The invention of the Stirling engine, also called
Stirling engine Stirling , is an evolution of existing hot-air engine, which competed at the beginning of 1800 with the steam engine
to provide mechanical energy to industrial machinery (In factories and mines) in the first
industrial revolution in England. In particular, the invention of Stirling, the adoption of a heat recovery system that actually turned out to be the right device to dramatically improve engine performance.
The competition between the air motor and the steam had reason to try to have an alternative to the steam engine itself, in its early achievements, despite having superior characteristics than air, because of the use of technologically inferior then available was extremely dangerous for the devastating explosion of the boilers. After a first phase of the engine with good success Stirling-sized business, improvement of the steam engine gave up the most reliable materials Stirling inconvenient, owing to its use was abandoned.
A second application of the Stirling engine came with the development of 'electronic
, the use of the first radio
and development of'
Aviation before
1960. The
Philips (Netherlands industry production of radios) to power the radio-transmitters and receivers of its construction created a small unit of Stirling power generation by burning oil, used to power appliances such charges in remote locations and without power supply. The device was made MP1002CA Philips (called Bungalow Set) with an output of 200 watts, the technology was so advanced that even with the use of light alloys (
1950) gives a good compromise between practicality and cost . The need for such power generation was particularly strong given power the radio (then with large and expensive vacuum tubes
) required for the stable connection with the fields of aviation, civil aviation network in the constitution (in the first phase for the postal service) in remote locations and without equipment. With the adoption of
transistor circuits electronics, since 1960, was enough power with limited electrical power, obtained with the simple
electric batteries of small size batteries, achieving also good battery life, so the use of the Stirling engine was abandoned.
Other applications were made later, and is currently developed with different engine sizes, or had some good technical achievements, and in some cases commercial niche markets.
Engine [edit ]
The engine works by using a closed-cycle gas as
thermodynamic fluid (usually air
, nitrogen
or
helium or hydrogen
versions with high efficiency). When it reached a suitable temperature difference between its hot spot and cold spot and is appropriately initiated, it triggers a pulse cycle, normally converted into reciprocating motion of the pistons. The pulse lasts as long as you continue to maintain the temperature difference, giving heat to the hot spot and subtracting the cold.
A peculiarity of this engine is to operate without the use of valves. The only moving parts are the piston and the displacer acting connected to a shaft with a pair of elbows out of phase with each other about 90 degrees. It is probably
one of the most interesting external combustion engine for its low maintenance, its silent and the feasibility of achieving yields close to the theoretical thermodynamic cycles, combustion is not bound to specific fuels.
You can also use the heat of
concentrated solar radiation, for example via a parabolic mirror
to produce the required temperature difference.
The discovery of new materials in construction technology can increase the temperature difference necessary for the operation, new fluid thermodynamic and environmental issues in recent years have given new impetus to the implementation of Stirling engines widely used. The major achievements are starting to have some commercial success are those for the domestic thermal power generation-low power, combining simplicity and low maintenance.
The smaller specimens (table models) are often objects of curiosity rather than practical value. These achievements at times and deliberately banal materials recovery (glass pipes, beer cans, rubber membranes, wire, etc.), or with materials, technology and excellent finishing modeling (bronze, light alloys, precious woods etc..) are functioning and able to make a difference-sometimes small, so they can "turn" with the heat of a candle, a hand, a cup of coffee or with the normal light of the sun even in winter. Even if placed on a piece of ice, can use the heat as the hot spring environment. It is clear, however, that with limited gradients of temperature and size, even if you can get modeling yields significant powers involved are negligible.
Variants [edit ]
In fact, the Stirling engine produces a cyclical fluctuation of the fluid contained in that part is transformed into mechanical energy. Under this principle there are variants of the Stirling engine in which, for example, the displacer moves dragged the pulse without being connected to the mechanical part (
Ringbom-Stirling engine ).
A particular application of the Stirling engine is to induce a pulse of the engine only fluid from the cold point and hot spot to a much higher frequency (
thermoacoustic engine), reciprocating motion of the conventional piston engine, the pulse, in almost total absence of moving parts such as pistons and displacers, self-sustaining until it delivers heat to the hot spot and it subtracts the cold spot, and this pulse has historically produced serious problems when it was made spontaneously and in an uncontrolled manner, usually in chimneys ( fireplaces singing), leading to annoying sound effects, uncontrolled violent vibrations and catastrophic failure. With technological progress in the problem moved unchanged devastating and inexplicable incidents in the operation of the combustion chambers of turbine and rocket engines. Events were primarily to avoid rather than to use. The effect
motor center gives a very accurate design and maintenance of specific physical conditions are checked, the advantage of this type of engine is the extreme simplicity and structural mechanics. Oscillations (pulsations) of the fluid can be transferred to the masses connected with linear electric generators
brought to solicit or piezoelectric plates
, producing energy.
special feature of the Stirling cycle is its reversibility, ie the machine can be made so that by providing mechanical energy (by turning) is obtained for a head against heat and cold on the other, so in effect acts as a heat pump, a successful application is the
chiller Stirling .
Advantages of the Stirling engine over internal combustion engines [edit ]
The Stirling engine is external combustion, this means that the parties most heated by the heat (which can be produced by combustion) are not contact with the flowing or rotating (
bearings, pistons
), therefore these parts and the lubricant
are not particularly stressed, then the parties have reduced maintenance requirements.
The engine has no valves and is not subject to outbreaks, and is the simplest, most vibration-free and much quieter than a combustion engine.
The application of heat for the operation is continuous, so if that heat is produced by burning this happens continuously, with
stoichiometric air-fuel that can be optimal, by far the best we can.
Administration of heat can be done by any means: concentrated solar heat, but also by burning wood, coal, gas, biogas, liquid fuels. Outside of special opportunities, technologies that are better managed are the sun's heat and liquid and gaseous fuels.
Disadvantages of the Stirling engine over internal combustion engines [edit ]
The heat is not produced inside the engine but it is applied from the outside, so you need to move it inside, too, since the engine uses the difference of heat, heat must be subtracted to create a cold spot. In summary: the fluid agent is within the engine, its heating or cooling his necessitate the presence of large areas (bundles or radiators) for heating and cooling. These heaters are great, the engine weight down, and make the same massive power output.
start of the engine, the heat flow from the heat source to the fluid inside is not sudden, so the start is slow, also the change of the transfer is too slow; therefore, the engine is not suitable for rapid starting or a substantial changes in regime.
energy (and power) output is proportional to the difference in temperature between hot and cold point source, with the temperature limit the cold as the ambient temperature. Then increase the gap means raising the temperature of the hot spot, with a limit due mainly to technical limitations and cost of materials capable of withstanding high temperatures.
One way to increase the power output is to increase the internal pressure of the fluid, thus increasing the size of the working fluid. The use of closed equipment, under pressure (pressurized), however, makes a careful structural and technological dimensions of the engine to be robust and heavier.
Although traditionally defined "hot-air engine" (the working fluid is air) the use of air poses a serious problem: a mixture in air pressure and liquid lubricants (oil derivatives) if enclosed inside the engine can produce explosive mixtures. The problem was solved preferring the use of reducing gases (hydrogen) or neutral (helium, nitrogen) as working fluids, safer but much less common and more expensive. It 'has also been suggested and implemented a reduced use of lubricants using high technology materials, but they are very expensive.
The design is complex and only partly related to certain parameters calculated, the movement of fluid and perfect without dead volumes is difficult to achieve (it is a reciprocating flow in a closed environment), each architecture optimizes engine some parameters and penalizes others.
Use modern [edit ]
The Stirling engine is not suitable for its size, its inertia and start the change of regime, other than for continuous delivery of energy and heat, is therefore suitable for transport.
The Stirling engine is suitable for home or small communities generating a fixed location (it is relatively big and heavy) for power ratings from 5 to 100 kW power (typically from household consumption to the family of a small building), outside values \u200b\u200bof these other types of generation are more convenient,
Otto (Petrol engines
)
Rankine cycle, and derivatives (steam turbines), Joule-Brayton cycle
(gas turbine) cycle and Diesel (diesel engine)
Given the adoption of advanced materials and construction techniques , and the miniaturization of parts with proven technologies, the gas turbine is a lethal competitor.
The convenience of the Stirling engine is mainly related to their ability, as well as the electricity generated on site using the heat "waste" (to use heating in value by about three times or four times the value of electric power) , and is favorable in the possibility of using fuels or sources heat available locally and not otherwise used (wood, coal, biogas, solar).
uses techniques of media power were obtained with production modules to keep up a long time the level of accumulation of electricity in Swedish military conventionally powered submarines. Heat production by combustion in a controlled environment (such as using submerged combustion
stocks of liquid oxygen) allows the continued supply of electricity for purposes of propulsion and other such as to extend the range of deep diving a few hours to several weeks. It is clear that the weight of the engine in this case is not a negative factor, the availability of water which refrigerant is obvious.
technologies for the developed world, for the third world, and high technology [edit ]
The heat source can be of any nature, which makes the Stirling engine used in a variety of contexts . While
are obvious advantages of the use in most developed countries, fuels from gasification technology (currently ages) and biogas, with chains of materials widely available (and currently often used) for the third world is extremely important however, also have only a small driving force (for threshing
, for pumping water, etc..) when the products that fuel the engine may be burning the same
husk of rice or other grain threshed, dried cattle dung, straw, peat, twigs, Segat of wood or wood chips. These fuels on the ground full untying technology from conventional fossil fuels.
The numbers of domestic and industrial heating appliances small. medium or large to produce
as waste heat, typically in the form of gas
combustion temperatures between 100 and 500 ° C. The energy in the form of heat contained in these gases can be partially recovered by
exchangers and generators Stirling. Stirling machines with more bulk, but cheaper technology, it is possible to evaluate the feasibility of energy recovery from manure even at lower temperatures.
E 'proposed application of the Stirling engine to generate electricity from nuclear heat
. The cooling of the reactor core of
is expected, some "chains
" nuclear, which is obtained by movement of sodium
liquid, which has a high caloric content
, but
radioactive by induction, and also arsonist, explosive and aggressive in case of accidental contact with air
Atmospheric (wet) or the 'water
. The intrinsic hazard has led to the abandonment of this sector, preferring to cool the core with radioactive water,
gas, or heavy water
. The adoption of the Stirling engine to dry air or gas in place of steam engines (steam turbines
), at least avoid the risk of accidental contact between the sodium and water in heat exchangers.
Use of high-acoustic Stirling engine technology have been developed by NASA
to provide electricity for satellites in deep space in the absence of solar radiation, in which case the heat source is the emission radioisotope thermal
, the cold spot is simply space. The real success of the great
Stirling cycle (reverse) occurs with the
chiller Stirling , which is the only machine really suitable for cooling fluids in the temperature ranging from -30, -40 ° C down to -200 ° C (73 K) because it uses the evaporation of fluids.
Stirling engine with gasifier [edit ]
The integration of the Stirling engine and the process of gasification
allows the use of biomass
as fuel for energy production
. The use of biomass
allows you to have a production cycle to no impact on CO 2
, (the carbon is released into the atmosphere that had been biologically incorporated, with water from the atmosphere, in which substances are burnt), this became very concerned because it is not introduced into the system new fossil carbon. The Stirling engine can become so technology should be exploited to facilitate the achievement of the objectives set by the Kyoto Protocol
. The organization of this type of system provides for the articulation of five main components:
- filing of the biomass gasifier
-
- boiler
- Stirling engine
- heat storage or accumulator
Through a system of augers
biomass (wood chips
woody) is brought to 'input
gasifier where
biomass is converted into syngas
that excerpt is taken from the combustion chamber
.
In the combustion chamber temperatures reach between 800 and 1250 ° C and the Stirling engine is in direct contact with the flame itself, going to be a single body among
boiler and engine Stirling.
The last element is the heat from the battery that lets you use the heat produced in the production cycle for the production of hot water and heating, thus maximizing the energy output. The maximum optimization is achieved by operating the plant only during periods when there is a demand for thermal energy. For small plants, it is possible to have an electrical capacity of 35 kW and 140 kW thermal power.
In 2008, the Province of Bologna
has created the first Italian project of this experimental type in the service of the school of the town of Castel d'Aiano
, which uses the
chips as fuel to start. The route taken involves the construction of other similar plants in the same.
The plant was built thanks to the center of the CISA, born in 2005 as a consortium between
Province of Bologna, Fondazione Cassa di Risparmio di Bologna and ISSI (Institute for Sustainable Development Italy), is proposed as a promoter of initiatives related dissemination of renewable energy and energy conservation with the ultimate goal of creating the sustainable energy of the Bologna District.
Operating configurations [edit ]
below represents the different configurations of the Stirling engine:
(α)
(β)
(γ)
Configuration Alfa [edit ]
The Stirling engine configuration in Alfa is perhaps more understandable in its operation, which can be considered based on 4 phases:
- push
- heating
- expansion
- cooling
In detail:
- pushes the piston down the ' air to the piston at the top, then move, letting the air;
- air warms, it expands , and then "return" back to the piston down, which then moves;
- moving the piston at the bottom does get warm air in contact with the heat sink, which then cools , and consequently shrinks, shifting to the right above the piston;
- the rightward shift of the piston top, helped by 'inertia accumulated fly, causes the pin, while continuing to spin, who will lower the lower piston, pushing again' s air towards the piston top, and the cycle begins again.
Configuration Beta [edit ]
There are different possibilities for the relative configuration between the engine piston and displacer. In the most simple-cycle operation can be summarized in steps as set out below (beta configuration). Consider a system more
cylinder piston. The cylinder head is connected to a room with a hot wall
while the cylinder body to a cold wall
.
The chamber is placed the
displacer, which consists of an insulating material, not required, can cover either the hot wall and cold wall.
cycle completed the engine is then as follows:
- displacer (a) covers the cold wall (s) of the chamber.
- The gas chamber, being heated, it expands.
- The piston (b) moves out of the room (in this case upwards) in his motion pushes the joint (c) that rotates and that in turn moves the displacer on the hot wall (d) heat insulation from the room starts to cool.
- gas contracts by invoking the piston.
- The piston moves inward (in this case down): As before, in his motion, move the displacer on the cold walls
Configuration Range [edit ]
The configuration range is substantially similar to the Beta, but with the option of not having coaxial pistons, but that can be run alongside or parallel (as described in scheme configurations) perpendicular, but trying to minimize the volumetric spaces "dead" in their place. The configuration range (without axes coaxial) simplifies the lubrication of the axles, and reduces leakage and friction losses of maintained, with a modest increase in dead space volume compared to Beta. The linkage represented by the Gamma (a pin hole on imboccolato) is not necessarily the optimal one, there is still the possibility of adopting rod system, or otherwise. All configurations described
always use a fly
positioned on the axis of rotation, which stores energy during active and passive ones in issue, that is where the engine does the work of passive fluid transfer. The flywheel allows the substantially uniform rotary motion.
pressurized system [ edit] The
adoption of engine under pressure (pressurized) expects a loss due to compression passive pumping of the fluid in the crankcase
, which must, if so, must be confined, that pumping, albeit limited, is minimized and even in strasformato functional through the adoption of multi-cylinder engines, with the cover in common.
References [edit ]
Other projects [edit ]
External links [edit ]
