Which Stirling engine has the best design for maximum efficiency. Powerful do-it-yourself stirling engine

The Stirling cycle is considered an indispensable accessory of the Stirling engine. At the same time, a detailed study of the principles of operation of many designs created to date shows that a significant part of them have a duty cycle that is different from the Stirling cycle. For example, alpha stirling with pistons of different diameters has a cycle that is more similar to the Ericsson cycle. Beta- and gamma-configurations, which have a sufficiently large diameter of the piston-displacer rod, also occupy some intermediate position between the Stirling and Ericsson cycles.

When the displacer moves in the beta configuration, the change in the state of the working fluid occurs not along the isochore, but along an inclined line intermediate between the isochore and isobar. With a certain ratio of the rod diameter to the total diameter of the displacer, an isobar can be obtained (this ratio depends on the operating temperatures). In this case, the piston, which was previously a worker, plays only an auxiliary role, and the displacer rod becomes a real worker. The specific power of such an engine turns out to be approximately 2 times greater than in the usual stirlings, lower friction losses, since the pressure on the piston is more even. A similar picture is in alpha stirlings with different piston diameters. An engine with an intermediate diagram can have a load evenly distributed between the pistons, i.e. between the working piston and the displacer rod.

An important advantage of the engine running on the Ericsson cycle or close to it is that the isochore is replaced by the isobar or a process close to it. When the working fluid expands along the isobar, there are no pressure changes, no heat transfer, except for the transfer of heat from the recuperator to the working fluid. And this heating immediately performs useful work. During isobaric compression, heat is transferred to the heat exchanger.
In the Stirling cycle, when the working fluid is heated or cooled along the isochore, heat losses occur due to isothermal processes in the heater and cooler.

Configuration

Engineers classify Stirling engines into three different types:

• Alpha Stirling- contains two separate power pistons in separate cylinders. One piston is hot, the other is cold. The hot piston cylinder is in a heat exchanger with a higher temperature, while the cold piston cylinder is in a colder heat exchanger. At of this type engine, the ratio of power to volume is quite large, but, unfortunately, the high temperature of the “hot” piston creates certain technical problems.

The regenerator is located between the hot part of the connecting tube and the cold part.

• 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. The gas is pumped from the cold part of the cylinder to the hot part through the regenerator. The regenerator may be external, as part of a heat exchanger, or may be combined with a displacing piston.

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

There are also varieties of the Stirling engine that do not fall under the above three classic types:

• rotary engine Stirling- tightness problems solved (Mukhin's patent for hermetic rotation input (GVV), a silver medal for international exhibition in Brussels "Eureka-96") and bulkiness (there is no crank mechanism, because the engine is rotary).

Flaws

• Material consumption- the main drawback of the engine. At engines external combustion in general, and the Stirling engine in particular, working body it is necessary to cool, and this leads to a significant increase in the weight and dimensions of the power plant due to increased radiators.

• For performance comparable to ICE characteristics, has to be applied high pressures (over 100 atm) and special types working body- hydrogen, helium.

• Heat is not supplied directly to the working fluid but only through the walls of the heat exchangers. The walls have limited thermal conductivity, due to which the efficiency is lower than expected. The hot heat exchanger operates under very stressful heat transfer conditions and at very high pressures, which requires the use of high quality and expensive materials. Creating a heat exchanger that would satisfy conflicting requirements is very difficult. The higher the heat exchange area, the lower the heat loss. At the same time, the size of the heat exchanger and the volume of the working fluid that is not involved in the work increase. Since the heat source is located outside, the engine responds slowly to changes in the heat flux supplied to the cylinder, and may not immediately produce the desired power at start-up.

• To quickly change engine power, methods are used that are different from those used in internal combustion engines: buffer capacity of variable volume, change in the average pressure of the working fluid in the chambers, change in the phase angle between the working piston and the displacer. In the latter case, the reaction of the engine to the control action of the driver is almost instantaneous.

Advantages

However, the Stirling engine has advantages that force it to be developed.

• "Omnivorous" engine- like all external combustion engines (or rather, external heat supply), the Stirling engine can operate from almost any temperature difference: for example, between different layers of water in the ocean, from the sun, from a nuclear or isotope heater, a coal or wood stove, etc. .
• Simplicity of design- the design of the engine is very simple, it does not require additional systems, such as a gas distribution mechanism. It starts on its own and does not need a starter. Its characteristics allow you to get rid of the gearbox. However, as noted above, it has a greater material consumption.
• Increased resource- simplicity of design, the absence of many "delicate" units allows Stirling to provide an unprecedented resource for other engines of tens and hundreds of thousands of hours continuous work.
• Economy- in the case of converting solar energy into electricity, stirlings sometimes give higher efficiency (up to 31.25%) than steam heat engines.
• Engine noiselessness- Stirling has no exhaust, which means it does not make noise. Beta stirling with rhombic mechanism is a perfectly balanced device and, with enough high quality manufacturing, does not even have vibrations (vibration amplitude is less than 0.0038 mm).
• Environmental friendliness- Stirling itself does not have any parts or processes that can contribute to environmental pollution. It does not consume the working fluid. The environmental friendliness of the engine is primarily due to the environmental friendliness of the heat source. It should also be noted that it is easier to ensure the completeness of fuel combustion in an external combustion engine than in an internal combustion engine.

Application

Stirling engine with linear generator alternating current

The Stirling engine is applicable in cases where a compact thermal energy converter is needed, which is simple in design, or when the efficiency of other heat engines is lower: for example, if the temperature difference is not enough to operate a steam or gas turbine.

Thermoacoustics is a branch of physics about the mutual transformation of thermal and acoustic energy. It was formed at the intersection of thermodynamics and acoustics. Hence the name. This science is very young. As an independent discipline, it arose in the late 70s of the last century, when the Swiss Niklaus Rott completed work on the mathematical foundations of linear thermoacoustics. And yet it didn't come out of nowhere. Its appearance was preceded by discoveries of interesting effects, which we simply must consider.

WHERE IT STARTED
Thermoacoustics has a long history dating back more than two centuries.

The first official record of heat-induced vibrations was made by Higgins in 1777. He experimented with an open glass tube in which acoustic vibrations were excited by a hydrogen burner positioned in a certain way. This experience has gone down in history as "the singing flame of Higgins".

Figure 1. Higgins Singing Flame

However, modern physicists are more familiar with another experiment called the Rijke tube. In the course of his experiments, Rijke created a new musical instrument from an organ pipe. He replaced the Higgins hydrogen flame with a heated wire screen and experimentally showed that the strongest sound is produced when the screen is located at a distance of a quarter of the tube from its lower end. The vibrations stopped when you cover upper end tubes. This proved that longitudinal convective draft was necessary to produce sound. The work of Higgins and Rijke later provided the basis for the science of combustion, which is now used everywhere that this phenomenon is used from

Figure 2. Rijke tube.

burning powder pellets to rocket engines. Thousands of dissertations all over the world are devoted to the phenomena occurring in the Rijke tube, but interest in this device has not weakened so far.

In 1850, Sondhauss turned to a strange phenomenon that glassblowers observe in their work. When the hot glass ball pushes air into the cold end of the blower's tube, a clear sound is generated. Analyzing the phenomenon, Sondhauss discovered that sound is generated by heating a spherical bulge at the end of a tube. In this case, the sound changes with a change in the length of the tube. Unlike the Rijke tube, the Sondhauss tube did not depend on convective draft.

Figure 3. Sondhaus tube.

A similar experiment was later carried out by Taconis. Unlike Sondhauss, he did not heat the end of the tube, but cooled it with a cryogenic liquid. This proved that it was not heating that was important for sound generation, but a temperature difference.
The first qualitative analysis of vibrations caused by heat was given in 1887 by Lord Rayleigh. Rayleigh's explanation of the phenomena listed above is now known to thermoacoustics as Rayleigh's principle. It sounds something like this: “If heat is transferred to the gas at the moment of greatest compression or heat is taken away at the moment of greatest rarefaction, then this stimulates oscillations. » Despite its simplicity, this formulation fully describes the direct thermoacoustic effect, that is, the conversion of thermal energy into sound energy.

swirl effect

swirl effect(Ranque-Hilsch effect) Ranque-Hilsch Effect) - the effect of separation of a gas or liquid when swirling in a cylindrical or conical chamber into two fractions. A swirling flow with a higher temperature is formed at the periphery, and a swirling cooled flow is formed in the center, and the rotation in the center occurs in the opposite direction than at the periphery. The effect was first discovered by the French engineer Joseph Rank in the late 1920s when measuring temperature in an industrial cyclone. At the end of 1931, J. Rank applied for an invented device, which he called the "Vortex tube" (in the literature it is found as the Ranke tube). It is possible to obtain a patent only in 1934 in America (US Patent No. 1952281). Currently, a number of devices have been implemented that use the vortex effect, vortex devices. These are "vortex chambers" for the chemical separation of substances under the action of centrifugal forces and "vortex tubes" used as a source of cold.

Since the 1960s, vortex motion has been the subject of many scientific studies. Specialized conferences on the vortex effect are regularly held, for example, at the Samara Aerospace University.

Vortex heat generators and microconditioners exist and are used.

In this world there are things of genius, incomprehensible and completely unreal. So unrealistic that they seem to be artifacts from some parallel universe. Among such artifacts, along with the Stirling engine, vacuum radio tube and Malevich's black square, the so-called. Tesla Turbine.
Generally speaking distinguishing feature of all such things - absolute simplicity. Not oversimplification, but simplicity. That is, as in the works of Michelangelo - there is no everything superfluous, some technical or semantic "props", pure consciousness, embodied "in iron" or splashed onto the canvas. And with all this, absolute non-circulation. The Black Square is a kind of "ort" of art. The second such written by another artist can not be.

All this fully applies to the Tesla turbine. Structurally, it consists of several (10-15) thin disks mounted on the turbine axis at a small distance from each other and placed in a casing resembling a police whistle.

It is not worth explaining that the disc rotor is much more technologically advanced and reliable than even the "Laval wheel", I am silent about the rotors of conventional turbines. This is the first advantage of the system. The second is that, unlike other types of turbines, where special measures must be taken to laminarize the flow of the working fluid. In the Tesla turbine, the working fluid (which can be air, steam or even liquid) flows strictly laminar. Therefore, the losses due to gas-dynamic friction in it are reduced to zero: the efficiency of the turbine is 95%.

True, it should be borne in mind that the efficiency of a turbine and the efficiency of a thermodynamic cycle are somewhat different things. Turbine efficiency can be characterized as the ratio of the energy converted into mechanical energy on the turbine rotor shaft to the energy of the working cycle (that is, the difference between the initial and final energies of the working fluid). So the efficiency of modern steam turbines is also very high - 95-98%, but the efficiency of the thermodynamic cycle due to a number of restrictions does not exceed 40-50%.

The principle of operation of the turbine is based on the fact that the working fluid (let's say - gas), spinning in the casing, due to friction "entrains" the rotor. At the same time, giving part of the energy to the rotor, the gas slows down, and due to the Coriolis force that arises when interacting with the rotor, like tea leaves, it "rolls" to the rotor axis, where there are special holes through which the "waste" working fluid is removed.
The Tesla turbine, like the Laval turbine, converts the kinetic energy of the working fluid. That is, the transformation of potential energy (for example compressed air or superheated steam) into the kinetic one must be made before it is fed to the turbine rotor using a nozzle. However, the Laval turbine, having in general enough high efficiency, proved to be extremely ineffective in low revs, which made it necessary to design gearboxes, the dimensions and mass of which many times exceeded the dimensions and masses of the turbine itself. The fundamental difference between the Tesla turbine is the fact that it operates quite efficiently in a wide range of rotational speeds, which allows its shaft to be connected directly to the generator. In addition, the Tesla turbine is easily reversible.

Interestingly, Nikola Tesla himself positioned his invention as a way of highly efficient use of geothermal energy, which he considered the energy of the future. In addition, the turbine, without any modifications, can turn into a highly efficient Vacuum pump- it is enough to unwind its shaft from another turbine or electric motor.

The manufacturability of the Tesla turbine allows you to make its variants literally from anything: a disk rotor can be made from old CDs or "pancakes" from a failed computer "hard drive". At the same time, the power of such an engine, despite the "toy" materials and dimensions, is very impressive. Speaking of dimensions: 110 hp engine. was no larger than the system unit of the current personal computer.

Rank effect devices

From the very beginning, the Rank effect attracted inventors with the seeming simplicity of its technical implementation - in fact, the simplest implementation vortex tube is a piece of the most common pipe, where on one side the original flow is tangentially fed in, and an annular diaphragm is installed on the opposite end, and the cooled part of the flow comes out of its inner hole, and its hot part comes out of the gap between the outer edge of the diaphragm and the inner surface of the pipe . However, in reality, not everything is so simple - it is far from always possible to achieve effective separation, and the efficiency of such installations is usually noticeably inferior to widespread compressor heat pumps. In addition, the parameters of the Ranque effect plant are usually calculated for a specific power, determined by the velocity and flow rate of the initial flow, and when the parameters of the inlet flow deviate from the optimal values, the efficiency of the vortex tube deteriorates significantly. Nevertheless, it should be noted that the capabilities of some installations based on the Ranque effect inspire respect - for example, the record cooling, which was achieved at one stage, is more than 200 ° C!

However, taking into account our climate, the use of the Ranque effect for heating is of much greater interest, and at the same time I would also like not to go beyond the “improvised means”.

The essence of the Rank effect

When a gas or liquid flow moves along the smoothly turning surface of a pipe, an area of ​​increased pressure and temperature is formed near its outer wall, and an area of ​​lower temperature and pressure is formed near the inner wall (or in the center of the cavity, if the gas is swirled over the surface of a cylindrical vessel). This well-known phenomenon is called Rank effect by the name of the French engineer Joseph Ranque (G.J. Ranque, sometimes spelled “Ranke”), who discovered it in 1931, or Ranque-Hilsch effect(German Robert Hilsh continued to study this effect in the second half of the 1940s and improved the efficiency of the Rank vortex tube). Designs using the Rank effect are a kind of heat pump, the energy for which is taken from the supercharger, which creates a flow of the working fluid at the pipe inlet.

The paradox of the Rank effect is that centrifugal forces in a rotating flow are directed outward. As is known, warmer layers of a gas or liquid have a lower density and must rise upwards, and in the case of centrifugal forces, tend to the center, colder ones have a higher density and, accordingly, must tend to the periphery. Meanwhile, at a high speed of the rotating flow, everything happens exactly the opposite!

The Ranque effect manifests itself both for a gas flow and for a liquid flow, which, as is known, is practically incompressible and, therefore, the adiabatic compression / expansion factor is not applicable to it. However, in the case of a liquid, the Ranque effect is usually much less pronounced - perhaps for this very reason, and the very small mean free path of particles makes it difficult to manifest. But this is true, if we remain within the framework of the traditional molecular kinetic theory, and the effect may have completely different reasons.

In my opinion, on this moment the most complete and reliable scientific description of the Rank effect is presented in the article by A.F. Gutsol (in pdf format). Surprisingly, at its core, his conclusions about the essence of the phenomenon coincide with those obtained by us “on the fingers”. Unfortunately, he ignores the first factor (adiabatic compression of the gas at the outer radius and expansion at the inner one), which, in my opinion, is very significant when using compressible gases, although it only acts inside the device. And A.F. Gutsol calls the second factor “separation of fast and slow microvolumes”.

Stirling's engine– engine with external heat supply. External heat supply - it is very convenient when there is a need to use as a heat source not organic species fuel. For example, you can use solar energy, geothermal energy, waste heat from various enterprises.

A nice feature of the Stirling cycle is that its efficiency is cycle efficiency Carnot. Naturally, real Stirling engines have lower efficiency and often much more. The Stirling engine began life as a device with many moving parts such as pistons, connecting rods, crankshaft, bearings . In addition, the generator rotor was also spinning (Figure 1).

Figure 1 - Alpha type Stirling engine

Look at the Stirling Alpha type engine. When the shaft rotates, the pistons begin to distill the gas either from a cold to a hot cylinder, or vice versa, from a hot to a cold one. But they do not just distill, but also compress and expand. The thermodynamic cycle takes place. You can mentally imagine in the picture that when the shaft turns so that the axis on which the connecting rods are attached is at the top, then this will be the moment of greatest compression of the gas, and when it is at the bottom, then expansion. True, this is not entirely true due to thermal expansions and compressions of the gas, but approximately all this is true.

The heart of the engine is the so-called core, which consists of two heat exchangers - hot and cold, and between them there is a regenerator. Heat exchangers are usually made of plate, and the regenerator is most often a stack made of metal mesh. It is clear why heat exchangers are needed - to heat and cool the gas, but why do we need a regenerator? And the regenerator is a real heat accumulator. When the hot gas moves to the cold side, it heats the regenerator and the regenerator stores thermal energy. When the gas moves from the cold to the hot side, the cold gas is heated in the regenerator, and thus this heat, which without a regenerator would have been irretrievably spent on heating the environment, is saved. So, the regenerator is extremely necessary thing. A good regenerator increases the efficiency of the engine by about 3.6 times.

For fans who dream of building such an engine on their own, I want to tell you more about heat exchangers. Majority homemade engines Stirling, of those that I have seen, do not have heat exchangers at all (I'm talking about alpha type engines). The heat exchangers are the pistons and cylinders themselves. One cylinder heats up, the other cools down. At the same time, the area of ​​the heat exchange surface in contact with the gas is very small. So, it is possible to significantly increase engine power by installing heat exchangers at the inlet to the cylinders. And even in Figure 1, the flame is directed straight at the cylinder, which is not entirely true in factory engines.

Let's return to the history of the development of Stirling engines. So, let the engine be good in many ways, but the presence oil scraper rings and bearings reduced the life of the engine, and the engineers thought hard about how to improve it, and came up with.

In 1969, William Bale investigated resonant effects in engine operation and was later able to make an engine that needed neither connecting rods nor a crankshaft. The synchronization of the pistons arose due to resonant effects. This type of engine came to be called a free piston engine (Figure 2).

Figure 2 - Free-piston Stirling engine

Figure 2 shows a beta type free piston engine. Here, the gas passes from the hot region to the cold region, and vice versa, thanks to the displacer (which moves freely), and the working piston does useful work. The displacer and piston oscillate on helical springs, which can be seen on the right side of the figure. The difficulty is that their oscillations must be at the same frequency and with a phase difference of 90 degrees, and all this is due to resonant effects. It is rather difficult to do this.

Thus, the number of parts was reduced, but at the same time, the requirements for the accuracy of calculations and manufacturing were tightened. But the reliability of the engine has undoubtedly increased, especially in designs where flexible membranes are used as a displacer and piston. In this case, there are no rubbing parts in the engine at all. Electricity, if desired, can be removed from such an engine using a linear generator.

But even this was not enough for the engineers, and they began to look for ways to get rid of not just rubbing parts, but generally moving parts. And they found a way.

In the 1970s, Peter Zeperli realized that the sinusoidal fluctuations in gas pressure and velocity in a Stirling engine, and the fact that these fluctuations are in phase, are remarkably similar to gas pressure and velocity fluctuations in a traveling sound wave (Fig. 3 ).

Figure 3 - Plot of pressure and velocity of a traveling acoustic wave as a function of time. It is shown that pressure and velocity oscillations are in phase.

This idea came to Zeperli not by chance, since before him there were many studies in the field of thermoacoustics, for example, Lord Rayleigh himself in 1884 qualitatively described this phenomenon.

Thus, he proposed to abandon the pistons and displacers altogether, and use only an acoustic wave to control the pressure and movement of the gas. This results in an engine with no moving parts and theoretically capable of reaching the efficiency of the Stirling cycle, and hence Carnot. In reality, the best performance is 40-50% of the efficiency of the Carnot cycle (Figure 4).

Figure 4 - Scheme of a thermoacoustic engine with a traveling wave

It can be seen that a traveling wave thermoacoustic engine is exactly the same core, consisting of heat exchangers and a regenerator, but instead of pistons and connecting rods, there is simply a looped pipe, which is called a resonator. But how does this engine work if there are no moving parts in it? How is this possible?

First, let's answer the question, where does the sound come from? And the answer is that it occurs by itself when there is a sufficient temperature difference between the two heat exchangers for this. The temperature gradient in the regenerator allows you to amplify sound vibrations, but only of a certain wavelength, equal to the length resonator. From the very beginning, the process looks like this: when a hot heat exchanger is heated, micro rustles appear, perhaps even crackles from thermal deformations, this is inevitable. These rustles are noise that has a wide frequency spectrum. From all this rich spectrum of sound frequencies, the engine begins to amplify that sound vibration, the wavelength of which is equal to the length of the tube - the resonator. And no matter how small the initial swing, it will be amplified to the maximum possible value. The maximum sound volume inside the engine occurs when the power of sound amplification with the help of heat exchangers is equal to the power of losses, that is, the power of attenuation of sound vibrations. And this maximum value sometimes reaches huge values ​​​​of 160 dB. So what's inside similar engine really loud. Fortunately, the sound cannot come out, since the resonator is sealed and therefore, standing next to a running engine, it is barely audible.

Amplification of a certain sound frequency occurs due to the same thermodynamic cycle - the Stirling cycle, which is carried out in the regenerator.

Figure 5 - Stages of the cycle roughly and simplified.

As I already wrote, in a thermoacoustic engine there are no moving parts at all, it generates only an acoustic wave inside itself, but, unfortunately, it is impossible to remove electricity from the engine without moving parts.

Usually energy is extracted from thermoacoustic engines using linear generators. The elastic membrane oscillates under the pressure of a high-intensity sound wave. Inside the copper coil with a core, magnets attached to the membrane vibrate. Electricity is generated.

In 2014, Kees de Blok, Pawel Owczarek, and Maurice Francois of Aster Thermoacoustics showed that a bidirectional impulse turbine connected to a generator is suitable for converting sound wave energy into electricity.

Figure 6 - Diagram of an impulse turbine

The impulse turbine rotates in the same direction, regardless of the direction of flow. Figure 6 schematically shows the stator blades on the sides and the rotor blades in the middle.
And this is what the turbine looks like in reality:

Figure 7 - Appearance of a bidirectional impulse turbine

It is expected that the use of a turbine instead of a linear generator will greatly reduce the cost of the design and will increase the power of the device up to the capacities of typical CHP plants, which is impossible with linear generators.

Well, we will continue to closely monitor the development of thermoacoustic engines.

List of sources used

M.G. Kruglov. Stirling engines. Moscow "Engineering", 1977.
G. Reeder, C. Hooper. Stirling engines. Moscow "Mir", 1986.
Kees de Blok, Pawel Owczarek. Acoustic to electric power conversion, 2014.

Stirling engine - a heat engine in which a liquid or gaseous working fluid moves in a closed volume, a type of external combustion engine. 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.

This type of engine was invented in the nineteenth century. They went through a stage of growth, then were forgotten, but survived steam engines, internal combustion engines and again revived in the twentieth century. Today, many engineers and amateurs are working on their creation.

It should be noted that there is still no universal method for calculating Stirling machines. The lion's share of technical solutions and calculation methods when creating prototypes of Stirling engines automatically becomes the "know-how" of the development companies and is carefully hidden. Stirling engines are not commercially available like lawn mowers or stand-alone generators. At the same time, Stirlings are used as power plants on space satellites, and are used as propulsion engines on modern submarines.

Stirling machines can just as well be "mounted" in a lawn trimmer or a rover. The design of the engine has no valves, camshafts, no ignition system in its usual form, no starter! Some designs have a self-starting effect. Any source of heat is suitable for work: solar energy, manure, hay, firewood, coal, oil, gas, a nuclear reactor - everything will do! And with this "omnivorous" efficiency of the "Stirling" is not inferior to the performance of internal combustion engines. But that's not all. Stirling machines are reversible. Those. Summing up thermal energy, we obtain mechanical energy, spinning the flywheel of the engine, we produce cold.

The Stirling engine depends only on external heat input. What this heat delivers is of fundamental importance. Therefore, the Stirling engine is an ideal candidate for converting solar radiation into mechanical energy:

1. In a Stirling engine, a constant amount of working gas (helium or hydrogen) is constantly heated and cooled.

2. Through expansion when heated and contracted when cooled, the working gas drives two pistons, each of which is attached to a shaft, thus transferring energy.

3. The efficiency of the Stirling engine increases with increasing temperature, so it is an ideal combination for generating energy through a solar collector.

4. There is no internal combustion, so the Stirling plant works almost silently.

5. The potential life cycle of a Stirling engine is very long since there is no internal wear due to fuel burning.

It can be used to store energy using molten salt heat accumulators as a heat source. These batteries have more energy than chemical batteries and cheaper than them. Using a change in the phase angle between the pistons to adjust the power, it is possible to accumulate mechanical energy by braking the engine. In this case, the engine turns into a heat pump.

Stirling pros

The efficiency of the Stirling engine can reach 65-70% of the efficiency of the Carnot cycle at modern level design and manufacturing technology. In addition, the engine torque is almost independent of the crankshaft speed. In internal combustion engines, on the other hand, maximum torque is achieved in a narrow speed range.

The engine design does not have a high-voltage ignition system, valve system and, accordingly, the camshaft. A well-designed and technologically manufactured Stirling engine does not require adjustment and tuning during the entire period of operation.

In an internal combustion engine, the combustion of a languid-air mixture in an engine cylinder is, in fact, an explosion with a blast wave propagation speed of 5-7 km/sec. This process produces monstrous peak loads on the connecting rods, crankshaft and bearings. Stirlings are devoid of this shortcoming.

The engine will not "act up" due to a loss of spark, a clogged carburetor or a low battery charge, since it does not have these units. The concept of "engine stalled" does not make sense to the Stirlings. Stirling may stop if the load exceeds the design. Restart is carried out by turning the crankshaft flywheel once.

The simplicity of the design allows you to operate Stirling offline for a long time.

The Stirling engine can use any source of thermal energy, from wood to nuclear fuel.

Fuel combustion occurs outside the internal volume of the engine (unlike internal combustion engines), which makes it possible to ensure uniform combustion of the fuel and its complete afterburning (i.e., the selection of the maximum energy contained in the fuel and minimization of the emission of toxic components).

Stirling cons

Since the combustion of fuel occurs outside the engine, and heat is removed through the walls of the radiator (Stirlings have a closed volume), the dimensions of the engine increase.

Another disadvantage is material consumption. The production of compact and powerful Stirling machines requires heat-resistant steels that can withstand high operating pressures and at the same time have low thermal conductivity. Conventional lubrication not suitable for Stirlings - it cokes at high temperatures, therefore materials with a low coefficient of friction are needed.

To obtain a high specific power, hydrogen or helium is used as a working fluid in Stirlings. Hydrogen is explosive high temperatures dissolves in metals, forming metal hydrides - i.e. destroys engine cylinders. In addition, hydrogen, like helium, has a high penetrating ability and seeps through the seals of the moving parts of the engine, reducing the operating pressure.

Comments:

I want to build myself a Stirling engine for my summer house, is it possible

“- In an internal combustion engine, the combustion of a languid-air mixture in an engine cylinder is, in fact, an explosion with a blast wave propagation speed of 5-7 km / s.”
———-
5-7 km / s - this is the speed of movement of the products of the explosion of the heating element and in the cumulative projectile, it is enough to penetrate a 20 cm package of homogeneous armor. Don't talk nonsense. The combustion products of the fuel mixture in the ICE cylinder move at a speed not exceeding 360 m (!) / s, i.e. subsonic combustion. Supersonic combustion is considered detonation and ruins the engine.

Detonation should be understood as an unusually high propagation speed of an explosive chemical reaction. In the engine cylinder during detonation, the flame propagation velocity in the last part combustible mixture reaches approximately 2000 m sec

Anyone can build a Stirling engine for a summer cottage by hand, but not in this life.

I advise you to make such an engine
http://www.valentru.ru/index/gibridja_teplovaja_mashina/0-5

The first drawing was drawn by a person who was unfamiliar with the principle of the subject. Along the way, I confused the displacer with the working piston. 1) The propellant cylinder has a smaller volume/diameter than the working cylinder. Otherwise it won't work.
2) The principle of operation. Direct move. The displacer enters its cylinder, pushing the gas through the cooler, regenerator, heater. Exactly in that order. In the heater, it expands, filling the working cylinder, and squeezes it out. Reverse stroke - the displacer leaves its cylinder, reducing pressure. The gas from the working cylinder passes through the heater, regenerator, cooler, is compressed and can fit into the displacer cylinder. The working piston squeezes gas out of its cylinder when lower pressure than in a straight line. Due to the pressure difference between the forward and reverse motion, mechanical energy is obtained on the shaft.

It replaced other types of power plants, however, work aimed at abandoning the use of these units suggests an imminent change in leading positions.

Since the beginning of technological progress, when the use of engines that burn fuel inside was just beginning, their superiority was not obvious. The steam engine, as a competitor, contains a lot of advantages: along with traction parameters, it is silent, omnivorous, easy to control and configure. But lightness, reliability and efficiency allowed the internal combustion engine to take over the steam.

Today, issues of ecology, economy and safety are at the forefront. This forces engineers to throw their forces on serial units operating on renewable fuel sources. In the year 16 of the nineteenth century, Robert Stirling registered an engine powered by external sources heat. Engineers believe that this unit is able to change modern leader. The Stirling engine combines efficiency, reliability, runs quietly, on any fuel, this makes the product a player in the automotive market.

Robert Stirling (1790-1878):

Stirling engine history

Initially, the installation was developed with the aim of replacing the steam-powered machine. Boilers of steam mechanisms exploded when the pressure exceeded the permissible norms. From this point of view, Stirling is much safer, functioning using a temperature difference.

The principle of operation of the Stirling engine is to alternately supply or remove heat from the substance on which work is performed. The substance itself is enclosed in a volume closed type. The role of the working substance is performed by gases or liquids. There are substances that perform the role of two components, the gas is transformed into a liquid and vice versa. The liquid-piston Stirling engine has: small dimensions, powerful, generates high pressure.

The decrease and increase in the volume of gas during cooling or heating, respectively, is confirmed by the law of thermodynamics, according to which all components: the degree of heating, the amount of space occupied by the substance, the force acting per unit area, are related and described by the formula:

P*V=n*R*T

• P is the force of the gas in the engine per unit area;
• V is the quantitative value occupied by gas in the engine space;
• n is the molar amount of gas in the engine;
• R is the gas constant;
• T is the degree of gas heating in the engine K,

Stirling engine model:

Due to the unpretentiousness of the installations, the engines are divided into: solid fuel, liquid fuel, solar energy, chemical reaction and other types of heating.

Cycle

The Stirling external combustion engine uses a set of phenomena of the same name. The effect of the ongoing action in the mechanism is high. Thanks to this, it is possible to design an engine with good characteristics within normal dimensions.

It should be taken into account that the design of the mechanism provides for a heater, a refrigerator and a regenerator, a device for removing heat from the substance and returning heat at the right time.

Ideal Stirling cycle, (diagram "temperature-volume"):

Ideal circular phenomena:

• 1-2 Change in the linear dimensions of a substance with a constant temperature;
• 2-3 Removal of heat from the substance to the heat exchanger, the space occupied by the substance is constant;
• 3-4 Forced reduction of the space occupied by the substance, the temperature is constant, heat is removed to the cooler;
• 4-1 Forced increase in the temperature of the substance, the occupied space is constant, the heat is supplied from the heat exchanger.

The ideal Stirling cycle, (pressure-volume diagram):

From the calculation (mol) of a substance:

Heat input:

Heat received by the cooler:

The heat exchanger receives heat (process 2-3), the heat exchanger gives off heat (process 4-1):

R – Universal gas constant;

CV - ability ideal gas retain heat with a constant amount of space occupied.

Due to the use of a regenerator, part of the heat remains, as the energy of the mechanism, which does not change during the passing circular phenomena. The refrigerator receives less heat, so the heat exchanger saves the heat of the heater. This increases the efficiency of the installation.

Efficiency of circular phenomenon:

ɳ =

It is noteworthy that without a heat exchanger, the set of Stirling processes is feasible, but its efficiency will be much lower. Running the set of processes backwards leads to a description of the cooling mechanism. In this case, the presence of a regenerator is a mandatory condition, since when passing (3-2) it is impossible to heat the substance from the cooler, the temperature of which is much lower. It is also impossible to give heat to the heater (1-4), the temperature of which is higher.

The principle of the engine

In order to understand how the Stirling engine works, let's look at the device and the frequency of the phenomena of the unit. The mechanism converts the heat received from the heater located outside the product into a force on the body. The whole process occurs due to the temperature difference, in the working substance, which is in a closed circuit.

The principle of operation of the mechanism is based on expansion due to heat. Immediately prior to expansion, the substance in the closed circuit heats up. Accordingly, before being compressed, the substance is cooled. The cylinder itself (1) is wrapped in a water jacket (3), heat is supplied to the bottom. The piston that does the work (4) is placed in a sleeve and sealed with rings. Between the piston and the bottom there is a displacement mechanism (2), which has significant gaps and moves freely. The substance in a closed circuit moves through the volume of the chamber due to the displacer. The movement of matter is limited to two directions: the bottom of the piston, the bottom of the cylinder. The movement of the displacer is provided by a rod (5) which passes through the piston and is operated by an eccentric 90° late compared to the piston drive.

• Position "A":

The piston is located in the lowest position, the substance is cooled by the walls.

• Position "B":

Displacer occupies top position, moving, passes the substance through the end slots to the bottom, it cools itself. The piston is stationary.

• Position "C":

The substance receives heat, under the action of heat it increases in volume and raises the expander with the piston up. Work is done, after which the displacer sinks to the bottom, pushing out the substance and cooling.

• Position "D":

The piston goes down, compresses the cooled substance, useful work is done. The flywheel serves as an energy accumulator in the design.

The considered model is without a regenerator, so the efficiency of the mechanism is not high. The heat of the substance after work is removed into the coolant using the walls. The temperature does not have time to decrease by the required amount, so the cooling time is extended, the motor speed is low.

Types of engines

Structurally, there are several options using the Stirling principle, the main types are:

The design uses two different pistons placed in different contours. The first circuit is used for heating, the second circuit is used for cooling. Accordingly, each piston has its own regenerator (hot and cold). The device has a good power to volume ratio. The disadvantage is that the temperature of the hot regenerator creates design difficulties.

• Engine "β - Stirling":

The design uses one closed circuit, with different temperatures at the ends (cold, hot). A piston with a displacer is located in the cavity. The displacer divides the space into cold and hot zones. The exchange of cold and heat occurs by pumping a substance through a heat exchanger. Structurally, the heat exchanger is made in two versions: external, combined with a displacer.

• Engine "γ - Stirling":

The piston mechanism provides for the use of two closed loops: cold and with displacer. Power is taken off a cold piston. The displacer piston is hot on one side and cold on the other. The heat exchanger is located both inside and outside the structure.

Some power plants are not similar to the main types of engines:

• Rotary Stirling engine.

Structurally, the invention with two rotors on the shaft. The part performs rotational movements in a closed cylindrical space. A synergistic approach to the implementation of the cycle has been laid. The body contains radial slots. Blades with a certain profile are inserted into the recesses. The plates are put on the rotor and can move along the axis when the mechanism rotates. All the details create changing volumes with phenomena taking place in them. The volumes of the various rotors are connected by channels. Channel arrangements are offset by 90° to each other. The shift of the rotors relative to each other is 180°.

• Thermoacoustic engine Stirling.

The engine uses acoustic resonance to carry out processes. The principle is based on the movement of matter between a hot and a cold cavity. The circuit reduces the number of moving parts, the difficulty in removing the received power and maintaining resonance. The design refers to the free-piston type of motor.

DIY Stirling engine

Today, quite often in the online store you can find souvenirs made in the form of the engine in question. Structurally and technologically, the mechanisms are quite simple; if desired, the Stirling engine is easy to construct with your own hands from improvised means. On the Internet you can find a large number of materials: videos, drawings, calculations and other information on this topic.

Low temperature Stirling engine:

• Consider the simplest version of the wave engine, for which you will need a tin can, soft polyurethane foam, a disk, bolts and paper clips. All these materials are easy to find at home, it remains to perform the following steps:
• Take a soft polyurethane foam, cut two millimeters smaller diameter from the inner diameter tin can circle. The height of the foam is two millimeters more than half the height of the can. Foam rubber plays the role of a displacer in the engine;
• Take the lid of the jar, make a hole in the middle, two millimeters in diameter. Solder a hollow rod to the hole, which will act as a guide for the engine connecting rod;
• Take a circle cut out of foam, insert a screw into the middle of the circle and lock it on both sides. Solder a pre-straightened paperclip to the washer;
• Drill a hole two centimeters from the center, three millimeters in diameter, thread the displacer through the central hole of the lid, solder the lid to the jar;
• Make a small cylinder out of tin, one and a half centimeters in diameter, solder it to the lid of the can in such a way that the side hole of the lid is clearly centered inside the engine cylinder;
• Make an engine crankshaft out of a paper clip. The calculation is carried out in such a way that the spacing of the knees is 90 °;
• Make a stand for the crankshaft of the engine. From a plastic film, make an elastic membrane, put the film on the cylinder, push it through, fix it;

• Make an engine connecting rod yourself, bend one end of the straightened product in the shape of a circle, insert the other end into a piece of eraser. The length is adjusted in such a way that at the lowest point of the shaft the membrane is retracted, at the extreme top point, the membrane is maximally elongated. Adjust the other connecting rod in the same way;
• Glue the engine connecting rod with a rubber tip to the membrane. Mount the connecting rod without a rubber tip on the displacer;
• Put a flywheel from the disk on the crank mechanism of the engine. Attach legs to the jar so as not to hold the product in your hands. The height of the legs allows you to place a candle under the jar.

After we managed to make a Stirling engine at home, the engine is started. To do this, a lighted candle is placed under the jar, and after the jar has warmed up, they give impetus to the flywheel.

The considered installation option can be quickly assembled at home, as a visual aid. If you set a goal and a desire to make the Stirling engine as close as possible to factory counterparts, there are drawings of all the details in the public domain. Step-by-step execution of each node will allow you to create a working layout that is no worse than commercial versions.

Advantages

The Stirling engine has the following advantages:

• A temperature difference is necessary for the operation of the engine, which fuel causes heating is not important;
• There is no need to use attachments and auxiliary equipment, the engine design is simple and reliable;
• The resource of the engine, due to the design features, is 100,000 hours of operation;
• Engine operation does not create extraneous noise, since there is no detonation;
• The process of engine operation is not accompanied by the emission of waste substances;
• Engine operation is accompanied by minimal vibration;
• Processes in the plant cylinders are environmentally friendly. Using the right heat source keeps the engine clean.

Flaws

The disadvantages of the Stirling engine include:

• It is difficult to establish mass production, since the engine design requires the use of a large number materials;
• high weight and large dimensions engine, since a large radiator must be used for effective cooling;
• To increase efficiency, the engine is boosted using complex substances (hydrogen, helium) as a working fluid, which makes the operation of the unit dangerous;
• The high temperature resistance of steel alloys and their thermal conductivity complicate the engine manufacturing process. Significant heat losses in the heat exchanger reduce the efficiency of the unit, and the use of specific materials makes the manufacture of the engine expensive;
• To adjust and switch the engine from mode to mode, special control devices must be used.

Usage

The Stirling engine has found its niche and is actively used where dimensions and omnivorousness are an important criterion:

• Stirling engine-generator.

A mechanism for converting heat into electrical energy. Often there are products used as portable tourist generators, installations for the use of solar energy.

• The engine is like a pump (electric).

The engine is used for installation in a circuit heating systems saving on electrical energy.

• The engine is like a pump (heater).

In countries with a warm climate, the engine is used as a space heater.

Stirling engine on a submarine:

• The engine is like a pump (cooler).

Almost all refrigerators use heat pumps in their design, installing a Stirling engine saves resources.

• The engine is like a pump that creates ultra-low heat levels.

The device is used as a refrigerator. To do this, the process is started in reverse side. The units liquefy gas, cool measuring elements in precise mechanisms.

• Underwater engine.

The submarines of Sweden and Japan work thanks to the engine.

Stirling engine as a solar installation:

• The engine is like a battery of energy.

Fuel in such units, salt melts, the engine is used as an energy source. In terms of energy reserves, the motor is ahead of chemical elements.

• solar engine.

Convert the sun's energy into electricity. Substance in this case, hydrogen or helium. The engine is placed in the focus of the maximum concentration of the energy of the sun, created using a parabolic antenna.

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

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

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

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

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

6. Benefits ……………………………………………………………………… 7

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

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

9. 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 building and the use of so-called "new" alternative fuels: wind, sun, 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 the growth of production, reduce distances. The most commonly used internal combustion engines are whole line disadvantages: their work is accompanied by noise, vibrations, they emit harmful exhaust gases, thereby polluting our nature, and consume a lot of fuel. But now there is an alternative to them. The class of engines, the harm from which 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 has been undeservedly forgotten.

The revival of interest in Stirling engines is usually associated with Philips. Work on the design of small power Stirling engines began in the company in the mid-30s of the twentieth century. The aim of the work was to create a small electric generator With low level noise and thermal drive to power radio equipment in areas of the world with no regular power supply. In 1958 the company General Motors concluded license agreement with Philips, and their cooperation continued until 1970. Developments were associated with the use of Stirling engines for space and underwater power plants, cars 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 duty, extended their interests to the field of engines for cars. The real interest in the Stirling engine was revived only during the so-called "energy crisis". It was then that the potential of this engine in relation to the economic consumption of conventional liquid fuels 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 27 September 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 is the addition of a cleaner, which he called "economy". In modern scientific literature, this purifier is called a "regenerator" (heat exchanger). It increases engine performance by keeping heat in the warm part of the engine while the working fluid is cooled. This process greatly improves the efficiency of the system. In 1843, James Stirling used this engine in a factory where he worked as an engineer at the time. In 1938 Philips invested in a Stirling engine with over 200 horsepower and over 30% efficiency. The Stirling engine has many advantages and was widely used during the age of steam engines.

Description

Stirling's engine- a heat engine in which a liquid or gaseous working fluid moves in a closed volume, a kind of external combustion engine. 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 work 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 the Stirling engine is the constantly alternating heating and cooling of the working fluid in a closed cylinder. Usually air acts as a working fluid, 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. A feature of Stirling with a liquid working fluid is its small size, high power density and high operating pressures. There is also a stirling with a two-phase working fluid. It is also characterized by high specific power, high working pressure.

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

, Where:

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

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

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

The Stirling cycle consists of four phases and is separated by two transitional phases: heating, expansion, transition to a cold source, cooling, compression, and transition to a heat source. Thus, when passing 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. Beta-type Stirling Engine Duty Cycle:

1

2

3

4

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

1. An external heat source heats the gas at the bottom of the heat exchange cylinder. The pressure generated pushes the working piston up (note that the expelling piston does not fit snugly against the walls).
2. The flywheel pushes the displacement piston down, thereby moving the heated air from the bottom to the cooling chamber.
3. The air cools and contracts, the piston moves down.
4. The displacement piston rises, thereby moving the cooled air to the bottom. And the cycle repeats.

In the Stirling machine, the movement of the working piston is shifted by 90 ° relative to the movement of the displacing piston. Depending on the sign of this shift, the machine can be an engine or a heat pump. With 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. The gas is pumped from the cold part of the cylinder to the hot part through the regenerator. The regenerator can be external, part of a heat exchanger, or combined with a displacing piston.

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