Turbine external combustion engine. Stirling external combustion engine

In engines external combustion the fuel combustion process and the source of thermal influence are separated from the working installation. This category usually includes steam and gas turbines, as well as Stirling engines. The first prototypes of such installations were constructed more than two centuries ago and were used throughout almost the entire 19th century.

When a rapidly developing industry needed powerful and economical power plants, designers came up with a replacement for explosive steam engines, where the working fluid was steam under high pressure. This is how external combustion engines appeared, which became widespread at the beginning of the 19th century. Only a few decades later they were replaced by internal combustion engines. They cost significantly less, which is why they were widely used.

But today, designers are looking more and more closely at external combustion engines that have fallen out of widespread use. This is due to their advantages. The main advantage is that such installations do not require highly purified and expensive fuel.

External combustion engines are unpretentious, although their construction and maintenance are still quite expensive.

Stirling's engine

One of the most famous representatives of the family of external combustion engines is the Stirling engine. It was invented in 1816, improved several times, but subsequently for a long time was undeservedly forgotten. Now the Stirling engine has received a rebirth. It is successfully used even in space exploration.

The operation of the Stirling machine is based on a closed thermodynamic cycle. Periodic processes of compression and expansion take place here at different temperatures. The work flow is controlled by changing its volume.

The Stirling engine can work as a heat pump, pressure generator, or cooling device.

In this engine, at low temperatures, gas is compressed, and at high temperatures, it expands. Periodic changes in parameters occur through the use of a special piston that has a displacer function. In this case, heat is supplied to the working fluid from the outside, through the cylinder wall. This feature gives the right

The Stirling engine, the principle of operation of which is qualitatively different from the usual internal combustion engine, once constituted a worthy competitor to the latter. However, for some time they forgot about him. 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, clearly demonstrating its operation), and what are the prospects for use in the future, read below.

Story

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

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

External combustion engine

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

Later, Erickson, an engineer from Sweden, improved the design by proposing to cool and heat the gas 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 they turned out to be too heavy for the crews.

External combustion engines from Philips

Similar 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 performance indicators compared to other types of units that appeared. However, Philips resumed operations in 1938. The engines began to be used 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, 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 motor operates in thermodynamic cycles, in which compression and expansion occur at different temperatures. In this case, regulation of the flow of the working fluid is realized due to changing volume (or pressure - depending on the model). This is the operating principle of most of these machines, which may have different functions and design 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 realized through valves. They are called Erickson engines, in addition to the common name Stirling. In an internal combustion engine, useful work is carried out after preliminary compression of air, injection of fuel, heating of the resulting mixture mixed with combustion and expansion.

The Stirling engine operates on the same principle: compression occurs at low temperatures, and expansion occurs at high temperatures. But heating is carried out differently: heat is supplied through the cylinder wall from the outside. That's why it got the name external combustion engine. Stirling used periodic temperature changes 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, high. When the piston moves up, gas moves from the hot to the cold cavity, and downwards it returns to the hot cavity. First, the gas gives a lot of heat to the refrigerator, and then from the heater it receives the same amount as it gave. A regenerator is placed between the heater and the refrigerator - a cavity filled with material to which the gas gives off heat. When the flow reverses, the regenerator returns it.

The displacer system is connected to a working piston, which compresses the gas when cold and allows it to expand when warm. Due to compression at a lower temperature, useful work occurs. The entire system goes through four cycles with intermittent movements. crank mechanism while ensuring continuity. Therefore, there are no sharp boundaries between the stages of the cycle, and Stirling does not decrease.

Considering all of the above, the conclusion suggests itself that this engine is a piston machine with an external heat supply, where the working fluid does not leave the enclosed space and is not replaced. 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 heat source can supply energy to the 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 effective regenerator, it will be able to work with higher efficiency. Regeneration, heating and cooling are provided by built-in heat exchangers operating without oils. It should be noted that the engine requires very little lubrication. The average pressure in the cylinder is usually from 10 to 20 MPa. Therefore, an excellent sealing system and the ability to get oil into the working cavities are required.

Comparative characteristics

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

The production costs of an engine are much higher than those of an internal combustion engine. But during operation the opposite is true.

Advantages

Any Stirling engine model has many advantages:

• Efficiency with modern design can reach up to seventy percent.
• There is no system in the engine high voltage ignition, camshaft and valves. It will not need to be adjusted during its entire service life.
• Stirlings do not have the same explosion as in an internal combustion engine, which heavily loads the crankshaft, bearings and connecting rods.
• They do not have the same effect when they say that “the engine has stalled.”
• Due to the simplicity of the device, it can be used for a long time.
• It can work with wood, nuclear or any other type of fuel.
• Combustion occurs outside the engine.

Flaws

Application

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

Renaissance

These engines began to develop again thanks to Philips. In the mid-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 possible use in

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

Future

The obvious advantages that piston and Stirling engines have, consisting of a long service life, the use of different fuels, noiselessness and low toxicity, make it very promising compared to the internal combustion engine. However, given that the internal combustion engine has been improved throughout time, it cannot be easily displaced. One way or another, it is precisely this engine that occupies a leading position today, and it should be handed over to soon I don't intend to.

Exacerbation of global problems requiring urgent solutions (depletion of natural resources, pollution environment etc.), led at the end of the 20th century to the need to adopt a number of international and Russian legislative acts in the field of ecology, environmental management and energy saving. The main requirements of these laws are aimed at reducing CO2 emissions, resource and energy conservation, converting vehicles to environmentally friendly motor fuels, etc.

One of the promising ways to solve these problems is the development and widespread implementation of energy-converting systems based on Stirling engines (machines). The principle of operation of such engines was proposed in 1816 by the Scotsman Robert Stirling. These are machines operating in a closed thermodynamic cycle, in which cyclic processes of compression and expansion occur at different temperature levels, and the flow of the working fluid is controlled by changing its volume.

The Stirling engine is a unique heat engine because its theoretical power is equal to the maximum power of heat engines (Carnot cycle). It works by thermal expansion of the gas, followed by compression of the gas as it cools. The engine contains a certain constant volume of working gas, which moves between a “cold” part (usually at ambient temperature) and a “hot” part, which is heated by the combustion of various fuels or other heat sources. Heating is carried out externally, so the Stirling engine is classified as an external combustion engine (ECE). Since, in comparison with internal combustion engines, in Stirling engines the combustion process takes place outside the working cylinders and proceeds in equilibrium, the working cycle is realized in a closed internal circuit at relatively low rates of pressure increase in the engine cylinders, the smooth nature of the thermal-hydraulic processes of the working fluid of the internal circuit and in the absence of a gas distribution mechanism valves

It should be noted that production of Stirling engines has already begun abroad, specifications which are superior to internal combustion engines and gas turbine units (GTU). Thus, Stirling engines from Philips, STM Inc., Daimler Benz, Solo, and United Stirling with a power from 5 to 1200 kW have efficiency. more than 42%, working life more than 40 thousand hours and specific gravity from 1.2 to 3.8 kg/kW.

In world reviews on energy-converting technology, the Stirling engine is considered the most promising in the 21st century. Low noise level, low toxicity of exhaust gases, ability to work on various fuels, great resource, good characteristics torque - all this makes Stirling engines more competitive compared to internal combustion engines.

Where can Stirling engines be used?

Autonomous power plants with Stirling engines (Stirling generators) can find application in regions of Russia where there are no reserves of traditional energy resources - oil and gas. Peat, wood, shale, biogas, coal, waste can be used as fuel Agriculture and timber processing industry. Accordingly, the problem with energy supply in many regions disappears.

Such power plants are environmentally friendly, since the concentration harmful substances in combustion products is almost two orders of magnitude lower than that of diesel power plants. Therefore, stirling generators can be installed in close proximity to the consumer, which will eliminate losses in the transmission of electricity. A 100 kW generator can provide electricity and heat to any locality with a population of more than 30-40 people.

Autonomous power plants with Stirling engines will find wide application in the oil and gas industry of the Russian Federation during the development of new fields (especially in the conditions of the Far North and the shelf of the Arctic seas, where serious power supply is needed for exploration, drilling, welding and other work). Unrefined fuel can be used as fuel here. natural gas, associated petroleum gas and gas condensate.

Now in the Russian Federation up to 10 billion cubic meters are lost annually. m of associated gas. It is difficult and expensive to collect; it cannot be used as motor fuel for internal combustion engines due to its constantly changing fractional composition. To prevent gas from polluting the atmosphere, it is simply burned. At the same time, its use as a motor fuel will provide a significant economic effect.

It is advisable to use power plants with a capacity of 3-5 kW in automation, communication and cathodic protection systems on main gas pipelines. And more powerful ones (from 100 to 1000 kW) are for power and heat supply to large rotation camps for gas and oil workers. Installations over 1 thousand kW can be used at onshore and offshore drilling sites in the oil and gas industry.

Problems of creating new engines

The engine, proposed by Robert Stirling himself, had significant weight and size characteristics and low efficiency. Due to the complexity of the processes in such an engine, associated with the continuous movement of the pistons, the first simplified mathematical apparatus was developed only in 1871 by the Prague professor G. Schmidt. The calculation method he proposed was based on an ideal model of the Stirling cycle and made it possible to create engines with efficiency. up to 15%. Only by 1953 Dutch company Philips created the first highly efficient Stirling engines, superior in performance to internal combustion engines.

In Russia, attempts to create domestic Stirling engines were made several times, but were not successful. There are several main problems hindering their development and widespread use.

First of all, this is the creation of an adequate mathematical model of the designed Stirling machine and the corresponding calculation method. The complexity of the calculation is determined by the complexity of implementing the thermodynamic Stirling cycle in real cars, due to the unsteadiness of heat and mass exchange in the internal circuit - due to the continuous movement of the pistons.

Lack of adequate mathematical models and calculation methods - main reason failures of a number of foreign and domestic enterprises in the development of both engines and refrigeration machines Stirling. Without exact mathematical modeling The fine-tuning of the designed machines turns into many years of grueling experimental research.

Another problem is creating structures individual nodes, difficulties with seals, power regulation, etc. Difficulties in design are due to the working fluids used, which include helium, nitrogen, hydrogen and air. Helium, for example, has superfluidity, which dictates increased requirements for the sealing elements of working pistons, etc.

The third problem is high level production technologies, the need to use heat-resistant alloys and metals, new methods of welding and soldering.

A separate issue is the manufacture of a regenerator and a nozzle for it to ensure, on the one hand, high heat capacity, and on the other, low hydraulic resistance.

Domestic developments of Stirling machines

Currently, Russia has accumulated sufficient scientific potential to create highly efficient Stirling engines. Significant results were achieved at the Stirling Technologies Innovation and Research Center LLC. Specialists conducted theoretical and experimental studies to develop new methods for calculating highly efficient Stirling engines. The main areas of work are related to the use of Stirling engines in cogeneration plants and systems for using the heat of exhaust gases, for example, in mini-CHPs. As a result, development methods and prototypes of 3 kW motors were created.

Particular attention during the research was paid to the development of individual components of Stirling machines and their design, as well as the creation of new circuit diagrams installations for various functional purposes. The proposed technical solutions, taking into account the fact that Stirling machines are less expensive to operate, make it possible to increase economic efficiency the use of new motors compared to traditional energy converters.

The production of Stirling engines is economically feasible given the virtually unlimited demand for environmentally friendly and highly efficient power equipment both in Russia and abroad. However, without the participation and support of the state and big business, the problem of their mass production cannot be solved in full.

How to help the production of Stirling engines in Russia?

It is obvious that innovative activity (especially the development of basic innovations) is a complex and risky type of economic activity. Therefore, it should rely on the mechanism of state support, especially at the start, with a subsequent transition to normal market conditions.

The mechanism for creating large-scale production of Stirling machines and energy-converting systems based on them in Russia could include:
- direct shared budget financing of innovative projects on Stirling machines;
- indirect support measures by exempting products produced under Stirling projects from VAT and other taxes at the federal and regional levels for the first two years, as well as providing a tax credit for such products for the next 2-3 years (taking into account that development costs it is inappropriate to include a fundamentally new product in its price, i.e. in the costs of the manufacturer or consumer);
- exclusion from the income tax base of the enterprise’s contribution to the financing of Stirling projects.

In the future, at the stage of sustainable promotion of energy equipment based on Stirling machines in the domestic and foreign markets, replenishment of capital for expanding production, technical re-equipment and support of next projects for the production of new types of equipment can be carried out through profits and the sale of shares of successfully developed production, credit resources commercial banks, as well as attracting foreign investment.

It can be assumed that thanks to the presence of a technological base and accumulated scientific potential in the design of Stirling machines, with reasonable financial and technical policies, Russia can in the near future become a world leader in the production of new environmentally friendly and highly efficient engines.

External combustion engines began to be used when people needed a powerful and economical source of energy. Before this, steam plants were used, but they were explosive because they used hot steam under pressure. At the beginning of the 19th century, they were replaced by devices with external combustion, and a few decades later the already familiar devices with internal combustion.

Origin of devices

In the 19th century, humanity was faced with the problem that steam boilers exploded too often and also had serious design flaws, which made their use undesirable. The solution was found in 1816 by Scottish priest Robert Stirling. These devices can also be called "hot air engines", which were used back in the 17th century, but this man added a purifier to the invention, now called a regenerator. Thus, the Stirling external combustion engine was capable of greatly increasing the productivity of the plant, since it retained heat in a warm working area while the working fluid was cooled. Because of this, the operating efficiency of the entire system has been significantly increased.

At that time, the invention was used quite widely and was on the rise in its popularity, but over time it was no longer used and was forgotten about. External combustion equipment was replaced by steam plants and engines, but already familiar ones, with internal combustion. They were remembered again only in the 20th century.

Installation operation

The operating principle of an external combustion engine is that it constantly alternates two stages: heating and cooling the working fluid in a confined space and generating energy. This energy arises due to the fact that the volume of the working fluid is constantly changing.

Most often, the working substance in such devices is air, but it is also possible to use helium or hydrogen. While the invention was at the development stage, substances such as nitrogen dioxide, freons, and liquefied propane-butane were used as experiments. In some samples they even tried to use ordinary water. It is worth noting that the external combustion engine, which was started with water as a working substance, was distinguished by the fact that it had a fairly high specific power, high pressure, and it itself was quite compact.

The first type of engine. "Alpha"

The first model to be used was Stirling's Alpha. The peculiarity of its design is that it has two power pistons located in separate cylinders. One of them had a fairly high temperature and was hot, the other, on the contrary, was cold. Inside the high-temperature heat exchanger there was a hot cylinder-piston pair. The cold steam was inside a heat exchanger at a low temperature.

The main advantages of external combustion heat engines were that they had high power and volume. However, the temperature of the hot steam was too high. Because of this, some technical difficulties arose in the process of manufacturing such inventions. The regenerator of this device is located between the hot and cold connecting tubes.

Second sample. "Beta"

The second sample was Stirling's Beta model. Basics design difference was that there was only one cylinder. One of its ends acted as a hot pair, while the other end remained cold. A piston moved inside this cylinder, from which power could be removed. There was also a displacer inside, which was responsible for changing the volume of the hot working area. This equipment used gas that was pumped from a cold zone to a hot zone through a regenerator. This type of external combustion engine had a regenerator in the form of an external heat exchanger or was combined with a displacer piston.

Latest model. "Gamma"

The latest variety of this engine became Stirling's Gamma. This type was distinguished not only by the presence of a piston and a displacer, but also by the fact that its design already included two cylinders. As in the first case, one of them was cold and it was used for power take-off. But the second cylinder, as in the previous case, was cold at one end and hot at the other. This is where the displacer moved. IN piston engine external combustion also had a regenerator, which could be of two types. In the first case, it was external and connected such structural parts as the hot zone of the cylinder with the cold zone, as well as with the first cylinder. The second type is an internal regenerator. If this option was used, it was included in the design of the displacer.

The use of Stirlings is justified if a simple and small thermal energy converter is needed. It can also be used if the temperature difference is not large enough to use gas or steam turbines. It is worth noting that today such samples have begun to be used more often. For example, they are used stand-alone models for tourists who are able to work from a gas burner.

Current use of devices

It would seem that such an old invention could not be used today, but this is not so. NASA has ordered a Stirling-type external combustion engine, but nuclear and radioisotope heat sources must be used as the working substance. In addition, it can also be successfully used for the following purposes:

• Using this engine model to pump liquid is much easier than using a conventional pump. This is largely due to the fact that the pumped liquid itself can be used as a piston. In addition, it will also cool the working fluid. For example, this type of “pump” can be used to pump water into irrigation canals using solar heat.
• Some refrigerator manufacturers are inclined to install such devices. The cost of production can be reduced, and ordinary air can be used as a refrigerant.
• If you combine an external combustion engine of this type with a heat pump, you can optimize the operation of the heating network in the house.
• Stirlings are used quite successfully on submarines of the Swedish Navy. The fact is that the engine runs on liquid oxygen, which is subsequently used for breathing. This is very important for a submarine. In addition, such equipment has sufficient low level noise. Of course, the unit is quite large and requires cooling, but these two factors are insignificant when it comes to a submarine.

Advantages of using an engine

If during design and assembly you apply modern methods, then it will be possible to increase the efficiency of the external combustion engine to 70%. The use of such samples is accompanied by the following positive qualities:

• Surprisingly, the torque in such an invention is practically independent of the speed of rotation of the crankshaft.
• In this power unit elements such as the ignition system and valve system. There is also no camshaft.
• It is quite convenient that throughout the entire period of use there will be no need to adjust and configure the equipment.
• These engine models are not capable of stalling. The simplest design of the device allows it to be used for quite a long time in a completely autonomous mode.
• Almost anything can be used as an energy source, from firewood to uranium fuel.
• Naturally, in an external combustion engine the process of combustion of substances is carried out externally. This ensures that the fuel is fully burned and the amount of toxic emissions is minimized.

Flaws

Naturally, any invention is not without its drawbacks. If we talk about the disadvantages of such engines, they are as follows:

1. Due to the fact that combustion occurs outside the engine, the resulting heat is removed through the walls of the radiator. This forces us to increase the dimensions of the device.
2. Material consumption. In order to create a compact and efficient model of the Stirling engine, it is necessary to have high-quality heat-resistant steel that can withstand high pressure and high temperature. In addition, there must be low thermal conductivity.
3. As a lubricant, you will have to buy a special product, since the usual one cokes when high temperatures, which are achieved in the engine.
4. To obtain a sufficiently high specific power, it will be necessary to use either hydrogen or helium as a working substance.

Hydrogen and helium as fuel

Obtaining high power is, of course, necessary, but you need to understand that using hydrogen or helium is quite dangerous. Hydrogen, for example, is quite explosive in itself, and at high temperatures it creates compounds called metallohydrites. This occurs when hydrogen dissolves in the metal. In other words, it is capable of destroying the cylinder from the inside.

In addition, both hydrogen and helium are volatile substances that are characterized by high penetrating ability. To put it simply, they leak through almost any seal quite easily. And loss of substance means loss in operating pressure.

Rotary external combustion engine

The heart of such a machine is a rotary expansion machine. For engines with an external combustion type, this element is presented in the form of a hollow cylinder, which is covered on both sides with covers. The rotor itself looks like a wheel, which is mounted on a shaft. It also has a certain number of U-shaped retractable plates. To extend them, a special retractable device is used.

Lukyanov external combustion engine

Yuri Lukyanov is a researcher at the Pskov Polytechnic Institute. He has been developing new engine models for quite some time. The scientist tried to make sure that the new models lacked elements such as a gearbox, camshaft and exhaust pipe. The main disadvantage of Stirling devices was that they were too large. It was this drawback that the scientist managed to eliminate by replacing the blades with pistons. This helped reduce the size of the entire structure several times. Some people say that you can make an external combustion engine with your own hands.

Last year, the magazine, in the first issue of which welcomed readers A. Einstein, fulfilled 85 years.

A small editorial team continues to publish IR, whose readers you are honored to be. Although this becomes more and more difficult every year. A long time ago, at the beginning of the new century, the Editorial Board had to leave their native place of residence on Myasnitskaya Street. (Well, really, this is a place for banks, not some body of inventors). However, it helped us Yu.Maslyukov(at that time Chairman of the Committee of the State Duma of the Federal Assembly of the Russian Federation on Industry) move to NIIAA near the Kaluzhskaya metro station. Despite the strict compliance by the Editorial Board with the terms of the contract and timely payment of rent, and the inspiring proclamation of a course for innovation by the President and Government of the Russian Federation, the new director at NIIAA informed us about the eviction of the Editorial Board “due to production needs.” This is with a decrease in the number of employees at NIIAA by almost 8 times and a corresponding release of space, and despite the fact that the area occupied by the editorial office did not account for even one hundredth of a percent of the vast areas of NIIAA.

We were sheltered by MIREA, where we have been located for the last five years. Moving twice is the same as burning once, the saying goes. But the editors are holding on and will hold on as long as they can. And it can exist as long as the magazine "Inventor and innovator" read and write out.

Trying to reach a larger number of interested people with information, we have updated the magazine’s website, making it, in our opinion, more informative. We are digitizing publications from previous years, starting with 1929 year - the time the magazine was founded. We are releasing an electronic version. But the main thing is the paper edition IR.

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