui d. Tests were l i mi t ed t o t he lower
p a i r l evel s (-4.5 kw ( 6 hp)) because the or i gi nal al t er nat or and a resi st ance
load bank were used and they were not capable of absorbing t he f u l l engine
output power. These r esul t s are presented i n reference 1. The det ai l ed data
taken duri ng those t est s are included on mi crof i che as par t of t hat report.
Also given are the engine aimensions necessary f o r carputer modeling as wel l
as the r esul t s of t he volume measurements and steady-state f l ow tests.
These data were used t o make the i n i t i a l di r ect comparisons wi t h the Lewis
computer si rsul ati an predi cti ons. The si mul ati on code i s described i n ref er-
ences 3 ana 4. Results of the si mul ati on conparisons wi t n the t est data are
given i n reference 4.
Test Setup
Fol l owi ng completion of the t est s described i n reference 1, t he exhaust
tubes of the preheater were fl ow-tested t o check f o r blockage. About 45 per-
cent of these tubes were plugged wi t h soot from combustion; some leakage
between t ut ?. i ndi cated t hat several of t he tubes had holes burned through
them. These f'ndiclgs expl ai n tne l arge ci rcumf erent i al tenperature var i at i on
of the exhaust i n these previous t est s and al so the low engine ef f i ci enci es
t hat were measured. For the nigh-power t est s i t was decided t o replace t he
preheater wi t h the one from the Smithsonian engine. Flow t est s on t hi s pre-
heater i ndi cate0 onl y one tube blocked ( of 560 tubes). Tni s preheater was
tnen instrumented and i nst al l ed on the engine. Changes i n i nstrumentati on
from t hat on tne former preheater are given i n appendix A.
Two separate crankcases were used duri ng the hi ghpower tests. The nyi an
ti mi ng gears f ai l ed under heavy load at the end of the helium basel i ne tests.
Tni s caused major damage t o the crankcase o f the For t Bel voi r engine, which
ha0 been used up t o t hat time. For tne hydrogen t est s the crankcase frm t he
jmitnsonian engine was i nst al l ed.
A schematic diagram of the GPU-3 t est setup i s snow3 i n f i gur e 2.
Fac i l i t y support systems shown i ncl ude fuel , ai r, cool i ng water, oi l , and
working f l ui d. Also shown i s tne dynamomete: f o r absorbing engine output.
This schematic was updated from tnat given i n reference 1. Numbers by the
i nstrumentati on symbols r ef er t o i n s t r a n t a t i o n i t em niunbers gi ven i n t abl e
I 1 1 of rzference 1. Only cnanges t o the t est setup from the previous t est s
are aiscussed here. A s ma r y of changes t o i nst rume~l t at i on i n tho support
systems i s includec! i n appendix A. For f ur t ner det ai l s of t ne t est setup see
reference 1. The fuel , nozzle ai r , and combustion a i r systems were not
changed.
A tank and p u q ~ were i nst al l ed t o supply t he desi red water f l ow r at e t o
the engine's three cool i ng paths (buffer space, coolers, and nozzle). The
water was not r eci r cul at ed and i t s i n l e t temperature was not control l ed. The
i nl et tecrperature was establ i shed by the terilperature of t he c i t y water supply-
i ng t he tank. The measureaents of t ot al water f l ow r at e and temperature r i s e
between out l et a m i n l e t f o r t he t ot al flow were el i mi nated as i t nas found
t hat the measurements I n t ne i ndi vi dual water c i r c ui t s were accurate and
suf f i ci ent . To iflprove r e1 i abi 1 i ty, t he thennopi l es f o r measuring t eqer at ur e
r i s e i n tnese i ndt vi dual ci r cui t s were replaced w i t h AT probes with j ust one
thermcoupl e per leg. Tne vol tage si gnal representi ng the t e r a t u r e r i s e
was then ampl i f i ed and recorded.
For t ne o i l system the t h e m i l e f o r measuring t-rature r i s e was re-
placed wi t h a AT probe ( t he sane as t he one described above f o r water).
Pressure transducers were added t o t ne pressuri zat i on system t o measure
raininrrr~ cycl e pressure i n the coapression and buf f er spaces. The transducers
were i nst al l ed between check valves a t t he engine and needie valves i n t ne
pressuri zati on lines, as shown i n f i gur e 2. These secti ons of l i ne tend t o
t r ap t hei r respecti ve miniawn pressures because of t he on+way act i on of t he
check valves. Also, connections were maae t o the vent l i nes t o al l ow t aki ng
working-f l ui d sanples f o r l at er analysis.
The or i gi nal GPU-3 al t ernat or and resi stance load bank were replaced by ?.
uni versal dynamometer t o absorb t he engine output. Thi s dynamometer i s c w
abl e of 50 np absorbing and 15 hp motoring and tkis can absorb t he f u l l engine
output. The al t er nat or l i mi t ed t he previous t est s t o a maximum output of
about 4.5 k i l owatts ( 6 hp).
Two changes were mado t o ilrprove t he measurement of i ndi cat ed power.
Yater-coolea adapters were i nst al l ed f or tne expansion-space and cocapression-
space mi ni ature pressure transducers. These were added t o minimize the trans-
ducers' zero s h i f t and sensi t i vi t y change wi t h temperature. Also, the shaf t
encoder was referenced t o di spl acer top dead cen5er (TOC = zero degrees shaf t
angle) by set t i ng at the midstroke posi t i ons (90 before and af t er TDC)
instead of a t TOC. Thi s method should be more accurate because tf the much
greater pi st on displacement per degree of crank t r avel at tne 30 poi nt s than
h t TDC.
Fi nal l y, new modules were added t o t ne recordi ng system f or the i ndi cated
work and dynamic pressure measurements. Thi s updated system i s shown i n f i g-
ure 3. Tne new modules are t he i ndi cated mean ef f ect i ve pressure (I WEP) mod-
ul es f or the conpression, expansion, and buf f er spaces; the two pedk detector
modules; and t he two event detector modules. The I#EP Wu l e s are simi l ar t o
t hat f or the t ot al I EEP measurement (compression-space pressure as a f unct i on
of t ot al mr k i n ~ s p a c e vo1. m) described i n reference 1. Each : l meri cal l y
i ntegrates the associated pressure-volume diagram t o obtai n tne work i n terms
of the IMP. The value of IWP cal cul ated and displayed i s an average value
obtained over 100 engine cycles. The peak detector moduies are used t o f i nd
the fiaximm and minimum value of pressure f o r t he mi ni ature pressure trans-
ducers i n t he expansion, compression, and buf f er spaces. The event modules
determine t ne crank angle r el at i ve t o di spl acer TOC a t whicn t he maximum and
minimum values occur. Tne prescure si gnal t hat i s i nput t o tnese l ast f our
,noau les i s determined by the sel ector swi tch shown i n t he middle of f i gur e 3.
References 5 and 6 provide more i nformati on on t hi s type of i nstrumentati on
syst w.
Tne maximum and niininrws values recorded frcnn t ne peak detectors are
sni f t ed somewhat as a r esul t of t-erature ef f ect s on t ne transducers
I a l though the water-cooled adapters minimized t hi s effect!. The ?rue values
or the coq)ression and buf f er pressures uere found by usi ng t he pressure di f -
ference from the peak detectors along with the miniaun values a#asured behind
t he check valves i n t he pressuri zat i on system. For t he expansion pressure,
onl y the di f f erence bet een the araxiura and mi ni am values coul d be detercained.
The GPU-3 t est setup i s shorn i n f i gur e 4. Recording systems and si gnal -
condi t i oni ng equipment are shown on the l ef t , wi t h the engine and dynaaosleter
on t he r l ght . Steady-state data were recorded and pr i nt ed out 081 a data
logger. Dynamic data were taken wi t h both an osci l lograph r e ~ o ~ d e r and an
0 x 1 l loscope.
Test Procedure
The desi red t est mat ri x range f o r botn t he helium and nydrogen runs
i ncluded mean cospression-space pressures of 2.8 t o 6.9 qapas c al s (400 t o
1000 psi ) ana engine speeds of 1500 t o 3500 rpcll. T h e heater-tube gas t-ra-
t ur e ano cooling-water i n l e t t me r a t u r e were not vari ed f o r these tests. The
heater-tuoe gas teaperature was raeasured w i t h tnenaocowle probes i nst al l ed
i nsi oe three of the 40 neater tubes and spaced ci r cuaf er ent i al l y around t he
neater nead. T n e o ma x i ~ reading of these three thermcoupl es was manually
cont r ol l ed t o 677 C (1250' F) by adj ust i ng t he f uel f l ow wi t h a needle
valve. T9e cooljng-watgr i nl et temperature was not cont r ol l ed and vari ed from
19 t o 21 C (60 t o 70 F) over t he seri es o f tests.
On each engine startup, cooling-water f l ow uas f i r s t provibed t o t he
engine and the mean conpression-space pressure was set a t approximately
2.1 megapascals (300 psi ) . Combustion was tnen st art ed wi t h no. 1 di esel
f uel (l ower heati ng value, 18 590 Bt ul l b) from the ?t art up f uel tank. As t he
heater-tube gas temperature approached 549' C (1000 f ) the engine was st ar t ed
r ot at i ng by motoring wi t h the dynamometer. Engine warmup condi ti ons were then
set t o Z.&negapascal ( 40Spsi ) man conpression-space pressure, 677' C
(1250 F) heater-tube gas temperature, and 2000-rpm engine speed. When t he
engine temper3tures were suf f i ci ent t o sustai n operation, the dynaraoraeter
motor was shut of f . The engine was st abi l i zed at t he reference condi t i on
I i st ed above t o a1 low i t t o reacn operati ng temperatures. About 30 minutes o f
wannup time was necessary.
Generally, one curve a t constant mean compression-space pressure, heater-
tube gas temperature, and cooling-water f l ow was run af t er each engine st ar t -
up. Tne curve consisted of data poi nt s taken at engine speeds varyi ng by
5Oerpm i nterval s, wi t h the highest speed set f i r s t . A t each poi nt t he speed
was set by adj usti ng the speed cont r ol on the dynamometer. The combustion
ai r f l ow was set t o mai ntai n an ai r - f uel r a t i o of about 35 t o 1. Af t er the
desi red condi ti ons were reached, the f uel run tank was valved t o t he engine.
Tnese condi ti ons were then maintained f or 15 minutes. A l l steady-state data
were recorded three times and dynamic data once duri ng t h i s period. The
st art up f uel tank was then again valved t o the engine, and the next data poi nt
establisned. The f uel f l ow was determined from the i n i t i a l and f i n a l weignts
af the f uel run tank. Thi s procedure was repeated f or each data poi nt.
RESULTS AND OISCUSSION - HIGH-POUER BASELINE TESTS
The r esul t s of the higwpower basel i ne t est s are presented i n f i gur es 5 t o
. Tnese f i gur es are sunmarized as fol l ows:
The i nfl uence of lean c ~ ~ s s i o n - s p a c e pressure and engine speed on
engirre output and brake spec1 i c f uel c o n r wt i o n (bsfc) i s shown i n f i gur es 5
and 6. The engine data obtained wi t h the dynzrraoereter are compared with previ -
ous engine data obtairred wi t h t he al t er nat or in f i gur e 7. The di f f erences
i ndi cated by t hi s comparison are explained wi t h t he ai d o f f i gur es 13 t o 12.
Fi gures 13 and 14 gi ve exwyl es of energy balances obtained on t he engtne.
Fi nal l y, i ndi cated power r esul t s as a f unct i on of inem compression-space pres-
sure and engine speed are shown i n f i gur es 15 and 16. The det ai l ed data taken
duri ng these t est s are not included as par t of t hi s r epor t but are avai l aol e
from t he author. A sample data poi nt t o i ndi cat e what i s avai l abl e i s given
i n appendix A.
Engine Performance wi t h He 1 i urn and Hydrogen
Fi gure 5 i 1 l ust r at es the ef f ect of engine speed and mean compressi o~space
pressure on engine performance wi t h he1 i m working f l ui d. The same i s shown
i n f i gur e b f or hydrogen mr k f ng f l ui d. The heater-tube gas temperature was
677. C (12M F) . and t he average c o o l i n ~wa t e r i n l e t tenperature was 20. C
(68
i) f o r both seri es of te:ts. O f t ne three steady-state data scans taken
a t eacn operati ng condi ti on, two were reduced and pl otted. When both scans
gave approximately the same resul ts, onl y one symbol was pl ot t ed f o r t hat
condi ti on.
An ext r a poi nt at an engine speed o f 1000 rptn and a mean compression-space
pressure of 2.8 megapascals (400 psi ) wi t h helium working f l ~ i d was added t o
tne planned t est matri x. Also, several poi nt s at t he low pressures and hi gn
engine speeds could not be run. Thi s was due t o the engine output being i n-
adequate a t those condi ti ons f o r t he engine-dynamometer system t o sustai n
operation.
The maximum engine output wi t h helium working f i ui d was 4.26 ki l owat t s
(5.71 hp) at a mean compression-space pressure of 6.9 megapascals (1000 psi )
and an engine speed of 2500 rpm. The lowest bsfc was 390 g/kw-hr
(O.b4 l ol hp-hr) at 6.9 megapascals (1000 psi ) and 1500 rpm. Thi s corresponds
t o a brake thermal ef f i ci ency of 21.3 percent.
di t h hydrogen working f l u i d the maximum power obtained was 6.82 kilowat'r
(9.14 np) at 6.3 megapascals (1000 psi ) and 3500 rpm. The minimum bsfc was
315 glkd-hr (0.52 l el hp-hr) at 6.9 megapascals (1000 psi ) and 1500 rpm. Thi s
corresponds t o a brake thermal ef f i ci ency of 26.4 percent. Thi s ef f i ci ency i s
i n the same range as t hat obtained by General Motors ( r ef . 7) .
I n addi t i on t o the f act t hat both t he engine output and ef f i ci ency are
greater wi t n hydrogen working f l u i d than wi t h nelium, the f i gur es show t hat
tne engine output tends t o peak at a hi gher speed wi t h hydrogen. The increase
i n bsfc i s al so mucn l ess at the higner speeds wi t h nydrcgen than w i t h
nelium. Tnese r esul t s are i ndi cat i ons of the lower f l ow losses through the
heat exchangers wnen using hyarogen as the working f l ui d. This ef f ect has
been substanti ated by computer si mul ati on predi cti ons.
CornParison of Engine Output w i t n Previous Oata Obtained wi t h tne A 1 ternator
F i g u ~ e 7 shows a comparison of t he engine output wi t h data obtained previ -
ously i n the lowpower basel i ne t est s t hat used the or i gi nal GPU-3 al t ernat or
and a resi stance load bank t o absorb the output. Reference 1 describes the
low-power baseline t est s i n det ai l . The hot- and cold-end temperatures w?re
not i dent i cal f or these two seri es of tests. For t he iiigh-power dynamometer
t est s the heater-tube gas temperature was 677' C (1250 F ) and the cooling-
water i n l e t temperature was LO' C (68' c). For fhe l o w power a1 t er nat or t est s
t he heater-tube gas temperature was 650 C (1200 F 1 and t he cool i ng-water
i n l e t temperature was i n t he range 13O t o 15' C (56 t o 53' F) . However, as
bot h temperatures were hi gher f o r t he dynamometer t est s, t he ef f ect s o f t he
two should somewhat of f s et each other.
With t he excepti on of one poi nt a t 4.1 megapascals (600 ps i ) hydrogen dat a
from the low-power al t er nat or t est s were l i mi t ed by t he a1 lowable al t er nat or
cur r ent t o curves f o r 1.4 and 2.8 megapascals (200 and 400 psi ) . As dat a were
taken f or pressures of 2.8 megapascals (400 ps i ) and hi gher f o r t he high-power
dynamometer tests, comparison coul d onl y be made a t 2.8 megapascals (400 ps i )
f or nydrogen as t he working f l ui d. Also, some or' t he previ ous hel i um t est s
were l i mi t ed by t he al t er nat or t o hi gh speeds, par t i c ul ar l y f o r hi gh pres-
sures; therefore comparisons agai n are incomplete.
The engine power outputs from t he two ser i es of t est s were about t he same
f or t he lower par t of t he speed range ( wi t h t he excepti on of t he 2.Smega-
pascal (400-psi) curves f or he1 i um) . However, t her e are 1 arge di screpanci es
at tne hi gher speeds. Thus t he var i at i on i n out put appears t o be r el at ed pr i -
mari l y t o speed.
I ncreasi ng pressure drop through t he heat exchangers coul d cause t h i s t ype
of ef f ect . Fi gure 8 shows t he set of ei ght cool er-regenerator car t r i dges as
we1 1 as t hree of t he end caps t hat connect t he cool ers t o t he compression
space. I n areas where the working f l u i d i s present - around t he regenerator
car?, a t t he out l et of cool er tubes, and around t he end cap - t her e were si g-
ni f i c ant deposi ts of whdt was analyzed t o be a cami nat i on of o i l and r ust .
Kust occurs duri ng teardowns wnen t he engine par t s are exposed t o t he atmos-
phere. Also, r ust i ng may take pl ace wnen tne assembled engin2 i s l e f t un-
pressuri zed as a r es ul t of severe engine leaks. The engine was cleaned bef ore
eacn rplssemoly, but obvi ousi y some of the r ust was not removed. The o i l con-
tami nati on was from o i l pumped past t he s l i di ng shaf t seal s dur i ng engine
operati on.
Steady-state f l ow t est s were r un on the vari ous heat exchangers t o measure
t he pressure drop. A i r at 793-ki l opascal ( 115ps i ) i n l e t pressure was used
f o r t he cal i or at i on, wi t h pressure drop as a f unct i oc o f mass f l ow r at e bei ng
recorded. Mass f l ow r at es were chosen t o gi ve aDcut the same range of
Reynolds number as act ual l y occurs i n t he engine. Thi s range was pr edi ct ed by
tne St i r l i n g si mul at i on computer program. For f ur t her expl anat i on of steady-
st at e f l ow t est s on t he heat exchangers, see reference 1.
Fi gure 9 shows pressure drop as a f unct i on of f l ow r at e f o r t he heater
nead assembly af t er t he high-power t est s wi t h t he dynamometer and af t er t he
low-power t est s wi t h t he al t er nat or . Thi s i ncl udes fl ow througn a l l t he heat
exchangers - cool ers, regenerators, and heater. The mass f l ow Jtes through
the neater nead assembly are ei gnt times the f l ow r at es shown i n t he next two
f i gur es f or t he i ndi vi dual cool er-regenerator cart ri dges. Thi s i s due t o t he
ei gnt cool er-regenerator paths i n t ne heater head. The t est f o r the heater
neaa assembly was made f or f l ow i n bot h di r ect i ons. The pressure drop has
increase0 by about 10 percent over most of t he f l ow range f o r t he l at est f l ow
t est s.
Throughout the GPU t est i ng t hree of t he cool er-regenerator car t r i dges were
f l ow t est ed at vari ous i nt er val s. Fi gure 13 gi ves f l ow t es t r es ul t s f o r these
three wnen they were ned, af t er 80 nours of engine t est i ng ( af t er t ne low-
power t est s wi t h tne al t er nat or ) , and af t er 131 nours of engine t est i ng ( af t er
tne hi gkpower t est s wi t h t he dynamometer).
The pressure drops through the car t r i dges have been i ncreasi ng througnout
t ne t est i ng except f o r or;e of t he car t r i dges between 80 and 191 hours. Also,
the spread from the l east ressure drop t o the yeat est pressure droQ has
e increased by a l arge amoun .
The range o f pressure drops f o r a1 l ei ght cooler-regenerators f 01 lowing
tne high-power t est wi t h the dynamometer i s shown i n f i gur e 11. A t t he maxi-
mum flow r at e tested, 18 gl sec (0.04 l bl sec), the pressure drop ranged from
about 234 t o 421 ki l opascal s (34 t o 61 psi ). Thi s compares wi t h a range of
165 t o 196 k i lopascals (24 t o 28.5 psi ) when t he cart ri dges were new. The
l arge spread f o r the cart ri dges af t er 191 hours of t est i ng i ndi cates t hat
there was poor di st r i but i on o f f l ow through t he ei ght cooler-regenerator ci r -
cui t s duri ng these engine tests.
The di f f erence i n pressure drop through t he heater head assembly shown i n
f i gur e 9 does not appear t o be l arge enough t o sol el y account f o r t he di f f er -
ences i n engine output a t hi gh speeds. Thi s i s substanti ated by t he NASA
Lewis St i r l i ng cycl e computer program. However, what ef f ect t he contamination
of t he heater head had on heat t r ansf er i n the heat exchangers i s not known.
Fi gure 8 shows deposits on t he water si de of the cool er tubes, so t h i s would
al so have adversely af f ect ed t he heat transfer. Estimates of new heat trans-
f er coef f i ci ent s f o r the heat exchangers would have t o be made t o f ur t her
analyze t he di fferences.
Two other areas whose ef f ect s were i ncl uded i n f i gur es 5 and 6 were
i nvesti gated i n attempting t o determine t he reasons f o r t he decrease i n engine
output. The f i r s t concerned t he accuracy o f t he torque measurement. To check
t hi s, a torquemeter and a 7.5-kilowatt (10-hp) el ect r i c motor were used t o
cal i br at e t he dynamometer system. The torquemeter was cal i br at ed and then
i nst al l ed between the el ect r i c motor and the dynamometer ( af t er the engine was
removed from t he t est stand). Tests were r un over a range of loods f o r each
speed wi t h the load c e l l tcrque reading f o r the dynamometer system being cow
pared wi t h t hat from t he torquemeter. Af t er analyzing t he resul ts, i t was
decided t o add a constant value of 0.6 l b- f t t o each value of torque as mea-
sured by t he load cel l .
Tne second area i nvesti gated r el at ed t o check valve losses. Pr i or t o t he
st ar t of the high-power t est s wi t h the dynamometer, new check valves were
i nst al l ed i n the vent l i nes o f t he buf f er and compression spaces. These two
l i nes are t i ed together and vented through a si ngl e needle valve. A pressure
transducer was i nst al l ed i n t he comnon l i n e t o determine i f these check valves
were working properly. Typi cal pressure traces obtained are shown i n f i gur e
12 f o r three speed;. Large osci 1 l at i ons are shown at the hi gher speeds, wi t h
l i t t l e or none at tne lower. These osci l l at i ons i ndi cated t hat the cneck
valves were opening at t he hi gher speeds and thus al l owi ng di r ect comnunica-
t i on between tne buf f er and compression spaces. An attempt was made t o deter-
mine t h i s ef f ect on t he engine output at 3000 rpm by i nst al l i ng a needle valve
i d trle l i ne between the two check valves. A data poi nt was taken wi t h the
valve open and closed, but no di f f erence i n engine output was detected.
Consequently, the t est s were concluded wi t h these check valves i n place.
However, motoring t est s were run f ol l owi ng the high-power basel i ne tests.
These motcring tests, wi t h fewer operating const rai nt s and cont rol r est r i c-
t i ons t o mask the resul t s, gave the capabi l i t y f o r determining the magnitude
of the losses t hat were not detected duri ng the engine tests. The motoring
t est s are described elsewhere i n t hi s report. Tests were run at various
speeas and pressures wi t h hydrogen dnd helium and wi t h t he needle valve i n t he
vent l i ne open and then closed. The losses were pr i mar i l y a f unct i on of
speed. It was decided t o use the foliow.ing correct i on factors:
Speed,
r pln
Cerrection,
kW (hp)
These values were added t o the measured engine power outputs. Note t nat t he
correct i on i s onl y si gni f i cant a t 3500 rpm.
Tnus t he r esul t s given i n fi gures S and 6 have been corrected f o r both
f act ors: t he torque measurement cor r ect i on and t he cor r ect i on due t o losses
associated wi t h t he check valves. The l at t er cor r ect i on was appl i cabl e t o
onl y t he t hree hi ghest pressure curves f o r hydrogen and f o r t he 4.1-caegapascal
(600-psi), 3000-rpn poi nt f o r helium. A l l otner data were run wi t h the needle
val ve i n t he vent l i nes closed t o minimize the losses.
Energy-Balance Resi i i ts
Energy balances obtained on t he engine duri ng these t est s and duri ng the
lo+power t est s wi t h the al t ernat or are compared i n f i gur e 13 wi t h hydrogen as
the working f l ui d. A comon poi nt of 2.8-megapascal (400-psi) mean
congression-space pressure and 1500-rpm engine speed i s used. The hot- and
cold-end temperatures are somhwat di f f er ent , but t he ef f ect s of these di f f er -
ences should tend t o of f set each other.
Although t he engine output i s about t he same f o r each, t he ef f i ci ency
increased f r o7 14.9 percent f or the al t ernat or t est t o 14.3 percent f o r these
aynamometer tests. The main reason f o r t h i s ef f i ci ency increase was the lower
exnaust losses. The exhaust losses were subst ant i al l y decreased by changing
preheaters and by lowering the ai r - f uel r at i o. Ihe ai r - f uel r a t i o was de-
creased from 49 f or t hi s par t i cul ar poi nt of the al t er nat or t est s t o about 35
f o r the dynamometer tests. Also, as described i n t he Test Setup secti on the
former preheater had almost one-half of tne exhaust tubes plugged and holes
ourned tnrough some of the tubes. I t was replaced wi t h the preheater of the
engine obtained from the Smithsonian I nst i t ut i on.
The heat losses t o tne o i l and buf f er water; the cycl e heat r ej ect i on
(aefi ned as the beat. l oss t o the water passing through the cool ers minus t he
conduct i on losses); and t he conduct ion, r a d i a t i o ~ and convect ion, and nozzle
water losses are essent i al l y the same f or both cases. However, they have
increased as a percentage of the heat i nput f o r the dynamometer t est s because
of the lower heat i nput r esul t i ng from the lower exhaust losses.
The ef f i ci ency gai n was obtained a t most of the data poi nt s t hat coul d be
compared wi t h the previous lowpower al t er nat or t est resul ts. Thus the in-
crease i n combustion system ef f i ci ency ( lower exhaust losses) more than of f set
the decrease i n thermodynamic cycl e ef f i ci ency (contaminated regenerators and
cool ers).
Fi gure 14 compares energy baf ances f o r helium and hydrogen working f l ui ds
at 6.9-megapascal (10UO-psi) pressure and 1500-rpm engine speed. Thi s was the
maximum ef f i ci ency poi nt f o r each working f l u i d duri ng t he dynamometer tests.
Note t nat the maximum ef f i ci ency was 21.3 percent f o r helium and 26.4 per-
cent f o r hydrogen. Di fferences i n ef f i ci ency and engine output between the
two working f l ui ds are not as si gni f i cant at the lower speeds as at the hi gher
speeds. A t t he maximun! speed of 3500 rpm f o r 6.9-megapascal (1000-psi) pres-
sure the respecti ve ef f i ci enci es were 8.6 percent f o r helium and 13.8 percent
f or h drogen. Again, t n i s l dr ger di f f er ence i s pr i mar i l y due t o t he hi gher
f l ow j osses wi t h helium.
Tne power i n from t he f uel was approxi matel y t he same f o r each poi nt
shown: 15.8 ki l owat t s (21.1 hp) f o r hydrogen and 15.4 ki l owat t s (20.7 hp) f o r
nelium. Also, t he exhaust losses as wel l as t he conduction, r adi at i on and
convection, and nozzl e water losses were about t he same; t her ef or e t he heat
i n t o t he working f l u i d was approxi matel y equal f o r each poi nt . The energy
balances i ndi cat e then t hat t he i ncrease i n ef f i ci ency wi t h hydrogen comes
from an i ncrease i n engine out put due t o decreasi ng cycl e heat r ej ec t i on and
heat losses t o t h2 o i l and buf f er water. The heat l oss t o t ne o i l and buf f er
water can be taken as an i ndi cat i on of t he engine mechanical losses. The
mechanical l ossrs are lower wi t h nydrogen working f l u i d than wi t h hel i um
because o f t he lower gas work l osses i n t he buf f er space f o r hydrogen.
I nai cat ed ?ower Resul t s
Fi gures 15 and 16 gi ve i ndi cat ed power r es ul t s as computed by several
r.?thods. The measurement c f i ndi cat ed power i s usef ul f o r di r ec t comparison
k i t h engine out put as determined by most computer si mul at i ons and al so f o r
i sol at i ng t he St i r l i ng- cycl e ef f ect s on engine output.
Fi gur e 15 shows i ndi cat ed power as a f unct i on of engine speed and mean
compression-space pressure f o r botn nel i um and nydrogei? working f l ui ds. It
compares i ndi cat ed power obtal ned from energy balances wi t h t hat obtai ned f rom
pressure-volume ( p- v) diagrams. The hot- and cold-end temperatures were t he
same as shown i n f i gur es 5 and 6.
Tne energy-balance r esul t s assume t hat t he heat losses t o t he o i l and
buf f er water represent the engine mechanical losses. These are then added t o
t he engine brake out put t o get t he i ndi cat ed powr . The p-v diagram r esul t s
were obtai nea from separate p-v diagrams f o r tne expansion and compression
spaces. The power from t he compression-space diagram i s subtracted from t hat
of the expansion-space diagram t o get the i ndi cat ed power. The instrumenta-
t i on system t o obt ai n these p-v diagrams i s descri bed i n reference ? and i n
the Test Setup sect i on of t h i s report .
The two methods compare we1 1 f o r hydrogen working f l ui d. The p-v r es ul t s
are lower at low speeds and hi gher at ni gh speeds than i n tne energy-balance
r esul t s. Thi s t r end was gener al l y t r ue f o r t he r esul t s f o r bot h nydrogen and
hel i um from the t est s report ed i n reference 1. Only several pr el i mi nar y p-v
diagrarns were shown i n t hat reference because of inadequacies i n t he p-v mea-
surement system; t h i s was mai nl y aue t o t he l ack of water cooling on t he
pressure transducers, which coul d have r esul t ed i n a s ens i t i v i t y s h i f t wi t h
temperature. Tnus al thougn approximately the same t r end was obtained, t he
r es ul t s were l ess consi st ent i n t he ear l i er t est s.
i o r nel i um the p-v diagrams gave r esul t s t hat were hi gner at a l l poi nt s
tnan were those f o r t he energy-balance metnod. As t h i s t r end i s not con-
si st ent wi t h previ ous data (even wi t h hel i um) and as the energy-balance
r esul t s agree wi t h expected values, these hel i um p-v r esul t s appear t o be
questionaole.
Consi deri ng a1 l p-v r esul t s from bot h a1 t er nat or and dynamometer t est i ng,
tne hydrogen data are more consi st ent i n t hei r trends and comparisons than are
t he hel i um data. Thi s may i ndi cat e a response problem wi t h t he hel i um pres-
sure measurements al though cal cul at i ons show t hat t he response times should be
adequate. The main concern i s i n t he expansion-space pressure measurement
where tne transducer i s l ocated at the end of a 15.2-cent irneter (b-i n)-l ong
tuoe.
The compression-space transducer i s approxi ni atel y tlush-mounted.
The maximum i ndi cat ed power f o r hydrogen i s 8.6 ki l owat t s (11.5 hp) a t
6.9-megapascal (1000-psi ) mean compression-space pressure and 3500-rpm engi ne
speed. I ndi cat ed power r esul t s f o r 6.9-megapascal (1000-psi ) hel i um appeared
t o be i n er r or and are not reported. The i ndi cat ed power curves tend t o peak
out a t s l i g h t l y hi gher speeds than do t he brake power curves. Thi s i s ex-
pected as t he mechanical losses i ncrease wi t h speed.
Fi gur e 16 compares p-v i ndi cat ed power r esul t s f or hydrogen bot h from two
p-v diagrams and from one p-v diagram. The use of two diagrams i s as st at ed
previ ousl y (expansion-space work mi nus compression-space work), and these
r esul t s are t he same as those shown i n f i gur e 15. The i ndi cat ed power can
al so be approximated wi t h one diagram by usi ng any pressure i n t he worki n
space (compression-space pressure i s used i n these t est s) versus t he t o t a
change i n working-space volume.
9
The r es ul t s i ndi cat e t hat t he use o f one diagram gi ves a somewhat hi gher
answer than does t he use of two diagrams. Thi s has been consi st ent f o r most
t est i ng and par t i c ul ar l y wi t h hydrogen. There are problems associ ated wi t h
ei t her method. The two-diagram metnod i nvol ves f i ndi ng a smal l answer by
t aki ng t he di f f er ence between two l ar ge numbers, each of which has measurement
er r or s i nvo lved. The one-diayram method negl ect s t he f u l l ef f ec t of pressure
drop througn t he heat exchangers as onl y one pressure i s used. On t he basi s
of a l l data taken t o t h i s time, t k? use o f separate p-v diagrams i n t he expan-
si on and compression spaces appear's t o gi ve t he more accurate r esul t s.
APPARATUS AN0 PROCEOURE - MOTORING TESTS
Test Setup
Motori ng t est s were run t o ai d i n determi ni ng engine mechanical losses,
wnich can be added t o t he brake power t o get t he engine i ndi cat ed power.
Several ot her methods, i n addi t i on t o motoring, are al so used t o determine t he
mechanical lossec and ' ndi cated power; thus each can be compared wi t h t he
others t o evai uate t he r esul t s. The ot her methods use energy-balance dat a t o
determine mechanical l osses (heat t o t he o i l and buffer-space cool i ng water)
and di r ec t measurement of the i ndi cat ed power wi t h pressure-volume diagrams.
Motori ng a St i r l i n g engine t o determine i t s mechanical l osses cannot be
ef f ect i vel y accomplished by dr i vi ng t he engine i n i t s normal :onfiguration.
To pr oper l y motor, t he di spl acer pi st on must be repl aced wi t h a pi st on of t he
same weight but causing negl i gi bl e pumping. For these t est s a s ol i d di spl acer
pi st on was made wi t h s i x hol es d r i l l e d through t he pi st on t o al l ow di r ec t f l ow
between the compression and expansion spaces and t o el i mi nat e f l ow through t he
heat exchangers. The weight was made i dent i cal t o t hat of t he normal hol l ow
st ai nl ess- st eel di spl acer by f abr i cat i ng t h i s pi st on from a combination of
aluminum and magnesiclm. As t he motori ng t est s were r un col d j no combustion
occurri ng), these mat er i al s di d not need t o be heat r esi st ant . The hol es
a r i l l e d tnrough t he di spl acer had a diameter o f 0.95 cent i net er (0.375 i n.)
and were si zed t o gi ve a f l ow area about 1.5 ti mes t he heater-tube f l ow area.
The pi st on r' ngs were i ns t al l ed i n t he same marler as f o r t he standard di s-
pl acer. The di spl acer pi st on f o r motori ng i s shown i n f i gur e 17.
A f ur t her problem wi t h mst ori ng i s t he di f f er ent loads on t he bearings,
seals, and pi st on r i ngs as compared wi t h engine operat i on because of t he di f -
f erence i n pressure var i at i ons. Thi s ef f ect was reduced by changing t he vol -
ume of the working space t o gi ve approxi matel y the same pressure r a t i o dur i ng
motori ng as occurs i n normal engine operat ion. The ei ght cool er-regenerator
car t r i dges were removed and repl aced wi t h pl ugs t o el i mi nat e a subst ant i al
m u n t of volrme. As the temperature effec' on pressure r a t i o are mi ni m1
duri ng motoring, an estimated pressure r a t i o coul d be cal cul at ed from t he
known volumes. The actual pressure r at i os were measured duri ng the motoring
tests. Those r esul t s are gi ven i n t he Results and Oiscussion section. One o f
the plugs t hat replaced a cooler-regenerator car t r i dge i s al so shown i n f i g-
ure 17. As no cornbustion was necessary f or these tests, t he preheater was
removed from the engine.
The f a c i l i t y setup was t he same as i- f i gur e 2 wi t h t he f ol l owi ng
cnanges. The a i r and f uel syst em and t he nozzle water l i nes e r e dis-
connected. The t urbi ne f lowmeter i n t he cool er water l i ne was replaced wi t h a
flowmeter of l ess range as the flow was reduced because o f t he pl ugs i r: t he
cool er passages. A small water fl ow was ci r cul at ed around t he pl ugs and
around the cyl i nder cool i ng passage t o reduce the temperature var i at i ons o f
the working f l u i d duri ng motar ng.
A second set of nyl on t i m i r y gears f ai l ed a t t he end of t he hydrosen base-
l i ne tests. For the motoring t est s these were replaced with a set of al wi num
ti mi ng gears. Also, a ccupl i ng wi t h greater t or si onal f l e x i b i l i t y was in-
st al l ed between the engine and dynamometer t o ai d i n reducing tne ef f ect o f
torque reversal on the t i mi ng gears.
Test Procedure
The motoring t est matri x f o r both heiiun, and hydrogen working f l ui ds con-
si st ed of mean compression-space pressures from 1.4 t o 6.9 megapascals (200 t o
1OOO psi ) and engine speeds from 1500 t o 3500 rpm.
On each startup, cooling-water f l ow was f i r s t provided t o the buf f er and
cool er ci r cui t s. Coo i ing-water i n l e t temperature was not cont r ol l ed and
vari ed from 4' t c j 8' C (40' t o 47' F ) f or these tests. Approximately 2.8-
megapascal (400-psi ) mean compression-space pressure was set i n t he engine,
and the engine was then rot at ed by motoring w i t h the dynamometer. Motoring
conai ti ons were maintained at 2.8-megapascal (400-psi) pressure $nd 2000-rpm
engine speed unt i 1 the oi 1 temperature reached 38 t o 41' C (100 t o 105' F).
Tnis took about 30 minutes. O i l temperature was not cont r ol l ed duri ng these
tests; vari at i ons i n o i l temperature were si mi l ar t o tnose i n normal engine
operation.
F 01 lowing engine warmup, one or two curves at constant mean conpression-
space pressure were run f o r eact engine startup. A curve consisted of data
poi nt s taken at engine speeds varyi ng by 50Grpm i nt erval s, wi t h the hi ghest
speed set f i r s t . The speed was set by adj usti ng the speed cont r ol on the
aynamometer. After the desired condi ti ons were established, the data poi nt
was neld f or about 10 minutes. During t hi s time steady-state data was
recordea three times and dynamic data once. Af t er completing t hi s, a new
speed was set and the procedure repeated.
RESULTS AND 01 SCUSSION - MOTORING TESTS
The f i gures presenting the motoring r er gl t s are sumnarized as f o l lows:
The measured motoring power i s given i n f i gur e 18 as a f unct i on of speed and
pressure. Fi gure 1 Y compares mechanical losses (as found by energy balances)
f or both the motoring t est s and t he engine t est s t o ver i f y t hat both r esul t s
are about the same. Figures 20 and 21 i 1 l ust r at e tne correct i on of the motor-
i no power by subtracti ng the i ndi cated work of the working f l ui d. The mech-
ani cal losses as determined by t hi s correct i on are then compared wi t h energy-
bal a~l ce r esul t s i n f i gures 22 and 23.
The pl ot t ed poi nt s i n f i gur es 18 t o 23 are averages of a l l data taken f or
a par t i cul ar condition. Each curve with helium working f l u i d was r un twice.
For hydrogen working f h i d , onl y the ti.!hnegapascal (1000-psi) curve was re-
peat t i before t he d~spl acer pi st on f ai l ed and t he motoring t est s were ended.
Some di f f i c ul t y was found i n obtai ni ng repeatable data. As t he reason f or
t hi s was not determined. i t was decided t o average a1 1 acceptable data f o r a
given poi nt, The average di fference between t he r esul t s f o r runni ng a data
poi nt several times was about 10 percent,
Determination of Mecnanical Losses from Hot or i r ~g Resul ts
Fi gure 18 shows the motoring power as a f unct i on o f mean corapression-space
pressure and engine speed f or h e l i m and hydrogen working f l ui ds. T he motor-
i ng power 1s t he p w ~ needed t o dr i ve t he engine wi t h t he dynanxnaeter motor
at the desi red engine speed and mean cmlpression-space pressure. The motori ng
power was determined from t he dynamometer load c e l l reading. The s l o ~ e s c f
the curves are i ncreasi n wi t h engine speed, i ndi cat i ng a more than l i near
9 var i at i on wi t n speed. A so, note the l arge values of motoring pouer t hat were
measured. A t maximum pressure and speed the motoring power was 3.5 ki l owat t s
(4.7 np) f or hydrogen working f l u i d and 4.5 ki l owat t s (6.0 hp) f o r hel i m.
This di fference al so s b s t nat a greater motoring power was requi red wi t h
helium working f l u i d than wi t h hydrogen at any gi ven condi ti on,
A comparison was made wi t h engine t est data t o determine if t he mechanical
losses f or motoring were approximately t he same as duri ng engine testi ng.
This was done on the basi s of mechanical losses as measured from t he energy
balance (heat t o o i 1 pl us heat t o buffer-space cool i ng water). Fi gure 19
shows t hi s c wa r i s o n f or two pressure l evel s f o r both helium and hydrogen
working f l ui ds. The curves f o r engine t est r esul t s are an average f o r runs
from t est i ng wi t n the al t er nat or and with tne dynamometer. The f i gur e i ndi -
cates t nat t he resu:ts are about the same, wi t h the motoring values being
somewhat l ess than the engine values f or nigher pressures. Thi s may be due t o
l ess hzdt conduction t o the buffer-space cool i ng water duri ng motoring t est s
as the cold-end metal temperatures were lower f or the motoring t est s than f or
engine tests.
Measurements of the i ndi cate0 work o f t he working f l u i d were made duri ng
the motoring t est s through the use of pressure-volume diagrams. The work was
determined by two metnods. The f i r s t was t o use separate p-v diagrams i n t he
expansion and compresson spaces wi t n tne t ot al work being tne di fference
be-ween expansion work and compression work. Thi s gave negati ve values of
worK, as i s expected as work i s bei i ~g done on the gas. f ne other methoa was
t o use j ust one p-v diagram, t hat being t he compression-space pressure as a
f unct i on of the t ot al volume change of the working space. Thi s al so gave
negative values as expected.
The work determined from t he one p-v diagram was more consi stent than t nat
found from two diagrams. I t i s probable t hat the er r or i nvol ved i n subtract-
i ng two l arge numbers (as i n expansion work minus compression work), each of
which nas a cer t ai n error, becomes ehcessive dhen determining the Small values
of gas work i nvol ved i n motoring. The one-diagram method does not properl y
account f or pressure drop losses i n the working space, and these er r or s appear
t o be I nport ant f or engine t est i ng. However, f o r motoring t he pressure drop
losses are small as a r esul t of removing the coole:-regenerators and using t he
di spl acer wi t h holes. Thus i t was decided f o r the motoring t est s t hat the
i ndi cated gas work i s best determined from one p-v diagram.
Fi gure 20 gives i ndi cated work r esul t s measured by t he on+diagram
method. These r esul t s are pl oeted as a f unct i on of mean cotnpression-space
pressure and engine Speed f or both hel i um and hydrogen working f l ui ds. Note
t hat the values f o r hel i um are si gni f i cant l y hi gher than those f o r hydrogen.
These i ndi cated work r esul t s represent losses i n t he working f l u i d due t o flow
losses, i r r ever si bi l i t i es and leaka e between t he corpression and buffer
i? spaces; these losses should nab IX c arged against t he mechanical Insses f o r
the engine. Thus a f irst-0:-&r at t -t t o s-arate these can be maw by sub-
t r act i ng t he working-f l ui d i nd-cated pwer fm t he t ot al motoring power.
Buffer-space as wr k was al so raeasured, but any losses occi4rring i n t he
8 buf f er space, i nc uding gas work. are \ w e d i n wi t h t he nte~hani cal losses.
f i gur e 21 shows the mec;~anical losses as determined by subtracti ng t he
worki ng-fl ui d i ndi cated power fm t he t ot al motoring power. O' reral l the
r esul t s remain reasonable i n terms of i ncreasi nq mechanicai losses w i t h in-
creasi ng pressure and speed. However, t he spacing between t he curves i s
varied; t hi s i s probably due t o the er r or s i nvol ved i n the seveual measure-
ments necessary t o obt ai n the f i nal nunber. Note t hat th* r esul t s shown rn
f i gur e 21 are si mi l ar i n value at a gi ven poi nt f o r both helium and nydrogen.
Some ai f f erence would be expected due t o t he hi gher gas work losses i n t he
bucfer space f or t~el i urn as cosl ~ared w i t h r~yarogen. However, t hi s di f f erence
i s small and may be l ost i n t he ra5asuremer.t error.
Coaparison of Mchani cal Losses by Motor-ing and Energy-balance Resul ts
A conparison was nade of t he mechanical losses as found from energy-
balance and motoring resul t s. TMse are shown i n f i gures LL and 23 f or hel i um
and nydrdgen working f l ui ds, respecti vel y. Tne energy-balance r esul t s are
determined b] aading tne nedt t o tne o i l and tne heat t o the buffer-space
cool i ng mater. The curves shcwn are an averaqe of those obtained f o r low-
power oaseline t est s wi t n tne al t ernat or and high-pouer basel i ne t est s wi t h
the djnamometor. Th2 motoring r esul t s are t he saw as those gi ven i n f i p
ure 21. They were determined by suotracti ng the worki ng-tl ui d i ndi cated power
i ur i ng motoring f rm the t ot al motoring power.
For both helium ana hydrogen the two metnods gi ve r esul t s t hat are aMut
tee same at the lower speeds, but t h e motaring r esul t s are s' gni f i cant l y
higher at the hi gh speeos. Also, the energy balance gi ves r esul t s t hat vary
l i near l y wi t h speed, whi l e t he ,notoring r esul t s y i el d a higher-crder curve.
Tnere are def i ci enci es i n each ~netnoa. For the energy balafice the heat t o
t ne buffer-spacz cool i ng water may i ncl ude some conduct i o~~ losses, which
snoula not oe cnargec agalnst the mechanical losses. Also, the heat t o t he
engine cool ,~rs i ncl udes s o w f r i c t i o n losses from the pi st on r i ngs and di s-
pl acer roa ~ e a l . Tnese snould be included i n the estimate of mecnanical
losses but are not. The motoritlg t est s have the problem of di f f er ent loads on
tne bearings, pi st on rl nqs, and shaf t seais when c q a r e a wi t h engine tests.
as wel l as the problem ot sor t i qg out t he gas Work losses.
To minimize the di fferences i n loading ouri ns tne motoring tests, the v9l -
ulne of the working space was changed by removing the cooler-regenerators and
by adding the vclume of the holes i n the di spl acer t o gi ve 3DCut the sane
pressure r a t i o dlrring motoring as i n engine operation. These cnanges are
described i n the Test Setup section. Fi gure 24 canpares pressure traces f or
tne canpression and buf f er spaces from motoring and engine tests. The traces
are f or a mean conrpressi~n-space pressure of 6.9 cegapascals (1000 psi ) , an
engine speed of 3000 rpm, and helium working f l ui d.
The compressslon-space pressure r at i o (maximum pressure/mlnimurn pressure)
was 1.39 f or the engine t est s and 1.95 f c r motoring. However, thece was d
di f f erence i n the phasing. ?he maximum pressure occurreo about 1 7 l at er f or
t he engine t est s than f o r motoring; t he a i n i u pressure occurred Bbwt 31.
i at er f or the engine tests. The buffer-rpace pressure r a t i o was 1.47 f or
engine t est s and 1.44 f o r motoring, T k phasing was approximately t he s i m
f or the buf f er space. Tne buffer-space mean pressures are a t di f f er ent
l evel s. Thi s i s a functi on of t he p w i n g of the pi st on r i ngs and does vary
sotaewnat as the sl ot s i n the pi st on r i s and the pi st on r i ng grooves becore
"9 cl i rty. usual l y wi t h a conbi nati on o f o i and r ust par t i cl es, The pi st on r i ngs
are cleaned or new r i ngs i nst al l ed wnen the mean buffer-space pfeSSUige becolres
excessi vel y hi gh with respect t o t he mean coqwession-space pressure,
The pressure traces with h rogen rsorking f l u i d are the same except t hat
t ne pressure r at i os are sl i gbt T' y lower. Thi s i s shorn i n f i gur e 25, which
c ma r e s compression-space and buf fer-space pressure traces f o r nel iun and
taydrogeq engine resul t s. Again, the mean coqwession-space pressure i s
6.9 megirpascals (1000 psi ). and t he engine speed i s 3000 rpm. The phasing i s
aoout t he sane f o r e x h working f hi d, but t he coqwess'on-space pressure
r a t i o f or nydrogen i s 1.88 ard t hat f o r h e l i m i s 1.99. The buffer-space
pressure r at i os are 1.38 for nydrogen and 1.47 f o r he1 iua. The mean buf f er-
space pressures are again saaewnat di f f er ent .
The mechanical losses can be used t o determine i ndi cat ed power by s m i n g
ti l e brake peer and mechanical losses. Thus a f ur t her check on both slethods
of determining t he mechanical losses i s t o coapare t he i ndi cat ed power found
by using the mechanical losses t o t hat found di r ect l y f raa p r e s s u r e v o l ~
(p-v) dilgrams. Fi gure 15 gi ves t h i s ctnpari son f o r the energy-balance r+
sul ts; the energy-balance r esul t s are determined by sumi ng brake power, heat
t o t he oi l , and heat t o t he buffer-space cool i ng water. The f i gur e shorn t nat
tne i ndi cated power by p-v diagrams i s hi gher at hi gh speeds and ei t her cl ose
t o or l ess than the energy-balance r esul t s at low speeds. Thi s sane trend i s
shown i n f i gures 21 and 22. where the motoring-determined mechanical losses
are greater a t t he hi gn speeds than the mechanical losses determined from an
energy 3alance and aoout t he same or l ess at the low speeds.
The i ndi cated power foucd from the brake power and t he mechanical losses
aetermined froin t he motoriag r esul t s are compared i n f i gur e 26 wi t h the i ndi -
cated power found from 9-v diagrams. The comparison i s shown f o r hydrogen
only. These curves are marc c i mi l ar i n snape tnan were the curves cocrpared i n
f i gur e 15. However, t he di f f er ent i al between t he curves i s general l y greater
than i n f i gur e 15. Thus the experimental data dc not i ndi cat e whicn method of
aetermining mechanical losses i s more correct par t i cul ar l y when not i ng t hat
some problems al so remain i n provi di ng f u l l y r el i abl e pressure-volunle diagrams
f o r tnese comparisons.
wi t h respect t o measuring i ndi cated power the three methods ( p- v di ay. as,
sumning brake power and mechanical losses from energy balances, and sumning
brake power and mecnanical losses from motoring r esul t s) gi ve r esul t s t hat are
a l l wi t hi n a reasonable experimental band but cone of which caq be i dent i f i ed
as the most correct.
CONCLUOI NG REMRKS
Tne ef f or t s t o colnglete the full-power basel i ne t est s were met wi t h ngmer-
ous engine and f a c i l i t y problems. These data are l ess r el i abl e than the data
taken i n the low-pcuer basel i ne t est s and publisnea i n reference 1. It i s
f e l t t hat the primary reason f o r t he di fferences i n engine performance between
these t est s and toe t est s reported i n reference 1 was poor heat exchanger per-
formance, par t i cul ar l y t ne regenerator. dowever, i t may be possi bl e t o obt ai n
cor r el at i on through tne use of a computer sirnulatior. i f the proper adjustments
f or botn increased f l ow losses at d reduced heat t ransf er coul d be made. Even
wi thout t r i s, t he low-speed data s k u i d be reasonakle as t he ef f ect s of de-
graded l eat exchanger performance are l ess at t he iower speeds.
Because of t he reduced engine output t he deta' l ed t est data have not bee3
inc!ubed as par t of t h i s report. However, the data are avai l abl e i n c w u t e r
pr i nt out f wm f m t he author. A s-le data poi nt i s i ncl uded i n the
appendixes t o sww what i s auai lable. The changes t o t he i nformati on neces-
sary t o understand t he data pr i nt out s are al so i n t he appendixes. The re-
mainder of tne information needed i s gi ven i n reference 1.
Motoring t est s were another method investigated, i n addi t i on t o usi ng
energy balances, t o detc?mine mechanical losses. Each method, umtoring or
energy balance, had cer t ai n defi ci enci es and the di fference between t he tm
was ?arge at hi gh speed. The i ndi cated power found frm pressure-volume d i t i
grams was corrpared wi t h t hat found by suas~ing t he brake power and mechanical
losses. I f the pressare-vo b e d i agr as are accurate, t h i s conpari son shows
t nat the shape of t he curve oased on t he motoring-determined mechanical losses
i s more correct than the shape of the curve oased on t ne mecnanical losses
frm the energy balance. However, t he over al l di f f er ent i a{ between t he curves
suggests t hat the magni tude of the energy-balance mechanical losses i s more
accurate. The beat estimate of t he mechanical losses f o r t h i s i nvest i gat i on
may be an average of the r esul t s from the motoririg and energy-balance methods.
Future t est work wi t h t he WU-3 engine w i l l i nvol ve t est i ng new conponent
concepts. These i ncl uae iow-cost regenerators as wel l as a method t o i n ~ r o v e
the heat tvar.sfer between t he heater tubes and t he combustion gases.
SIIWhY W RESULTS
Tne SPU-3 St i r l i ng engine was i nszal i ed on a dynamometer t est bed and
tested over ~ t s f u l l rdnge of engine speeds and pressures at a neater-tube gas
tanperature of 677° C (1250° F ) . The mean cwnpression-space vressure was
vari ed f r an 2.d t o 0.3 megayascais (4W t o 10iK) psi ) wni l e engine speed was
vari ed from 1503 t o 3500 rp~l. Performance f i gur es c;re presented wi t h both
nel i un and hydrogen as tne uorki ng f l ui d.
dot ori ng t est s were tnerl run af t er ranoving the cooler-regenerator car-
tri dges ana 1nstal:ing a speci al di spl acer pi ston. The purpose of tnese t est s
uas t o ai d i n uetennining engine mechanical losses. Tests were run wi t n both
helium and nyaro en over a range of mean compression-space pressures of 1.4 t o
0.9 megapascals TZUU t o lcOO psi ) and engine speeds of 1500 t o 3500 rp..
The major r e wl t s oDtained f r a n these t est s are as fol l ows:
1. The maximum power obtained w i t h hydrogen was 6.62 ki l owat t s (9.14 hp)
at ~.~-rnegaoascal (1000-psi) mean corryression-space pressure and 3500-rpm
engine speed. The minimum brake speci f i c f uel consumption ( bsf c) was
315 gl kk-hr !O.52 l bl hp-nr) at 6.3 ~rugapascals (IWO psi ) and 1500 rpm. Thl s
represents a brake thermal ef f i ci ency of 26.4 percent. Thi s ef f i ci ency i s i n
the sane range as t hat obtained by General Motors duri ng i t s testi ng.
2. Tne maximum power obtained wi t h helium was 4.26 ki l owat t s (5.7i hp) at
5 .S-mega9asca l (1000-psi ) mean compression-space pressure and 2500-rpm engine
speed. Tne minimum ~ s f c was 330 gIkrc9r (0.64 l bl hp-nr) at 6.9 megapascal
(1W psi ) and 1500 rpm. This represents a brake thermal ef f i ci ency of
21.3 percent.
3. The engine output f or these high-power baseline t est s wi t h the dyna-
lnoaseter was low cowared with previ ousl y reported low-power basel i ne t est
r esul t s obtained wi t h an al ternator. Thi s was pr i mar i l y t r ue at hi gh speeds.
It i s f e l t t hat t h i s was caused by degradation of heat exchanger performance
due t o contamination by r ust and oi l .
4. Engine brake theriual ef f i ci ency was hi gher f o r t est s with the dyna-
raoraeter than f o r t he previous al t ernat or t est i ng because a noncontiminated
preheaterm was i nst al l ed t o reduce c ms : i o n system losses. These lower
losses faore than of f set tne addi t i onal lusses i n tne degraded heat exchangers
of the heater head.
5. Motoring t est s were r us t o ai d i n determining mecha~i cal losses; t he
wt or i ng r esul t s nere conpared with energy-balance estimates of t he arech-
ani cal losses. The energy-balance r ecul t s yi el ded a l i near var i at i on of
tnecnanical losses wi t h engine speed, but the motoring r esul t s showed a higher-
order var i at i on wi t h speed. The mechanical losses were about the same at
low speeds f or each metnod but si gni f i cant l y di f i er ent at hi gh speeds. The
experitner.ta1 data do not i noi cat e t hat one method i s more cor r ect than t he
other.
0. Indi cated power r esul t s were obtained as a f unct i on of mean
compression-space pressure ana engine speed f or both nelium and hydrogen as
tne working f l ui d. Three methods were used: pressure-volume diagrams,
sumning brake power and mechanical losses from an energy balance, and sumning
brake power and mechanical losses from motoring resul t s. Although i t i s not
possi bl e t o conclude whicn i s the most correct, a1 1 three gi ve r esul t s t hat
are wi t ni n a reasonable experimental band.
Tne detai l ed data taken during these t est s have not been included as part
of t ni s report. However, computer pri nt out s of the data are available from
the author. A sample data poi nt i s shown here t o i ndi cate what i s available.
Host of the information necessary t o understand the data pri nt out s i s
given i n reference 1. Cn~nges t o the instrunentation f or these t est s are
l i st ed i n table I. Tnese are siven as raeasureuents that were removed as w e l l
as those added or changed. Figure 27 shorn the new preheater thernmouple
locations. I n addition, the following calculations were eliminated: PWRALT,
a1 ternator output power; ALTEFF, al ternator efficiency; and QCVTOC, heat out
t o cooling water per cycle - t ot al flour. The cal cul ati on of PWWT, engine
output power, was changed t o use the measurement of engine torque.
Fi nal l y, tne explanation of the run nucaber f or each data poi nt i s the same
as given i n reference 1 wi t h the fol l owi ng exception. The heater-tube gas
tenperature f or eacn poi nt was 1250- F, and t hi s i s i dent i f led by a '25" i n
the run number.
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WORCING FLUID SAMPLES
At vari ous ti mes duri ng t he engine t est s, wor ki ng- f l ui d samples were taken
before and af t er engine runs. The sample bot t l e was evacuated, and t he sample
was then taken from t he engine vent 1 ine. The samples were analyzed wi t h a
mass s pec t r mt er . Typi cal samples f o r hel i um and hydrogen working f l u i d s ar e
gi ven below.
For hel i um working f l u i d t he t es t condi t i ons were
Heater-tube gas temperature, OC (OF) . . . . . . . . . . . . . . . . 677 (1250)
. . . . . . . . . . . . . Mean compressiorkspace pressure, MPa ( psi ) 2.8 (400)
Engi neseed. r pm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2000
These condi t i ons were hel d f o r about 2 hours bef ore t he f i nal sample was taken.
F o r hydrogen working f l u i d t he t es t condi t i ons were
'42
He
CH4
N2
02
A r
' 32
*
tIeat2r-tube gas temperature. OC ('F ) . . . . . . . . . . . . . . . 677 (1250)
Mean compressiowspace pressure, MPa ( ps i ) . . . . . . . . . . . . . 5.5 (800)
Engine speed, rpm . . . . . . . . . . . . . . . . . . . . . . . 1500 t o 3500
These samples were taken before and af t er obt ai ni ng t he 5.5-megapascal
(800-psi) hydrogen t es t data shown i n t h i s r epor t . The t o t a l engine r un t i me
f o r t h i s t es t was 2 hours and 50 minutes.
Before r un
I
Af t er r un
Worki ng-fl ui d content, ppm
0
Parent
3
90 1
0
0
29
0
Parent
0
968
130
2 4
0 3
-
'42
He
cH4
N2
02
A r
co2
Before run Af t er r un
Worki ng-fl ui d content, ppm
Parent
0
94
5503
5 1
0
0
Parent
884
426
6179
50
9 5
0
REFERENCES
1. Thieme, Lanny G.: Low-Power Baseline Test Resul ts f o r t he GPU-3 St i r l i n g
Engine. NASA TM-79103, 00E/NASA/1040-7916, 1979.
2. Cai r el l i , 3. E.; Thi ei i , L. G.; and hal t er, R. 3.: I n i t i a l Test Resul ts
wi t h a Single-Cylinder Rhombic-Drive St i r l i ng Engine. NASA TM-78919,
DOE/ NASA/1040-78/1, 1978.
3. Tew Roy; Jef f r i es, Kent; and Miao, David: A St i r l i n g Engine Computer
Moor l f or Performance Calcu 1 ac ions. NASA TM-78884, OOEI NASAIlGll-78/24,
1978.
4. few, Roy C., Jr.; Thieme, Lanny 6.; and Miao, David: I n i t i a l Comparison
of Single-Cylinoer St i r l i ng Engine Computer Model Predi ct i ons wi th r est
Results. NASA TM-79044, DOEINASA/1040-78/30, 1979.
5. Rice, W i 1 l i am d. : Indi cated Mean-Effective Pressure Instrument. WSA
Tecn Br i ef 876-10542, 1977.
6. Rice, W i l l i a m 3; and Birchenough, Arthur 6.: Modular Instrumentati on
System f o r Real-T ime Measurements and Control on Reci procati ng Engines.
NASA TP-1757, 1980.
7. Perci val , W. H.: Hi st or i cal Review of St i r l i n g Engine Development i n the
United States from 1960 t o 1970. (REPT-4-E8-00595, General Motors
Research Labs.; EYA Contract EPA4E8-00595. ) NASA CR-121097, 1974.
TABLE I. - CHANGES TO GPU-3 INSTRUMENTATION FOR DY,AMOETER TESTS
[A1 1 thermocouples are C hromel-A1 umel ( type K) . L i sted ranges
are f ul l - scal e rapge f or pdbsssure transducers and l oad c e l l
and measurement range f or thermotouples. Maximum pressures
( items 94 and 95) are found by adding t he pressure swing
determined by t he mi ni at ur e transducers t o t he val ues o f
minimum pressure ( items 92 and 93) .]
( a) Removed
Mnemonic
TALTH
TDLWT
TPHI T l
T?H I T2
TPHI T3
TPHI B l
TPHI B2
TPHIB3
AW
VOLT
CWFLOT
RLOAO
POCOR
P DBUF
Parameters
A1 t er nat or housi ,lg temperature
Cool ing-water del t a t e mp e r a t ~ r ~ - t o t a l f l ow out t o i n
Preheater i nsi de surface temperature:
Top - 0'
Top - 120'
Top - 240'
Bottom - 0'
Bottom - 120a
Bottom - 240'
Al t er nat or out put cur r ent
A1 t er nat w output vol t age
Cooling-water f l ow - t o t a l
Resistance l oad bank set t i ng
Pressure swing (minimum t o maximum) - compression space
, Pressure swinq - buf f er space
( b) Added o r changed
I t em
85
86
87
88
89
90
91
92
93
94
95
Mnemonic
TEXHOl
TEXHO2
TEXHQ3
TEXH04
TEXHOS
TEXH06
TORQUE
MINCP
MINBP
MAXCP
MAXBP
Range
350'-600- F
1
0-50 1b
((I-75 l t b f t )
0-1000 psi g
0-1000 psi g
0-2000 psi g
0-2000psi g
P ar amet er
Exhaust temperature
out of preheater:
0'
60'
120°
180'
24aa
300a
Engine torque
Minimum compression-
space pressure
Instrument
Thermocouple
I
Load c e l l
Strain-gage
I
transducer
Minimum buffer-space Strain-gage
pressure transducer
Maximum compression-
space pressure
Maximumbuffer-space
pressure
Mi ni at ur e st r ai n-
gage transducer
Mi ni dt ur est r ai n-
g a ~ e transducer
-
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r Conductm. radbtW!
f
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f
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f
[email protected]
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-
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mR yro
0 2 I M
o 55rm
- Enplnr tnl r u m
--- m l q tnt rnut b
Flgurr 19. C m p r l u n d mrcmnlal lmw as Mu-
ni ~nrd tq mergy Muncrr that b otl + hat \O hrUU
* at r r ~ b mo(wlnq trcts and nqlnr tnts
_~._1__1_2
!a1H)dra)m rati ng fluid
-
oL 1- 1- - - 1. a
0 I * a m u m o m o
tnpint r p d . rpm
Flqurt Zl - Wh r n l a l hl.r rr drhrmlnd tho 211hr-
ena in mobring para and rwtl w~4l ui d 1ndlCJldpar
as r fundlon d ma l l mmp n c m~ p c q p n 5 u r r JIM
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fludr
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tnptna W. r m
ngurr 22 - (rrm(.rtloc, d mutunloll krmas Ml ml n d by arrgy-
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Crank angle. dqrecr after
dlSpUW TDC
f qurc 24 - Conprl vn d mmprns nnl pl cc and
b u k - l g l c e p n s u r c tncn br c;lqtnc and mom-
.ng tcs'.. Wwk l y llud helrirm. ma n cDcDrer-
s ~ o n - s p ~ u prnsu-: 6. 9 MPa tlm: pr ~t englnt
m u morvm
Hellurn Wqnr resul t
Crank [email protected] d q r m J ~ M
d1W-r TDC
I I I I
1 WD mmc m
Cngilu rpd, rpm
Fqurc 26. - @mprism ol dndlatldpam *om prnrure-rolun.t ; q n mr
and @ u r l q molpriq raultr lor ml nqfluid.

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