A description is given of the results of dynamic property tests that were carried out using a trial produced prototype of a 50 KW Sterling engine. The features of the engine are shown graphically. A high thermal efficiency is found in the low rotation region

Seibara, M.

Takenai, K.

Tani, Y.

Yamaguchi, W.

English

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https://ntrs.nasa.gov/search.jsp?R=19840021156 2020-03-20T22:34:47+00:00Z
NASA TECHNICAL MEMORANDUM 	 NASA TM
-77719
	
(NASA-VI-77719) DYNAlIIC PIOPEBTY STUDIES OF
	 N84-29225
STU LING ENGINES (National Aeronautics and
Space Administratiou) 12 p HC A02/AF A01
	
CSCL 131
	 Unclas
.t7 20045
DYNAMIC PROPERTY STUDIES OF STERLING
ENGINES
Y. Tani, M. Seibara, K. Takenai, and
W. Yamaguchi
Translation of "Sutaringu enjin no
doryoku tokusei shiken", Nihon Kikai
Gakkai Koen Ronbunshu, No. 810-5,
pp. 132-4
^^ xx
 
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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
Washington D.C. 20546
	
FEBRUARY 1984
ORIGINAL PAGE '13
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Translation of "Sutaringu enjin no doryoku tckusei shiken",
Nihon Kikai Gakkai Koen Ronbunshu, No. 810-5, pp. 132-4
11♦ Abp'
A description is given of the results
of dynamic property tests that were carried out
using a trial-produced prototype of a
50 KW Sterling engine. The features of
the engine are shown graphically. It
is found that a high thermal efficiency
is found in the low rotation region.
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DYNAMIC PROPERTY STUDIES ON STERLING ENGINES*
Yukio Tani**, Maraseio Seibara**, Kanewa
Takenai**, and Wamei Yamaguchi**
1.	 Introduction
There has been a recent demand for sterling engines as
future fuel engines because of their high efficiency, fuel
diversity, low toxicity, etc. Progress has been particularly
strong in the U.S. on the development of sterling engines
because of their low energy consumption. On the other hand,
several Japanese research institutes and companies have been
carrying out studies on sterling engines. However, there
are few experimental reports on the dynamic properties of
the engine in the test results on theoretical analyses and
component features.
/132***
We will report here on the results of dynamic property
tests that were carried out using a trial-produced prototype
of a 50 KW sterling engine.
2.	 Engine Summary
The features of the trial-produced engine are shown in
Table 1 and its cross section is shown in Figure 1.
*April, 1981, 58th Regular Convention- Thermal Engineering
and Internal Combustion Engines
**Aishin Seiki Co., Ltd.
***(Translator's note): Numbers in margin indicate foreign pagination.
1
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Or POOR QUAU7Y
TABLE 1. Features of Sterling Engine
Operating gas
Fuel
Piston type
Number of air cylinders
Bore x stroke
Hcatei tube temperature
Coolant temperature
Output pick up device
Axial sealing method
Output control method
Combustion method
Air preheater
High temperature heat
exchanger
Low temperature heat
exchanger
Regenerative materials
He gas
Kerosene
Double acting
4
X68 x 52
750°C
200C
Rotating swash plate engine
Sliding seal
Minimum pressure control method
Ultrasonic wave fogging combustion method
Multitube type
SUS tube type
Shell and tube type
SUS net
ti
y
	
air preheater^Q^` Qti	 outputa,^y a
s ,-- ti°	 pick:-up device
burner 4
expansion _J^	 low temperature heat exchanger
chamber	 regenerator ^—
Figure 1. Cross section of Sterling Engine.
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This engine is the same as that reported previously [1].
It uses the 4 air cylinder double-acting system and has
4 pistons in a circle at a distance of 90 0 . The output is
picked up by a rotating swash plate engine. The fuel is kerosene
and the operating gas is helium. Output control is carried out
by control of the minimum pressure of the operating gas
with a check valve. Moreover, a sliding seal is used as the
rod seal.
3.	 Testing Method
In this test the dynamic measurements of the engine were
carried out by controlling the r.p.m. using a direct current
electric dynamometer. Friction loss of the piston ring, rod
seal, and output pick-up device was determined from the amount
of heat transmitted to the coolant. Heat loss of the
exhaust was computed from the air ratio, which was determined
from gas analysis, and the exhaust temperature. The amount
of heat exchanged by the air preheater was determined from
the flow and temperature of air used in combustion. The temperature
control of the heater tube was carried out by setting up 16 CA
thermocouples on the outside of the tube and controlling the amount
of fuel fed so that the mean temperature would be constant.
Furthermore, extra blowers and fuel pumps were used in the tests
and were operated separately.
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4. Test Results and Considerations
The engine property curves obtained during these
tests and the equivalent efficiency curves are shown in
	 /133
Figure 2. Axial output is shown with regard to an operating
gas minimum pressure of 10 MPa (during total load), 6 MPa
and 4 MPa. The mean temperature of the heater tube was 750 0C
and the operating gas pressure ratio at this time was
approximately 1.8.
The maximum output obtained in these tests was 57 KW (71P)/
2,500 r.p.m. and the maximum efficiency was 31%(fuel consumption
rate of 196 g/psH)/700 r.p.m. The maximum torque was
30 kg-m
 /500 r.p.m. Furthermore, the torque in the low
rotation region was practically flat up to 200 r.p.m.
and smooth operation was possible. Moreover, this engine
showed a higher efficiency in the low rotation region.
4-1) Thermal Calculations
The thermal calculation chart during maximum efficiency
is shown in Figure 3. Approximately 65% of the thermal
energy of the exhaust is recovered by the air preheater in this
engine. Exhaust loss is very low at 15%. Heat leaks show
an almost constant value under a constant heater tube temperature.
The measures
	 are approximately 3 KW through the sealing walls,
etc. to the coolant and approximately 1KW from the heating
furnace walls, etc. to the atmosphere. Seal loss is due to
fraction loss of the piston ring and the rod seal.
4-2 Effects of R.P.M.
The correlation between the efficiency of the entire unit
and each section during engine total load and the number of
r.p.m.s is shown in Figure 4. Thermal efficiency 19 3ross is at
the maximum with approximately 700 r.p.m. and decreases on the
high rotation side. Burner efficiency n B is at a maximum
near 1,500 r.p.m. (fuel input of 140 KW)
and shows a tendency to be lower than the reduction in the
heat efficiency of the air preheater and high temperature
heat exchanger on a higher rotation side. The illustrated
efficiency hind is approximately 5.2% in the low rotation
4
In
Im
r^
.G
region and decreases with an increase in the r.p.m.
The Carnot efficiency shown in the figure is computed from
ncar=(TH-TC)/TH from the temperature TH of the expansion chamber
walls and the pressure chamber temperature TC. The curve
coefficient n dia is the ratio of the illustrated efficiency
to the Carnot efficiency. The curve coefficient appears
to decrease in the high rotation region because of pressure
loss of the operating gas. Moreover, the engine
efficiency nm is at a maximum near 1,000 r.p.m. The reduction
in the engine efficiency at the high rotation region appears to
be due to the fact that in constrast to the decrease in the rate
at which the output increases with r.p.m., friction
loss of the sea! and output pick up device increases almost
proportionally to the r.p.m.
4-3) Effect of Operating Gas Pressure
The correlation between the output and operating gas
pressure with 1,000 r.p.m. is shown in Figure 5 and the correlation
between the efficiency of the total unit and each section
and the operating gas pressure is shown in Figure 6. Thermal
efficiency shows a tendency to increase with an increase in	 i
the operating gas pressure. Huwever, the rate of increase
decreases at approximately 10 MPa. Burner efficiency decreases
on the low pressure side because the heat leak from the 	 /134
heating furnace is practically constant. The illustrated
efficiency decreases slightly with an increase in operating
gas pressure. This is due to the reduction in Carnot
efficiency. The reduction in the Carnot efficiency occurs
for the following reasons. (1) The input to the operating
gas increases almost proportionally to the operating
gas pressure and therefore, the operating gas temperature of
the expansion chamber decreases at a constant heater tube
temperature. (2) The amount of heat transmitted by the low
temperature heat exchanger increases with an increase in pressure
and therefore, the temperature of the operating gas in
the pressure chamber increases. Engine efficiency shows
a tendency to decrease in thelow rotation region and
increase monotonously with an increase in pressure. This
is due to the fact that the friction loss of the driving
section and seal to the illustrated output is very high 	 5
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F^
of
"i
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ORIGINAL PAGE i.
OF POOR QUALITY
on the low pressure side. Moreover, the friction loss of the
seal is proportional to the operating gas pressure
and the high pressure side and the driving section loss is
proportional to approximately 1/2 this pressure. Therefore,
the total of both friction losses decreases relative to the
illustrated output.
4-4 Effect of Heater Tube Temperature
The effect of the heater tube temperature
on output and efficiency is shown in Fgiure 7. Here the case
where the temperature is varied under each operation condition
in relation to the maximum output and maximum efficiency
is shown. The efficiency increased 1.5% and output increased
5 KW with each 50°C increase in the heater tube temperature
within the range of this test. This is obviously due to
the increase in the Carnot efficiency.
^..^	 1 am i'^ jx
heater to
a
-( %I
^""^!^,'5 temperature
1750 0 C IH1 O41
^"a 6^
o i
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m	 / ^4WG R
cC
iu u
IOMY u
iCK^
.
	M^^ x w
rotations d
Figure 2 Engine Property Curves and Equivalent
Efficiency Curves
burner efficiency:	 ;'.- ` +DD+I+'
D+L+Iillustrated efficiency: ''M ° c+D+s +F
r
engine efficiency:	 L o.`s:r
6
n
1
Curve of f is
Carnot
u
G
a^
u
w
ORIGINAL PAGE 19
OF POOR QUALITY
	
lot%	 Operating asP	 g g pressure 8 MPa
	
npi w	 O Number of rotations 700 rpm
Ai preheat ratm
ex uat lua A iW%
eat lea
a*Burner efficiency
	
Low temp.	 r'
	P 	 t exchangernw c „^illua^Xtrated efficiency
	
a	 n ^aA EnF ne efficiency
Output ic"
	 ^, " to
a
xial ouptpu Nam	 uAc
Figure 3. Thermal computation chart
-	 1
Operating gas pre
Heater tube temp.
!c^ ''" •
	Burner of
icf iency _"''in
-0o--o. ...a.-
I_llustrated e
^a
Thermal eflic
o_o
^o
sure 10 MP3
750 0 
Lciency nB
efficiency nM
ficiency hind
^ncy rlGross
0
Rotations (rpm;
Figure 4. Correlation between efficiency and R.P.M.
7
i
r-	 -- -	 -- -	 - —	 -_
ova
di
ORIGINAL PAGk: 'M
	
' I
OF POOR QU.:UTY
10D Rotations
	 1000 pm	 ^Oc
.o Heater tube temp. 75 C
	
`Lea excbs
c	 ° ¢^ t,^	 and `^eeLQ° sL	 , ^, se	 aL Ls e09 .r^ w	
eti 
^, * ^ t{s^ ^ J^ L ° b9 1°w c
O 40	 Qe ^^ C
o L	
Seal ring loss	 w
ro	 tput p ck-up device loss
N
M o	
Axial output	 +
a	 4	 1	 I	 to	 +H	 Operating gas pressure(MPa)
Figure 5. Correlation between input and output and
operating gas pressure.
Rotations
	 1000 rpm
Heater tube temp. 750 °C
Burner iff ic
. c^ `  n
Fn ine of f i iency nf.^
o ...ow.- dt ff	 enc n m
u	 Illusstrat`ged of iciency n ind
u	 ^,
w	 Thermal Fff icie cy nGrossW	 --0^o-o-o
W
01
	 .	 •	 0
Operating gas pressured)
Figure 6. Correlation between efficiency and operating
gas pressure.	 +
8
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..pr^L Di%IyE r'Y
OF POOR QUALi,
50	 I
arr
6 	 ~	 ?w4J
	
322
L _
	 °'
4+	 r "'
	
dq Mlt
-,4
.	 100 rpm	 Cl
-4 10,
ro	 w
o ^-
	 --	 d
heater tubE fd
mean temperature
Figure 7. Effect of heater tube temperature
5.	 Conclusion
Knowledge on the basic dynamic properties of the sterling
engine was obtaired from these tests. The particularly important
points are as follows: ( 1) Torque is very large in the low
rotation region and smooth operation is possible. ( 2) A high
thermal efficiency is shown in the low rotation region. Moreover,
in this test the maximum output was 52 KW and the maximum
efficiency was 31 %. However, it was also shown that improved
efficiency and output can be anticipated with an increase
in the operating gas pressure and the temperature. It is a
known fact that when hydrogen is used as the operating gas,
the output is increased 1.5 times in comparison to the case of
helium ( 2). Therefore, we will also carry out tests on the use
of hydrogen.
In conclusion we would like to express ovr thanks to the
Ministry of International Trade and Industry Industrial Technology
Agency for their help in making this study possible, and to the
Tokyo Engineering University for their assistance.
9
	
'' 1
i
Bibliography	 j
[1' Ishizaki, Tani, and Haramura: "Experimental Research on
the Sterling Engine", Nihon Kikai Gakkai Ronbun Shu,
No. 790-16 (10/1979).
[23 Roy C. Tew, et al.: SAE Paper 790327(1979).
1
10	 t


Dynamic property studies of Sterling engines

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