External combustion engine history of creation. Stirling engine (1 gif)

20.10.2019

Ecology of consumption. Science and technology: The Stirling motor is most often used in situations where an apparatus for converting thermal energy is required, characterized by simplicity and efficiency.

Less than a hundred years ago engines internal combustion tried to win their rightful place in the competition among other available machines and moving mechanisms. Moreover, in those days superiority gasoline engine was not so obvious. Existing machines powered by steam engines 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, due to their efficiency, reliability and simplicity, gained the upper hand.

The further race to improve units and driving mechanisms, which gas turbines and rotary types of engines entered in the mid-20th century, led to the fact that, despite the supremacy of the gasoline engine, attempts were made to introduce completely the new kind engines - thermal, first invented back in 1861 by a Scottish priest named Robert Stirling. The engine received the name of its creator.

STIRLING ENGINE: PHYSICAL SIDE OF THE ISSUE

To understand how a tabletop Stirling power station works, you need to understand general information on the principles of operation of heat engines. Physically, the principle of operation is to use mechanical energy, which is obtained when gas expands when heated and its subsequent compression when cooled. To demonstrate the principle of operation, we can give an example based on an ordinary plastic bottle and two pans, 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 at which ice forms and the air inside the plastic container is sufficiently cooled, it should be closed with a stopper. Further, when the bottle is placed in boiling water, after some time the cork “shoots” with force, since in this case the heated air performed work many times greater than that done during cooling. If the experiment is repeated many times, the result does not change.

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

But even the use of this innovation could not save the situation, since the first Stirlings were large in size and had low power output. Subsequently, attempts were made more than once 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 actual power output produced by the Stirling power plant of 183 kW was in fact 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. The transition stage is considered to be the transition to the cold generator and the transition to the heating element. The useful work performed 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 two active pistons located in independent cylinders. Of all three options this model distinguished by the highest power, having the highest temperature of the heating piston;
beta stirling, based on one cylinder, one part of which is hot and the other cold;
Gamma Stirling, which in addition to the piston also has a displacer.

The production of the Stirling power station will depend on the choice of engine model, which will take into account all the positive and negative sides similar project.

ADVANTAGES AND DISADVANTAGES

Thanks to your design features These engines have a number of advantages, but are not without disadvantages.

Tabletop Stirling power station, which cannot be purchased in a store, but only from hobbyists who independently assemble such devices, include:

large sizes, which are caused by the need for constant cooling of the working piston;
usage high pressure what 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 of efficiency;
a sharp reduction in power requires the use 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 using thermal energy, this engine able to function at different temperatures of any environment;
efficiency. These devices can be an excellent replacement for steam units in cases where it is necessary to process solar energy, providing an efficiency of 30% higher;
environmental Safety. Since the tabletop kW power station does not create exhaust torque, it does not produce noise or emit emissions into the atmosphere. harmful substances. The source of power is ordinary heat, and the fuel burns out almost completely;
structural simplicity. For its work, Stirling will not require additional parts or devices. It is capable of starting independently without using a starter;
increased performance resource. Due to its simplicity, the engine can provide hundreds of hours of continuous operation.

AREAS OF APPLICATION OF STIRLING ENGINES

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

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 solar rays into electrical energy. To carry out this process, the engine is placed at the focal point of a mirror that accumulates solar rays, which provides permanent illumination of the area requiring heating. This allows solar energy to be focused on a small area. The fuel for the engine in this case is helium or hydrogen. published

1. Introduction………………………………………………………………………………3

2. History………………………………………………………………………………4

3. Description……………………………………………………………………………………… 4

4. Configuration……………………………………………………………………. 6

5. Disadvantages……………………………………………………………………….. 7

6. Advantages……………………………………………………………… 7

7. Application…………………………………………………………………………………. 8

8. Conclusion………………………………………………………………………. eleven

9. List of references……………………………………………………….. 12

Introduction

At the beginning of the 21st century, humanity looks to the future with optimism. There are the most compelling reasons for this. Scientific thought does not stand still. Today we are offered more and more new developments. More and more economical, environmentally friendly and promising technologies are being introduced into our lives

This concerns, first of all, alternative engine construction and the use of so-called “new” alternative fuels: wind, solar, water and other energy sources

Thanks to engines of various types, a person receives energy, light, heat and information. Engines are the heart that beats in time with the development of modern civilization. They ensure production growth and reduce distances. Currently widespread internal combustion engines have a number of disadvantages: their operation is accompanied by noise, vibrations, they emit harmful exhaust gases, thereby polluting our environment, and consume a lot of fuel. But today an alternative to them already exists. The class of engines from which the harm is minimal is Stirling engines. They operate in a closed cycle, without continuous micro-explosions in the working cylinders, with virtually no emission of harmful gases, and they require much less fuel

Invented long before the internal combustion engine and diesel, the Stirling engine was undeservedly forgotten

The revival of interest in Stirling engines is usually associated with the activities of Philips. Work on the design of small-power Stirling engines began at the company in the mid-30s of the twentieth century. The goal of the work was to create a small electric generator with low noise and thermal drive to power radio equipment in areas of the world with no regular power supply. In 1958, General Motors entered into a licensing agreement with Philips, and their cooperation continued until 1970. Developments have focused on the use of Stirling engines for space and underwater power plants, automobiles and ships, as well as for stationary power supply systems. The Swedish company United Stirling, which concentrated its efforts mainly on engines for Vehicle heavy lifting capacity, have expanded their interests to the field of engines for passenger cars. Real interest in the Stirling engine was revived only during the so-called “energy crisis”. It was then that the potential capabilities of this engine in relation to the economic consumption of conventional liquid fuel seemed especially attractive, which seemed very important in connection with rising fuel prices

Story

The Stirling engine was first patented by Scottish clergyman Robert Stirling on September 27, 1816 (English patent no. 4081). However, the first elementary “hot air engines” were known at the end of the 17th century, long before Stirling. Stirling's achievement was the addition of a purifier, which he called "economy". In modern scientific literature, this purifier is called a “regenerator” (heat exchanger). It increases engine performance by retaining heat in a warm part of the engine while the working fluid cools. This process greatly improves the efficiency of the system. In 1843, James Stirling used this engine in the factory where he was working as an engineer at the time. In 1938, Philips invested in a Stirling engine with a capacity of more than two hundred Horse power and a return of more than 30%. The Stirling engine has many advantages and was widely used during the era of steam engines.

Description

Stirling's engine- a heat engine in which a liquid or gaseous working fluid moves in a closed volume, a type of engine external combustion. It is based on periodic heating and cooling of the working fluid with the extraction of energy from the resulting change in the volume of the working fluid. It can operate not only from fuel combustion, but also from any heat source.

In the 19th century, engineers wanted to create a safe alternative to the steam engines of the time, whose boilers often exploded due to high steam pressures and unsuitable materials for their construction. Good alternative steam engines appeared with the creation of Stirling engines, which could convert any temperature difference into work. The basic principle of operation of the Stirling engine is constantly alternating heating and cooling of the working fluid in a closed cylinder. Usually the working fluid is air, but hydrogen and helium are also used. Freons, nitrogen dioxide, liquefied propane-butane and water were tested in a number of experimental samples. In the latter case, water remains in a liquid state in all parts of the thermodynamic cycle. The peculiarity of stirling with a liquid working fluid is its small size, high specific power and high operating pressures. There is also Stirling with a two-phase working fluid. It is also characterized by high power density and high operating pressure.

From thermodynamics it is known that pressure, temperature and volume of a gas are interrelated and follow the law of ideal gases

, Where:

P - gas pressure;
V - gas volume;
n is the number of moles of gas;
R is the universal gas constant;
T is the gas temperature in Kelvin.

This means that when a gas is heated, its volume increases, and when it cools, it decreases. This property of gases underlies the operation of the Stirling engine.

The Stirling engine uses the Stirling cycle, which is not inferior in thermodynamic efficiency to the Carnot cycle, and even has an advantage. The fact is that the Carnot cycle consists of isotherms and adiabats that differ little from each other. Practical implementation this cycle has little prospects. The Stirling cycle made it possible to obtain a practically working engine in acceptable dimensions.

The Stirling cycle consists of four phases and is divided by two transition phases: heating, expansion, transition to a cold source, cooling, compression and transition to a heat source. Thus, when moving from a warm source to a cold source, the gas in the cylinder expands and contracts. The difference in gas volumes can be converted into work, which is what the Stirling engine does. Duty cycle of beta type Stirling engine:

where: a - displacement piston; b - working piston; c - flywheel; d - fire (heating area); e - cooling fins (cooling area).

An external heat source heats the gas at the bottom of the heat exchange cylinder. The pressure created pushes the displacement piston upward (note that the displacement piston does not fit tightly against the walls).
The flywheel pushes the displacement piston down, thereby moving heated air from the bottom into the cooling chamber.
The air cools and contracts, the piston moves down.
The displacement piston rises upward, thereby moving cooled air to the lower part. And the cycle repeats.

In a Stirling machine, the movement of the working piston is shifted by 90° relative to the movement of the displacer piston. Depending on the sign of this shift, the machine can be an engine or a heat pump. At a shift of 0, the machine does not produce any work (except for friction losses) and does not produce it.

Beta Stirling- there is only one cylinder, hot at one end and cold at the other. A piston (from which power is removed) and a “displacer” move inside the cylinder, changing the volume of the hot cavity. Gas is pumped from the cold part of the cylinder to the hot part through a regenerator. The regenerator can be external, part of the heat exchanger, or combined with a displacer piston.

Gamma-Stirling- there is also a piston and a “displacer”, but at the same time there are two cylinders - one is cold (the piston moves there, from which the power is removed), and the second is hot at one end and cold at the other (the “displacer” moves there). The regenerator connects the hot part of the second cylinder with the cold one and at the same time with the first (cold) cylinder.

Doctor of Technical Sciences V. NISKOVSKIKH (Ekaterinburg).

Limited reserves of hydrocarbon fuels and high prices are forcing engineers to look for a replacement for internal combustion engines. The Russian inventor proposes a simple engine design with an external heat supply, which is designed for any type of fuel, even for heating by solar rays. The creator of the engine project, Vitaly Maksimovich Niskovskikh, is a designer widely known to metallurgical specialists not only in our country, but also abroad. He is the author of more than 200 inventions in the field of steel casting equipment, one of the founders of the national school of designing machines for continuous casting of curved billets (CCM). Today, 36 such machines, manufactured under the leadership of V. M. Niskovskikh at Uralmash, operate at metallurgical plants in Russia, as well as in Bulgaria, Macedonia, Pakistan, Slovakia, Finland, and Japan.

In 1816, Scotsman Robert Stirling invented an engine with external heat supply. The invention did not become widespread at that time - the design was too complex compared to the steam engine and internal combustion engines (ICEs) that appeared later.

However, these days there has been a renewed interest in Stirling engines. Information constantly appears about new developments and attempts to establish their mass production. For example, on Dutch company Philips built several modifications of the Stirling engine for heavy vehicles. External combustion engines are installed on ships, at small power plants and thermal power plants, and in the future they are going to equip space stations with them (there they are supposed to be used to drive electric generators, since the engines are capable of operating even in the orbit of Pluto).

Stirling engines have high efficiency, can operate with any heat source, are silent, and do not consume a working fluid, which is usually hydrogen or helium. The Stirling engine could be successfully used on nuclear submarines.

Dust particles are necessarily introduced into the cylinders of a running internal combustion engine along with the air, causing wear of the rubbing surfaces. This is impossible in engines with external heat supply, since they are completely sealed. In addition, the lubricant does not oxidize and requires replacement much less frequently than in an internal combustion engine.

The Stirling engine, if used as an externally driven mechanism, turns into a refrigeration unit. In 1944, in Holland, a sample of such an engine was spun using an electric motor, and the temperature of the cylinder head soon dropped to -190°C. Such devices are successfully used to liquefy gases.

And yet the complexity of the system of cranks and levers in piston engines Stirling limits their use.

The problem can be solved by replacing the pistons with rotors. The main idea of the invention is that two working cylinders of different lengths with eccentric rotors and spring-loaded separating plates are installed on a common shaft. The discharge (conditionally compression) cavity of the small cylinder is connected to the expansion cavity of the large cylinder through grooves in the separating plates, pipeline, heat exchanger-regenerator and heater, and the expansion cavity of the small cylinder is connected to the discharge cavity of the large cylinder through the regenerator and refrigerator.

The engine works as follows. At each moment of time, a certain volume of gas enters the high-pressure branch from the small cylinder. To fill the discharge cavity of a large cylinder and still maintain pressure, the gas is heated in a regenerator and heater; its volume increases and the pressure remains constant. The same thing, but with the opposite sign, occurs in the low pressure branch.

Due to the difference in the surface areas of the rotors, a net force arises F=∆p(S b-S m), where ∆ p- pressure difference in the high and low pressure branches; S b- working area of the large rotor; S m- working area of the small rotor. This force rotates the shaft with rotors, and the working fluid continuously circulates, sequentially passing through the entire system. The useful displacement of the engine is equal to the difference in the volumes of the two cylinders.

See the issue on the same topic

This article is devoted to one invention patented back in the nineteenth century by the Scottish priest Stirling. Like all its predecessors, it was an external combustion engine. The only difference between it and the others is that it can run on gasoline, fuel oil, and even coal and wood.

In the 19th century, there was a need to replace steam engines with something safer, as boilers often exploded due to high steam pressure and some serious design flaws.

A good option was the external combustion engine, which was patented in 1816 by the Scottish priest Robert Stirling.

True, “hot air engines” were made before, back in the 17th century. But Stirling added a purifier to the installation. In the modern sense, it is a regenerator.

It increased the productivity of the installation by retaining heat in the warm zone of the machine at a time when the working fluid was cooling. This significantly increased the efficiency of the system.

The invention found wide practical application, there was a stage of rise and development, but then the Stirlings were undeservedly forgotten.

They gave way to steam engines and internal combustion engines, and were revived again in the twentieth century.

Due to the fact that this principle of external combustion in itself is very interesting, today the best engineers and amateurs in the USA, Japan, Sweden are working on the creation of new models...

External combustion engine. Principle of operation

“Stirling” is, as we have already mentioned, a type of external combustion engine. The basic principle of its operation is the constant alternation of heating and cooling of the working fluid in a confined space and obtaining energy due to the resulting change in the volume of the working fluid.

As a rule, the working fluid is air, but hydrogen or helium can be used. The prototypes tested nitrogen dioxide, freons, liquefied propane-butane and even water.

By the way, water remains in a liquid state throughout the entire thermodynamic cycle. And the “stirling” itself with a liquid working fluid has compact dimensions, high specific power and high operating pressure.

Types of Stirling

There are three classic types of Stirling engine:

Application

The Stirling engine can be used in cases where a simple, compact thermal energy converter is required or when the efficiency of other types of heat engines is lower: for example, if the temperature difference is insufficient to use gas or.

Here are specific usage examples:

Already today, autonomous generators are being produced for tourists. There are models that operate from a gas burner;

NASA has ordered a version of the Stirling-based generator, which runs on nuclear and radioisotope heat sources. It will be used in space missions.

"Stirling" for pumping liquids is much more easier to install"motor-pump". As a working piston, it can use the pumped liquid, which will at the same time cool the working fluid. With such a pump, you can pump water into irrigation channels using solar heat, supply hot water from the solar collector to the house, pump chemical reagents, since the system is completely sealed;
Manufacturers of household refrigerators are introducing Stirling models. They will be more economical, and ordinary air is supposed to be used as a refrigerant;
Combined Stirling with a heat pump optimizes the heating system in the house. It will release the waste heat of the “cold” cylinder, and the resulting mechanical energy can be used to pump up heat that comes from the environment;
Today, all Swedish Navy submarines are equipped with Stirling engines. They operate on liquid oxygen, which is subsequently used for breathing. A very important factor for a boat, low level noise, and disadvantages such as “large size”, “need for cooling” are not significant in submarine conditions. The latest Japanese Soryu-class submarines are equipped with similar installations;
The Stirling engine is used to convert solar energy into electrical energy. To do this, it is mounted at the focus of a parabolic mirror. Stirling Solar Energy builds solar collectors with a capacity of up to 150 kW per mirror. They are used at the world's largest solar power plant in southern California.

Advantages and disadvantages

The modern level of design and manufacturing technology makes it possible to increase the efficiency of Stirling to 70 percent.

Surprisingly, engine torque is practically independent of crankshaft speed;
The power plant does not contain an ignition system, valve system and camshaft.
No adjustments or settings are needed throughout the entire service life.
The engine does not stall, and the simplicity of the design allows it to be operated in autonomous mode for a long time;
You can use any source of thermal energy, from wood to uranium fuel.
Fuel combustion occurs outside the engine, which contributes to its complete afterburning and minimization of toxic emissions.

Since the fuel burns outside the engine, heat is removed through the walls of the radiator, which means additional dimensions;
Material consumption. To make a Stirling machine compact and powerful, expensive heat-resistant steels are required that can withstand high operating pressure and have low thermal conductivity;
Need special lubricant, the usual one for Stirlings is not suitable, as it cokes when high temperatures;
To obtain high power density, the working fluid in Stirlings is hydrogen and helium.

Hydrogen is explosive, and at high temperatures it can dissolve in metals, forming metal hydrites. In other words, the engine cylinders are destroyed.

Hydrogen and helium also have a high penetrating ability and easily seep through seals, lowering the operating pressure.

If, after reading our article, you want to purchase a device - an external combustion engine, do not run to the nearest store, such a thing is not for sale, alas...

You understand that those who are involved in the improvement and implementation of this machine keep their developments secret and sell them only to reputable buyers.

Watch this video and do it yourself.

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

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

At that time, the British Isles were experiencing an industrial revolution: manufacturing was rapidly developing. And clergymen do not remain indifferent to the enormous income that promises new way production.

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

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

Both designs had a lot in common. These were external combustion engines. In both machines, the working fluid was air, and in both machines, the basis of the engine was a regenerator, passing through which the hot exhaust 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, you can see how the air through the suction pipe 10 and valve 4 enters the compressor 3, is compressed and exits through valve 5 into the intermediate tank. 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, performing useful work, which is partly aimed at lifting the heavy piston, partly at compressing cold air in compressor 3. As the piston descends, it pushes 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 - discharge valve; 6 - intermediate tank; 7 - regenerator; 8 - bypass valve; 9 - exhaust pipe; 10 - suction pipe; 11 - firebox.

Both designs were not economical. But for some reason there were more problems with the Scotsman’s engine, and it was less reliable than Erickson’s engine. Perhaps that is why they overlooked one very important detail: with equal power, the Stirling engine was more compact. In addition, it 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 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 environment(adiabatic process). By making closed chains of various combinations of such processes, it is not difficult to obtain theoretical cycles according to which all modern heat engines. Let's say a combination of two adiabats and two isochores form the theoretical cycle of a gasoline engine. If you replace the isochore, through which the gas is heated, with an isobar, you get a diesel cycle. Two adiabats and two isobars will give the theoretical cycle of a gas turbine. Among all conceivable cycles, the combination of two adiabats and two isotherms plays a particularly important role in thermodynamics, since the engine with the highest efficiency should operate on such a cycle - the Carnot cycle.

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

At the beginning of this century, Erickson engines of low power (about 10-20 hp) found use in various countries. Thousands of such installations worked in factories, printing houses, mines and mines, turning machine shafts, pumping water, raising elevators. They were also known in Russia under the name “warmth and strength”.

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 from its place” and even crossed the Atlantic Ocean. But the inventor’s expectations were also deceived: four gigantic engines instead of 1000 hp. With. developed only 300 hp. With. Coal consumption was the same as that of steam engines. In addition, the bottoms of the working cylinders burned through at the end of the voyage, and in England the engines had to be removed and secretly replaced with an ordinary steam engine. To top off all the misfortunes, on the way back to America, the ship suffered an accident and the entire crew perished.

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

Abandoning the idea of building high-power “caloric machines,” Erickson began mass production of small engines. The fact is that the level of science and technology of that time did not allow us to design and build an economical and powerful machine.

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

...A century has passed. In the 30s, one of the military departments commissioned the Philips company to develop a power plant with a power of 200-400 watts for a traveling radio station. Moreover, the engine must be omnivorous, that is, run on any type of fuel.

The company's specialists set to work thoroughly. We started by researching various thermodynamic cycles and, to our surprise, discovered that theoretically the most economical was the long-forgotten Stirling engine.

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

Isolated from external environment, they are practically independent of it. Stirling can operate from any heat source anywhere: under water, underground, in space - that is, where internal combustion engines that require air cannot work. In such conditions, it is basically impossible to do without heaters and coolers that transfer heat through the wall. And this is where the Stirlings beat their rivals even in terms of weight. The first prototypes had a specific gravity per unit of power of about 6-7 kg per liter. s., like 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 has become double-circuit: one circuit with the working agent and the second - heat supply; this made it possible to increase energy consumption to 200 liters. With. per liter of working volume, and efficiency - up to 38-40 percent. For comparison: modern

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

Working part modern Stirling is a closed volume filled with working gas (Fig. 2). The upper part of the volume is hot, it is continuously heated. The lower one is cold, constantly cooled by water. In the same volume there is a cylinder with two pistons: a displacer and a working one. When the piston goes up, the gas volume is compressed; down - expands. The up and down movement of the piston-displacer produces an alternating distribution of heated and cooled gas. When the displacer piston is in the upper position (in the hot zone), most of the gas is forced into the cold zone. At this time, the working piston begins to move upward and compresses the cold gas. Now the displacer piston rushes down to contact the working piston, and the compressed cold gas is pumped into the hot space. Expansion of heated gas - working stroke. Part of the power stroke energy is stored for subsequent compression of the cold gas, and the excess goes to the engine 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 piston-displacer, it passes through a dense bundle of thin copper wires and gives them the heat it contains. During the return stroke, compressed cold air, before entering the hot part, it takes this heat back.

1 - fuel burner; 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 real car things don't look that simple (Fig. 3). It is impossible to quickly heat gas through a thick cylinder wall; 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 injector is preheated by the exhaust gases - this creates a rather complex combustion circuit.

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

Under the working piston there 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 durable and heat-resistant materials, the difficult problem of cooling, since the heat release here is one and a half to two times greater compared to classical engines.

The results of these experiments sometimes lead to the most unexpected findings. For example, specialists from the Philips company, running their engine on Idling(without heating), we noticed that the cylinder head was getting very cold. The completely accidentally discovered effect led to a whole series of developments, and ultimately the birth of a new refrigeration machine. Nowadays, such high-performance and small-sized refrigeration units are widely used throughout the world. But let's return to heat engines.

Subsequent events grow like a snowball. In 1958, with the acquisition of licenses by other companies, Stirling stepped overseas. It began to be tested in a variety of areas 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 about 10 hp), and have such a low noise level that it cannot be heard for 20 steps.

A demonstration unit operating on twenty types of fuel caused a huge sensation. Without turning off the engine, by simply turning the tap, gasoline, diesel fuel, crude oil, olive oil, flammable gas - and the machine perfectly “ate” any “food”. There were reports in the foreign press about a 2.5 thousand liter 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 used for biological protection of the reactor.

Another interesting development is a drive for an artificial heart weighing 600 g and with a power of 13 watts. The weakly radioactive isotope provides it with a virtually 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, and the noise level and toxicity exhaust gases 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. It drives along city streets “without smoking”: the engine runs on the heat stored in the melt. One of the companies has manufactured a scooter, the tank of which is filled with about 10 liters of molten lithium fluoride. This charge is enough for 5 hours of operation with an engine power of 3 liters. With.

Work on the Stirlings continues. In 1967, a prototype of a pilot plant with a capacity of 400 hp was manufactured. With. per 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 four-cylinder industrial engine with 200 hp. With. with a total weight of 800 kg. His balance is so high that a coin (the size of a nickel) placed edge-on on the casing stands without moving.

The advantages of the new type of engine include a long service life of about 10 thousand hours. (there are separate data about 27 thousand), and smooth operation, since the pressure in the cylinders increases smoothly (along a sine wave), and not in explosions, like in a diesel engine.

We are also carrying out promising developments of new models. Scientists and engineers are working on the kinematics of various options, using electronic computers to calculate different types of “heart”, Stirling regenerator. The search for new ones is underway engineering solutions, which will form the basis of economical and powerful engines capable of displacing conventional diesel engines and gasoline engines, thereby correcting the unfair mistake of history.

A. ALEXEEV

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