The Stirling engine, the principle of operation of which is qualitatively different from the usual for all internal combustion engines, was once the last worthy competition. However, they forgot about it for a while. How this motor is used today, what is the principle of its operation (in the article you can also find drawings of the Stirling engine that clearly demonstrate its operation), and what are the prospects for future use, read below.
Story
In 1816, in Scotland, Robert Stirling patented the one named today in honor of its inventor. The first hot air engines were invented before him. But Stirling added a purifier to the device, which in the technical literature is called a regenerator, or heat exchanger. Thanks to him, the performance of the motor increased while keeping the unit warm.
The engine was recognized as the most durable steam engine available at that time, since it never exploded. Before him, on other motors, this problem arose often. Despite its rapid success, its development was abandoned at the beginning of the twentieth century, as it became less economical than other engines that appeared then. internal combustion and electric motors. However, Stirling still continued to be used in some industries.
External combustion engine
The principle of operation of all heat engines is that to obtain gas in an expanded state, greater mechanical forces are required than when compressing a cold one. To demonstrate this, you can conduct an experiment with two pots filled with cold and hot water, as well as a bottle. The latter is dipped in cold water, plugged with a cork, then transferred to hot. In this case, the gas in the bottle will begin to perform mechanical work and push the cork out. First engine external combustion based entirely on this process. True, later the inventor realized that part of the heat can be used for heating. Thus, productivity has increased significantly. But even this did not help the engine become common.
Later, Erickson, an engineer from Sweden, improved the design by suggesting that the gas be cooled and heated at constant pressure instead of volume. As a result, many copies began to be used for work in mines, on ships and in printing houses. But for the crews, they were too heavy.
External combustion engines from Philips
Such motors are of the following types:
- steam;
- steam turbine;
- Stirling.
The latter type was not developed due to low reliability and other not the highest rates compared to other types of units that appeared. However, Philips reopened in 1938. Engines began to serve to drive generators in non-electrified areas. In 1945, the company's engineers found the opposite use for them: if the shaft is spun by an electric motor, then the cooling of the cylinder head reaches minus one hundred and ninety degrees Celsius. Then it was decided to use an improved Stirling engine in refrigeration units.
Principle of operation
The action of the motor is to work on thermodynamic cycles, in which compression and expansion occur at different temperatures. In this case, the regulation of the flow of the working fluid is implemented due to the changing volume (or pressure - depending on the model). This is the principle of operation of most of these machines, which may have different functions and structural diagrams. Engines can be piston or rotary. Machines with their installations work as heat pumps, refrigerators, pressure generators and so on.
In addition, there are open-cycle motors, where flow control is implemented through valves. They are called Erickson engines, except common name Stirling's name. In an internal combustion engine, useful work is carried out after pre-compression of air, fuel injection, heating of the resulting mixture mixed with combustion and expansion.
The Stirling engine has the same principle of operation: at low temperatures, compression occurs, and at high temperatures, expansion occurs. But heating is carried out in different ways: heat is supplied through the cylinder wall from the outside. Therefore, he received the name of the external combustion engine. Stirling used a periodic change in temperature with a displacement piston. The latter moves gas from one cavity of the cylinder to another. On the one hand, the temperature is constantly low, and on the other, it is high. When the piston moves up, the gas moves from a hot to a cold cavity, and when it moves down, it returns to a hot one. First, the gas gives off a lot of heat to the refrigerator, and then it receives as much heat from the heater as it gave out. A regenerator is placed between the heater and the cooler - a cavity filled with a material to which the gas gives off heat. In the reverse flow, the regenerator returns it.
The displacer system is connected to a working piston, which compresses the gas in the cold and allows it to expand in the heat. Due to compression at a lower temperature, useful work is done. The whole system goes through four cycles with intermittent movements. The crank mechanism at the same time ensures continuity. Therefore, sharp boundaries between the stages of the cycle are not observed, and Stirling does not decrease.
Considering all of the above, the conclusion suggests itself that this engine is a reciprocating machine with an external heat supply, where working body does not leave the enclosed space and is not replaced. The drawings of the Stirling engine well illustrate the device and the principle of its operation.
Work details
The sun, electricity, nuclear power, or any other source of heat can supply power to a Stirling engine. The principle of operation of his body is to use helium, hydrogen or air. An ideal cycle has a thermal maximum possible efficiency equal to thirty to forty percent. But with an efficient regenerator, it will be able to work with more high efficiency. Regeneration, heating and cooling are provided by built-in oil-free heat exchangers. It should be noted that the engine needs very little lubrication. The average pressure in the cylinder is usually 10 to 20 MPa. Therefore, an excellent sealing system and the possibility of oil entering the working cavities are required here.
Comparative characteristics
Most engines of this kind in operation today use liquid fuels. At the same time, continuous pressure is easy to control, which helps to reduce emissions. The absence of valves ensures silent operation. Power to weight is comparable to turbocharged engines, and the output power density is equal to that of a diesel unit. Speed and torque are independent of each other.
The cost of producing an engine is much higher than that of an internal combustion engine. But during operation, the opposite is obtained.
Advantages
Any model of the Stirling engine has many advantages:
- Efficiency with modern design can reach up to seventy percent.
- The engine has no system high voltage ignition, camshaft and valves. It will not need to be adjusted during the entire period of operation.
- In Stirlings, there is no explosion, as in an internal combustion engine, which heavily loads the crankshaft, bearings and connecting rods.
- They do not have that effect when they say that "the engine has stalled."
- Due to the simplicity of the device, it can be operated for a long time.
- It can work both on wood, and with nuclear and any other type of fuel.
- Combustion takes place outside the engine.
Flaws
Application
Currently, the Stirling engine with a generator is used in many areas. It is a universal source of electrical energy in refrigerators, pumps, submarines and solar power stations. It is thanks to the use different kind fuel has the possibility of its wide use.
rebirth
These motors have been developed again thanks to Philips. In the middle of the twentieth century, she entered into an agreement General Motors. She led developments for the use of Stirlings in space and underwater devices, on ships and cars. Following them, another company from Sweden, United Stirling, began to develop them, including the possible use on
Today, the linear Stirling engine is used in installations of underwater, space and solar vehicles. Great interest in it is due to the relevance of the issues of environmental degradation, as well as the fight against noise. In Canada and the USA, Germany and France, as well as Japan, there are active searches for the development and improvement of its use.
Future
The obvious advantages that piston and Stirling have, consisting in a long service life, the use of different fuels, noiselessness and low toxicity, make it very promising against the background of an internal combustion engine. However, given the fact that the internal combustion engine has been improved over time, it cannot be easily displaced. One way or another, it is precisely such an engine that occupies a leading position today, and to hand them over to soon doesn't intend to.
Modern automotive industry has reached a level of development at which it is almost impossible to achieve cardinal improvements in the design of traditional internal combustion engines without fundamental scientific research. This situation forces designers to pay attention to alternative power plant designs. Some engineering centers have focused their efforts on the creation and adaptation to serial production of hybrid and electrical models, other automakers are investing in the development of engines powered by renewable sources (for example, biodiesel with rapeseed oil). There are other projects of power units, which in the future may become the new standard propulsion for Vehicle.
Among the possible sources of mechanical energy for cars of the future is the external combustion engine, which was invented in the middle of the 19th century by the Scot Robert Stirling as a thermal expansion machine.
Scheme of work
The Stirling engine converts thermal energy supplied from the outside into useful mechanical work due to changes in the temperature of the working fluid(gas or liquid) circulating in a closed volume.
In general, the scheme of operation of the device is as follows: in the lower part of the engine, the working substance (for example, air) heats up and, increasing in volume, pushes the piston up. Hot air enters the top of the motor, where it is cooled by a radiator. The pressure of the working fluid is reduced, the piston is lowered for the next cycle. In this case, the system is sealed and the working substance is not consumed, but only moves inside the cylinder.
There are several design options for power units using the Stirling principle.
Stirling modification "Alpha"
The engine consists of two separate power pistons (hot and cold), each of which is located in its own cylinder. Heat is supplied to the cylinder with the hot piston, and the cold cylinder is located in the cooling heat exchanger.
Stirling modification "Beta"
The cylinder containing the piston is heated on one side and cooled on the opposite side. A power piston and a displacer move in the cylinder, designed to change the volume of the working gas. The return movement of the cooled working substance into the hot cavity of the engine is performed by the regenerator.
Stirling modification "Gamma"
The design consists of two cylinders. The first is completely cold, in which the power piston moves, and the second, hot on one side and cold on the other, serves to move the displacer. The regenerator for circulating cold gas can be common to both cylinders or be included in the design of the displacer.
Advantages of the Stirling engine
Like most external combustion engines, Stirling is inherent multi-fuel: the engine runs on a temperature difference, regardless of the reasons that caused it.
Interesting fact! Once, an installation was demonstrated that operated on twenty fuel options. Without stopping the engine, gasoline was supplied to the external combustion chamber, diesel fuel, methane, crude oil and vegetable oil - the power unit continued to work steadily.
The engine has simplicity of design and does not require additional systems And attachments(timing, starter, gearbox).
Features of the device guarantee a long service life: more than one hundred thousand hours continuous work.
The Stirling engine is silent, since detonation does not occur in the cylinders and there is no need to remove exhaust gases. Modification "Beta", equipped with a rhombic crank mechanism, is a perfectly balanced system that does not have vibrations during operation.
There are no processes in the engine cylinders that can have a negative impact on environment. By choosing a suitable heat source (e.g. solar power), Stirling can be absolutely environmentally friendly power unit.
Disadvantages of the Stirling design
With all the set of positive properties, the immediate mass use of Stirling engines is impossible due to the following reasons:
The main problem lies in the material consumption of the structure. Cooling of the working fluid requires the presence of large volume radiators, which significantly increases the size and metal consumption of the installation.
The current technological level will allow the Stirling engine to compare in performance with modern gasoline engines only through the use of complex types of working fluid (helium or hydrogen) under pressure of more than one hundred atmospheres. This fact raises serious questions both in the field of materials science and user safety.
An important operational problem is related to the issues of thermal conductivity and temperature resistance of metals. Heat is supplied to the working volume through heat exchangers, which leads to inevitable losses. In addition, the heat exchanger must be made of heat-resistant metals that are resistant to high pressure. Suitable materials very expensive and difficult to process.
The principles of changing the modes of the Stirling engine are also fundamentally different from the traditional ones, which requires the development of special control devices. So, to change the power, it is necessary to change the pressure in the cylinders, the phase angle between the displacer and the power piston, or to affect the capacity of the cavity with the working fluid.
One way to control the shaft speed on a Stirling engine model can be seen in next video:
Efficiency
In theoretical calculations, the efficiency of the Stirling engine depends on the temperature difference of the working fluid and can reach 70% or more in accordance with the Carnot cycle.
However, the first samples realized in metal had an extremely low efficiency for the following reasons:
- inefficient variants of the coolant (working fluid), limiting the maximum heating temperature;
- energy losses due to friction of parts and thermal conductivity of the engine housing;
- lack of structural materials resistant to high pressure.
Engineering solutions have constantly improved the design of the power unit. So, in the second half of the 20th century, a four-cylinder automobile Stirling engine with a rhombic drive showed an efficiency equal to 35% in tests on a water coolant with a temperature of 55 ° C. Careful study of the design, the use of new materials and fine-tuning of the working units ensured the efficiency of the experimental samples at 39%.
Note! Modern gasoline engines of similar power have a coefficient useful action at the level of 28-30%, and turbocharged diesel engines within 32-35%.
Modern examples of the Stirling engine, such as the one built by the American company Mechanical Technology Inc, show efficiency up to 43.5%. And with the development of the production of heat-resistant ceramics and similar innovative materials, it will be possible to significantly increase the temperature of the working environment and achieve an efficiency of 60%.
Examples of successful implementation of automotive Stirlings
Despite all the difficulties, there are many workable models of the Stirling engine applicable to the automotive industry.
Interest in Stirling, suitable for installation in a car, appeared in the 50s of the XX century. Work in this direction was carried out by such concerns as Ford motor company, Volkswagen Group and others.
UNITED STIRLING (Sweden) developed Stirling, which made maximum use of serial components and assemblies produced by automakers ( crankshaft, connecting rods). The resulting four-cylinder V-shaped motor had a specific gravity of 2.4 kg / kW, which is comparable to the characteristics of a compact diesel engine. This unit was successfully tested as a power plant for a seven-ton cargo van.
One of the successful examples is four-cylinder engine Stirling of the Dutch production of the Philips 4-125DA model, intended for installation on a passenger car. The motor had a working power of 173 liters. With. in sizes similar to the classic gasoline unit.
Engineers have achieved significant results General Motors, having built an eight-cylinder (4 working and 4 compression cylinders) in the 70s V-engine Stirling with a standard crank mechanism.
Similar power plant in 1972 equipped limited edition ford cars Torino, whose fuel consumption has decreased by 25% compared to the classic gasoline V-shaped eight.
Currently, more than fifty foreign companies are working to improve the design of the Stirling engine in order to adapt it to mass production for the needs of the automotive industry. And if it is possible to eliminate the shortcomings of this type of engine, while at the same time retaining its advantages, then it is Stirling, and not turbines and electric motors, that will replace gasoline internal combustion engines.
It replaced other types of power plants, however, work aimed at abandoning the use of these units suggests an imminent change in leading positions.
At first technical progress when the use of engines that burn fuel inside was just beginning, their superiority was not obvious. 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 the 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 exceeded allowable norms pressure. 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, required 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 rotates in enclosed space cylindrical shape. 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 Stirling engine.
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 central hole lids, 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 on crank mechanism engine flywheel from disk. 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. Stepping through 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;
- No need to use hinged and auxiliary equipment, the design of the engine is simple and reliable;
- The resource of the engine, due to the design features, is 100,000 hours of operation;
- The operation of the engine 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:
- Difficult to set up mass production, since structurally the engine requires the use a large number materials;
- high weight and large dimensions engine, because effective cooling you need to use a large radiator;
- 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, you must apply special devices management.
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.
Many people are interested in the principle of operation of the Stirling engine, and not only out of idle curiosity, but also because if you do not understand the basis of its operation, then it is very difficult to make a working model. In this publication, in detail and as concisely as possible, the answer to this question is given. And everything is clearly presented in the video tutorial with all the schemes.
You can find an excellent generator in this Chinese store.
Consider first
The engine itself consists of a cylinder in which the displacer moves and a second cylinder in which the working piston moves. The side walls of the large cylinder do not conduct heat. The top is cold, the bottom is hot. When the displacer moves down, blocking the hot plate, the air cools sharply and compresses, drawing in the working piston (green in the video).
When the displacer moves up, it covers the cold plate, the air from the bottom plate heats up sharply, expands (due to heating) and displaces the working green piston up.
The principle of operation of a high-temperature Stirling motor
The left and right sides of the cylinder do not touch each other. Between them is a heat insulator. When the displacer is on the left side, it displaces the entire hot air to the right, the air cools, sucking in the working piston. When the displacer goes to the right, it expels all the air into the hot chamber, the air heats up, expands and displaces the working piston to the right. The working piston and displacer are interconnected by a crankshaft with an offset of 90 degrees. Then the cycle repeats.
To finally understand the principle of operation of the Stirling motor, you need to assemble its working design and, in the process of fine-tuning, improve it and test it in different configurations.
For the simplest understanding of the laws by which the engine works, it is enough to do this:
- make a cylinder with a displacer;
- instead of the working piston, install a rubber balloon;
- do not install the flywheel yet;
– heat the lower part of the device, cool the upper part and start changing the position of the displacer;
- if you try to lift the displacer up - the ball will inflate sharply;
- if you lower the displacer down - the ball will be blown away.
So these simple steps will clearly show how everything happens in the engine mechanism.
- Next, replace the balloon with a piston;
- the piston should move freely, but everything should be adjusted so that it does not let air through;
– lubricate the piston with silicone grease;
- do the same steps that were previously performed with the ball, but with the piston;
- observe the stroke of the piston, fix it in the notes in the working notebook in order to calculate the stroke (bend) of the crankshaft;
- make a flywheel, connecting rod, crankshaft and that's it, the Stirling engine is ready!
- final test of the finished device.
Important points if you are making the engine yourself
1. The walls of the cylinder, where the displacer goes, must be made so as not to conduct heat.
2. One end of the cylinder is cold, the other is hot. The greater the temperature difference, the higher the efficiency.
3. There should be a gap between the walls of the cylinder and the displacer (3 mm is enough) so that there is room for air to leak from the cold chamber to the hot one.
4. There must be no air leaks (minimize them). This is one of the main reasons that prevent the engine from working.
5. Remove all friction to the maximum. Use silicone grease- it gives a very good result.
Good luck with your tech work!
How to adapt a current generator for this engine. And here is another model that you can assemble at home.
How do Stirling engines work?
For nearly 200 years, thermal engines, known by their inventor's name, have been known as Stirling engines. Their inventor worked on building the most efficient or optimal working heat engine. Stirling approached the problem in a rather scientific way. That is, the engine (its theoretical circulation) was analyzed and verified computationally before the prototype was built. Everything in theory looked very promising. In principle, until now it has been assumed that they should be one of the most efficient heat engines. So why shouldn't we travel with Stirling vehicles despite their many benefits?
Drawing of a Stirling engine from the original 1816 patent. Source: Wikimedia Commons, .
To get useful power from a piston engine, it must develop a sufficiently high torque or reach a high rotational speed. Stirling engines do not reach high speeds rotation, so let's look at the moment. Basically, this will depend on the force acting on the piston, and this, in turn, on the pressure of the working fluid in the working stroke and the surface of the piston that works. These simplistic considerations will help us understand the structural problems of Stirling engines. In order for an engine to be larger than the model on the table, it must be huge - have a large diameter of the working piston, or the piston must be under high pressure during the power stroke.
A typical "desktop" model of a Stirling engine from the turn of the 20th and 21st centuries. Flywheel diameter: about 30mm. It should be included in the group of so-called "Gadgets".
History of the Stirling engine in the 19th century
In the early 19th century, engines were mainly used to drive machines (e.g. pumps in mines, drives central machines in factories) and engines could be huge. Working cylinders with a diameter of more than 0.5-1 m were on the agenda. Despite this, Watt's steam engines won the competition for Stirling engines. True, Stirling engines were simpler in design and processing, but steam engines, including the entire system (boiler room) and all their shortcomings, however, were more efficient (read: cheaper to run) and provided more power. Even in mobile systems, such as ships and trains (in England and Scotland in the middle of the 19th century, the railway network was already developed), steam engines were much better.
An industrial Stirling engine from about 1860. Ericsson-produced engine introduced, implemented a modified Stirling cycle named after its creator Ericsson. Source: Wikimedia Commons. Vasarnapi Ujsag, 1861/8 .
Sure, Stirling engines were used here and there, but they didn't dominate the market. Moreover, installed Stirling engines were often replaced by steam engines, and those that remained were already considered rarities and niche applications. In Europe, perhaps the most famous Stirling engines from the turn of the 19th and 20th centuries were those used in… aquarium pumps. One of the most famous manufacturers of such engines during this period was the company Louis Heinrici .
The Stirling engine family from Louis Heinrici. Illustration from the company's catalog from 1914. Source: Wikimedia Commons.
But back to the topic. At the end of the 19th century, internal combustion engines appeared, first with gas and then with liquid fuels. Besides, in automotive drives there were also electric motors. Theoretically, Stirling engines should be the best (whatever that means), so all the time the world of science and technology was periodically interested in them. Since the construction of huge Stirling engines in the 19th century lost its meaning, attempts were made to build small engines, but with a high pressure of the working fluid, so that the created propulsion systems would be competitive with internal combustion engines. The peak of work on such engines occurred in the 1950s and 1960s. Of course, a significant group of problems arose, which were more or less successfully solved.
A commercially available electrical generator driven by a Philips Stirling engine from the mid-20th century (1953). Electric power: about 180W. Case height: about 0.5 m. Source: Wikimedia Commons, Norbert Schnitzler.
Helium use
At the same time, the idea to replace the working factor appeared. Until now, under the slogan "working factor" in Stirling engines, we understood the usual atmospheric air. At some point, engineers and scientists asked the question, is there something better in terms of thermodynamic properties? Yes. More or less since the 1930s, this gas has been commercially sold in industrial quantities. This is helium. The use of helium as a working medium significantly increases the efficiency of Stirling engines. However, the use of a new factor caused completely new problems. Helium is poorly stored even at room temperature. That is. due to very small particles, it tends to penetrate most materials used in steel head technology. In the 60s and 70s, helium engines were studied. Their salient feature, visible in the photographs ... is attached to the engine of a helium cylinder used to replenish the gas escaping from the engine through almost all of its elements. The problem was serious. In order to be competitive with other propulsion systems (i.e., mainly internal combustion engines), the average pressure of the working medium in Stirling engines was 20…30 bar, and the temperature of the hot parts of the engines (heater) often exceeded 500 degrees Celsius (with a temperature difference of 400 degrees). Leakage problems for "helium" engines have not yet been solved practically and economically. In order to be competitive with other propulsion systems (i.e., mainly internal combustion engines), the average pressure of the working medium in Stirling engines was 20…30 bar, and the temperature of the hot parts of the engines (heater) often exceeded 500 degrees Celsius (with a temperature difference of 400 degrees). Leakage problems for "helium" engines have not yet been solved practically and economically. In order to be competitive with other propulsion systems (i.e., mainly internal combustion engines), the average pressure of the working medium in Stirling engines was 20…30 bar, and the temperature of the hot parts of the engines (heater) often exceeded 500 degrees Celsius (with a temperature difference of 400 degrees). Leakage problems for "helium" engines have not yet been solved practically and economically.
Stirling motors, their use at the end of the 20th century
At the end of the 20th century, Stirling engines returned again. Both NASA, the US State Department and the European Union have invested in research into new generations of Stirling engines. They were primarily intended for solar systems (i.e., the heat source had to be sunlight focused on the engine heater by a large parabolic mirror). Many of these engines had uneven designs.
An example of a Stirling engine design proposed by Mr. Maciej Zukas in accordance with patent P.389415. The project was carried out as part of a master's work at the Faculty of SiMR at the Warsaw University of Technology (supervisor: Prof. Wiasław Ostapski, PhD, Eng.
The idea of this idea was that the whole engine with electric generator must be sealed in a sealed (for helium) non-removable case, considering that it cannot be used throughout its entire service life. However, this time the technology failed. If positive results were obtained, they were associated with too high costs. Best of all, the most common twentieth-century Stirling engines remained in India table fans, structurally similar to the aforementioned aquarium pumps...
An example of a solar system with an electrical generator driven by a Stirling engine.
Ecology of consumption. Science and technology: The Stirling motor is most often used in situations where a device for converting thermal energy is required, which is simple and efficient.
Less than a hundred years ago, internal combustion engines tried to win their rightful place in the competition among other machines and moving mechanisms available. At the same time, in those days, superiority gasoline engine was not so obvious. Existing machines on steam engines distinguished by noiselessness, excellent power characteristics for that time, ease of maintenance, the possibility of using various types of fuel. In the further struggle for the market, internal combustion engines prevailed due to their efficiency, reliability and simplicity.
A further race for the improvement of aggregates and driving mechanisms, which was entered in the middle of the 20th century gas turbines and rotary engine varieties, 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 was named after its creator.
STIRLING ENGINE: THE PHYSICAL SIDE OF THE ISSUE
To understand how a Stirling benchtop power plant works, you need to understand the basics of how heat engines work. Physically, the principle of operation is to use mechanical energy, which is obtained by expanding the gas during heating and its subsequent compression during cooling. To demonstrate the principle of operation, an example can be given based on an ordinary plastic bottle and two pots, one of which contains cold water, the other hot.
When lowering the bottle into cold water, the temperature of which is close to the temperature of ice formation, with sufficient cooling of the air inside the plastic container, it should be closed with a cork. Further, when the bottle is placed in boiling water, after a while the cork “shoots” with force, since in this case the work done by the heated air is many times greater than that done during cooling. When the experiment is repeated many times, the result does not change.
The first machines that were built using the Stirling engine faithfully reproduced the process demonstrated in the experiment. Naturally, the mechanism required improvement, consisting in the use of part of the heat that was lost by the gas during cooling for further heating, allowing heat to be returned to the gas to accelerate heating.
But even the application of this innovation could not save the situation, since the first Stirlings were different large sizes at low power output. In the future, more than once attempts were made to modernize the design to achieve a power of 250 hp. led to the fact that in the presence of a cylinder with a diameter of 4.2 meters, the real output power that the Stirling power plant produced at 183 kW was actually only 73 kW.
All Stirling engines operate on the principle of the Stirling cycle, which includes four main phases and two intermediate ones. The main ones are heating, expansion, cooling and compression. As the transition stage, the transition to the cold generator and the transition to the heating element are considered. 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 in two active pistons located in independent cylinders. Of all three options this model differs most high power, having the most high temperature heated piston;
- beta stirling, based on one cylinder, one part of which is hot and the other is cold;
- gamma-stirling, which, in addition to the piston, also has a displacer.
The production of the Stirling power plant 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 their design features These engines have a number of advantages, but they are not without drawbacks.
Stirling's desktop power station, which cannot be bought in a store, but only from amateurs who independently collect such devices, includes:
- large sizes, which are caused by the need for constant cooling working piston;
- the use of high pressure, which is required to improve engine performance and power;
- heat loss, which occurs due to the fact that the generated heat is transferred not to the working fluid itself, but through a system of heat exchangers, whose heating leads to a loss in efficiency;
- a sharp decline power requires the application of special principles that differ from those traditional for gasoline engines.
Along with the disadvantages, power plants operating on Stirling units have undeniable advantages:
- any type of fuel, since like any engines using heat energy, this engine able to function at a temperature difference of any environment;
- economy. These devices can be an excellent replacement for steam units in cases where it is necessary to process solar energy, giving out an efficiency of 30% higher;
- environmental Safety. Since the kW tabletop power plant does not generate exhaust torque, it does not produce noise and does not emit into the atmosphere harmful substances. Ordinary heat acts as a source of power, and the fuel burns out almost completely;
- constructive simplicity. For his work, Stirling will not require additional parts or fixtures. It is able to start independently without the use of a starter;
- increased resource performance. Due to its simplicity, the engine can provide more than one hundred hours of continuous operation.
STIRLING ENGINE APPLICATIONS
The Stirling motor is most often used in situations where an apparatus for converting thermal energy is required, which is simple, while the efficiency of other types of thermal units is significantly lower under similar conditions. Very often, such units are used in the power supply of pumping equipment, refrigerators, submarines, batteries that store energy.
One of the promising areas for the use of Stirling engines is solar power plants, since this unit can be successfully used to convert the energy of sunlight into electrical energy. To carry out this process, the engine is placed in the focus of a mirror that accumulates the sun's rays, which provides permanent illumination of the area requiring heating. This allows you to focus solar energy on a small area. The fuel for the engine in this case is helium or hydrogen. published
