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Lonnie JOHNSON
Thermo-Electric Generator
http://www.johnsonems.com/company.html
Until now, thermodynamic engines that use compressible working fluids have generally been mechanical devices. These devices have inherent difficulties in achieving high compression ratios and in achieving the near constant temperature compression and expansion processes needed to approximate Carnot equivalent cycles. Solid-state thermoelectric converters that utilize semiconductor materials have only been able to achieve single digit conversion efficiency. Extensive resources have been applied toward Alkali Metal Thermoelectric Converters (AMTEC), which operate on a modified Rankine cycle and on the Stirling engine. However, because of inherent limitations, these systems have not achieved envisioned performance levels.
The JTEC is an all solid-state engine that operates on the Ericsson cycle. Equivalent to Carnot, the Ericsson cycle offers the maximum theoretical efficiency available from an engine operating between two temperatures. The JTEC system utilizes the electro-chemical potential of hydrogen pressure applied across a proton conductive membrane (PCM). The membrane and a pair of electrodes form a Membrane Electrode Assembly (MEA) similar to those used in fuel cells. On the high-pressure side of the MEA, hydrogen gas is oxidized resulting in the creation of protons and electrons. The pressure differential forces protons through the membrane causing the electrodes to conduct electrons through an external load. On the low-pressure side, the protons are reduced with the electrons to reform hydrogen gas. This process can also operate in reverse. If current is passed through the MEA a low-pressure gas can be "pumped" to a higher pressure.
The JTEC uses two membrane electrode assembly (MEA) stacks. One stack is coupled to a high temperature heat source and the other to a low temperature heat sink. Hydrogen circulates within the engine between the two MEA stacks via a counter flow regenerative heat exchanger. The engine does not require oxygen or a continuous fuel supply, only heat. Like a gas turbine engine, the low temperature MEA stack is the compressor stage and the high temperature MEA is the power stage. The MEA stacks will be designed for sufficient heat transfer with the heat source and sink to allow near constant temperature expansion and compression processes. This feature coupled with the use of a regenerative counter flow heat exchanger will allow the engine to approximate the Ericsson cycle.
The engine is scaleable and has applications ranging from supplying power for Micro Electro Mechanical Systems (MEMS) to power for large-scale applications such as fixed power plants. The technology is applicable to skid mounted, field generators, land vehicles, air vehicles and spacecraft. The JTEC could utilize heat from fuel combustion, solar, low grade industrial waste heat or waste heat from other power generation systems including fuel cells, internal combustion engines and combustion turbines. As a heat pump, the JTEC system could be used as a drop in replacement for existing HVAC equipment in residential, commercial, or industrial settings.
http://www.physorg.com/news119107136.html
Nuclear Engineer Lonnie Johnson, best known for his invention of the super soaker squirt gun, has recently designed a new type of solar energy technology that he says can achieve a conversion efficiency rate of more than 60 percent. Considering that the best solar energy systems today have an efficiency of 30-40 percent, Johnson´s method could cut the cost of solar energy nearly in half.
A recent article in Popular Mechanics describes how Johnson´s system would work. Rather than use photovoltaic cells, where silicon converts light into electricity, the new system works like a heat engine. But instead of using heat to turn an axle, it uses heat to force hydrogen ions through a membrane-electrode, and create electricity.
The system, called the Johnson Thermoelectric Energy Converting System (JTEC) consists of two stacks of electrodes --- a high-temperature stack heated by the sun (and by concentrated mirrors) and a low-temperature stack.
An electrical jolt triggers a voltage across the electrode stacks, with the low-temperature stack pumping out hydrogen from low to high pressure in order to maintain the pressure differential. As the hydrogen passes through the high-temperature stack of electrodes, it generates power. In a sense, the system works similar to a fuel cell.
Johnson plans to build a system whose high temperature reaches 600 degrees centrigrade, within the current solar concentration ability of parabolic mirrors, which can produce temperatures of more than 800 degrees centigrade. At 600 degrees, the system would have an efficiency of close to 60 percent. At higher temperatures, the efficiency would increase even more.
The system should be able to produce several megawatts of power, according to Johnson. It could also harvest waste heat from internal combustion engines, turbines, and even the human body.
Johnson, a former NASA employee, funds his work with the millions of dollars he made from inventing the super soaker.
http://www.popularmechanics.com/science/earth/4243793.html
Popular Mechanics ( Jan. 8, 2008)
Super Soaker Inventor Aims to Cut Solar Costs in Half
by
Logan Ward
Solar energy technology is enjoying its day in the sun with the advent of innovations from flexible photovoltaic (PV) materials to thermal power plants that concentrate the sun’s heat to drive turbines. But even the best system converts only about 30 percent of received solar energy into electricity—making solar more expensive than burning coal or oil. That will change if Lonnie Johnson’s invention works. The Atlanta-based independent inventor of the Super Soaker squirt gun (a true technological milestone) says he can achieve a conversion efficiency rate that tops 60 percent with a new solid-state heat engine. It represents a breakthrough new way to turn heat into power.
Johnson, a nuclear engineer who holds more than 100 patents, calls his invention the Johnson Thermoelectric Energy Conversion System, or JTEC for short. This is not PV technology, in which semiconducting silicon converts light into electricity. And unlike a Stirling engine, in which pistons are powered by the expansion and compression of a contained gas, there are no moving parts in the JTEC. It’s sort of like a fuel cell: JTEC circulates hydrogen between two membrane-electrode assemblies (MEA). Unlike a fuel cell, however, JTEC is a closed system. No external hydrogen source. No oxygen input. No wastewater output. Other than a jolt of electricity that acts like the ignition spark in an internal-combustion engine, the only input is heat.
Here’s how it works: One MEA stack is coupled to a high- temperature heat source (such as solar heat concentrated by mirrors), and the other to a low-temperature heat sink (ambient air). The low-temperature stack acts as the compressor stage while the high-temperature stack functions as the power stage. Once the cycle is started by the electrical jolt, the resulting pressure differential produces voltage across each of the MEA stacks. The higher voltage at the high-temperature stack forces the low-temperature stack to pump hydrogen from low pressure to high pressure, maintaining the pressure differential. Meanwhile hydrogen passing through the high-temperature stack generates power.
“It’s like a conventional heat engine,” explains Paul Werbos, program director at the National Science Foundation, which has provided funding for JTEC. “It still uses temperature differences to create pressure gradients. Only instead of using those pressure gradients to move an axle or wheel, he’s using them to force ions through a membrane. It’s a totally new way of generating electricity from heat.”
The bigger the temperature differential, the higher the efficiency. With the help of Heshmat Aglan, a professor of mechanical engineering at Alabama’s Tuskegee University, Johnson hopes to have a low-temperature prototype (200-degree centigrade) completed within a year’s time. The pair is experimenting with high-temperature membranes made of a novel ceramic material of micron-scale thickness. Johnson envisions a first-generation system capable of handling temperatures up to 600 degrees. (Currently, solar concentration using parabolic mirrors tops 800 degrees centigrade.) Based on the theoretical Carnot thermodynamic cycle, at 600 degrees efficiency rates approach 60 percent, twice those of today’s solar Stirling engines.
This engine, Johnson says, can operate on tiny scales, or generate megawatts of power. If it proves feasible, drastically reducing the cost of solar power would only be a start. JTEC could potentially harvest waste heat from internal combustion engines and combustion turbines, perhaps even the human body. And no moving parts means no friction and fewer mechanical failures.
As an engineer, Johnson says he has always been interested in energy conversion. In fact, it was while working on an idea for an environmentally friendly heat pump (one that would not require Freon) that he came up with the Super Soaker, which earned him millions of dollars in royalties. That money allowed Johnson to quit NASA’s Jet Propulsion Lab (where he worked on the Galileo Mission, among other projects) and go independent. His toy profits have funded his research in advanced battery technology, specifically thin-film lithium-ion conductive membranes. And that work sparked the idea for JTEC. Besides, he jokes, “All inventors have to have an engine. It’s like a rite of passage.”
National Science Foundation
http://www.nsf.gov/awardsearch/showAward.do?AwardNumber=0646367
Award Number: 0646367
Johnson ThermoElectrochemical Converter (JTEC) Solar Powered Cell Tower Generator
ABSTRACT --- JTEC SOLAR POWERED CELL TOWER GENERATOR
This project will attempt to resolve the key technical issues and uncertainties
regarding a breakthrough concept for low-cost high-efficiency solar power.
The proposed approach is based on a conceptual system for providing independent
power for cell towers that will allow them to function even after emergencies
like hurricane Katrina. The solar engine is based on the Johnson
ThermoElectrochemical Converter (JTEC) concept for converting heat
to electricity invented by (Lonnie) Johnson, who will be available to assist
Tuskegee University in carrying out this work. Except for the working fluid,
JTEC is an all solid state engine that does not have mechanical moving
parts. Different from conventional solid state thermoelectric devices,
it does not have inherent parasitic heat loss paths. JTEC uses Membrane
Electrode Assemblies (MEA) similar to those used in fuel cells; however,
it does not require oxygen or a special fuel, only heat. The availability
of a range of proton conductive membrane materials that operate from room
temperature up to and exceeding 1200 C suggests that JTEC could generate
electricity from practically any heat source, from very small, just a few
degrees, to very large temperature differences. JTEC approximates the Ericsson
thermodynamic cycle which is Carnot equivalent. Research on this technology
offers the potential for achieving solar power efficiency of 50% in the
short-term and 80% in the long-term, far beyond what is expected from photovoltaics
both in efficiency and in cost.
(1) Intellectual merit of the proposed activity
JTEC is a fundamentally new solid state engine concept. Critical research is needed to enable a credible analysis of its potential. Research is needed into the properties of proton conductive materials needed to make a working system. The materials are similar those being studied in fuel cell research, but new material properties must be investigated in order to optimize the choices for this application. Research is needed to model, simulate and optimize an integrated systems design for cost-effective recharge power for cell towers.
(2) Broader impacts resulting from the proposed activity:
Cell towers running out of battery power were a crucial problem in the wake of Katrina and resulted unnecessary deaths and destruction. This project, with follow-on research, could provide un-interruptible, cost effective power for communications in areas threatened by hurricanes and other disasters that is not limited by battery life. The proposed engine technology will have major impacts on the international energy economy particularly with respect to the need for economical, green, renewable energy. This research is consistent with NSF goals for minority education and outreach. Tuskegee University is a HBCU institution and Johnson Research is a minority owned small business.
US Patent # 4,368,416
Thermionic-Thermoelectric Generator System and Apparatus
( 1983-01-11 )
Jasper L. JAMES ( deceased January 11, 1983 )
Abstract --- Apparatus is disclosed including a compact thermionic generator formed with an outer cathode cylinder and an axially concentric inner anode cylinder. The cylinders are sealed and evacuated and provided with external electrical connections leading to the cathode and anode cylinders. A thermoelectric generator formed of a folded length of thermocouples is nested within the anode cylinder with respective ends thermically and electrically coupled to the cathode and anode cylinders. Sufficient heat applied to the outer cylinder causes the thermionic emission from the cathode to anode cylinders to be enhanced by the positive potential applied to the anode cylinder from the internal thermoelectric generator which is also responsive to the applied heat to generate the positive potential relative to the potential of the cathode cylinder. A generator system is also disclosed in which a pair of these generators is interconnected by a solid state switching circuit to an output load via intermediate charging capacitors.
Current U.S. Class: 322/2R ; 136/205; 310/306
Current International Class: H02N 3/00 (20060101); H01J 45/00
(20060101); H02N 003/00 ()
Field of Search: 310/306 136/200,202,204,220,205 322/2
References Cited [Referenced By]
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Description
BACKGROUND OF INVENTION
This invention relates to a combination thermionic-thermoelectric generator and more particularly to an apparatus and system which provides improved performance over prior known apparatus of this general type.
Thermionic and thermoelectric generators are well known in the art to be capable of generating electric currents by the application of heat to the devices. In the case of thermionic generators, current is created by the emission of electrons from a surface which has been heated sufficiently to allow the electron energy to overcome the potential barrier energy level of the surface. The basic theory of thermionic energy conversion is discussed in U.S. Pat. No. 2,980,819--Feaster issued Apr. 18, 1961. One difficulty known to exist with converters of this type is the relatively low usuable potential that can be developed unless a relatively large number of converters are cascaded in series with consequent increase in bulk and cost. Also, converters that give usuable current levels generally require extremely close interelectrode spacing between the emitters and collector electrodes, generally on the order of one millimeter. The difficulty in achieving and maintaining such close spacing, particularly at the high temperatures, e.g. 1200.degree. C. required to have usable electron emission, has limited the commercial usefulness of thermionic converters to highly specialized applications.
Thermoelectric converters, comprising a series of thermocouples, are also well known. In this device a current is generated by electron flow at the interface between the abutting surfaces of dissimilar materials maintained at different temperatures. By cascading a large number of these thermocouples, a thermopile can be produced which generates usable potential levels limited, in general, only by the practical length of the thermopile.
In the past, a number of combined thermionic and thermoelectric generators have been proposed in which the two types of devices are packaged together and electrically connected at a common therminal so that the heat applied to the package causes both generators to develop current outputs, usually at separate output terminals. Examples of such devices are shown and described in U.S. Pat. Nos. 3,189,765 and 3,430,079 issued June 15, 1965, and Feb. 25, 1969, respectively.
Despite the prior art which exists in this technology, it is believed that heretofore there has not existed a small, compack thermionic-thermoelectric generator apparatus capable of producing usable levels of current at usable potential levels. It is an object of this invention to provide a system embodying the improved apparatus with suitable switching circuits to furnish electrical current at usable potential levels to a load impedance.
SUMMARY OF THE INVENTION
Thus in accordance with one aspect of the invention, there is provided thermionic-thermoelectric generator apparatus comprising a first elongated metallic cylindrical electrode having its internal surface coated with a thermionic electron emmissive material and a second elongated metallic cylindrical electrode nested coaxially within the first cylinder electrode, this second cylinder having at least the outer surface thereof coated with graphite to serve as a collector electrode for the electrons emitted from the first cylinder surface. Preferably the interelectrode spacing between the two cylinders is substantially uniform along the axial length thereof. The apparatus is further provided with a plurality ofthermopiles nested within the second cylinder, the thermopiles being electrically connected in series with one end consisting of electron donor material electrically coupled to the first cylinder, the other end consisting of electron acceptor material being electrically coupled to the second or inner cylinder. Means, such as sealable vacuum fittings are provided by which the outer cylinder may be evacuated and the vacuum maintained in the interelectrode space between the two cylinders. Means are also provided , such as at the end of the cylinders opposite the vacuum fitting, to provide external electrical connections from the cylinder electrodes to a load circuit.
In the system of the invention, there is also included, with a pair of generators such as just described, circuit means for coupling in repetitive alternating sequence, each of the generators to output load terminals to provide a continuous electrical current flow to a load impedance connected to the load terminals.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general perspective view of the generator apparatus of the present invention.
FIG. 2 is a side view in partial section showing the details of the apparatus of the invention.
FIG. 3 is a perspective view showing the thermopile construction used in the FIG. 2 apparatus.
FIG. 4 is an exploded perspective view of the interior cylinder and thermopile support of the FIG. 2 apparatus.
FIG. 5 is a cross-sectional side view showing details of the connection terminals for the FIG. 1 apparatus.
FIG. 6 is a schematic circuit diagram illustrating a timing and current switching circuit useful in one form of the present invention.
DETAILED DESCRIPTION
Referring jointly to FIGS. 1-5,the thermionic-thermoelectric generator apparatus 10 includes a first or outer cylinder 11, preferably of stainless steel, enclosed at one end by an end cap 12 and suitable vacuum fittings 13 and at the other end by an end cap 14 having an elongated output terminal electrode 15 sealed at the distal end by a ceramic seal and the extension 17a of interior terminal electrode 17. As best seen in FIG. 2, the generator apparatus comprises first outer cylinder 11 in which is nested, in coaxial manner, a second or inner cylinder 20, preferably also of stainless steel. As seen in the drawings, the righthand end of cylinder 20 is supported by four L-shaped aluminum oxide mounts 21 attached to stainless steel blocks 22 which in turn are secured in suitable manner to the interior face of end cap 12. The interior surface 11a of the outer cylinder 11 is coated in well known manner with a suitable thermionic electron emissive material such as a mixture of barium oxide, strontium oxide and calcium oxide, mixed in the ratio of 1:1:1 by weight. The outer surface 20a of inner cylinder 20 is coated in known manner with graphite to serve as a collector of electrons emitted from outer cylinder surface 11a.
Nested within inner cylinder 20 is a thermopile assembly best seen in FIGS. 3 and 4 and comprised of a plurality, in this case four, thermopile sections 30a, 30b, 30c, 30d, each of which consists of approximately 380 thermocouples formed of thin wafers of carbon and silicon carbide in alternating sequence. The sections are electrically connected in series by tungsten connectors 31. One end 32 of the thermopile series, formed of a wafer of the electron donor material silicon carbide is adhered to a stainless steel block 33. The other end 34 of the thermopile series formed of a wafer of electron acceptor material carbon is attached to a stainless steel block 35 to which is attached an electode rod 36 of stainless steel. The thermopile sections 30a-30d are positioned snugly within recesses of a ceramic extruded cruciform shaped insulator support 37 (best seen in FIG. 4) and thereafter the tungsten connectors 31 are attached. Ceramic end caps 38 and 39 are positioned at the ends of the cruciform thermocouple assembly and the entire assembly is then placed inside a ceramic housing 40 which is closed at one end 41. The housing 40 is then placed inside inner cylinder 20. Preferably, the cross-sectional diagonal dimension of housing 40 is the same as the inner diameter of cylinder 20 so that the housing is properly supported and held in place within cylinder 20. A stainless steel end cap 45 is placed over the end of housing 40 so as to touch thermopile terminal block 33 and secured to the end of inner cylinder 20 to provide electrical coupling between the end of the thermopile and cylinder 20. Electrode rod 36, extends through an opening 46 suitably provided in end cap 45 and touches end cap 14 of outer cylinder 11 so as to provide electrical electrical coupling from the other end of the thermopile 30 to the outer cylinder 11 which comprises the cathode of the generator.
An elongated electrically conductive stainless steel rod 17 extends axially outward from inner cylinder end cap 45 and serves as the positive connection for the generator. Rod 17 extends concentrically through an outer tube 15 and secured by a suitable collar fitting to extension rod 17a which projects through ceramic seal fitting 16. Rod 17a ends in a terminal connector 17b which serves as the positive terminal of the generator 10 while tube 15 ends with an electrical connector 15a which serves as the negative terminal of the generator 10.
In an actually constructed and operated device, the length of cylinder 11 is 22 inches long and 4 inches in outer diameter. The inner cylinder 20 is 16 inches in length and 3 inches in diameter. Both cylinders are made of stainless steel, the inner cylinder 20 being 16 gauge while outer cylinder 11 is 0.237 inches thick. The thermopile consists of 380 junctions of silicon carbide and carbon. Any suitable heat source capable of heating the generator to temperatures of 400.degree.-450.degree. C. may be used to operate the generator.
Referring now to FIG. 6, a suitable switching and control circuit is shown for use in a system of the invention utilizing a pair of the thermionic-thermoelectric generators 10 and 10' as described above. Thus, the circuit of FIG. 6 includes a timer circuit 60 of the well known 555 integrated circuit type operated in the astable mode at a frequency of, for example, 400 Hz., as determined principally by the value of resistors 61-64 and the value of capacitor 65. The output of timer 60 is coupled by line 60a to the input of J-K flip-flop 68 to cause the output states on line 68a and 68b to reverse at the aforementioned 400 Hz. rate. A pair of Darlington connected transistors 70 and 80 are alternately biased into conduction by flip-flop 68 causing SCR 79 and 89, respectively, to be triggered into conduction. When, for example, SCR 89 is conducting, the current output of generator 10 is coupled to charging capacitor 96. At this time, SCR 79 is off and charging capacitor 94 is isolated from generator 10'.
The circuit further includes transistors 75 and 85, the outputs of which are cross-coupled to opposite branches of the balanced switching circuit including SCR 79 and current transistor 90 in one branch and SCR 89 and current transistor 92 in the other branch. In this manner, when Darlington transistor 80 has triggered SCR 89 into conduction to couple generator 10 to charging capacitor 96, the output of transistor 85 causes transistor 90 to conduct resulting in coupling of current from previously charged capacitor 94 to output terminals 87, 98 and through load 100. When flip-flop 68 switches state, the sequence is reversed and generator 10' is coupled to charging capacitor 94 through SCR 79 and transistor 92 is pulled into conduction to couple charging capacitor 96 to output terminals 97, 98 and load 100.
By way of example and without limitation thereto, the following circuit values were used in an actually constructed embodiment of the invention, viz:
______________________________________ Resistors 78, 88 100 Ohms, 1 W. Resistors 77, 87 27 Ohms, 1 W. Resistors 74, 84 470 Ohms Resistors 73, 83 39K Ohms Resistors 72, 82 8K Ohms Resistors 71, 81 1 Megohm Resistors 61, 63 1 Megohm Resistors 62, 64 10K Ohms Capacitors 94, 96 GE Dielektrol, 25KVAR 240 g Capacitor 67 .01 mf Capacitor 65 1.0 mf Transistors 90, 92 GE ZJ-499 Transistors 75, 85 GED40D8 Darlington Transistors 70, 80 ECG 268 Diodes 69a, b, c and d 1R5333A Diodes 101a, b, c and d 1R350 Diode 102 1N914 Zener Diodes 76, 86 2.5v, 1W - ECG 5062A SCR 79, 89 GE C230C Flip-flop 68 4027 Cos/Mos - Dual J-K (Radio Shack) Timer 60 555 (Radio Shack) V.sub.bb.sup.66 12 v. ______________________________________
With generator apparatus 10 as described, it will be appreciated that the generator system of the invention is compact and efficient in operation. Using the thermopile nested within the inner cylinder 20 to operate from the same heat source as used for the thermionic converter stage to apply a positive potential to the collector cylinder 20 allows greater interelectrode spacing to be used between cylinders 11 and 20 and provides high currents at usable potential levels. For example, with the generator system as described, currents of 200 amps at 108 volts are possible when the generators are heated only to 400.degree.-450.degree. C., assuming 380 thermocouple junctions in each of the thermopile sections 30a-30d. Since the system is compact, portable and requires low temperatures available from conventional heat sources to operate, it can be installed for use in, for example, electrically powered vehicles without the limitations associated with electric storage batteries. It can also readily be used as a source of electric power for residential purposes of as a back-up power source for emergency facilities such as hospitals.
While there has been described what at present is believed to be one preferred embodiment of the invention, it will be appreciated that modifications therein can be made by those skilled in the art without departing from the spirit of the invention and it is intended that all such modifications are to be covered as are within the scope of the appended claims.
Wikipedia, the free encyclopedia
Ericsson Cycle
The Ericsson Cycle is named after inventor John Ericsson. John Ericsson
designed and built many unique heat engines based on various thermodynamic
cycles. He is credited with inventing two unique heat engine cycles
and developing practical engines based on these cycles. His first cycle
is very similar to what we now call the "Brayton Cycle" except that it
was external combustion. His second cycle we now call the "Ericsson Cycle".
Ideal Ericsson Cycle
The following is a list of the four processes that occur between the four stages of the ideal Ericsson cycle:
Process 1 -> 2: Isothermal Compression. The compression space is assumed to be intercooled, so the gas undergoes isothermal compression. The compressed air flows into a storage tank at constant pressure. In the ideal cycle, there is no heat transfer across the tank walls.
Process 2 -> 3: Isobaric Heat-addition. From the tank, the compressed
air flows through the regenerator and picks-up heat at a high constant-pressure
on the way to the heated power-cylinder.
Process 3 -> 4: Isothermal Expansion. The power-cylinder expansion-space is heated externally, and the gas undergoes isothermal expansion.
Process 4 -> 1: Isobaric Heat removal. Before the air is released as exhaust, it is passed back through the regenerator, thus cooling the gas at a low constant pressure, and heating the regenerator for the next cycle.
Comparison with Stirling, Carnot and Brayton cycles
The Ericsson Cycle is often compared to the Stirling cycle, since the
engine designs based on these respective cycles are both external combustion
engines with regenerators. The Ericsson is perhaps most similar to
the so called "double-acting" type of Stirling engine, in which the displacer
piston also acts as the power piston. Theoretically, both of these cycles
have so called "ideal" efficiency, which is the highest allowed by the
Second law of thermodynamics. The most well known ideal cycle is the Carnot
cycle, although ironically, a real Carnot Engine is not known to have been
invented.
Comparison with the Brayton Cycle
The first cycle Ericsson developed, is now called the "Brayton Cycle", commonly applied to the rotary jet engines for airplanes.
The second Ericsson cycle is the cycle most commonly referred to as simply the "Ericsson cycle". The (second) Ericsson cycle is also the limit of ideal gas-turbine Brayton cycle, operating with multistage intercooled compression, and multistage expansion with reheat and regeneration. Compared to the Brayton cycle which uses adiabatic compression and expansion, the second Ericsson cycle uses isothermal compression and expansion, thus producing more net work per stroke. Also the use of regeneration in the Ericsson cycle increases efficiency by reducing the required heat input. For further comparisons of thermodynamic cycles, see Heat engine.
Ericsson Engine
The Ericsson engine, (see figure), is based on the Ericsson cycle, and is known as an "external combustion engine", because it is externally heated. To improve efficiency, the engine has a regenerator or recuperator between the compressor and the expander. The engine can be run open-cycle or closed-cycle. Expansion occurs simultaneously with compression, on opposite sides of the piston.
The Regenerator
Ericsson coined the term "regenerator" for his independent invention of the mixed-flow counter-current heat-exchanger. However, Rev. Robert Stirling had invented the same device, prior to Ericsson, so the invention is credited to Stirling. Stirling called it an "economiser" or "economizer", because it increased the fuel economy of various types of heat processes. The invention was found to be useful, in many other devices and systems, where it became more widely used, since other types of engines became favored over the Stirling engine. Interestingly, the term "regenerator" is now the name given to the component in the Stirling Engine!
The term "recuperator" refers to a separated-flow, counter-current heat exchanger. As if this weren't confusing enough, a mixed-flow regenerator is sometimes used as a quasi-separated-flow recuperator. This can be done through the use of moving valves, or by a rotating regenerator with fixed baffles, or by the use of other moving parts. When heat is recovered from exhaust gases and used to preheat combustion air, typically the term recuperator is used, because the two flows are separate.
History
In 1791, before Ericsson, Barber proposed a similar engine. The Barber engine used a bellows compressor and a turbine expander, but it lacked a regenerator/recuperator. There are no records of a working Barber engine. Ericsson invented and patented his first engine using an external version of the Brayton Cycle in 1833 (number 6409/1833 British). This was 18 years before Joule and 43 years before Brayton. Brayton engines were all piston engines and for the most part, internal combustion versions of the un-recuperated Ericsson engine. The "Brayton Cycle" is now known as the gas turbine cycle, which differs from the original "Brayton Cycle" in the use of a turbine compressor and expander. The gas turbine cycle is used for all modern gas turbine and turbojet engines, however simple cycle turbines are often recuperated to improve efficiency and these recuperated turbines more closely resemble Ericsson's work.
Ericsson eventually abandoned the open cycle in favor of the traditional closed Stirling cycle.
The Ericsson Cycle Engine (The second of the two discussed here) was used to power a 2000 ton ship, The Caloric Ship Ericsson and the engine ran flawlessly for 73 hours. The combination engine produced about 300 horsepower. It had a combination of 4 dual-piston engines; the larger expansion piston/cylinder, at 4.267 meters or 14 feet in diameter, was perhaps the largest piston ever built. Rumor has it that tables were placed on top of those pistons and dinner was served and eaten, while the engine was running at full power. At 6.5 RPM the pressure was limited to 8 psi. The one sea trial proved that even though the engine ran well it was underpowered. ometime after the trials the Ericsson sank. When it was raised the Ericsson cycle engine was removed and a steam engine took its place.
Ericsson designed and built a very great number of engines running on various cycles including steam, Stirling, Brayton, externally heated diesel air fluid cycle. He ran his engines on a great variety of fuels including coal and solar heat.
Ericsson also was the inventor of the screw propeller for ship propulsion, in the USS Princeton.