TECHNICAL PAPER #1
Fred L. Heltsley
David M. Berchowitz
Michael F. Feeney
Robert C. Wagman
Francis E. Woodling
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Understanding Stirling Engines
Volunteers in Technical Assistance
This paper is one of a series published by Volunteers in
Technical Assistance to provide an introduction to specific
state-of-the-art technologies of interest to people in
countries. The papers are intended to be used as guidelines
to help people choose technologies that are suitable to
their situations. They are not intended to provide
or implementation details. People are urged to contact
VITA or a similar organization for further information and
technical assistance if they find that a particular
seems to meet their needs.
The papers in the series were written, reviewed, and
almost entirely by VITA Volunteer technical experts on
a purely voluntary basis. Some 500 volunteers were involved
in the production of the first 100 titles issued,
approximately 5,000 hours of their time. VITA staff
included Leslie Gottschalk as primary editor, Julie Berman
handling typesetting and layout, and Margaret Crouch as
William Beale, author of this paper, is president of
Incorporated. He has designed, developed, manufactured, and
marketed Stirling engines in Bangladesh and other developing
countries, and has published widely in the solar energy
field. Reviewers David M. Berchowitz, Michael F. Feeney,
Robert C. Wagman, and Francis E. Woodling are also
in the area. Artist Fred Heltsley has an engineering
background and is a professional technical illustrator on a
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VITA offers information and assistance aimed at helping
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STIRLING ENGINES FOR DEVELOPING COUNTRIES
by VITA Volunteer William Beale
Stirling engines are external combustion engines that use
or other gases as working fluid. They can burn any solid or
liquid fuel as their heat source. This makes them very
attractive, particularly in situations where conventional
fuels are expensive and hard to obtain. Because some types
Stirling engine are so simple to make and yet so effective,
they are excellent choices for power generation in
This paper describes the basic Stirling engine, as well as
some of the most promising modern varieties. The intent here
is to familiarize people in developing countries with the
engine's operation and range of applications.
The Stirling engine was invented by Robert Stirling, a
minister, in 1816. The early Stirling engine had a history
of good service and long life (up to 20 years). It was
used as a relatively low-power water-pumping engine from the
middle of the nineteenth century to about 1920, when the
internal combustion engine and the electric motor replaced
it. The hot-air engine was known for its ease of operation;
its ability to use any burnable material as fuel; its safe,
quiet, moderately efficient operation; and its durability
low maintenance requirements. It was very large for its
power output, however, and had a high purchase cost.
its low operating cost usually justified choosing it
over the steam engine--the only alternative at the time--
which burned much more fuel for the same power and demanded
constant attention to avoid dangerous explosions or other
The other major disadvantage of the early hot-air engine was
its tendency to fail if the heater head got too hot.
a result of the relatively low heat resistance of the cast
iron heater head. The problem was overcome by redesigning
burner, which prevented the engine from overheating. This
improvement resulted in safe, but even lower, power
Despite this improvement, the Stirling engine could not
compete with the cheaper, more powerful internal combustion
engine, and it disappeared from the commercial scene.
The advent of newer stainless steels and advances in the
understanding of the engine's complex thermodynamic process
brought new attention to the engine during and after World
War II. The performance of the old hot-air engine was
and its size and cost were reduced. Its simplicity of
construction and operation, and most important, its ability
to use rough fuels were retained. These efforts on Stirling
engines were almost exclusively aimed at difficult
that were not appropriate for developing countries--namely,
the advanced automotive engine, space power, and
artificial hearts. Almost no effort was put into the
easy task of designing an engine for ordinary uses.
The highly developed countries in which the Stirling engine
work was being done did not need a simple engine, so there
was no economic incentive to design one.
This situation changed in 1980, when the U.S. Agency for
International Development (USAID) funded the development of
simple Stirling engine specifically intended for manufacture
and use in developing countries. The engine was designed,
built, tested, and delivered to Bangladesh, and copies of it
were built and put into operation there. This demonstrated
the Possibility of the engine's manufacture in simple
shops of the type found in many regions of Africa, Asia, and
As a result of this and other recent developments, the
dim prospects for the application of Stirling engines
in developing countries have improved enormously. Plans are
now in motion to bring a new design of the Stirling engine
into commercial production in a much improved form. This
modern version will be much more powerful for its weight and
much more efficient; at the same time, it will be as quiet,
easy to use, reliable, and rugged as the original engine.
Additional models, capable of generating electricity,
pumping water, and serving in other useful ways not
possible with the old hot-air engine, are also coming into
NEEDS SERVED BY THE TECHNOLOGY
Although the Stirling engine is an old machine, modern
materials and design methods make it much more attractive
than ever before. The crank-drive Stirling engine is
useful to anyone who has solid fuel. This type of
Stirling engine can burn any local fuel as its source of
to produce electricity, pump water, or perform tasks
mechanical power such as food processing.
Very simple machines using atmospheric air as working fluid
can be built from local materials such as metal containers.
People who are inclined to try such designs have a good
chance of success.
II. OPERATING PRINCIPLES
BASIC THEORY OF THE TECHNOLOGY
The Stirling cycle is shown in the diagram in Figure 1 . The
basic idea is that when gas in a closed cylinder is moved
into the hot part of the cylinder, it expands, its pressure
increases, and it can do work. When the gas moves into the
cold part of the cylinder, its pressure is reduced. Once the
gas reaches the lower pressure, it is compressed back to its
original volume. The gas performs more work during its
than is required to be put into it during its compression.
Thus, the entire cycle results in the net positive
output of work.
As shown in Phase 1 of Figure 1, the piston is out (bottom
dead center), and the displacer is in as far as it can go.
The gas is in the cold space, and the gas pressure is low.
(Note that the gas is at the same pressure at any instant in
every part of the engine, but that this pressure is changing
with time. Because
the pressure is low, the piston can be
moved in easily to compress the gas at the low temperature.
At the end of this compression process, the engine has
reached Phase 2, as shown in Figure 1.
Now it is time to increase the gas pressure. This is not
by burning a fuel inside the gas as is done in an internal
combustion engine. The gas is moved from the cold space
through a series of heat exchangers, which cause it to enter
the hot space at a high temperature. Note that the gas in
heater, cooler, regenerator, and hot and cold spaces, is
always at the same pressure at any instant, since the gas
flow passages are large and do not restrict the passage of
As shown in Phase 3 of Figure 1, the gas is compressed, hot,
and at high pressure. At this point it is ready to expand
to work on the piston. As the piston moves out of the
the displacer moves with it, in order to keep as much
of the gas as possible in the hot space so that the pressure
is kept as high as possible to do the maximum amount of work
on the piston. This expansion and outward movement of the
piston results in the attainment of Phase 4, as shown in
The next step is to reduce the gas pressure by moving it
the hot space through the heat exchangers to the cold space.
This is done by moving the displacer from its position, as
shown in Phase 4, back to its inward position, as shown in
Phase 1. The cycle is now complete. Notice that the piston
has expanded the gas by moving outward when the gas is hot
and at high pressure, and has compressed the gas when it is
cold and at low pressure. Thus, the original plan has been
accomplished, and the cycle has produced net work to the
For this four-phase process to continue indefinitely, heat
must be continually added to the hot heat exchanger from
outside source like a fire or a solar collector, and the
end must be continually cooled by a stream of water or air.
You might now wonder how the movements of the piston and the
displacer are accomplished,
since they clearly cannot move
their own. The answer is that there are at least two ways to
make the two components of the simple Stirling engine move
we wish: (1) we can attach them to cranks through connecting
rods, as is commonly done in automobile engines; or (2) we
can use gas forces in a carefully designed way so that they
bounce on gas springs, with the displacer always ahead of
piston in its in-and-out oscillation. Of the two methods,
use of cranks called the crank-drive, or kinematic Stirling,
is the more easily understood method. The second method,
which uses oscillating motions of the piston and displacer
springs, is called the free-piston Stirling. The crank-drive
Stirling is easier to understand yet harder to make, while
the free-piston Stirling is harder to understand yet easier
to make in at least some of its forms.
III. DESIGN VARIATIONS
This section of the paper describes a variety of promising
Stirling engines. It emphasizes their physical characteristics,
advantages and disadvantages, applications, and fuel
TYPES OF STIRLING ENGINES
Crank-drive Stirling Engine
A schematic of the crank-drive Stirling engine is shown in
Figure 2, and a crank-drive Stirling engine pumping water is
shown in Figure 3. While this engine is unusually large for
the small amount of power (5 kilowatts) it produces, it is
nevertheless very simple to make and operate. It uses no oil
in the crankcase; here it is important to avoid getting oil
into the hot working parts of the engine, because it could
block the flow of air through the heat exchangers and also
cause an explosion. Any of the following three types of
bearings can be used: sealed roller bearings, ball bearings,
or unlubricated bushings made of a plastic like Teflon. If
necessary, the ball and roller bearings can be replaced by
journal bearings and sealed in grease.
Since the engine is slightly pressurized, up to about
atmospheres (atm), it uses a simple crank shaft seal to keep
the air in, and a small air pump to maintain the pressure
against slow leakage past the seal. The air pump as well as
all other accessories needing power are driven directly from
the rotating engine shaft.
Other accessories requiring shaft power. are the auger
the fuel, the combustion air blower, and the cooling water
pump and radiator fan.. With these accessories, the engine
able to work without any
other source of power, and needs
only fuel to operate.
Typical operating instructions are as follows:
1. Make sure the engine is in good operating condition and
the hopper is full
2. Start a fire in the burner with kindling (e.g., wood
dried leaves), and
operate the air blower by hand
until the interior
of the burner is sufficiently hot to
receive and ignite
the fuel from the fuel feed.
3. Hand operate the combustion air blower and the fuel auger
until the heater
head of the engine reaches a moderate
300[degrees]C). The engine is now ready to
4. Turn the flywheel over, and the engine should begin to
on its own power
immediately (easy starting is one of the
best features of
5. Allow a short time for the engine to pressurize itself
to drive the
burner until it is at full operating pressure
During this time, the engine will gradually
grow stronger and
more capable to do work. The load
can be increased
as the engine grows stronger. This happens
the engine is attached to loads such
water pumps or generators, but loads such
as saws and
milling machines have the capability to stall
the engine if
their load is applied too quickly. If the
engine is stalled,
it can be restarted immediately by
unloading it and
turning the flywheel again.
6. Once the engine is up to full power and doing its work,
the operator needs
only to keep the fuel hopper full and
maintain a load.
If the load is removed for any reason,
the engine will
speed up, but not to a harmful degree; it
will quickly reach
a speed at which its power output drops
to zero, and it
will continue to run.
7. When it is time to shut off the engine, simply cut off
fuel and the
engine will slowly come to a stop. It can be
quickly at any time by releasing the internal
reduces the power to a low value.
Since there are very few critical adjustments of fuel, air,
or water flow, and there is no fuel injector or spark
the crank-drive Stirling engine is extremely reliable and
easy to run. But in order to achieve maximum performance it
is important to make correct adjustments of these flows,
which someone with only a little experience can do easily,
Because of its ease of operation, durability, local
and the ability to use any local fuel as its heat
source, the modern crank-drive Stirling engine is remarkably
well suited for power generation in developing countries.
Plans for this Stirling engine will be available from USAID
in 1984 or 1985. Commercial production of the engine, or
of it, is expected to begin in 1984.
Simple Free-Piston Engine
Figure 4 portrays a slow-speed free-piston engine, which is
simple version of the Stirling engine. This engine is almost
the ultimate in simplicity compared to other Stirling engine
designs. It is the so-called overdriven configuration in
which the displacer is floated by springs and will move
either up or down under the influence of the
slightest force or disturbance of the pressure inside the
engine. The great advantage of this arrangement is that the
engine is not only self-starting (requiring only that a good
temperature difference be established between the hot and
cold spaces), but it will adjust to any load, even a
stopping of the piston, and still cycle up and down. Thus,
the engine is very. forgiving and easy to operate. Its major
disadvantage is that it is too big for its small power
this is because it uses atmospheric air as working fluid
and operates at a very low frequency. Counterbalancing this
disadvantage are the very high lift capacity and efficiency
of the simple positive displacement pump which the engine
The displacer and piston diameter can be the same. The
displacer should be at least as long as its diameter, with a
maximum length of three times its diameter, and the end cap
should. be domed to allow some strength against collapse.
gap between the displacer and the cylinder should be about
one to two hundredths of the diameter, with a preference for
the smaller gap. In order to keep the displacer centered, it
should have raised bumps of the gap thickness that rub
slightly against the cylinder in its cold section.
The heater section length should be about one fourth of the
displacer diameter, and the cooler about the same. This
leaves one half of the displacer to act as a regenerator,
which serves to store the heat of the air as it comes from
the heater to the cooler, and releases it to the air as it
comes back from the cooler to the heater. This action
the fuel efficiency of the engine.
The displacer movement available should be about one third
The displacer drive rod should cover about 15 percent of the
area of the displacer cylinder. The drive rod should fit
closely in its sleeve but be free to move.
The best material for the displacer hot end is any one of
300 series stainless steels, such as 304, 316, or 321. These
are also called 18-8 type stainless, the kind used in
pots. The hot end of the displacer cylinder must be of
steel also, or
possibly ceramic if it can be made airtight.
Of course, if only short-term experiments are the aim,
then ordinary carbon steel sheet can be used for both
and heater head.
The displacer itself can be quite thin, provided that a
non-return valve is installed in its cold end to allow the
interior to reach the maximum cycle pressure and stay there.
Otherwise, the displacer could collapse under pressure. It
also important to make the displacer shell thick enough to
prevent its collapse under outside pressure.
The rest of the engine can be of steel, cast iron, aluminum,
or whatever is locally available, since it is not exposed to
heat. Care should be taken to make the displacer as light as
is practical. Otherwise, it will respond too slowly to gas
pressure and will not develop the lead in motion over the
piston necessary to accomplish the Stirling cycle.
A simple free-piston engine with a 60-cm diameter displacer,
operating at one cycle per second, can be expected to
about 500 watts of power (50 liter-meter/sec) of pumped
water. Of course, as with any first attempt, the actual
output could be much less.
Another excellent candidate for use in developing countries
is the free-cylinder engine. It shares many of the virtues
the crank-drive Stirling engine and is even simpler to make.
Moreover, because it is hermetically sealed, it is
to damage from outside contaminants. However, because it is
basically a reciprocating output machine, it must have some
sort of power-transforming device such as a ratchet drive
gearbox to provide rotary motion if such is needed.
many uses for simple reciprocating motion, such as water
pumping, and in these uses the free-cylinder engine is an
Figure 5 shows a model of a typical free-cylinder engine
as a water pump. The power is taken from the oscillating
cylinder, which moves in reaction to the opposite motion of
the heavy piston inside. The displacer is driven by the gas
pressure on its rod, which is attached to the piston.
The free-cylinder engine, like all Stirling engines, can
operate on any heat source. Use of a ratchet drive permits
the high-frequency short-stroke free-cylinder engine to
any load requiring a rotating shaft, and thus greatly
The free-cylinder engine used as a reciprocator can easily
drive not only fluid pumps but air or gas compressors as
well. It can also drive refrigerant pumps for food
Starting the free-cylinder engine can be automatic if the
engine is in a vertical position; otherwise, a slight jar is
necessary to start the initial motions, after which the
engine will run vigorously as long as the temperatures
for both the hot end and the cold end of the cylinder
are maintained. The temperature required is usually from 400
to 700[degrees]C on the hot end and up to 100[degrees]C on
Since there are only two moving parts inside the cylinder,
the free-cylinder engine is even easier to make than the
crank-drive Stirling engine described earlier in this paper.
Moreover, Since the cylinder is hermetically sealed, the
engine does not need an air pump or a sliding seal to
its working gas. Therefore, the engine can operate at a high
pressure, say up to 15 atm, making it very compact and cheap
for its power.
Duplex Stirling Engine
The duplex Stirling engine is a heat-driven cooling machine;
that is, it takes in heat and produces cold without
any other external effect. It is very simple, almost as
as the free-cylinder water pump, and is very fuel-efficient
if carefully designed. Figure 6 shows a typical
of the duplex Stirling engine designed as a heat-driven
food refrigerator. Figure 7 shows it in operation.
The basic idea behind the operation of the duplex Stirling
engine is that when driven, it becomes a heat pump. In the
duplex Stirling, a Stirling engine is used to drive a
heat pump. This can be done with only three moving
parts--the hot displacer, the piston which acts as the
for both the heat engine and the heat pump, and the cold
This combination of parts makes a simple and effective
heat-drive heat pump, which can be scaled to any size or
temperature range, from very cold temperatures necessary to
liquify air to mild temperatures useful for space cooling.
The duplex Stirling engine will be commercially available
within the next few years, probably as a portable,
freezer-refrigerator in small sizes.
Free-Piston Alternator Engine
Recent efforts to develop the free-piston alternator engine
have produced outstanding results. While the engine will not
become a commercial item as quickly as the crank-drive
engine, it will follow with only about a year's delay.
The one most developed at the moment is a 1-kW output
that has excellent fuel efficiency, promises long life, and
is very compact. This machine is not simple, however, and
requires highly sophisticated manufacturing procedures and
materials. On the other hand, because it is hermetically
sealed, it cannot be damaged by any sort of rough treatment,
although the control system and other auxiliaries are not so
The free-piston alternator engine is ideally suited to the
task of developing electricity from solar energy, especially
when matched to a low-cost plastic film concentrator of the
type now coming on the market. Such machines are being
developed in sizes up to 10 kW, and could be available
in even larger sizes in a few years. The one shown in Figure
has a 10-kW output.
USES OF THE STIRLING ENGINE
Irrigation with Biomass
Both the crank-drive Stirling engine and the free-cylinder
engine are practical for irrigation with biomass, provided
that ample biomass is available for fuel as well as cheap
labor to feed the engine with fuel and tend its operation.
The crank-drive engine is practical from about 500 watts to
tens of kilowatts of delivered power, but in power above 3
it will require a wheeled cart to transport it. The
engine makes a good irrigation pump up to about 500
watts. Either engine can drive both shallow well and deep
well pumps, as well as low-lift ditch pumps. Also, the
generator free piston can be attached to an electric
pump for this service.
Electricity Generation--Small Sizes--Solid Fuel
Both the crank-drive Stirling engine and the free-piston
alternator engine are practical for this use. The
alternator engine has the advantage of very low noise and
long life, but is harder to repair in the field. The
Stirling engine is simple, easy to repair, and cheaper,
and can be manufactured in simple repair shops; however, it
is not as fuel efficient.
Electricity Generation--Village Power--Solid Fuel
Here again, both the crank-drive Stirling engine and the
free-piston alternator engine would serve for any power up
about 100 kW. Stirling engines of higher power output are
likely in the near future, although it is always possible to
combine smaller units into a larger unit for more power.
In this application, constant attendance is required to
assure the proper operation of the fuel feed and other
Useful by-products include hot water from the cooling
system and ash from the burner.
Grain Processing--Grain Waste as Fuel
This is an ideal application because of the availability of
the biomass by-product as fuel for the engine. The
simple hot-air engine, referenced earlier in this
paper as having been developed for manufacture in
is an excellent example. Figure 9 shows this hot-air engine
millng rice. It burns the rice husk produced by the mill it
drives. Only a fraction of the husk produced by the mill is
needed to fuel the engine, so ample amounts are left over
the engine to use while pumping irrigation water for the
rice crop. In this way, solar energy, in the form of
is used as the primary energy input for the rice-growing
process, and no outside fuel is necessary.
It is important to recognize that the Stirling engine is a
It cannot run well on the low
temperatures available from simple flat plate solar
It must use a concentrating, sun-tracking solar collector.
This device adds considerably to the cost and maintenance
requirements of the system. Also, such a device does
not make use of the diffuse component of solar energy, only
the direct component. So hazy sun is not good enough.
clear skies are needed before the concentrating collector
will develop the high temperature necessary to operate the
Stirling engine. For all these reasons, Stirling systems
using concentrating, sun-tracking solar collectors will be
much more expensive and
will require more care in their
operation than those using fuel as their heat source.
With those reservations in mind, it is right to point out
that there are situations in which such solar-driven systems
are worthy of consideration: where intense sunlight is the
rule, where there is no biomass available and none derivable
from the effects of the engine (as there would be eventually
if the engine were irrigating a formerly desert area), and
where the cost of the engine, collector, tracker, mount, and
maintenance thereof is not prohibitive. Such a situation
could exist where several kilowatts of electricity are
needed, and the cost of photovoltaic systems is too high. It
is likely that a solar electric system based on a
Stirling engine will cost considerably less per watt
delivered than will a photovoltaic system in the kilowatt
range of power.
A cautionary note on solar Stirling systems: although the
Stirling engine will be commercially available in one or two
years, the concentrating collectors and their auxiliaries
still some distance away from production. For all these
reasons, solar Stirling engine systems are likely to be much
more costly than other systems except where nothing else is
available, as might be the case in extreme desert zones.
More often than not, a direct solar system is less practical
than one that uses biomass grown with the help of irrigation
provided by the engine. By this means, land that would
grow nothing could conceivably be made to produce food
as well as fuel for the irrigating pump. Put simply, a field
of weeds, harvested to be burned in the engine, is a much
easier route to solar power than an elaborate optical
mount, and tracker. And weeds, unlike the sun, do not hide
behind clouds or go away at night.
FUEL EFFICIENCY AND POWER OUTPUT
The Stirling engine is likely to burn roughly 10 kilograms
(kg) per kilowatt-hour (kWh) of biomass fuel, and 6 kg/kWh
coal. This is less than the rate of fuel consumption of
steam engines. Depending on how well an operator guides the
machine, this burning rate can easily vary as much as 20
percent, up or down; with well-designed and well-attended
engines, it could be as little as half as much.
The power output per unit of weight varies greatly with the
design. Generally, it ranges from about .04 Kw/Kg for a
crank-drive model to about .07 Kw/Kg for a commercial
high-technology free-piston alternator engine.
IV. COMPARING THE ALTERNATIVES
The Stirling engine is capable of accepting heat from any
source above about 400[degrees]C and converting part of the
useful work. This makes it capable of a wide variety of
Which of them are practical and worth consideration in
with the other sources of mechanical energy?
If conventional fuels and machines are available and
it is probably not practical to consider replacing
them with a Stirling engine. Only when petrol or diesel or
clean gaseous fuels are scarce, expensive, or otherwise
and when the spark-ignition internal combustion
engine or diesel engine is too short lived or too expensive
to maintain or purchase, is it sensible to consider the
application of the Stirling engine. If you consider
the Stirling engine, you must carefully evaluate its
availability, proven performance characteristics, and
lest disappointment result.
COMPETITORS OF THE STIRLING ENGINE
The competition for the Stirling engine is the internal
engine, including the spark-ignition engine running
on petrol, natural gas, alcohol, biogas, or producer gas,
the diesel engine running on diesel fuel, or a mixture of
diesel and other gaseous or liquid fuels. The various solar
cell devices as well as the steam engine are also considered
to be competition for the Stirling engine.
The Stirling engine is most likely to be the best choice
where the power required is between 100 watts and 20 kW, and
some sort of biomass, coal, or peat is available as fuel. If
gaseous or liquid fuel is readily available, a properly
adapted internal combustion engine is likely to be cheaper,
at least in the short run, although, depending on the
cost of the fuels, the Stirling engine could be cheaper
in the long run, due to lower maintenance and fuel costs.
Because the Stirling engine has been reintroduced only
recently, it is hard to project the relative purchase costs
of the several types of Stirling machines. It is likely that
the Stirling engine will cost more than the spark-ignition
internal combustion engine, and roughly the same as a
diesel engine of the same quality. But the Stirling
engine is likely to have lower maintenance costs than either
of these because of its great simplicity.
The Producer Gas Engine as a Competitor of the Stirling
The producer gas engine runs on gas by means of a
converter called a producer gas generator. The engine
using the producer gas can be a converted petrol engine or a
diesel engine using mainly producer gas but also requiring a
small amount of diesel fuel as igniter for the producer gas.
Since this combination can in fact do the same thing as a
Stirling engine--that is, develop mechanical power from wood
and other biomass--one is compelled to ask whether the
engine has any advantage over the combination of producer
gas generator and conventional internal combustion
engine. In some cases, the answer is yes.
The Stirling engine has three advantages:
(1) it can burn
fuels with high ash content such as rice husks, which the
producer gas system cannot; (2) since the combustion
do not enter the Stirling engine, they require no cleanup,
in contrast to the producer gas internal combustion engine;
and (3) the Stirling engine, in combination with a simple
wrought fuel burner, is a much simpler and more
system than the combination of producer gas generator,
cleanup system, and internal combustion engine.
The Stirling engine overtakes the producer gas engine system
if the fuel to be used is not of high quality, such as rice
husks, and if the cost of maintaining the ignition system,
injection system, lubrication, and other relatively delicate
components of the internal combustion engine and the gas
is a problem, as it so often is.
The Steam Engine as a Competitor of the Stirling Engine
It is logical to consider the steam engine as natural
for the Stirling engine, as it in fact was at the time
Rev. Stirling invented it. At that time the steam engine was
the dominant power producer, whereas the Stirling engine was
more fuel efficient, and much safer since it is almost
to cause a Stirling engine to blow up, and rather
easy to do with a steam engine. Also at that time, the great
disadvantage of the Stirling engine was the poor temperature
resistance of the cast iron heater head.
Today, the situation is different. The steam engine has
fallen into disuse, and the Stirling has leapt ahead in performance,
life, and availability. With the use of series 300
stainless steel, a commonly available material, there is no
longer the danger of heater head failure, at least below
700[degrees]C, which a normal solid fuel combuster produces
running Stirling engine. And it is feasible to make the
heater head of ceramic, especially in very low-pressure
engines such as the simple free-piston water pumper.
Therefore, for low-power applications below several tens of
kilowatts, the Stirling engine is likely to be much more
efficient, much easier to operate, much safer, and require
much less maintenance. It is also likely to cost less, since
the Stirling engine has so few parts and such simple ones in
comparison to the steam engine. For example, the Stirling
engine needs no valves, whereas the steam engine requires
many, each one of which must work unfailingly in a hot,
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and Lift Irrigation: Synergistic Relations
Technology and Natural Resources in
India." January 1983, p. 1-16. (Mimeographed)
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Development. Washington, D.C.: National Academy
Press, 1981, pp.
National Academy of Sciences. 'External Combustion Engines--
Stirling Engines as Small-Scale Power
Developing Countries." Energy for Rural
D.C.: National Academy Press,
4, pp. 246-269.
Ross, A. Stirling Cycle Engines. Phoenix, Arizona, 1977.
Urieli, I., and Berchowitz, D.M. Stirling Cycle Engine
Bristol, England: Adam Hilger, 1984.
Walker, G. Stirling Cycle Machines. Oxford, England: Oxford
Walker, G. Stirling Engines. Oxford, England: Oxford
Wood, J. Gary; Chagnot, Bruce J.; and Penswick, Lawrence B.
a Low Pressure Air Engine for Third World
presented at the 17th Annual Intersociety
Conference, Los Angeles, California, August 1982.