Only about a hundred years ago, internal combustion engines had to win the place they occupy in modern automotive industry in a fierce competition. Then their superiority was by no means as obvious as it is today. Indeed, the steam engine - the main rival of the gasoline engine - had enormous advantages in comparison with it: noiselessness, ease of power control, excellent traction characteristics and amazing "omnivorousness" that allows it to work on any type of fuel from wood to gasoline. But in the end, the efficiency, lightness and reliability of internal combustion engines prevailed and made us come to terms with their shortcomings as inevitable.
In the 1950s, with the advent of gas turbines and rotary engines, an assault began on the monopoly position occupied by internal combustion engines in the automotive industry, an assault that has not yet been crowned with success. Approximately in the same years, attempts were made to bring to the scene a new engine, which amazingly combines the efficiency and reliability of a gasoline engine with the noiselessness and "omnivorous" steam installation. This is the famous external combustion engine that the Scottish priest Robert Stirling patented on September 27, 1816 (English Patent No. 4081).
Process physics
The principle of operation of all heat engines, without exception, is based on the fact that when a heated gas expands, more mechanical work is performed than is required to compress a cold one. To demonstrate this, a bottle and two pots of hot and cold water are sufficient. First, the bottle is dipped into ice water, and when the air in it cools, the neck is plugged with a cork and quickly transferred to hot water. After a few seconds, a pop is heard and the gas heated in the bottle pushes the cork out, doing mechanical work. The bottle can be returned to the ice water again - the cycle will repeat.
the cylinders, pistons, and intricate levers of the first Stirling machine reproduced this process almost exactly, until the inventor realized that part of the heat taken from the gas during cooling could be used for partial heating. All that is needed is some kind of container in which it would be possible to store the heat taken from the gas during cooling, and give it back to it when heated.
But, alas, even this very important improvement did not save the Stirling engine. By 1885, the results achieved here were very mediocre: 5-7 percent efficiency, 2 liters. With. power, 4 tons of weight and 21 cubic meters of occupied space.
External combustion engines were not saved even by the success of another design developed by the Swedish engineer Erickson. Unlike Stirling, he proposed heating and cooling the gas not at a constant volume, but at a constant pressure. In 1887, several thousand small Erickson engines worked perfectly in printing houses, in houses, in mines, on ships. They filled the water tanks, powered the elevators. Erickson even tried to adapt them to drive crews, but they turned out to be too heavy. In Russia, before the revolution, a large number of such engines were produced under the name "Heat and Power".
Last year, the magazine, in the first issue of which readers were greeted A. Einstein, turned 85 years.
The small staff of the Editorial Board continues to publish IR, whose readers you are honored to be. Although it becomes more and more difficult to do this every year. For a long time, at the beginning of the new century, the editors had to leave their native place of residence on Myasnitskaya Street. (Well, actually, this is a place for banks, not for some body of inventors). Helped us though Y. Maslyukov(at that time the chairman of the Committee of the State Duma of the Federal Assembly of the Russian Federation for Industry) to move to NIIAA near the Kaluzhskaya metro station. Despite the fact that the Editorial Board complied with the terms of the contract and paid the rent on time, and the inspiring proclamation of the course for innovation by the President and the Government of the Russian Federation, the new director at NIIAA informed us about the eviction of the Editorial Office "due to operational necessity." This is despite the reduction in the number of employees at NIIAA by almost 8 times and the corresponding release of space, and despite the fact that the area occupied by the editorial office did not amount to one hundredth of a percent of the boundless areas of NIIAA.
We were sheltered by MIREA, where we have been located for the last five years. Move twice to burn once, says the proverb. But the editors hold out and will hold out as long as they can. And can it exist as long as the magazine "Inventor and innovator" read and write.
Trying to cover more interested people with information, we have updated the magazine's website, making it, in our opinion, more informative. We are engaged in the digitization of publications of past years, starting from 1929 year - the time the journal was founded. We are releasing an electronic version. But the main thing is the paper edition IR.
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One of the promising sources of mechanical energy for cars is the external combustion engine, developed by Scottish-born Robert Stirling a couple of centuries ago. The Stirling external combustion engine, according to the principle of operation, is very different from the usual for all internal combustion engines. But for some time after development, they safely forgot about it.
History of creation
In 1816, Scottish-born Robert Stirling patented the heat engine, which today is named after its creator. However, the very idea of hot air engines was not invented by him at all. But the first conscious project to create such a unit was implemented by Stirling.
He improved the system by adding a purifier to it, in the technical literature called a heat exchanger. Thanks to this, the performance of the motor has greatly increased by keeping it warm. This model for that time was recognized as the most durable, since it never exploded.
Despite such rapid advancement of the model, at the beginning of the twentieth century, further development of the external combustion engine was abandoned due to its cost in favor of the internal combustion engine.
Stirling engine: principle of operation and modification
The principle of operation of any heat engine is that in order to obtain gas in an expanded state, considerable mechanical efforts are needed. As an illustrative example, we can cite the experiment with two pans, according to which they are filled with cold and hot water. Immerse a bottle with a screw cap in cold water. After that, the bottle is transferred to hot water.
With this movement, the gas in the bottle performs mechanical work and pushes the cork out of the neck. The first model of an external combustion engine worked on exactly the same principle. However, later the creator realized that part of the heat generated could be used for heating. The productivity of the unit from this only increased.
A little later, an engineer from Sweden, Erickson, improved the design, putting forward the idea of cooling and heating gas at constant pressure instead of volume. This allowed the engine to "move up the career ladder" and begin to be used in mines and printing houses. For crews and vehicles, the unit was too heavy.
The figure clearly shows the operating cycle of the Stirling engine.
How does a Stirling engine work? It converts thermal energy supplied from outside into useful mechanical work. This process occurs due to a change in the temperature of a gas or liquid circulating in a closed volume. In the lower part of the unit, the working substance heats up, increases in volume and pushes the piston up.
Hot air enters the top of the motor and is cooled by a radiator. The pressure of the working fluid is reduced, and the piston is lowered to repeat the entire cycle. The system is completely sealed, so that the working substance is not consumed, but only moves within the cycle.
In addition, there are open-cycle motors in which flow control is implemented using valves. These models are called the Erickson engine. In general, the principle of operation of an external combustion engine is similar to an internal combustion engine. At low temperatures, compression occurs in it and vice versa. Heating is carried out in different ways.
Heat in an external combustion engine is supplied through the cylinder wall from the outside. Stirling guessed to use a periodic change in temperature with a displacement piston. This piston moves gases from one cavity of the cylinder to another. At the same time, low temperatures are constantly maintained on the one hand, and high temperatures on the other. As the piston moves upward, the gas moves from the hot to the cold cavity.
The propellant system in the engine is connected to a working piston, which compresses the gas in the cold and allows it to expand in the heat. Useful work is done just due to compression at lower temperatures. Continuity is provided by a crank mechanism. There are no special boundaries between the stages of the cycle. Thanks to this, the efficiency of the Stirling engine does not decrease.
Some engine details
In theory, any heat source (sun, electricity, fuel) can supply energy to an external combustion engine. The principle of operation of the engine body is to use helium, hydrogen or air. The ideal cycle has the highest possible thermal efficiency. The efficiency in this case is from 30 to 40%. An efficient regenerator can provide higher efficiency. Built-in heat exchangers provide regeneration, exchange and cooling in modern engines. Their advantage is oil-free operation. In general, the engine needs little lubrication. The average pressure in the cylinder varies from 10 to 20 MPa. A good sealing system and the possibility of oil entering the working cavities are essential.
According to theoretical calculations, the efficiency of the Stirling engine is highly dependent on temperature and can even reach 70%. The very first engine samples implemented in metal had low efficiency, since the coolant options were inefficient and limited the maximum heating temperature, there were no structural materials resistant to high pressure. In the second half of the 20th century, an engine with a rhombic drive during tests exceeded 35% efficiency on a water coolant and at a temperature of 55 degrees Celsius. Improving the design in some experimental samples made it possible to achieve almost 39% efficiency. Almost all modern gasoline engines with similar power have an efficiency of 28 - 30%. Turbo diesels reach about 35%. The most modern examples of Stirling engines, developed by Mechanical Technology Inc in the USA, show efficiency up to 43%.
After the development of heat-resistant ceramics and other innovative materials, it will be possible to further increase the temperature of the medium. Efficiency can even reach 60% under such conditions.
There are several modifications of the Stirling external combustion engine.
Modification "Alpha"
Such an engine consists of hot and cold separate power pistons located in their own cylinders. Heat is supplied to the cylinder with the hot piston, and the cold piston is located in the cooling heat exchanger.
Modification "Beta"
In this version of the engine, the cylinder in which the piston is located is heated on one side and cooled on the other. A displacer and a power piston move inside the cylinder. The displacer is designed to change the volume of the working gas. The regenerator returns the cooled working substance to the heated engine cavity.
Modification "Gamma"
The entire simple design of the Gamma modification is made of two cylinders. The first one is completely cold. It moves the power piston. And the second is cold only on one side, and on the other - heated. It serves to move the displacer mechanism. The cold gas circulation regenerator in this modification can be common to both cylinders and be included in the design of the displacer.
Advantages of an external combustion engine
This type of engine is unpretentious in terms of fuel, since the basis of its operation is the temperature difference. What caused this difference - it does not really matter. The Stirling engine has a simple design and does not need additional systems and attachments (starter, gearbox). Some features of the engine design are a guarantee of a long service life: the engine can work continuously for about one hundred thousand hours. Another major advantage of an external combustion engine is its quietness. It is due to the fact that there is no detonation in the cylinders and there is no need to remove exhaust gases. Particularly distinguished by this parameter is the Beta modification. Its design is equipped with a diamond-shaped crank mechanism, which ensures the absence of vibration during operation. And finally, environmental friendliness. There are no processes in the engine cylinders that can adversely affect the environment.
When choosing alternative sources of heat (solar energy), the Stirling engine turns into a kind of environmentally friendly power unit.
Disadvantages of an external combustion engine
Mass production of such engines is currently impossible. The main problem is the material consumption of the structure. Cooling the working fluid of the engine requires the installation of radiators with large volumes. As a result, the dimensions increase. The use of complex types of working fluid like hydrogen or helium raises the question of engine safety. Thermal conductivity and temperature resistance must be at a high level. Heat is supplied to the working volume through heat exchangers. Thus, part of the heat is lost along the way. In the manufacture of heat exchangers, it is necessary to use heat-resistant metals. In this case, the metals must be resistant to high pressure. All these materials are expensive and take a long time to process. The principles of changing the modes of an external combustion engine are very different from traditional ones. The development of special control devices is required. The change in power is caused by a change in pressure in the cylinders and the phase angle between the displacer and the power piston. You can also change the capacity of the cavity with the working fluid.
Examples of the implementation of external combustion engines on cars
Workable models of such an engine were released, despite all the manufacturing difficulties. In the 50s of the 20th century, automotive companies became interested in this type of power unit. Basically, the implementation of Stirling engines on cars was carried out by the Ford Motor Company and the Volkswagen Group. The Swedish company UNITED STIRLING has developed such an engine in which the developers tried to use serial units and components (crankshaft, connecting rods) more often. A four-cylinder V-shaped engine was developed with a specific gravity of 2.4 kg / kW. A compact diesel has a similar mass. They tried to install the engine on seven-ton cargo vans.
The most notable success was the Philips 4-125DA, available for installation in passenger cars. The working power of the engine was 173 horsepower. The dimensions were not much different from the usual gasoline ICE.
General Motors has developed an eight-cylinder V-shaped external combustion engine with a serial crank mechanism. In 1972, a limited version of Ford Torino cars were equipped with such an engine. Moreover, fuel consumption has decreased by as much as 25% compared to previous models. Today, several foreign companies are trying to improve the design of this engine in order to adapt it for mass production and installation in passenger cars.
Principle of operation
The proposed innovative technology is based on the use of a highly efficient four-cylinder external combustion engine. This is a heat engine. Heat can be supplied from an external heat source or produced by burning a wide range of fuels inside a combustion chamber.
The heat is maintained at a constant temperature in one engine compartment, where it is converted into pressurized hydrogen. Expanding, hydrogen pushes the piston. In the low-temperature engine compartment, hydrogen is cooled by heat accumulators and liquid coolers. As it expands and contracts, the hydrogen causes a piston to reciprocate, which is converted to rotation by a swash plate that drives a standard, capacitive electrical generator. The hydrogen cooling process also produces heat that can be used for combined power and heat generation in ancillary processes.
general description
The FX-38 thermal power plant is a single engine-generator module that includes an external combustion engine, a combustion system powered by propane, natural gas, associated petroleum gas, other medium and low energy-intensity fuels (biogas), an inductive generator, engine control system, weatherproof housing with built-in ventilation system and other auxiliary equipment for parallel operation with a high voltage network.
The rated electrical power when operating on natural gas or biogas at a frequency of 50 Hz is 38 kW. In addition, the plant produces 65 kWh of recoverable heat with an optional combined heat and power system.
The FX-38 can be equipped with a variety of cooling system options to provide installation flexibility. The product is designed to be easily connected to electrical contacts, fuel supply systems and external cooling system pipes, if equipped.
Additional details and options
- Power measurement module (provides installed current transformer to read AC parameters on display)
- Remote monitoring option via RS-485 interface
- Integral or remote mounted heatsink options
- Propane fuel option
- Natural gas option
- Associated petroleum gas option
- Low energy fuel option
The FX-48 can be used in several ways as follows:
- Parallel connection to a high voltage network at 50 Hz, 380 V AC
- Combined heat and power mode
Plant performance
In power and heat production mode at 50 Hz, the plant produces 65 kWh of recoverable heat. The product is equipped with a piping system ready for connection to a customer-supplied liquid/liquid heat exchanger. The hot side of the heat exchanger is a closed loop circuit with an engine case cooler and an integrated system radiator, if present. The cold side of the heat exchanger is dedicated to the customer's heat sink circuits.
Maintenance
The unit is designed for continuous operation and power take-off. A basic performance test is performed by the customer at 1000 hour intervals and includes checking the cooling water system and oil level. After 10,000 hours of operation, the front of the unit is serviced, including the replacement of the piston ring, rod seal, drive belt and various seals. Specific key components are checked for wear. The motor speed is 1500 rpm for 50 Hz operation.
Continuity
Plant uptime is over 95% based on operating intervals and is taken into account in the maintenance schedule.
Sound pressure level
The sound pressure level of the unit without built-in radiator is 64 dBA at a distance of 7 meters. The sound pressure level of the unit with built-in radiator with cooling fans is 66 dBA at a distance of 7 meters.
Emissions
When running on natural gas, engine emissions are less than or equal to 0.0574 g/Nm 3 NO x , 15.5 g/Nm 3 volatile organic compounds and 0.345 g/Nm 3 CO.
gaseous fuel
The engine is designed to operate on various types of gaseous fuels with lower calorific values from 13.2 to 90.6 MJ/Nm 3 , associated petroleum gas, natural gas, coal methane, secondary processing gas, propane and landfill biogas. To cover this range, the unit can be ordered with the following fuel system configurations:
The combustion system requires a regulated gas supply pressure of 124-152 mbar for all types of fuel.
Environment
The standard version of the unit operates at an ambient temperature of -20 to +50°C.
Installation description
The FX-38 thermal power plant is completely ready for power generation in factory delivery. The built-in electrical panel is mounted on the unit to meet interface and control requirements. A weatherproof digital display built into the electrical console provides the operator with a pushbutton start, stop and restart interface. The electrical panel also serves as the main connection point for the customer's electrical terminal, as well as with wired communication terminals.
The unit is capable of reaching full load output power in approximately 3-5 minutes from start-up, depending on the initial temperature of the system. The start-up and installation sequence is activated at the push of a button.
After the start command, the unit is connected to the high voltage network by closing the internal contactor to the network. The engine turns over immediately, clearing the combustion chamber before the fuel valves open. After opening the fuel valve, energy is supplied to the ignition device, igniting the fuel in the combustion chamber. The presence of combustion is determined by the increase in the temperature of the working gas, which activates the run-up control procedure to the operating temperature point. Thereafter, the flame remains self-sustaining and constant.
After the command to stop the installation, the fuel valve is first closed to stop the combustion process. After a pre-set time, during which the mechanism cools down, the contactor will open, disconnecting the unit from the mains. If installed, the radiator fans may run for a short time to reduce the coolant temperature.
The unit uses a constant stroke external combustion engine connected to a standard induction generator. The device operates in parallel with the high voltage network or in parallel with the power distribution system. An induction generator does not create its own excitation: it receives excitation from a connected power supply. If the mains voltage fails, the unit switches off.
Description of installation nodes
The design of the unit ensures its easy installation and connection. There are external connections for fuel pipes, electrical power terminals, communication interfaces and, if provided, an external radiator and a liquid/liquid heat exchanger piping system. The unit can be ordered with an integrated or remote mounted radiator and/or liquid/liquid heat exchanger piping system for engine cooling. Safe shutdown tools and control logic designed specifically for the desired mode of operation are also provided.
The enclosure has two access panels on each side of the engine/generator compartment and an external single hinged door for access to the electrical compartment.
Installation weight: about 1770 kg.
The engine is a 4-cylinder (260 cm 3 /cylinder) external combustion engine that absorbs the heat of continuous combustion of gas fuel in an internal combustion chamber, and includes the following built-in components:
- Combustion chamber fan driven by engine
- Combustion chamber air filter
- Fuel system and combustion chamber housing
- Lubricating oil pump, engine driven
- Cooler and filter for lubricating oil
- Engine cooling water pump, engine driven
- Water temperature sensor in the cooling system
- Lube oil pressure sensor
- Gas pressure and temperature sensor
- All necessary control and safety equipment
The characteristics of the generator are given below:
- Rated power 38 kW at 50 Hz, 380 V AC
- 95.0% electrical efficiency at 0.7 power factor
- Excitation from the public mains with an induction motor/generator exciter
- Less than 5% total harmonic distortion from no load to full load
- Insulation class F
Operator interface - digital display provides control of the unit. The operator can start and stop the unit from the digital display, view run time, operating data and warnings/failures. By installing the optional power measurement module, the operator can view many electrical parameters such as generated power, kilowatt-hours, kilowatt-amperes, and power factor.
The equipment diagnostics and data collection function is built into the plant control system. Diagnostic information simplifies remote data collection, data reporting, and device troubleshooting. These functions include the collection of system data such as operating status information, all mechanical operating parameters such as cylinder temperature and pressure, and, if an optional power meter is connected, electrical output values. The data can be transferred via a standard RS-232 connection port and displayed on a PC or laptop using data acquisition software. For multiple installations or in cases where the signal transmission distance exceeds RS-232 capability, the optional RS-485 port is used to receive data using the MODBUS RTU protocol.
Stainless steel pipes are used to transport hot exhaust gases from the combustion system. A balanced exhaust flap with a protective cap from rain and snow is attached to the exhaust pipe at the exit from the casing.
Various application technologies and configurations can be used for cooling:
Built-in Heatsink – Provides a heatsink rated for ambient temperatures up to +50°C. All pipes are factory connected. This is a typical technology if waste heat recovery is not used.
External radiator - designed for installation by the customer, designed for ambient temperatures up to +50°C. The short support legs are supplied with a heatsink for mounting on a contact table. If indoor installation is required, this option can be used instead of providing the ventilation system required to supply cooling air to the built-in radiator.
External Cooling System - Provides piping outside the enclosure for a customer-supplied cooling system. It can be a heat exchanger or a remotely mounted radiator.
The refrigerant consists of 50% water and 50% ethylene glycol by volume: can be replaced with a mixture of propylene glycol and water, if necessary.
The FX-38 uses hydrogen as the working fluid to drive engine pistons due to hydrogen's high heat transfer capability. During normal operation, a predictable amount of hydrogen is consumed due to normal leakage caused by the permeability of the material. To account for this rate of consumption, the installation site requires one or more sets of hydrogen cylinders, adjusted and connected to the unit. Inside the unit, a built-in hydrogen compressor pressurizes the tank to a higher engine pressure and injects small portions at the request of the firmware. The built-in system is maintenance-free, and the cylinders must be replaced depending on the operation of the engine.
Fuel supply pipe is supplied with 1" NPT for all standard fuel types except low energy options which use 1 1/2" NPT. The fuel pressure requirements for all gaseous fuels are between 124 and 152 mbar.
