Stirling's engine. Stirling External Combustion Engine External Combustion Turbine Engine

From the past to the future! In 1817, the Scottish priest Robert Stirling received ... a patent for a new type of engine, later named, like Diesel engines, after the inventor - Stirling. The parishioners of a small Scottish town have long and with obvious suspicion looked askance at their spiritual shepherd. Still would! The hissing and rattling coming through the walls of the barn where Father Stirling often disappeared could not only confuse their God-fearing minds. There were persistent rumors that the barn contains a terrible dragon, which the holy father tamed and feeds with bats and kerosene.

But Robert Stirling, one of the most enlightened people in Scotland, was not embarrassed by the hostility of the flock. Worldly affairs and worries occupied him more and more, to the detriment of serving the Lord: the pastor was carried away by ... cars.

The British Isles at that time were experiencing an industrial revolution: manufactories were rapidly developing. And the ministers of the cult do not remain indifferent to the enormous income that the new mode of production promises.

With the blessing of the church and not without the help of the manufacturers, several Stirling machines were built, and the best of them, 45 hp. s., worked for three years at a mine in Dundee.

Further development of the Stirlings was delayed: in the 60s of the last century, a new Erickson engine entered the arena.

Both designs had a lot in common. These were external combustion engines. In both machines, air was the working fluid, and in both, the basis of the engine was the regenerator, passing through which the exhausted hot air gave off all the heat. A fresh portion of air, seeping through a dense metal mesh, took away this heat before entering the working cylinder.

According to the diagram in Figure 1, it can be seen how the air enters the compressor 3 through the suction pipe 10 and valve 4, is compressed and exits through the valve 5 into the intermediate reservoir. At this time, the spool 8 closes the exhaust pipe 9, and the air through the regenerator enters the working cylinder 1, heated by the firebox 11. Here the air expands, doing useful work, which is partly directed to the lifting heavy piston, partly to compress the cold air in the compressor 3. As the piston descends, it pushes the exhaust air through the regenerator 7 and spool 8 into the exhaust pipe. When the piston is lowered, a fresh portion of air is sucked into the compressor.

1 - working cylinder, 2 - piston; 3 - compressor; 4 - suction valve; 5 - delivery valve; 6 - intermediate tank; 7 - regenerator; 8 - bypass valve; 9 - exhaust pipe; 10 - suction pipe; 11 - furnace.

Both designs were not economical. But for some reason there were more problems with the Scot's engine, and it was less reliable than the Erickson engine. Perhaps that is why they overlooked one very important detail: at equal powers, the Stirling engine was more compact. In addition, he had a significant advantage in thermodynamics ...

Compression, heating, expansion, cooling - these are the four main processes necessary for the operation of any heat engine. Each of them can be carried out in different ways. For example, heating and cooling of a gas can be carried out in a closed cavity of constant volume (isochoric process) or under a moving piston at constant pressure (isobaric process). Compression or expansion of a gas can occur at a constant temperature (isothermal process) or without heat exchange with the environment (adiabatic process). Compiling closed chains from various combinations of such processes, it is not difficult to obtain theoretical cycles according to which all modern heat engines operate. Let's say a combination of two adiabats and two isochores form the theoretical cycle of a gasoline engine. If we replace the isochore in it, along which the gas is heated, with an isobar, we get a diesel cycle. Two adiabats and two isobars will give the theoretical gas turbine cycle. Among all conceivable cycles, the combination of two adiabats and two isotherms plays a particularly important role in thermodynamics, since such a cycle - the Carnot cycle - should operate the engine with the highest efficiency.

If in the Stirling engine heat was supplied along isochores, then in Erickson this process occurred along the isobar, and the processes of compression and expansion proceeded along isotherms.

At the beginning of our century, Erickson engines of low power (about 10-20 hp) found application in various countries. Thousands of such installations worked in factories, printing houses, mines and mines, turned the shafts of machine tools, pumped water, raised elevators. Under the name "warmth and strength" they were known in Russia.

Attempts were made to make a large marine engine, but the test results discouraged not only skeptics, but also Erickson himself. Contrary to the prophecies of the first, the ship "moved" and even crossed the Atlantic Ocean. But the inventor's expectations were also deceived: four gigantic-sized engines instead of 1000 hp. With. developed only 300 liters. With. The consumption of coal turned out to be the same as that of steam engines. In addition, the bottoms of the working cylinders burned through by the end of the voyage, and in England the engines had to be removed and secretly replaced with an ordinary steam engine. On top of all the misfortunes on the way back to America, the ship crashed and died with the entire crew.

1 - working piston 2 - piston-displacer; 3 - cooler; 4 - heater; 5 - regenerator; 6 - cold space; 7 - hot space.

Abandoning the idea of ​​building "caloric machines" of high power, Erickson launched the mass production of small engines. The fact is that the level of science and technology of that time did not allow designing and building an economical and powerful machine.

But the main blow to Erickson came from the inventors of the internal combustion engine. The rapid development of diesels and carburetor engines forced a good idea to be forgotten.

… A century has passed. In the 1930s, one of the military departments instructed Philips to develop a power plant with a capacity of 200-400 watts for a traveling radio station. Moreover, the engine must be omnivorous, that is, it must work on any type of fuel.

The specialists of the firm set to work with all thoroughness. We started with research on various thermodynamic cycles and, to our surprise, found that theoretically the most economical is the long-forgotten Stirling engine.

The war suspended research, but at the end of the 40s, work was continued. And then, as a result of numerous experiments and calculations, a new discovery was made - a closed circuit, in which under a pressure of about 200 atm. the working fluid (hydrogen or helium, as having the lowest viscosity and the highest heat capacity) circulated. True, having closed the cycle, the engineers were forced to take care of the artificial cooling of the working fluid. So there was a cooler, which was not in the first external combustion engines. And although the heater and cooler, no matter how compact they are, make the stirling heavier, they tell it one very important quality.

Isolated from the external environment, they practically do not depend on it. Stirling can run from any source of heat everywhere: under water, underground, in space - that is, where internal combustion engines that need air cannot work. Under such conditions, it is in principle impossible to do without heaters and coolers that transfer heat through the wall. And then Stirling beat their rivals even in weight. In the first prototypes, the specific gravity per unit of power was about 6-7 kg per hp. with., as in marine diesel engines. Modern stirlings have an even lower ratio - 1.5-2 kg per liter. With. They are even more compact and lightweight.

So, the scheme became two-circuit: one circuit with a working agent and the second - heat supply; this made it possible to bring the power output to 200 liters. With. per liter of working volume, and efficiency. - up to 38-40 percent. For comparison: modern

diesel engines have efficiency. 34-38 percent, and carbureted engines - 25-28. In addition, the Stirling fuel combustion process is continuous, and this sharply reduces toxicity - in terms of carbon monoxide output by 200 times, in terms of nitrogen oxide - by 1-2 orders of magnitude. Here is perhaps one of the radical solutions to the problem of urban air pollution.

The working part of a modern Stirling is a closed volume filled with a working gas (Fig. 2). The upper part of the volume is hot, it heats up continuously. The lower one is cold, it is constantly cooled by water. In the same volume - a cylinder with two pistons: a displacer and a worker. When the piston goes up, the gas in the volume is compressed; down - expands. The up and down movement of the displacer piston produces an alternate distribution of heated and cooled gas. When the displacing piston is in the upper position (in the hot space), most of the gas is displaced into the cold zone. At this time, the working piston begins to move up and compresses the cold gas. Now the displacer piston rushes down until it contacts the working piston, and the compressed cold gas is pumped into the hot space. Expansion of heated gas - working stroke. Part of the energy of the working stroke is stored for the subsequent compression of the cold gas, and the excess goes to the motor shaft.

The regenerator is located between the cold and hot spaces. When the expanded hot gas is pumped into the cold part by the movement of the displacing piston, it passes through a dense bundle of thin copper wires and gives them the heat contained in it. During the return stroke, compressed cold air takes this heat back before reaching the hot part.

1 - fuel injector; 2 - exhaust of cooled gases, 3 - air heater; 4 - outlet of hot gases; 5 - hot space; 6 - regenerator; 7 - cylinder; 8 - cooler tubes; 9 - cold space; 10 - working piston; 11 - rhombic drive; 12 - combustion chamber; 13 - heater tubes; 14 - piston-displacer; 15 - air intake for fuel combustion; 16 - buffer cavity.

Of course, in a real machine, everything does not look so simple (Fig. 3). It is impossible to quickly heat the gas through the thick wall of the cylinder; this requires a much larger heating surface. That is why the upper part of the closed volume turns into a system of thin tubes heated by the flame of the nozzle. In order to use the heat of the combustion products as fully as possible, the cold air supplied to the nozzle is preheated by the exhaust gases - this is how a rather complex combustion circuit appears.

The cold part of the working volume is also a system of tubes into which cooling water is injected.

Under the working piston is a closed buffer cavity filled with compressed gas. During the working stroke, the pressure in this cavity increases. The energy stored in this case is sufficient to compress the cold gas in the working volume.

As they improved, the temperature and pressure increased uncontrollably. 800° Celsius and 250 atm. - this is a very difficult task for designers, this is the search for especially strong and heat-resistant materials, the difficult problem of cooling, since the heat generation here is one and a half to two times greater than in classical engines.

The results of these experiments sometimes lead to the most unexpected findings. For example, Philips specialists, while running their engine at idle (without heating), noticed that the cylinder head is very cool. Quite by accident, this effect led to a whole series of developments, and as a result, the birth of a new refrigeration machine. Now such high-performance and small-sized refrigeration units are widely used all over the world. But back to heat engines.

Subsequent events are growing like a snowball. In 1958, with the acquisition of licenses by other firms, Stirling stepped overseas. It began to be tested in various fields of technology. A project is being developed to use the engine to power the equipment of spacecraft and satellites. For field radio stations, power plants are being created that operate on any type of fuel (with a power of the order of 10 hp), which have such a low noise level that it is not audible for 20 steps.

A huge sensation was caused by a demonstration plant operating on twenty types of fuel. Without shutting off the engine, by simply turning the tap, gasoline, diesel fuel, crude oil, olive oil, combustible gas were alternately fed into the combustion chamber - and the car perfectly “ate” any “feed”. There were reports in the foreign press about a 2.5 thousand hp engine project. With. with a nuclear reactor. Estimated efficiency 48-50%. All dimensions of the power unit are significantly reduced, which allows the released weight and area to be given under the biological protection of the reactor.

Another interesting development is a drive for an artificial heart weighing 600 g and 13 watts. A weakly radioactive isotope provides it with an almost inexhaustible source of energy.

The Stirling engine was tested on some cars. In terms of its operating parameters, it was not inferior to the carburetor one, and the noise level and exhaust toxicity decreased significantly.

A car with stirling can run on any type of fuel, and if necessary, on melt. Imagine: before entering the city, the driver turns on the burner and melts several kilograms of aluminum oxide or lithium hydride. On the city streets, he rides "without smoke": the engine runs on heat stored by the melt. One of the firms made a motor scooter, into the tank of which about 10 liters of lithium fluoride melt is poured. Such a charge is enough for 5 hours of operation with an engine power of 3 liters. With.

Work on the Stirlings continues. In 1967, a sample of a pilot plant with a capacity of 400 liters was made. With. for one cylinder. A comprehensive program is being carried out, according to which by 1977 it is planned to mass-produce engines with a power range from 20 to 380 hp. With. In 1971, Philips released a 200 hp four-cylinder industrial engine. With. with a total weight of 800 kg. His balance is so high that a coin (the size of a penny) placed on its edge on the casing stands without moving.

The advantages of the new type of engine include a large motor resource of about 10 thousand hours. (there is separate data on 27 thousand), and smooth operation, since the pressure in the cylinders increases smoothly (according to a sinusoid), and not by explosions, like a diesel engine.

Promising developments of new models are also carried out here. Scientists and engineers are working on the kinematics of various options, on electronic computers they calculate various types of “heart”, a Stirling regenerator. There is a search for new engineering solutions that will form the basis of economical and powerful engines that can push the usual diesel and gasoline engines, thereby correcting the unfair mistake of history.

A. ALEKSEEV

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Ecology of consumption. Science and technology: The Stirling motor is most often used in situations where a device for converting thermal energy is required, which is simple and efficient.

Less than a hundred years ago, internal combustion engines tried to win their rightful place in the competition among other machines and moving mechanisms available. At the same time, in those days, the superiority of the gasoline engine was not so obvious. Existing steam-powered machines were distinguished by their quietness, excellent power characteristics for that time, ease of maintenance, and the ability to use various types of fuel. In the further struggle for the market, internal combustion engines prevailed due to their efficiency, reliability and simplicity.

The further race to improve the units and driving mechanisms, which gas turbines and rotary engines entered in the middle of the 20th century, led to the fact that, despite the supremacy of the gasoline engine, attempts were made to introduce a completely new type of engine onto the “playing field” - thermal, for the first time invented back in 1861 by a Scottish priest named Robert Stirling. The engine was named after its creator.

STIRLING ENGINE: THE PHYSICAL SIDE OF THE ISSUE

To understand how a Stirling benchtop power plant works, you need to understand the basics of how heat engines work. Physically, the principle of operation is to use mechanical energy, which is obtained by expanding the gas during heating and its subsequent compression during cooling. To demonstrate the principle of operation, an example can be given based on an ordinary plastic bottle and two pots, one of which contains cold water, the other hot.

When lowering the bottle into cold water, the temperature of which is close to the temperature of ice formation, with sufficient cooling of the air inside the plastic container, it should be closed with a cork. Further, when the bottle is placed in boiling water, after a while the cork “shoots” with force, since in this case the work done by the heated air is many times greater than that done during cooling. When the experiment is repeated many times, the result does not change.

The first machines that were built using the Stirling engine faithfully reproduced the process demonstrated in the experiment. Naturally, the mechanism required improvement, consisting in the use of part of the heat that was lost by the gas during cooling for further heating, allowing heat to be returned to the gas to accelerate heating.

But even the application of this innovation could not save the situation, since the first Stirlings were large in size with low power output. In the future, more than once attempts were made to modernize the design to achieve a power of 250 hp. led to the fact that in the presence of a cylinder with a diameter of 4.2 meters, the real output power that the Stirling power plant produced at 183 kW was actually only 73 kW.

All Stirling engines operate on the principle of the Stirling cycle, which includes four main phases and two intermediate ones. The main ones are heating, expansion, cooling and compression. As the transition stage, the transition to the cold generator and the transition to the heating element are considered. The useful work done by the engine is based solely on the temperature difference between the heating and cooling parts.

MODERN STIRLING CONFIGURATIONS

Modern engineering distinguishes three main types of such engines:

• alpha stirling, the difference of which is in two active pistons located in independent cylinders. Of all three options, this model has the highest power, having the highest temperature of the heated piston;
• beta stirling, based on one cylinder, one part of which is hot and the other is cold;
• gamma-stirling, which, in addition to the piston, also has a displacer.

The production of the power plant at Stirling will depend on the choice of engine model, which will take into account all the positive and negative aspects of such a project.

ADVANTAGES AND DISADVANTAGES

Due to their design features, these engines have a number of advantages, but they are not without drawbacks.

Stirling's desktop power station, which cannot be bought in a store, but only from amateurs who independently collect such devices, includes:

• large dimensions, which are caused by the need for constant cooling of the working piston;
• the use of high pressure, which is required to improve engine performance and power;
• heat loss, which occurs due to the fact that the generated heat is transferred not to the working fluid itself, but through a system of heat exchangers, whose heating leads to a loss in efficiency;
• a sharp reduction in power requires the application of special principles that differ from those traditional for gasoline engines.

Along with the disadvantages, power plants operating on Stirling units have undeniable advantages:

• any type of fuel, since, like any engines that use heat energy, this engine is able to function at a temperature difference in any environment;
• economy. These devices can be an excellent replacement for steam units in cases where it is necessary to process solar energy, giving out an efficiency of 30% higher;
• environmental Safety. Since the kW tabletop power plant does not generate an exhaust moment, it does not produce noise or emit harmful substances into the atmosphere. Ordinary heat acts as a source of power, and the fuel burns out almost completely;
• constructive simplicity. For his work, Stirling will not require additional parts or fixtures. It is able to start independently without the use of a starter;
• increased resource of working capacity. Due to its simplicity, the engine can provide more than one hundred hours of continuous operation.

STIRLING ENGINE APPLICATIONS

The Stirling motor is most often used in situations where an apparatus for converting thermal energy is required, which is simple, while the efficiency of other types of thermal units is significantly lower under similar conditions. Very often, such units are used in the power supply of pumping equipment, refrigerators, submarines, batteries that store energy.

One of the promising areas for the use of Stirling engines is solar power plants, since this unit can be successfully used to convert the energy of sunlight into electrical energy. To carry out this process, the engine is placed in the focus of a mirror that accumulates the sun's rays, which provides permanent illumination of the area requiring heating. This allows you to focus solar energy on a small area. The fuel for the engine in this case is helium or hydrogen. published

The Stirling engine, the principle of operation of which is qualitatively different from the usual for all internal combustion engines, once was a worthy competitor to the latter. However, they forgot about it for a while. How this motor is used today, what is the principle of its operation (in the article you can also find drawings of the Stirling engine that clearly demonstrate its operation), and what are the prospects for future use, read below.

Story

In 1816, in Scotland, Robert Stirling patented the one named today in honor of its inventor. The first hot air engines were invented before him. But Stirling added a purifier to the device, which in the technical literature is called a regenerator, or heat exchanger. Thanks to him, the performance of the motor increased while keeping the unit warm.

The engine was recognized as the most durable steam engine available at that time, since it never exploded. Before him, on other motors, this problem arose often. Despite its rapid success, its development was abandoned at the beginning of the twentieth century, as it became less economical than other internal combustion engines and electric motors that appeared then. However, Stirling still continued to be used in some industries.

External combustion engine

The principle of operation of all heat engines is that to obtain gas in an expanded state, greater mechanical forces are required than when compressing a cold one. To demonstrate this, you can conduct an experiment with two pots filled with cold and hot water, as well as a bottle. The latter is dipped in cold water, plugged with a cork, then transferred to hot. In this case, the gas in the bottle will begin to perform mechanical work and push the cork out. The first external combustion engine was based entirely on this process. True, later the inventor realized that part of the heat can be used for heating. Thus, productivity has increased significantly. But even this did not help the engine become common.

Later, Erickson, an engineer from Sweden, improved the design by suggesting that the gas be cooled and heated at constant pressure instead of volume. As a result, many copies began to be used for work in mines, on ships and in printing houses. But for the crews, they were too heavy.

External combustion engines from Philips

Such motors are of the following types:

• steam;
• steam turbine;
• Stirling.

The latter type was not developed due to low reliability and other not the highest rates compared to other types of units that appeared. However, Philips reopened in 1938. Engines began to serve to drive generators in non-electrified areas. In 1945, the company's engineers found the opposite use for them: if the shaft is spun by an electric motor, then the cooling of the cylinder head reaches minus one hundred and ninety degrees Celsius. Then it was decided to use an improved Stirling engine in refrigeration units.

Principle of operation

The action of the motor is to work on thermodynamic cycles, in which compression and expansion occur at different temperatures. In this case, the regulation of the flow of the working fluid is implemented due to the changing volume (or pressure - depending on the model). This is the principle of operation of most of these machines, which may have different functions and designs. Engines can be piston or rotary. Machines with their installations work as heat pumps, refrigerators, pressure generators and so on.

In addition, there are open-cycle motors, where flow control is implemented through valves. It is they who are called Erickson engines, in addition to the common name of the Stirling name. In an internal combustion engine, useful work is carried out after pre-compression of air, fuel injection, heating of the resulting mixture mixed with combustion and expansion.

The Stirling engine has the same principle of operation: at low temperatures, compression occurs, and at high temperatures, expansion occurs. But heating is carried out in different ways: heat is supplied through the cylinder wall from the outside. Therefore, he received the name of the external combustion engine. Stirling used a periodic change in temperature with a displacement piston. The latter moves gas from one cavity of the cylinder to another. On the one hand, the temperature is constantly low, and on the other, it is high. When the piston moves up, the gas moves from a hot to a cold cavity, and when it moves down, it returns to a hot one. First, the gas gives off a lot of heat to the refrigerator, and then it receives as much heat from the heater as it gave out. A regenerator is placed between the heater and the cooler - a cavity filled with a material to which the gas gives off heat. In the reverse flow, the regenerator returns it.

The displacer system is connected to a working piston, which compresses the gas in the cold and allows it to expand in the heat. Due to compression at a lower temperature, useful work is done. The whole system goes through four cycles with intermittent movements. The crank mechanism at the same time ensures continuity. Therefore, sharp boundaries between the stages of the cycle are not observed, and Stirling does not decrease.

Considering all of the above, the conclusion suggests itself that this engine is a reciprocating machine with an external heat supply, where the working fluid does not leave the enclosed space and is not replaced. The drawings of the Stirling engine well illustrate the device and the principle of its operation.

Work details

The sun, electricity, nuclear power, or any other source of heat can supply power to a Stirling engine. The principle of operation of his body is to use helium, hydrogen or air. An ideal cycle has a thermal maximum possible efficiency of thirty to forty percent. But with an efficient regenerator, it will be able to work with a higher efficiency. Regeneration, heating and cooling are provided by built-in oil-free heat exchangers. It should be noted that the engine needs very little lubrication. The average pressure in the cylinder is usually 10 to 20 MPa. Therefore, an excellent sealing system and the possibility of oil entering the working cavities are required here.

Comparative characteristics

Most engines of this kind in operation today use liquid fuels. At the same time, continuous pressure is easy to control, which helps to reduce emissions. The absence of valves ensures silent operation. Power to weight is comparable to turbocharged engines, and the output power density is equal to that of a diesel unit. Speed ​​and torque are independent of each other.

The cost of producing an engine is much higher than that of an internal combustion engine. But during operation, the opposite is obtained.

Advantages

Any model of the Stirling engine has many advantages:

• Efficiency with modern design can reach up to seventy percent.
• The engine does not have a high-voltage ignition system, camshaft and valves. It will not need to be adjusted during the entire period of operation.
• In Stirlings, there is no explosion, as in an internal combustion engine, which heavily loads the crankshaft, bearings and connecting rods.
• They do not have that effect when they say that "the engine has stalled."
• Due to the simplicity of the device, it can be operated for a long time.
• It can work both on wood, and with nuclear and any other type of fuel.
• Combustion takes place outside the engine.

Flaws

Application

Currently, the Stirling engine with a generator is used in many areas. It is a universal source of electrical energy in refrigerators, pumps, submarines and solar power stations. It is thanks to the use of various types of fuel that it is possible to use it widely.

rebirth

These motors have been developed again thanks to Philips. In the middle of the twentieth century, General Motors entered into an agreement with it. She led developments for the use of Stirlings in space and underwater devices, on ships and cars. Following them, another company from Sweden, United Stirling, began to develop them, including the possible use on

Today, the linear Stirling engine is used in installations of underwater, space and solar vehicles. Great interest in it is due to the relevance of the issues of environmental degradation, as well as the fight against noise. In Canada and the USA, Germany and France, as well as Japan, there are active searches for the development and improvement of its use.

Future

The obvious advantages that piston and Stirling have, consisting in a long service life, the use of different fuels, noiselessness and low toxicity, make it very promising against the background of an internal combustion engine. However, given the fact that the internal combustion engine has been improved over time, it cannot be easily displaced. One way or another, it is precisely such an engine that occupies a leading position today, and does not intend to give them up in the near future.

External combustion engines

An important element in the implementation of the energy saving program is the provision of autonomous sources of electricity and heat to small residential formations and consumers remote from centralized networks. To solve these problems, innovative installations for the generation of electricity and heat based on external combustion engines are the best suited. As a fuel, both traditional fuels and associated petroleum gas, biogas obtained from wood chips, etc. can be used.

The past 10 years have seen rising fossil fuel prices, an increased focus on CO 2 emissions, and a growing desire to de-dependence on fossil fuels and become fully self-sufficient in energy. This was a consequence of the development of a huge market for technologies capable of producing energy from biomass.

External combustion engines were invented almost 200 years ago, in 1816. Together with the steam engine, two- and four-stroke internal combustion engines, external combustion engines are considered one of the main types of engines. They were designed with the goal of creating engines that were safer and more efficient than the steam engine. At the very beginning of the 18th century, the lack of suitable materials led to numerous deaths due to explosions of pressurized steam engines.

A significant market for external combustion engines developed in the second half of the 18th century, particularly in connection with smaller applications where they could be operated safely without the need for skilled operators.

After the invention of the internal combustion engine in the late 18th century, the market for external combustion engines disappeared. The cost of producing an internal combustion engine is lower compared to the cost of producing an external combustion engine. The main disadvantage of internal combustion engines is that they require clean, CO2-emission-increasing fossil fuels to run. However, until recently the cost of fossil fuels has been low and CO2 emissions have been neglected.

The principle of operation of an external combustion engine

Unlike the well-known internal combustion process, in which fuel is burned inside the engine, an external combustion engine is driven by an external heat source. Or, more precisely, it is driven by temperature differences generated by external sources of heating and cooling.

These external sources of heating and cooling can be biomass waste gases and cooling water, respectively. The process results in the rotation of a generator mounted on the engine, whereby energy is produced.

All internal combustion engines are driven by temperature differences. Gasoline, diesel and external combustion engines are based on the fact that less effort is needed to compress cold air than to compress hot air.

Gasoline and diesel engines draw in cold air and compress that air before it is heated by the internal combustion process that takes place inside the cylinder. After heating the air above the piston, the piston moves down, whereby the air expands. Since the air is hot, the force acting on the piston rod is large. When the piston reaches the bottom, the valves open and the hot exhaust is replaced by new, fresh, cold air. When the piston moves up, cold air is compressed, and the force acting on the piston rod is less than when it moves down.

An external combustion engine works according to a slightly different principle. There are no valves in it, it is hermetically sealed, and the air is heated and cooled using hot and cold circuit heat exchangers. An integrated pump, driven by the movement of a piston, moves air back and forth between the two heat exchangers. During cooling of the air in the cold circuit heat exchanger, the piston compresses the air.

After being compressed, the air is then heated in the hot circuit heat exchanger before the piston starts to move in the opposite direction and use the expansion of the hot air to power the engine.

Steam engines, widely used in the nineteenth century, did not provide sufficient safety in their operation. The mechanisms had multiple design flaws, they could not withstand high steam pressure, which led to boiler ruptures. , patented in 1816 by a Scottish priest named Robert Stirling, was a successful solution for that time. Its uniqueness consisted in the use of a special cleaner (regenerator) in the previously known "hot air engines".

The presented diagram in an accessible form illustrates the device of the piston mechanism and the procedure for its operation.

The essence of Stirling's invention

In the diagram, the heat engine consists of two compression and working cylinders. The left and right sides of the elongated cylinder are separated by a heat-insulating wall. A special displacement piston runs inside, which does not come into contact with the side walls.

1. Heat is supplied to the left side of the device, cooling is supplied to the right.
2. As the piston moves to the left, the hot air is pushed into the cold right zone and cooled.
3. As a result, the volume of the gas decreases.
4. The working piston retracts to the left.
5. When the displacement piston moves to the right, cold air is forced into the hot zone, where it heats up and expands.
6. Pushes the working piston to the right.
7. The working and displacing pistons are connected to each other through a crankshaft with a displacement angle of 90 degrees.

Important: - this is a piston-type mechanism with heat supply from an external source. The working body of the device is constantly in a confined space and cannot be replaced. The following sources can be used to supply the required amount of heat:

• electricity;
• Sun;
• nuclear energy, etc.

History of development of external combustion engines

Unlike internal combustion engines (ICE), where energy is released as a result of the expansion of the air volume during the combustion of fuel mixtures, here the heating of the working material is carried out through the outer walls of the cylinder. This is where the name "External Combustion Engine" comes from.

Due to the appearance of a regenerating element in the engine design, heat is stored for a long time in the action zone when the working fluid is cooled, which contributes to a significant increase in engine performance. The invention made it possible to increase the efficiency of mechanisms, it began to be widely used in industrial production.

Over time, Stirling devices lost popularity, but by inertia continued to be used in some of the few industries. Steam engines have given way to the leading step of the new generation of mechanisms:

• internal combustion engines;
• steam engines;
• electric motors.

The merits of thermal devices were again remembered only in the twentieth century. The introduction of Stirling engines into modern developments is carried out by the best engineering teams of well-known manufacturers in America, Sweden, Japan, etc.

How a Stirling heat engine works

The principle of operation of an external combustion engine lies in the constant change of modes - heating / cooling of the working material located in a confined space. Based on the laws of physics, when a gas is heated, its volume increases, and when the temperature decreases, it decreases accordingly. The amount of generated energy depends on the coefficient of change in the volume of the working fluid.

The term "working fluid" means the following substances:

1. Air.
2. Gas (helium, hydrogen, freon, nitrogen dioxide).
3. Liquid (water, liquefied butane or propane).

Scope of application of external combustion engines

As a result of subsequent improvements in the design of the motor, the gas is heated / cooled at a constant pressure in the system (instead of maintaining volume). This invention of an engineer from Sweden named Erickson made it possible to create engines intended for use by workers in mines, printing houses, ships, etc. Heat engines were not used in passenger crews of that time, because they had a relatively large weight.

External combustion engines were often used to power generators in areas without electrical power.

Interesting: In 1945, Philips inventors-enthusiasts came up with the reverse use of thermal devices. When the shaft is untwisted by an electric motor, the cylinder head is cooled down to minus 190°C. This made it possible to use the improved Stirling external combustion piston engine in refrigeration units.

Is it possible to use Stirling engines instead of internal combustion engines

Since the second half of the 20th century, General Motors has begun to introduce V-shaped stirlings for crank mechanisms into production. When testing external combustion engines, it was noticed that they work perfectly without sounds and noise. There is no carburetor, ignition system, nozzles that require high pressure, candles, valves, etc. To create sufficient pressure in the engine cylinders, it is not necessary to explode the fuel, as in an internal combustion engine. By using vehicles equipped with external combustion engines, the problem of noise reduction in large cities can be solved.

As a result of the tests, the following advantages and disadvantages of external combustion engines were revealed.

• The advantages of these devices:
• silent operation (no need to install a silencer);
• lack of vibrations;
• there is no need to create high pressure in the system;
• versatility, the ability to work from various heat sources;
• ease of adjustment.

The disadvantages of engines include:

• relatively large weight of the structure;
• low economy;
• high cost of the mechanism.

Simplified diagram of a V-shaped external combustion engine:

One of the engine cylinders is working (1), the other, respectively, is compression (7). Each of them has its own piston (2). In the central part of the scheme are placed: cooler (6), heat exchanger (4), heating element (3). At the maximum speed of one of the pistons, the other at the same time is in a stationary state, its speed is zero. The phase displacement angle is 90°, due to the mutually perpendicular arrangement of the cylinders.

How does an external combustion engine work and where is it used?

Despite the fact that Stirling engines were forgotten for a certain period, in modern production, when new modifications are created, an outstanding invention is gaining new popularity. Craftsmen have appreciated the advantages of external combustion engines and build various devices on their own at home based on their use. To make a heat engine with your own hands in home workshops, various materials and improvised means are used:

1. Large and medium containers borrowed from the household.
2. Bearings from old mechanisms.
3. Disks.
4. Metal rods of various diameters for axles, racks.
5. Sheets of metal, wood boards for the manufacture of platforms.

These devices are used in the household for a variety of tasks:

1. Generation of electrical energy on a small scale.
2. Creation of thermal energy.

The amount of power of some samples of home-made Stirling engines is enough to equip the electrical network and provide heat to private houses, small schools, medical buildings, sports facilities, industrial workshops, etc.

Do-it-yourself engines operate from various heat sources:

• natural gas;
• firewood;
• coal;
• peat;
• propane and other locally produced fuels or minerals.

Due to the simplicity of the design, do-it-yourself thermal devices do not need regular maintenance of the unit. Fuel combustion is carried out outside the cylinder body, so the working fluid is not polluted by combustion products, harmful deposits do not accumulate on the internal walls of the equipment.

In comparison with the internal combustion engine, this design includes half as many moving parts and components. Much less lubrication is required here to care for high-wear parts. Requirements for the quality of lubricants are minimal.

To connect the power grid to consumers, it is not necessary to purchase expensive equipment. Connecting wires to the electrical network is carried out by simple, familiar methods.

External combustion engines produced in domestic conditions are easily mounted on flat areas covered with gravel, without strong fixation. These installations are not subject to harmful atmospheric influences. To ensure uninterrupted stable operation, the engine does not require a special protective housing.