The development and testing resulting in the Vanguard engine and some of the characteristics of the Stirling engine based power conversion unit are described. The major part of the solar engine development is concentrated to the three different areas, the receiver, the lubrication system and the control system. Five engines are on test within the solar project. The function of the components are validated in actual solar tests

Holgersson, S.

English

NASA Technical Reports Server

~UNIn:D
STIRLING
Abstract
United Stirling's Solar Engine Development
- the background for the Vanguard Engine
Author: Sten Holgersson
United Stirling AB Sweden
Introduction
Fig 1. United Stirlings engine family
ENGINES
United Stirling is a company within the indus-
trial corporation FFV. The company's task is
to develop the Stirling engine for commercial
applications.
The development work has been going on
since 1969 resulting in engines in different
sizes of our own designs. The present engine
family is shown in figure 1. United Stirling is
now concentrating the efforts on four different
application projects. One is the Automotive
Stirling project with the ASE engine, a second
one ;s the Submarine project mainly concen-
trating on a 4-275 engine, a third is the Auxili-
ary Power Unit project with the V160 engine
and the fourth is the Solar project with the
4-95 Solar engine, the subject for this presen-
tation.
The Vanguard project engine, named 4-95 Mk
II Solar Stirling Engine, represents the result
from four years of solar engine development
at United Stirling. In these development ac-
tivities United Stirling has participated in pro-
grams on contracts from JPL and DOE, the
latest being the Vanguard project. A major
part of the development has also been intern-
ally funded.
The development started in 1979 based on the
then existing 4-95 laboratory test engine which
thru the 4 years has been converted to a solar
version and significantly improved in several
areas. The conclusion of the Vanguard project
results in a new engine generation of a design
that can be regarded as a preproduction pro-
totype. .
The major part of the solar engine develop-
ment has been concentrated to the three dif-
ferent areas, the receiver, the lubrication sys-
tem and the control system, but improvements
have been made on most components. The
new components were first tested on engines
in United Stirling's laboratory in Malmo. Five
such engines are on test within the solar pro-
ject. Thereafter the function of the compo-
nents has been validated in actual solar tests.
These tests started at Georgia Institute of
Technology in 1981 and have then from the
beginning of 1982 been performed at JPL's
test station at Edwards Air Force Base.
This paper describes the development and
testing resulting in the Vanguard engine and
some of the caracteristics of the Stirling
engine based power conversion unit.
95
4-95
4-275
ASE
V-160
40kW
75kW
55kW
12kW
https://ntrs.nasa.gov/search.jsp?R=19840020173 2020-03-22T10:05:31+00:00Z
~UNITED
STIRLlNB
Solar development programs
Although it of course has always been an
awareness at United Stirling of the possibility
to use the Stirling engine for solar energy con-
version our activities in the field were very low
until 1978. We then became participants in a
NASA-funded study together with MTI. This
study identified both the kinematic and the
free-piston Stirling engine as viable candidates
for the solar application. The next year, 1979,
we accepted participation in a JPL-program.
Our task was to redesign the drive unit to fit
to and be able to operate in the EAFB test bed
concentrator and to deliver one drive unit
while JPL developed the receiver. Partici-
pation in this program rose our interest in
receiver design and we decided in 1980 to
develop a receiver design of our own. This was
a natural step since in the Stirling engine the
receiver is an integral part of the engine and
our intention was to be capable to deliver a
complete Stirling engine for an application in
which the commercialization of the engine
could be realized. From 1980 and on our own
extensive solar engine development program
has been going on. In addition to that, and as
one of the significant components of our solar
engine development we 1982 became mem-
bers of the Vanguard program which now is
being realized in hardware in Palm Springs
through delivery of the concentrator from
Advanco and the PCU from United Stirling.
The Stirling engine in the Vanguard project is
the first engine in the new generation intern-
ally at United Stirling called the 4-95 Mk II
Solar SE. This engine is of course a product
of the Vanguard project, but in reality the re-
sult of a much broader development program
at United Stirling. This development program
is the combination of the Vanguard project
and internally funded solar engine develop-
ment. A summary of the externally funded
solar development programs in which we have
participated is given in figure 2.
96
USAB SOLAR ACTIVITIES
• NASA STUOY 1978 - 1979
15 KW SOLAR STIRLING ENGINE
• JPL PROJECT 1979 - 1981
INSTALLATION OF THE FIRST SOLAR
STIRLING ENGINE WITH HYBRID RECEIVER
IN A PARABOLIC DISH
.DOE PROJECT 1982-
TEAM MEMBER OF THE VANGUARD PROJECT
Fig 2. Solar programs
The engine choice for
solar applications: 4-95
The development of the Solar Stirling engine
has during the last 3-4 years been concentrat-
ed to the 4-95 engine, figure 3. The reasons for
choosing this engine were several. The engine
size fits to a concentrator within the size range,
10-18 m diameter, that seems to be most cost
effective. The existing JPL test bed concen-
trator and the 4-95 engine are almost perfect
in sizes for each other which means that an
opportunity to performe realistic hardware
tests existed. The 4·95 engine was one of
United Stirling's engines, that had the highest
amount of accumulated running hours with
rather good results. Figure 4 shows a sum-
mary of the present experience with the 4·95
engine.
The 4·95 engine was originally designed as a
laboratory test engine in 1975. It has since
then been used as the baseline engine in the
beginning of the Automotive Stirling Engine
program and as the first underwater engine
designed by United Stirling. The further devel-
oped 4-95 engine is now chosen as the solar
Stirling engine.
~UNITED
STIRLING
Fig 3. 4-95 cross section
4-95 ENGINE STATUS
• Number of engines built
• Running hours
• in total
• single engine
Fig 4. 4-95 Status
Nov 1983
27
41000
11 000
changer for convective heat transfer from com-
bustion gases. It was therefore necessary to
develop a new heater suitable as a radiative
heat exchanger together with a cavity sur-
rounding it and thus fit the engine with a solar
receiver. The receiver of a Stirling engine, in
contrast to other engines, is an integral engine
component. The control systems of the 4-95
engine were designed for applications with
other and more complex control functions
and with stronger requirements on response
times than needed for the solar application.
This was the case for both the pressure
(power) control system and the electronic
control system. Therefore new control systems
had to be developed. Also in order to design
an autonomous power conversion unit to be
placed up in the focal mount a new radiator
system had to be developed.
The major development work has been con-
centrated to the mentioned four areas, but
significant changes have also been introduced
on a large number of the engine components.
So many improvements have been made that
the Vanguard engine represents a new en-
gine generation .
MAIN AREAS OF REDESIGN
FOR SOLAR APPLICATION
Main areas of redesign
Although the 4-95 engine in many respects was
suitable as a solar energy converter there was
also a need to redesign and further develop the
engine in a number of areas. The engine must
be able to operate in all different orientations
from horizontal to upside down when following
the movement of the concentrator. In the
Advanco concentrator with its gimble mecha-
nism it also rotates around its vertical axis.
This means that it was necessary to complet-
ely redesign the lubrication system. The orig-
inal heater was strictly designed as a heat ex-
97
• Heat system (receiver)
• Lubrication system
• Control systems
• Radiator systems
Fig 5. Areas of redesign
~UNITED
STlRLlNIi
Pressure - Max
Level
I
12:00
Noon
I
12:00
Midnight
I
6:00
P.M.
J
---,----,------r---..,...-
A special engine stand was designed in order
to turn the engines in the same way as in the
actual concentrator. One of the engines was
mowed out on our yard in order to gain ex-
perience from the outside environment. During
the last three years 13000 hours of solar en-
gine tests have been accumulated in Malmo.
After testing in our facilities all the subsystems
have been on verification tests at Edwards
Air Force Base, where the sixth of the 4-95
engines has been located.
Fig 6. Vanguard engine cross section
'-----------------------'
Testing at United Stirling Fig 7. Simulated solar test cycle
A very vital part of the solar engine develop-
ment has been engine testing. Six of United
Stirling's 4-95 engines have been designated for
development tests for the solar application.
Fig 8 shows the main content of our develop-
ment program. In addition during the last year
tests have also been performed on JPL's
engine, the 4-95 No 21 engine, located at
Edwards Air Force Base. Five of United Stir-
ling's engines have been tested in our labora-
tory in Malmo, Sweden. Two of these engines
were used for component development tests,
Le. functional tests, usually of relatively short
duration, of redesigned components and sub-
systems. Three of the engines were used for
simulated solar cycle endurance tests. This
test cycle, shown in fig 7, was based on loads
and transients calculated from insolation
statistics from Barstow and Albuquerque.
The lubrication system, the control system
and the radiator system were first developed
and tested on the engines in our laboratory.
Fig 8. PCU on test stand
Actual solar tests
Testing of engines actually running on solar
energy started 1981 at the test facility at
Georgia Institute og Technology in Atlanta.
This test facility is designed for higher power
98
~UNITED
STIRLING
than the 4-95 engine but testing was possible
to perform by shielding the excessive flux with
a watercooled plate. The testing in Atlanta
gave very useful information for the further
development of the receiver and control sys-
tems, but in order to evaluate the function of
all components in a matched system there
was still a need to test in a parabolic dish.
Therefore the testing was transferred to JPL's
test station at Edwards Air Force Base early
in 1982 where testing has been going on since
then jointly with JPL in their test bed concen-
trator.
Significant results evolving from these tests
are among others the functions of the control
systems during start, stop and cloud passages.
The principal operation characteristics of the
Vanguard PCU during these transients are
shown in fig 11, 12 and 13.
Fig 10. Tests at EAFB
VANGUARD PROJECT START SEQUENCE
PPRESSURE
START
INtATED
TRACK
TIME
TIME
TIME
GENERATOR IN
STARTER
MOTOR
IN OUT
TIME
PRESSURE
CONTROL
STARTS
TEMP
OUTPUT
POWER
RPM
Fig 11. Start sequence
Fig 9. Tests in Atlanta
99
~UNI1EI
mRUN
VANGUARD PROJECT STOP SEQUENCE VANGUARD PROJECT CLOUD PASSAGE
TIME
TIME
TIME
IiGENERATOR
IN
I
I
I
I
I
I STARTER
q MOTOR
I
I GENERATOR
lOUT
I PRESSURE I
'I CONTROL II I
~.. p.S :. I
.. I
I t
I
RPM
OUTPUT
POWER
A ~ CLOUD~
P PRESSURE I I
I
I
I
I
'------------"1---+-------+
TIME
TIME
TIME
TIME
TIME
ENGINE
STOPS
GENERATOR
OUT
PRESSURE
CONTROL
STOPSTEMP
RPM
OUTPUT
POWER
PPRESSURE
Fig 12. Stop sequence Fig 13. Cloud passage
The Vanguard project
4-95 Mk II (VANGUARD)
ENGINE OBJECTIVES
• Keep Mk I performance level
• Increase reliability
• Reduce production cost
Fig 14. Vanguard engine objectives
United Stirling became member of the Van-
guard project responsible for design and de-
livery of the power conversion unit. The con-
tract was signed in May 1982. Our task in this
project has included modification of the 4-95
engine in the earlier mentioned areas to fit
together with the Advanco concentrators. The
main objectives for the engine for this project
are shown in fig 14. Laboratory tests have veri-
fied that the performance goals are met and
calculations show a reduction of 30% in pro-
duction costs. Several modifications of com-
ponents aimed at increased reliability have
been introduced. The results of these modifi-
cations can only be achieved thru future test-
ing of the engine.
The PCU is now delivered to the test site and
ready for testing.
100
~UNITED
STIRLING
Fig 15. Laboratory testing of
the Vanguard engine
Fig 16. Vanguard engine with
alternator and mounting ring
101
? ";"'".. '.,
Fig 17. Vanguard PCU ready
for delivery


United Stirling's Solar Engine Development: the Background for the Vanguard Engine

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server