Patent Application
20240271588
A device for converting heat energy into electrical or mechanical energy. The invention relates to Stirling engines and particularly, but not exclusively, to Stirling engines in which each cylinder is an expansion cylinder or a compression cylinder, such that each cylinder is entirely “hot” or entirely “cold”. Other aspects of the invention will be apparent from a reading of the specification.
Global warming, shrinking fossil fuel resources and increasing energy demand make it essential to improve the efficiency of existing power consuming processes and to access new sources of energy that have not, until recently, been economically or practically available.
Biomass, geothermal energy and waste heat from industrial, commercial and other low temperature heat sources are widely available for exploitation as sources of useful energy, but their potential has been largely neglected, partly due to the relative cheapness of fossil fuels and because the reduction of CO2 emissions has not been considered an important political and environmental issue until relatively recently.
Also, many waste industrial and geothermal energy sources provide heat at relatively low temperatures, in the range from 100 to 200° C. and it is difficult to extract useful work at these low thermal values. The lower the temperature, the more economically challenging the process of energy conversion becomes as the equipment tends to become increasingly expensive relative to the energy available for conversion, until the point where the construction of heat energy conversion plant is economically impractical.
Nevertheless, many industrial processes are extremely energy consuming and generate large quantities of waste heat. Temperatures vary with the process and industry, but as with geothermal energy, the lower the temperature, the more waste heat resource is available for conversion to electrical or mechanical energy, though at a lower quality.
Previously, for heat sources below 200° C., Organic Rankine binary cycle plants have been employed. These plants generally use a working fluid, such as pentane, which changes phase from liquid to gas at a relatively low temperature, in order to drive a turbine. However, the plants tend to be volumetrically large, and contain expensive and complex machinery and so may be difficult to install and retrofit, and may require regular and expensive maintenance cycles. Generally, binary cycles using a turbine system are not considered to be economic for smaller scale power generation.
Stirling engines, which are a type of heat engine powered by an external heat source, are in principle particularly suitable devices for the conversion of heat into energy. The thermodynamic cycle is simple and they are highly robust, quiet, and reliable, and take up less space than the Organic Rankine Cycle. However, they are at present relatively inefficient when operating with a low temperature heat source.
A Stirling engine extracts power by utilising the cycle of a fixed mass of gas, known as the working fluid, using the temperature difference between the hot end and cold ends of the device. The gas is alternately heated and expanded, and then cooled and compressed, and the cyclically varying volume of the gas generates a pressure wave which acts on a power piston and converts thermal energy into mechanical energy. The higher the temperature difference between the hot source and cold heat sink, the higher will be the theoretical thermal efficiency of a Stirling device.
A displacer piston moves the working gas back and forth between the warm expansion and the cold compression spaces while passing hot and cold heat exchangers, which may be external or internal to the device, and are typically located on either side of a regenerator. As the working fluid moves through the regenerator between the hot and the cold side, its heat is transferred into the regenerator's matrix. The heat is reabsorbed by the gas on the return cycle, and so a high temperature gradient is maintained. The working fluid or gas is most commonly air, hydrogen or helium. In normal operation, the engine is sealed and no gas enters or leaves the engine. No valves are required, unlike other types of piston engines. The heat exchangers may be in the form of tubes, fins or plates which are in contact with a heat source which may be, for instance, a fuel burner, geothermal brine or hot gas. Similarly, the cold heat exchanger is in thermal contact with an external heat sink which may be air at ambient temperature. The lack of development of heat engines for lower temperature operation is partly a consequence of the limiting factor of the relatively low temperature differential between the hot and cold sides of the system. However, within these constraints, economic efficiencies can be made by reducing maintenance and lowering the costs of fabrication and materials, and operational and mechanical efficiencies can be achieved through reducing friction and improving heat exchange.
Three different basic types of Stirling Engine can be distinguished as follows:
Alpha engines: the enclosed gas volume is expanded and compressed between two pistons in two separate chambers and generates an oscillatory pressure waveform inside the engine. Coupling to the pressure waveform, the pistons move and so extract the mechanical work that is produced by the thermodynamic cycle of the Stirling engine. Each piston is typically connected to a crankshaft or other kinematic device in order that the correct phase delay between pistons may be maintained and that overall momentum of the system may be sustained.
Beta engines: a displacer piston, typically connected to a flywheel or similar arrangement, shuttles the working gas between hot and cold areas of a cylinder as above. A power piston within the same cylinder, connected to the same kinematic arrangement, compresses and expands the fluid.
Gamma engines: these are similar to beta engines, but piston and displacer are not located in the same cylinder.
Free piston engines may theoretically be incorporated into any of the above configurations. The free-piston Stirling engine is a comparatively recent type of heat engine, developed in the 1960s by Prof. William T. Beale at Ohio University. It has mainly been deployed within beta configuration engines and comprises a displacer and a power piston which are unconnected, and which oscillate freely within a single common cylinder. The oscillations between the displacer and the power piston may be supported by physical springs, by the use of elastomeric materials, or by the compressibility of the working gas. The springs or elastomeric materials or other similar element, provide the forces necessary to maintain the harmonic oscillations of the displacer piston relative to the power piston. The absence of a crank mechanism significantly reduces the number of moving parts and the complexity of the engine and thus reduces frictional losses. In particular, the absence of a crankshaft eliminates losses from crankshaft bearings and piston rod seals, and the linear motion leads to very low side loads on the piston, which also reduces the need for cylinder lubrication. The displacer characteristically has a very small mass compared to the power piston, and its oscillation is damped by the gas flowing through the regenerator. The heavier power piston oscillates undamped, except for the forces from the electromagnetic field of an alternator or other arrangement which may act as the power take off.
Free Piston engine systems have previously been found to be most useful for applications where a high temperature difference is available, and where high reliability with low or zero maintenance is required, such as solar dish arrays, or for space exploration, where a radioactive heat source may be deployed to power the device.
Stirling Engines may also be described in terms of Single or Multiple Systems. A single acting Stirling system comprises one or two cylinders and is the arrangement used almost invariably for small low power units, say up to 10 KW capacity and includes the alpha, beta and gamma arrangements as outlined above, including free piston Stirling engine embodiments.
In a single acting system, the there is only one continuous volume or thermodynamic system of working fluid. Single acting systems may however be connected by linkages to provide multiple systems as outlined below. Typical alpha type free piston Stirling engines are considered to be single acting systems.
Double acting systems are generally alpha Stirling engine arrangements of at least two cylinders, in which at least one cylinder is equipped with a common double acting piston serving two separate Stirling systems, such that two separate volumes of working fluid are employed on each side of the common piston. Examples of this arrangement include the Franchot arrangement of
A major advantage of double acting arrangements is that the number of reciprocating parts per Stirling system is effectively half the number necessary in single acting systems. The configuration also eliminates the need for a rebound device, as the working piston provides the work to drive the compression process in the other cylinder. This allows a simple and more compact device with a higher power density ratio than single acting engines.
A multiphase Stirling engine arrangement incorporates at least three double acting systems and therefore at least three pistons. In a typical multiphase Stirling arrangement, an alpha-type Stirling engine is connected to its adjacent two engines via its two pistons. The hot side of each cylinder is connected via a regenerator to the cold side of the adjoining cylinder so that, as with a typical double acting system, the working fluid in each engine of a multiphase system is contained between two pistons in two separate cylinders. Each piston is therefore linked to its adjacent two pistons via the pressure waveform of the working fluids. Each piston within each cylinder is typically connected via a piston rod to a crankshaft piston or wobble plate piston rod so that the correct phase angle or delay between pistons may be maintained.
The Dutch electronics company, Philips, produced the first double acting twin and multiphase cylinder devices in the 1940s, originally as part of a research effort to provide a cheap and portable electrical generator to power radios in remote and underdeveloped regions. These were based upon designs by Siemens in the 19th Century and Rinia the mid-20th Century and are generally referred to as Siemens/Rinia double acting multiphase arrangements. Research and production ceased in the 1950s when the devices proved to be uneconomic. However, variations on these original multiphase designs were later taken up by companies such as Whispergen, which utilises a wobble yoke mechanism connected to four pistons within a double acting alpha type cylinder arrangement.
Free piston versions of multiphase arrangements have also been proposed, but have not, as yet, been successfully commercialized.
Drawbacks of current systems include the following issues. As outlined above, for low temperature heat energy conversion devices the power available for use is limited by the temperature of the thermal resource, and therefore the mechanical efficiencies need to be high in order for a device to be economically viable. Friction and wear reduce efficiencies significantly. In particular, the need to maintain effective piston and displacer seals against leakage of working fluid may result in unacceptably high frictional losses. Kinematic connections between pistons, including piston rod seals and crankshaft bearings, may also increase such inefficiencies, may be expensive to fabricate and maintain, and may lead to losses of working fluid from within pressurised systems.
Additionally, for the efficient operation of a heat engine there needs to an effective thermal separation between the hot and cold parts, or ends, of the device or system. If the expansion and compression spaces are contained within the same cylinder then there may be high thermal conduction losses from the hot to the cold sides via the cylinder walls, and also through the piston. This is typically addressed by designing pistons and the cylinders which are long relative to the bore dimeter in order to provide a greater spatial and so thermal separation between each end of a cylinder, while reducing the length of the thermal path. The insertion of thermal breaks within the pistons and cylinder walls is also required. These solutions are generally expensive and may generate system inefficiencies. The issue is even more problematic in lower temperature Stirling devices, as a maximal area of heat exchange is required, which will preferably include the hot side cylinder walls and which may result in the need for further hardware and components in order to effectively separate the heat source from the heat sink within the same cylinder.
Heat exchangers are typically the most expensive and the most critical components of any heat energy conversion device. The cost of fabricating, installing and maintaining complex heat exchanger assemblies has generally resulted in devices failing to succeed in the market place. Additionally, the characteristics and configurations of heat exchanger assemblies tend to be specific to each heat energy conversion device, and depending on the design of the arrangement, the layout and configuration of the pistons and cylinders may be incompatible with an optimal heat exchanger design.
In order to minimise fluid friction, a low temperature device requires short and straight heat exchanger tubes, whereas for the Finkelstein arrangement as shown in
A device which provides free piston operation and negates kinematic crank mechanisms, which offers efficient operation and high power densities over a broad range of temperatures, which incorporates short and equal fluid heat exchanger and regenerator connections, and which provides entirely hot or entirely cold cylinders, has not previously been available and so is provided within at least some of the described arrangements herein.
It would be desirable to provide an engine or device for efficiently and economically extracting usable electrical energy from a wide range of heat sources, including low to medium temperature heat sources such as waste heat, biomass and geothermal energy and from heat sources at higher temperatures. It would be desirable to provide an engine or device which, through the application of oscillating mechanical energy to piston shafts, may be capable to extract heat from an environment or system and so may operate as a cooling device or cryocooler.
According to a first aspect of the invention, there is provided a Stirling engine comprising:
The Stirling engine may be an alpha Stirling engine. The Stirling engine may be a double acting system. The Stirling engine may be a double acting alpha Stirling engine. The Stirling engine may be a multiphase Stirling engine.
The engine is a heat energy conversion device. It will be understood that the engine could be used to convert mechanical movement of the pistons to extract heat from an environment or system, such that the device may operate as a cooling device or cryocooler.
The engine may comprise one or more piston assemblies, two or more piston assemblies, three or more piston assemblies, four or more piston assemblies, six or more piston assemblies, eight or more piston assemblies, 12 or more piston assemblies, 16 or more piston assemblies, or any suitable number of piston assemblies. The number of piston assemblies of the engine may be a multiple of 2, a multiple of 4, or any suitable number.
The engine may comprise one or more additional piston assemblies. The, or each additional piston assembly, may be arranged such that the first cylinders thereof are fluidly connected to a first cylinder of a piston assembly of the engine and such that the second cylinders thereof are fluidly connected to a second cylinder of another piston assembly of the engine. The, or each additional piston assembly, may have a piston connection between the first and second cylinders thereof. In this arrangement, any suitable number of piston assemblies can be arranged in sequence.
The engine may comprise the second piston assembly. The engine may comprise the third piston assembly. The engine may comprise a fourth piston assembly. The engine may comprise a fifth piston assembly.
The piston assemblies may be identical.
Each cylinder of each piston assembly may comprise a piston configured to separate at least two expansion/compression chambers of the cylinder.
The pistons of the first and second cylinders of each piston assembly may be connected.
Each chamber of the second cylinder of the second piston assembly may be fluidly connected to a chamber of a second cylinder of the fourth piston assembly, such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers of the second and fourth piston assemblies.
Each chamber of a first cylinder of the third piston assembly may be fluidly connected to a chamber of a first cylinder of the fifth piston assembly such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers of the third and fifth piston assemblies.
Each chamber of the first cylinder of the fourth piston assembly may be fluidly connected to a chamber of a first cylinder of the third piston assembly.
The engine may be configured in a closed loop arrangement. In this arrangement, the engine comprises at least four piston assemblies, with all cylinders having fluid connections to another cylinder of the engine. For example, the fourth piston assembly may be connected to the third piston assembly in a sequence: 1, 3, 4, 2, then back to 1, and it will be understood that the sequence depends on the number of piston assemblies employed. For 8 piston assemblies, the sequence could be: 1, 3, 5, 7, 8, 6, 4, 2, and back to 1. The engine may be configured in a series closed loop arrangement. It will be understood that the engine may be configured in an open loop. In this arrangement, there may be end piston assemblies. The end piston assemblies could be the second and third piston assemblies, the third and fourth piston assemblies, the fourth and fifth piston assemblies, or any subsequent piston assemblies. The end piston assemblies may be fluidly connected to one other piston assembly of the engine.
Each odd numbered piston assembly may be fluidly connected to an even numbered piston assembly. The chambers of each first cylinder of each even numbered piston assembly may be fluidly connected to the chambers of a first cylinder of an odd numbered piston assembly. The chambers of each second cylinder of each even numbered piston assembly may be fluidly connected to the chambers of a second cylinder of an odd numbered piston assembly.
Each first cylinder of each piston assembly may be configured as an expansion cylinder, or as a compression cylinder. Each second cylinder of each piston assembly may be configured as an expansion cylinder or as a compression cylinder. In these arrangements, the at least two chambers of each cylinder are each expansion spaces, or are each compression spaces, depending on whether the cylinder is an expansion or compression cylinder. It will be understood that in this example, each cylinder is a “hot” cylinder or a “cold” cylinder, and each cylinder does not have a combination of expansion and compression spaces (as is common in some types of Stirling engine).
Each first cylinder and each second cylinder of each piston assembly may be configured as an expansion cylinder or a compression cylinder.
The first and second cylinders of each piston assembly may be configured to be the opposite type of expansion/compression cylinder to each other. In this example, if the first cylinder of a piston assembly is an expansion cylinder, the second cylinder of the same piston assembly would be a compression cylinder, or vice versa.
The first cylinder of each piston assembly may be configured to be the opposite type of expansion/compression cylinder to the cylinder to which it is fluidly connected. The second cylinder of each piston assembly may be configured to be the opposite type of expansion/compression cylinder to the cylinder to which it is fluidly connected.
The first cylinder of the first piston assembly may be configured to be an expansion cylinder and the second cylinder of the first piston assembly may be configured to be a compression cylinder, or vice versa.
The first and second cylinders of each piston assembly may be fluidly isolated from each other. The chambers of the first cylinder of each piston assembly may be fluidly isolated from the chambers of the second cylinder of the piston assembly.
The engine may be configured such that the first and second cylinders of each piston assembly are fluidly connected to different piston assemblies. Each first cylinder of each piston assembly may be fluidly connected to a first cylinder of a piston assembly, and each second cylinder may be fluidly connected to a second cylinder of another piston assembly. Each first cylinder of each piston assembly may be fluidly connected to a first cylinder of a piston assembly, and each second cylinder may be fluidly connected to a second cylinder of another piston assembly, such that the first and second cylinders of each piston assembly are fluidly connected to different piston assemblies.
The term “cylinder” is used to convey its function within an engine, and is not an indication of its shape. It will be understood that each cylinder may take any suitable shape and form. Each cylinder may be substantially cylindrical, or any other suitable shape, such as cuboidal, ovoidal, or the like.
Each cylinder may be a substantially rigid cylinder.
Each cylinder may be spaced apart from the other cylinders.
Each chamber of each cylinder may be fluidly isolated from the other chamber, or chambers of the cylinder. The piston of each cylinder may be configured to fluidly isolate each chamber of the cylinder from the other chamber, or chambers, of the cylinder.
Each cylinder may comprise at least a first chamber and a second chamber. Each cylinder may comprise two or more chambers, or any suitable number of chambers.
The first chamber of the first cylinder of the first piston assembly may be fluidly connected to the first chamber of the first cylinder of the second piston assembly. The second chamber of the first cylinder of the first piston assembly may be fluidly connected to the second chamber of the first cylinder of the second piston assembly.
The first chamber of the second cylinder of the first piston assembly may be fluidly connected to the first chamber of the second cylinder of the third piston assembly. The second chamber of the second cylinder of the first piston assembly may be fluidly connected to the second chamber of the second cylinder of the third piston assembly.
Each first chamber of each first cylinder of each piston assembly may be fluidly connected to a first chamber of a first cylinder of another piston assembly. Each second chamber of each first cylinder of each piston assembly may be fluidly connected to a second chamber of a second cylinder of another piston assembly.
Each first chamber of each second cylinder of each piston assembly may be fluidly connected to a first chamber of a second cylinder of another piston assembly. Each second chamber of each second cylinder of each piston assembly may be fluidly connected to a second chamber of a second cylinder of another piston assembly.
Each first chamber of each cylinder may be fluidly isolated from the second chamber thereof.
Each of the fluidly connected chambers may have a fluid flow path therebetween for the working fluid.
Each of the fluidly connected chambers may have a fluid flow path therebetween for the working fluid, and the fluid flow paths between the chambers of the fluidly connected first cylinders may be substantially identical.
Each of the fluidly connected chambers may have a fluid flow path therebetween for the working fluid, and the fluid flow paths between the chambers of the fluidly connected second cylinders may be substantially identical.
The fluid flow paths between each of the fluidly connected chambers may be substantially identical.
The fluid connections between each first cylinder may be configured such that the fluid flow path between the first chambers is substantially equal in length to the fluid flow path between the second chambers. The fluid connections between each second cylinder may be configured such that the fluid flow path between the first chambers is substantially equal in length to the fluid flow path between the second chambers.
The fluid connections between each first cylinder may be configured such that the fluid flow path between the first chambers is substantially identical to the fluid flow path between the second chambers. The fluid connections between each second cylinder may be configured such that the fluid flow path between the first chambers is substantially identical to the fluid flow path between the second chambers.
The fluid flow path between the first chambers of the first and second piston assemblies may be configured to be substantially equal in length to the fluid flow path between the second chambers of the first and second piston assemblies. The fluid flow path between the first chambers of the first and third piston assemblies may be configured to be substantially equal in length to the fluid flow path between the second chambers of the first and third piston assemblies.
The engine may comprise one or more fluid conduits for fluidly connecting the chambers of the cylinders. The fluid conduits may take any suitable form and shape, and it will be understood that single or multiple fluid conduits may be used to fluidly connect the chambers of the cylinders.
Each of the fluid conduits connecting the chambers of the fluidly connected first cylinders may be substantially identical. Each of the fluid conduits connecting the chambers of the fluidly connected second cylinders may be substantially identical. Each fluid conduit may be substantially identical.
Each of the fluid conduits connecting the chambers of the fluidly connected first cylinders may have a substantially identical fluid flow path. Each of the fluid conduits connecting the chambers of the fluidly connected second cylinders may have a substantially identical fluid flow path. Each fluid conduit may have a substantially identical fluid flow path.
At least a portion of each of each of the fluid conduits connecting the chambers of the fluidly connected first cylinders may be arranged to be substantially parallel. At least a portion of each of the fluid conduits connecting the chambers of the fluidly connected second cylinders may be arranged to be substantially parallel.
The fluidly connected first cylinders may include substantially parallel fluid conduits, or substantially parallel fluid conduit portions. Each of the fluidly connected second cylinders may include substantially parallel fluid conduits, or substantially parallel fluid conduit portions.
The engine may be configured such that all of the chambers of the first cylinder of the first piston assembly are all expansion spaces or are all compression spaces. The engine may be configured such that all of the chambers of the second cylinder of the first piston assembly are all expansion spaces or are all compression spaces. The engine may be configured such that all of the chambers of the first cylinder of the second piston assembly are all expansion spaces or are all compression spaces. The engine may be configured such that all of the chambers of the second cylinder of the second piston assembly are all expansion spaces or are all compression spaces. The engine may be configured such that all of the chambers of the first cylinder of the third piston assembly are all expansion spaces or are all compression spaces. The engine may be configured such that all of the chambers of the second cylinder of the third piston assembly are all expansion spaces or are all compression spaces.
The engine may be configured such that every expansion cylinder is fluidly connected to a compression cylinder. The engine may be configured such that the chambers of each expansion cylinder are fluidly connected to the chambers of a compression cylinder.
The engine may be configured to have only expansion cylinders and compression cylinders. In this arrangement, the engine does not include any cylinders that have both an expansion space and a compression space. In this example, this means that each cylinder could be either entirely “hot” or entirely “cold”.
The engine may be operable to apply heating to one or more cylinders of the engine. The engine may be operable to apply cooling to one or more cylinders of the engine. The engine may be operable to apply heating or cooling to one or more of the cylinders of the engine.
One or more cylinders may be connectable to a source of heat energy or a cooling element, such as a heat sink. Each cylinder may be connectable to a source of heat energy or a cooling element. The engine may comprise a source of heat energy for applying heat energy to one or more of the cylinders thereof. The engine may comprise a cooling element for cooling one or more of the cylinders thereof.
It will be understood that the engine may be configured to apply heat to the expansion cylinders and/or to apply cooling to the compression cylinders, as is known in the field of Stirling engines.
The source of heat may include a heat exchanger, or the like. The cooling element may include a heat exchanger, or the like. The source of heat may be from one or more radiation sources. The radiation source may be solar radiation, or another source of radiation. The source of heat may include an external heat source, or sources. The source of heat may include a heating medium for conveying heat from an external source to the cylinder or working fluid therein. The heating medium may be a fluid, a liquid, a gas, a plasma, or the like, configured to convey heat from the external source to the cylinder or working fluid therein. The heating medium may be transferred to the cylinder or working fluid therein via the heat exchanger.
The cooling element may include an external cooling sink, or sinks. The cooling element may include a cooling medium for conveying heat from the cylinder or working fluid therein to the external cooling sink. The cooling medium may be a fluid, a liquid, a gas, a plasma, or the like, configured to convey heat from the cylinder or working fluid therein to the external cooling sink. The cooling medium may be transferred from the cylinder or working fluid therein via the heat exchanger.
The engine may be configured to apply heat to the working fluid within one or more of the cylinders of the engine. The engine may be configured to transfer heat from one or more heat exchangers of the source of heat to the working fluid within one or more of the cylinders of the engine. The engine may be configured to transfer heat from the working fluid of one or more cylinders of the engine to one or more heat exchangers of the cooling element.
One or more of the cylinders of the engine may be configured to apply heating to the working fluid therein. One or more of the cylinders of the engine may be configured to withdraw heat from the working fluid therein. One or more of the cylinders of the engine may be configured to apply heating to the working fluid therein, and one or more of the cylinders of the engine may be configured to withdraw heat from the working fluid therein.
The source of heat may include one or more regenerators. The cooling element may include one or more regenerators.
The cooling element may be connected to a source of cooling fluid. The cooling fluid may be air, ambient air, or the like.
The heat source may be configured to heat the cylinder, or cylinders to which it is connected by a temperature of up to about 1,000 degrees Centigrade, optionally up to about 700 degrees Centigrade, up to about 300 degrees Centigrade, optionally up to about 220 degrees Centigrade, optionally up to about 200 degrees Centigrade, optionally between about 80 degrees Centigrade and about 1,000 degrees Centigrade, optionally between about 80 degrees Centigrade and about 300 degrees Centigrade, optionally between about 100 degrees Centigrade and about 200 degrees Centigrade, optionally at least 600 degrees Centigrade, optionally at least 700 degrees Centigrade.
The engine may be configured to apply a temperature difference between each fluidly connected expansion and compression cylinders of up to 1,000 degrees Centigrade, optionally up to about 800 degrees Centigrade, optionally up to about 750 degrees Centigrade, optionally up to about 500 degrees Centigrade, optionally up to about 300 degrees Centigrade, optionally up to about 200 degrees Centigrade, optionally between about 100 degrees Centigrade and about 200 degrees Centigrade.
The, or each, piston may be a double acting piston. The engine may be configured to permit free-piston operation. The engine may be a free-piston engine. The, or each piston may be reciprocating pistons. The connected pistons may be reciprocating pistons. Each cylinder may comprise one or more pistons. Each cylinder may comprise one or more pistons, the, or each piston being configured to separate at least two expansion/compression chambers of the cylinder. Each cylinder may comprise a single piston.
Each piston may comprise one or more piston heads. The piston heads may be rigid piston heads.
The piston head, or heads, may be configured to fluidly isolate the at least two chambers of the cylinder. Each piston head may be configured to form a seal between a wall, or walls, of the cylinder and the piston head.
At least one, or each, piston may comprise one or more biasing members for applying a biasing force to the piston. The, or each biasing member may be connected between the piston and the cylinder, and configured to apply a biasing force to the piston as the piston moves within the cylinder. The, or each biasing member may be a flexible member, an elastomeric member, or a flexible elastomeric member. The elastomeric member may be an annulus-shaped member. The, or each biasing member may be connected to the piston head of each piston. The, or each biasing member may be connected to a wall, or walls, of the cylinder. The piston and the, or each, biasing member may be configured to fluidly isolate the at least two chambers of each cylinder. Each piston and the, or each, biasing member may be configured to form a diaphragm piston assembly. Each piston may be a rigid piston and the, or each biasing member may be a flexible member, an elastomeric member, or a flexible elastomeric member.
The engine may comprise one or more damping assemblies. The, or each damping assembly may be configured to apply a damping force to one or more of the pistons of the engine. The, or each damping assembly may be configured to apply a damping force to two or more connected pistons of the engine. The, or each damping assembly may include a biasing element. The biasing element may be a spring member. The spring member may be a planar spring, or the like.
Each piston may comprise at least one connecting member for connecting the piston to another piston. The connecting member may be a shaft, rod, elongate member, or the like. The connecting member may be rigid. The connecting member may be a straight connecting member.
The, or each, piston may be connectable to a power take off means. The power take off means may be an alternator assembly, a linear alternator assembly, or the like.
The engine may comprise any suitable number of cylinders. For example, the engine may comprise 4 or more cylinders, 8 or more cylinders, 12 or more cylinders, 16 or more cylinders, or the like.
The working fluid may be a gas. The gas may be air, hydrogen or helium, or any suitable gas.
Each cylinder may comprise a longitudinal axis. Each cylinder may comprise a lateral axis.
The longitudinal axes of the first and second cylinders of the first piston assembly may be in alignment, or substantially in alignment. The longitudinal axes of the first and second cylinders of the second piston assembly may be in alignment, or substantially in alignment. The longitudinal axes of the first and second cylinders of the third piston assembly may be in alignment, or substantially in alignment. The longitudinal axes of the first and second cylinders of the fourth piston assembly may be in alignment, or substantially in alignment. The longitudinal axes of the first and second cylinders of the fifth piston assembly may be in alignment, or substantially in alignment.
The longitudinal axes of the first and second cylinders of each piston assembly may be in alignment, or substantially in alignment. The longitudinal axes of the first and second cylinders of each piston assembly may be coaxial, or substantially coaxial.
Each piston of the engine may be configured to move, in use, along the longitudinal axis of the cylinder in which the piston is located.
The pistons of the fluidly connected cylinders may be parallel.
Each of the fluidly connected first cylinders may be adjacent to each other. The first and second cylinders of each piston assembly may be adjacent to each other. The fluidly connected second cylinders may be adjacent to each other.
Each first cylinder may be spaced apart from the second cylinder to which it is connected.
Each cylinder may be parallel to the cylinder to which it is fluidly connected. The longitudinal axis of each cylinder may be parallel to the longitudinal axis of the cylinder to which it is fluidly connected.
The longitudinal axis of each cylinder may be axially offset from the longitudinal axis of the cylinder to which it is fluidly connected. The axial offset may be along the lateral axis of the cylinder.
Each first cylinder may be spaced apart from the first cylinder to which it is fluidly connected. Each second cylinder may be spaced apart from the second cylinder to which it is connected.
According to a second aspect of the invention, there is provided a system comprising a Stirling engine, the engine comprising:
Embodiments of the second aspect of the present invention may include one or more features of the first aspect of the present invention or its embodiments. Similarly, embodiments of the first aspect of the present invention may include one or more features of the second aspect of the present invention or its embodiments.
According to a third aspect of the invention, there is provided a method of operating an engine, the method comprising the steps of:
Embodiments of the third aspect of the present invention may include one or more features of the first or second aspects of the present invention or its embodiments. Similarly, embodiments of the first or second aspects of the present invention may include one or more features of the third aspect of the present invention or its embodiments.
According to a fourth aspect of the invention there is provided a Stirling engine comprising:
Embodiments of the fourth aspect of the present invention may include one or more features of the first, second or third aspects of the present invention or its embodiments. Similarly, embodiments of the first, second or third aspects of the present invention may include one or more features of the fourth aspect of the present invention or its embodiments.
According to a fifth aspect of the invention, there is provided a system comprising a Stirling engine, the engine comprising:
Embodiments of the fifth aspect of the present invention may include one or more features of the first, second, third or fourth aspects of the present invention or its embodiments. Similarly, embodiments of the first, second, third or fourth aspects of the present invention may include one or more features of the fifth aspect of the present invention or its embodiments.
According to a sixth aspect of the invention there is provided a method of operating an engine, the method comprising the steps of:
Embodiments of the sixth aspect of the present invention may include one or more features of the first, second, third, fourth or fifth aspects of the present invention or its embodiments. Similarly, embodiments of the first, second, third, fourth, or fifth aspects of the present invention may include one or more features of the sixth aspect of the present invention or its embodiments.
The invention will now be described solely by way of example and with reference to the accompanying drawings in which:
In some embodiments, the invention is an improved double acting alpha type Stirling engine device of the type whereby pairs of axially adjacent cylinders may bound pairs of expansible spaces which are separated by oscillating pistons. Each expansible space of a first cylinder of each pair is fluidly connected by conduits to an expansible space of a first cylinder of each pair such that two pairs of thermodynamic systems may be formed. Each expansible space of a second cylinder of each pair is fluidly connected by conduits to an expansible space of a second cylinder of each pair, such that two pairs of thermodynamic systems may be formed. Each double acting piston may be coaxially rigidly connected to at least one similar piston of another pair of cylinders and thermodynamic systems.
In some embodiments, at least four pairs of cylinders are fluidly and coaxially interconnected in a series loop (an example of a closed loop), whereby the specific number, order, distribution and interconnection of each pair of cylinders of the arrangement and method may permit the following: short and direct fluid connections between cylinders, the capability for cylinders to operate entirely as heat rejecters or as heat absorbers, the time variable mutually resonant, symmetric and cumulative oscillation of the pressure waves of each thermodynamic system and the mutually resonant oscillation of each piston assembly such that the device may be capable of free piston operation and may efficiently provide useful power. It will be understood that in other embodiments, the cylinders need not be pairs of cylinders, and any suitable number of cylinders can be employed. In some embodiments, the cylinders could be arranged in an open configuration, rather than a closed loop arrangement.
A large number of Stirling heat engine designs and concepts have been produced over recent decades, generally with little commercial success, despite the fact that, in principle. Stirling cycle heat engines have significant advantages over other external or internal combustion heat engines. They are quiet, they are able to utilise a wide range of fuels and heat sources, including waste heat, and they require lower maintenance cycles than internal combustion engines. The Carnot efficiency, which describes the maximum theoretical efficiency of external combustion heat engines, is also high compared to other devices. However, the theoretical Carnot cycle and equation also shows that the percentage of supplied energy which is theoretically possible for capture and conversion at the lower end of the temperature scale is small, making the design of an economic low temperature device problematic.
Thus the specific power density of a Stirling device is inherently relatively low at lower temperatures. To improve thermodynamic efficiencies, highly pressurised working fluid systems are generally employed, requiring expensive seals and robust containment. More importantly, bulky, expensive and complicated heat exchanger systems are necessary, and make up the major fraction of the cost of a typical device. Compared with high temperature heat source engines, the heat exchangers need to be of much larger size in order to achieve a particular engine power output, as the device requires a large surface area to permit sufficient heat transfer from the lower temperature source to the working gas, and also when rejecting the heat. The provision of high surface areas relative to volume for improved heat exchange, for instance in the form of large numbers of narrow tubes, will tend to increase fluid friction and pumping losses. The pumping losses may be further increased due to the necessarily long and sometimes indirect paths of the combined heat exchanger and regenerator assemblies which connect the hot to cold side spaces and which are typical of many Stirling cycle systems, examples of which can be seen in FIGS. 2 and 3 of the Prior Art. Thus, whereas for a high temperature device the pumping losses are small relative to power output, fluid friction represents a main loss mechanism within low temperature devices.
Another significant design challenge associated with lower temperature devices is the provision of an effective thermal separation between the hot expansion spaces and the cool compression spaces. For low temperature devices the temperature difference between the hot and cold sides of each thermodynamic system is already small, and so it is therefore essential to ensure that the highest possible temperature gradient is maintained through design. For double acting arrangements in which cylinders contain both hot and cold spaces separated by double acting pistons, expensive thermal breaks are typically needed between the top and bottom cylinder casings and within pistons in order to minimise axial thermal conduction losses.
Double acting Stirling based heat engines have been proposed which attempt to maximise power densities and working efficiencies, the most relevant of which are described below.
The Siemens Rinia arrangement of FIGS. 3, 4 & 5, which is familiar to those skilled in the art of external combustion engines, is composed of a series of connected double acting cylinders whereby the expansion space 1h of one cylinder is connected to the back of the compression space 1c of the following cylinder such that the cylinders are connected in series in a closed series loop of a minimum of three thermodynamic systems separated by double acting reciprocating pistons. As is typical for series connected Stirling engines, the working gas cyclically flows between the expansion space to the compression space by means of a conduit 5 which is typically composed of two heat exchangers each side of a regenerator 10. A first heat exchanger 7 is connected to the expansion space and applies heat to the working gas and the second heat exchanger 8, which is connected to the compression space, removes rejected heat from the working gas. The regenerator typically contains a mesh matrix which is capable to rapidly absorb or reject heat and is known from prior art to substantially improve the overall efficiency of the device.
However, The Siemens Rinia arrangement has certain inherent shortcomings when applied to lower temperature operation. Because an expansion and compression space are contained within each cylinder, long pistons and cylinders, preferably incorporating thermal breaks, are generally deployed in order that thermal conduction may be reduced and axial conduction losses may be minimised. The connecting conduits, which typically incorporate heat exchangers and regenerator assemblies, follow a path from the head of one cylinder to the base of the following cylinder are therefore also necessarily long. The consequence for lower temperature operation is high pumping and pressure losses and expensive and complicated heat exchanger assemblies, and with a low specific power density.
The Finkelstein double acting multi-cylinder arrangement of
In some embodiments of the Finkelstein arrangement, and similarly to the Siemens Rinia arrangement, the cooling compression spaces and heating expansion spaces are deployed within the same cylinder on each side of the double acting reciprocating piston. The conduits therefore connect the upper expansion space of one cylinder to the lower compression space of a following cylinder in order to provide fluidly linked thermodynamic systems. In these embodiments the pistons and cylinders are typically long in order to provide an adequate thermal separation between the expansion and compression spaces, and with a thermal break separating the top and bottom parts of each piston and cylinder. Elongated and thermally broken cylinders and pistons tend to reduce power densities and increase the expense of these components. The conduits which fluidly connect the top of one cylinder to the bottom of the following cylinder are, similarly to the cylinders, also necessarily long and complex, with consequent high pumping or shuttle losses, excess dead space and high fabrication costs.
Thus, for practical and economic reasons, the only significant deployment of Stirling based thermodynamic systems in recent years has been within small scale combined heat and power and concentrated solar reflector arrays, and in which working fluid temperatures are typically relatively high.
In at least some embodiments, the invention is designed to addresses and resolves these fundamental issues, and also is capable of free piston operation and the provision of embodiments with different thermodynamic phase angles such that high and low temperature operation is available, and such that the balance of power and efficiency may be optimised.
In some embodiments, a plurality of thermodynamic systems are enclosed within double acting cylinders which are interconnected by rigid reciprocating piston assemblies in specific configurations or arrays such that short and equal conduits can fluidly connect axially adjacent thermodynamic spaces in a series loop such that pumping losses and fluid friction are minimised. In some embodiments, the conduits may be composed of connected heat exchanger and regenerator assemblies which are identical and which use common parts which are inexpensive to manufacture. It will be understood that in other embodiments, other fluid connections between cylinders are possible. In some embodiments, the provided heat exchanger and regenerator assemblies may be easily dismantled for cleaning and maintenance, which is of particular value and importance when the heat source is geothermal brine or industrial waste heat with a heavy contaminant load.
In some of the embodiments, the provided configurations may be composed of cylinders that are either entirely heat absorbers or heat rejecters such that coaxial thermal conduction losses may be negated, and which are capable to be distributed and thermally isolated, one from the other, in order that thermal losses may be minimised and the area of heat transfer may be maximised. As well as optimising heat exchange efficiencies, such an arrangement negates the requirement for thermal breaks within cylinders and pistons, and for long cylinder and piston configurations, improving power densities and economic viability. Because the hot and cold expansible spaces of each thermodynamic cycle are adjacent, heat exchanger designs may be similar, straight and relatively simple, and may be optimised to minimise pumping losses and dead space. In other embodiments, different arrangements of cylinders may be used.
In some embodiments, each thermodynamic system may therefore possess similar time variable characteristics of temperature, volume and pressure, and so the provided device may generate symmetric and regular thermodynamic pressure cycles such that some embodiments may be capable of free piston operation. In some circumstances, the capability for free piston operation is thought to be of considerable value and importance for the efficient operation of an economic device with low maintenance cycles. Free piston arrangements provide the benefits of low side forces acting on piston rods, seals and bearings and greatly reduced wear and friction as a result of the absence of a crank mechanism. By deploying linear alternators as the power take off mechanism it is also possible to hermetically seal the entire device against gas leakage, negating expensive piston rod seals and bearings and the associated higher maintenance cycles. It is known by those skilled in the art that the Siemens Rinia arrangement is not considered suitable for free piston operation because the pressure peaks of the oscillating pressure cycles are asymmetrically spaced over time and are insufficiently close for regular and smooth operation. It will be appreciated that some embodiments of the invention may use a different piston configuration.
An important benefit of some embodiments is that it is so configured such that the thermodynamic phase angle may be changed by the addition or removal of two pairs of interconnected cylinders. For a double acting alpha arrangement that is designed to be configured for low temperature operation, the thermodynamic phase angle is a critical design parameter, as the balance of the power and efficiency of the arrangement are to a large extent a function of this angle.
The phase angle of the arrangement (a) describes the amount by which the expansion volume leads the compression volume and the relationship of these spaces to piston motion. Higher phase angles result in an improved efficiency but lower power. A lower phase angle will produce a higher compression ratio, which will cause an adiabatic temperature increase in the working fluid such that it becomes more difficult for the device to add and reject heat within a low temperature device. For a low temperature device, a high compression ratio may increase the temperature of the working fluid to close that of the heat source, reducing efficiencies substantially.
For a double acting alpha type engine, the phase angle is a function of the number of cylinders.
So, for a for a typical four cylinder Siemens Rinia device, if Nc is the number of cylinders then the phase angle between interconnected hot and cold volumes will be as follows:
Therefore, for a low temperature device it is preferable to reduce the compression ratio and to increase the volume of gas that is shuttled from the compression and expansion spaces by increasing the phase angle, such that more gas is heated during expansion, and more gas is cooled during compression and the convective heat transfer coefficient is improved. However, this results in smaller variations in volume and so lower pressure amplitudes, so that higher cylinder numbers and phase angle will tend to result an increase in efficiency but a decrease in power.
The phase angle and mutually resonant operation of the thermodynamic systems of the provided arrangement is determined by the order and disposition of the fluidly connecting conduits and piston assemblies and by the order of piston motion. Depending on the configuration and number of cylinders, various embodiments of the provided device are available, which are capable of high and lower temperature operation. The optimum phase angle for a low temperature device will generally be between 120° and 150° degrees whereas for a high temperature device the optimum phase angle may be closer to 90° and a consequently much higher compression ratio.
By adding cylinders to embodiments of the provided arrangement in pairs of two thermodynamic systems, the phase angle can be incrementally increased, such that, for instance, an eight cylinder device produces a phase angle of 90° and is suitable for higher temperature power generation, and a twelve cylinder device may provide 120° phase angle and may operate more efficiently using low temperature heat sources. An embodiment of the provided arrangement with eight interconnected cylinders of four pairs of thermodynamic systems may provide a power density and phase angle which is approximately equivalent to two of the four-cylinder Siemens Rinia arrangements and which, because it is compounded, may be capable of free piston operation. It will be understood that other methods of permitting free-piston operation and altering the phase angle may be employed.
In some embodiments, a plurality of pairs of double acting thermodynamic systems may therefore be deployed in various interconnected arrays composed of a minimum of eight cylinders, which may be capable to provide embodiments of the arrangement which may efficiently operate at either high or lower temperatures and which may provide a symmetric, smooth and efficient transmission of power.
In other embodiments, any suitable number of cylinders may be used. Identical, short and direct connecting conduits composed of heat exchanger and regenerator assemblies may greatly reduce pumping losses, may permit the use of common parts, and may substantially reduce the costs of manufacture. They may also ensure that the thermodynamic characteristics of each Stirling cycle may be cyclically similar and symmetric over time, such that the time variable pressures generated by the thermodynamic cycles may be approximately equal, balanced and cumulative and may be capable of free piston operation. It will be understood that other ways of fluidly connecting cylinders may be used. The present invention will now be described. Without wishing to be bound by theory, the embodiments of the invention as described herein result in at least some of the following: provide an improved heat engine that may accommodate comparatively low production costs: permit inexpensive installation, inspection, maintenance and repair: provide a high power density relative to engine size and temperature differentials: be economically fitted or retrofitted into existing factory or other power plant systems for the extraction and conversion of waste heat to electrical energy: be capable to convert thermal energy from a wide range of temperatures and heat sources, including from lower temperature heat sources, into electrical energy; and be capable to operate as a cooling device or cryocooler.
With reference to
Each chamber 11a′, 11a″ of the first cylinder 13a is fluidly connected to a chamber 11b, 11b″ of a first cylinder 13b of a second piston assembly 16b such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers 11a′ and 11b′, and 11a″ and 11b″, of the first and second piston assemblies 16a, 16b.
Each chamber 12a′, 12a″ of the second cylinder 14a is fluidly connected to a chamber 12c′, 12c″ of a second cylinder 14c of a third piston assembly 16c such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers 12a′ and 12c′, and 12a″ and 12c″ of the first and third piston assemblies 16a. 16c.
Each chamber 12b′, 12b″ of the second cylinder 14b of the second piston assembly 16b is fluidly connected to a chamber 12d′, 12d″ of a second cylinder 14d of a fourth piston assembly 16d, such that a working fluid to be compressed/expanded can flow between the fluidly connected chambers 12b′ and 12d′, 12b″ and 12d″ of the second and fourth piston assemblies 16b, 16d.
In the embodiments illustrated in
In these embodiments, the chambers 11 of each first cylinder 13 are each expansion spaces 1h, or are each compression spaces 1c, depending on whether the cylinder is an expansion 1h or compression cylinder 1c, and the chambers 12 of each second cylinder 14 are each expansion spaces 1h or are each compression spaces 1c, depending on whether the cylinder is an expansion or compression cylinder. It will be understood that in these embodiments, each cylinder is a “hot” cylinder 1h or a “cold” cylinder 1c, and each cylinder does not have a combination of expansion and compression spaces (as is common in some types of Stirling engine).
It will be appreciated that in some embodiments the first cylinder 13a of the first piston assembly 16a is configured to be an expansion cylinder 1h and the second cylinder 14a of the first piston assembly 16a is configured to be a compression cylinder 1c, which determines the sequence of expansion-compression cylinders throughout the engine 100, or vice versa, with the first cylinder 13a of the first piston assembly 16a being a compression cylinder 1c.
The first and second cylinders 13, 14, of each piston assembly 16 are fluidly isolated from each other.
For example, the first cylinder 13a is fluidly isolated from the second cylinder 14a.
The chambers 11 of the first cylinder 13 of each piston assembly 16 are fluidly isolated from the chambers 12 of the second cylinder 14 of the piston assembly 16.
The at least two chambers 11a′, 11a″ of the first cylinder 13a are each expansion 1h or compression spaces 1c. The at least two chambers 12a′, 12a″ of the second cylinder 14a are each expansion 1h or compression spaces 1c.
The Stirling engine 100 is a double acting, multiphase alpha Stirling engine.
It will be understood that the engine 100 could be used to convert mechanical movement of the pistons to extract heat from an environment or system, such that the engine 100 could operate as a cooling device or cryocooler.
In the embodiment shown in
In the embodiments illustrated and described here, the piston assemblies 16 are identical, although in other embodiments they may be different.
As shown in
The pistons 2 of the first and second cylinders 13, 14, of each piston assembly 16 are connected.
Each chamber 11c′, 11c″ of a first cylinder 13c of the third piston assembly 16c can be fluidly connected to a chamber 11 of a first cylinder 13 of a fifth piston assembly 16e (as shown in
As shown in
It will be understood that the engine 100 can be configured in an open loop. In this arrangement, there may be end piston assemblies 16. For example, in
Each odd numbered piston assembly 16a, 16c, etc, can be fluidly connected to an even numbered piston assembly 16b, 16d, etc. In this example, the chambers 11 of each first cylinder 13 of each even numbered piston assembly 16b, 16d, are fluidly connected to the chambers 11 of a first cylinder 13 of an odd numbered piston assembly 16a, 16c. The chambers 12 of each second cylinder 14 of each even numbered piston assembly 16b, 16d, are fluidly connected to the chambers 12 of a second cylinder 14 of an odd numbered piston assembly 16a, 16c.
As shown in
The term “cylinder” is used to convey its function within an engine, and is not an indication of its shape. It will be understood that each cylinder may take any suitable shape and form. Each cylinder may be substantially cylindrical, or any other suitable shape, such as cuboidal, ovoidal, or the like.
Each cylinder 13, 14, is a substantially rigid cylinder 13, 14. Each cylinder 13, 14, is spaced apart from the other cylinders 13, 14.
In the embodiments illustrated and described here, the piston 2 of each cylinder 13, 14, is configured to fluidly isolate each chamber 11, 12, of the cylinder 13, 14, from the other chamber 11, 12, of the cylinder 13, 14.
With reference to
Each first chamber of each cylinder is fluidly isolated from the second chamber of that cylinder. For example, the first chamber 11a′ is fluidly isolated from second chamber 11a″ of cylinder 13a (
Each of the fluidly connected chambers has a fluid flow path therebetween for the working fluid, and in the embodiments illustrated and described here, the fluid flow path is implemented by fluid conduits 5. In the embodiments shown here, the fluid flow paths provided by the conduits 5 are substantially identical. In other embodiments, this may not be required, but as described in more detail below, it is thought to be advantageous.
In the embodiments illustrated and described here, the fluid connections between each first cylinder 13 are configured such that the fluid flow path between the first chambers is substantially equal in length to the fluid flow path between the second chambers. The fluid connections between each second cylinder 14 are configured such that the fluid flow path between the first chambers is substantially equal in length to the fluid flow path between the second chambers.
The fluid flow path between the first chambers 11a′, 11b′, of the first and second piston assemblies 16a, 16b, are configured to be substantially equal in length to the fluid flow path between the second chambers 11a″, 11b″ of the first and second piston assemblies 16a, 16b. The fluid flow path between the first chambers 12a′, 12c′ of the first and third piston assemblies 16a, 16c, are configured to be substantially equal in length to the fluid flow path between the second chambers 12a″, 12c″ of the first and third piston assemblies 16a, 16c.
The engine 100 comprises a plurality of fluid conduits 5 for fluidly connecting the chambers of the cylinders. The fluid conduits 5 can take any suitable form and shape, and it will be understood that single or multiple fluid conduits 5 can be used to fluidly connect the chambers of the cylinders.
In this embodiment, each of the fluid conduits 5 connecting the chambers of the fluidly connected first cylinders 13 are substantially identical, and each of the fluid conduits connecting the chambers of the fluidly connected second cylinders 14 are substantially identical.
As shown in
The fluidly connected first cylinders 13 include substantially parallel fluid conduits 5, or substantially parallel fluid conduit portions and each of the fluidly connected second cylinders 14 includes substantially parallel fluid conduits 5.
The engine 100 is configured such that every expansion cylinder 1h is fluidly connected to a compression cylinder 1c. The engine 100 is configured such that the chambers of each expansion cylinder 1h are fluidly connected to the chambers of a compression cylinder 1c.
The engine 100 is configured to have only expansion cylinders 1h and compression cylinders 1c, and the embodiments illustrated and described here the engine 100 does not include any cylinders that have both an expansion space 1h and a compression space 1c. Each cylinder can be either entirely “hot” or entirely “cold”.
The engine 100 is operable to apply heating to the expansion cylinders 1h of the engine 100 and cooling to the compression cylinders 1e of the engine, as described in more detail below.
Each piston 2 is a double acting, reciprocating piston 2 and the engine 100 is configured to permit free-piston operation.
In the embodiments illustrated and described here, each cylinder comprises a single piston 2, but in other embodiments two or more pistons 2 within each cylinder could be used.
Each piston 2 comprises a piston head, which is rigid and configured to form a seal between a wall 1, or walls, of the cylinder and the piston head.
The working fluid is a gas, which in this embodiment is air. However, hydrogen or helium, or any suitable gas can be used for the working fluid, and in some embodiments liquid could be used.
As shown in
The longitudinal axes 1y of the first and second cylinders 13, 14, that are connected via a piston 2 are in alignment and are coaxial, such as cylinders 13a and 14b shown in
Each piston 2 of the engine 100 is configured to move, in use, along the longitudinal axis 1y of the cylinder in which the piston 2 is located.
The pistons 2 of the fluidly connected cylinders are parallel.
Each of the fluidly connected first cylinders 13 are adjacent to each other. The first and second cylinders 13, 14, of each piston assembly 16 are adjacent to each other. The fluidly connected second cylinders 14 are adjacent to each other.
Each first cylinder 13 is spaced apart from the second cylinder 14 to which it is connected.
In the embodiments illustrated here each cylinder is parallel to the cylinder to which it is fluidly connected. The longitudinal axis 1y of each cylinder is parallel to the longitudinal axis 1y of the cylinder to which it is fluidly connected, as shown in
The axial offset is along the lateral axis 1x of the cylinder.
The Stirling engine 100 may be included within a system, such as an engine apparatus, a vehicle, a generator or the like.
There is provided a double acting alpha Stirling heat engine arrangement as shown in
Such that each first cylinder 13 of each thermodynamic system 15 of the embodiment of
Referring again to
Thus one of the first cylinders 13 may be described as an expansion cylinder 1h and another of the first cylinders 13 may be described as a compression cylinder 1c and whereby each pair of expansion 1h and compression 1c first cylinders 13 may bound two separate thermodynamic systems 15 composed of a working fluid and connected by at least one conduit 5, and separated by said reciprocating double acting pistons 2 such that the working fluid may be capable to oscillate synchronously within each thermodynamic system 15 relative to the adjacent system, and whereby the heated expansion spaces 11 and the cooled compression spaces 11 of each thermodynamic system 15 are distributed and isolated, one from the other. It will be appreciated from
And whereby as shown in
And whereby each expansible expansion space 11 of a first cylinder 13 is fluidly connected to an adjacent expansible compression space 11 of another first cylinder 13 such that as can be seen in
Because the interconnected thermodynamic systems 15 are so disposed such that all of the expansion and compression spaces 1h, 1c, of the fluidly connected systems are axially adjacent, the provided heat exchanger assemblies 7, 8 of the fluidly connecting conduit apparatus 5 are direct, straight and short, and fluid pumping or pressure losses may consequently be small, which is an advantageous condition for the efficient operation of a low temperature device. Additionally, because the physical and volumetric characteristics of all conduits 5 are identical, the thermodynamic cycles of each thermodynamic system 15 are also identical, such that they may oscillate harmonically and symmetrically relative to all other thermodynamic systems 15 within the device, and the provided compounded arrangement is capable of generating frequent and regular pressure peaks, such that the arrangement may be capable to operate as a free piston device. Therefore, crank shafts may be negated, and accordingly side forces on the piston rods 3 may be negated, frictional wear from crank shaft bearings and piston rod seals 17 may be negated, and the device may be capable to be hermetically sealed and highly pressurised, and may be capable to self-start. It will be appreciated that in other embodiments, the thermodynamic systems 15 need not be identical.
In the embodiment shown in
The shell 37 and tube 36 heat exchanger assemblies 7, 8 as shown in
In other embodiments as shown in plan in
In the embodiment of
In the embodiment shown in
A plurality of embodiments of the arrangement may be provided, whereby as a consequence of the specific configuration and interconnection by said rigid compounding and reciprocating piston assemblies 16 of said paired thermodynamic systems 15 composed of an expansion cylinder and compression cylinder and fluidly connected by short and equal conduits disposed on a plane generally perpendicular to said piston assemblies 16, each thermodynamic system 15 may oscillate harmonically relative to all other said thermodynamic systems 15 in a series connected loop and such that the pressure waves of each thermodynamic system 15 acting upon each double acting piston 2 may be cumulative and harmonic and so may provide useful power.
As shown in the embodiments of
As shown in the three dimensional depiction of
The capability for consonant, harmonic and cumulative oscillation of each thermodynamic system can be seen in
It is known by those skilled in the art that low temperature devices with higher thermodynamic phase angles may provide higher system efficiencies. Therefore, the provided method and arrangement may permit the addition of pairs of piston and cylinder assemblies whereby the phase angle of the provided arrangement may be increased and the balance of the power output relative to efficiency may be optimised. Each new phase angle is provided by the addition of a pair of cylinders whereby, for example, by the incremental addition of two pairs of pistons 2 and cylinders 13, 14, on the same plane and in a series loop as shown in
And such that as can be seen from the directional arrows of
In other embodiments of the arrangement as shown in
As can be seen in
As shown in
In addition to the action of the planar springs, the gas forces of each thermodynamic system may act as a gas spring upon the reciprocating mass of each piston and the connected oscillating component of the alternator 29 in order to provide a resonant system. In further embodiments the device may be capable to operate in reverse, whereby as a consequence of the mechanical oscillation of at least one of the piston rods, the arrangement may be capable to operate as a cooler or a cryocooler.
In the embodiment as shown in
Diaphragm piston assemblies are known from prior art in relation to Stirling engine arrangements.
However, as far as is known, they have only been proposed in arrangements in which the diaphragm piston 19 separates an expansion space and a compression space. No prior art is known whereby a diaphragm piston 19 separates either a pair of compression spaces 1c or a pair of expansion spaces 1h within a cylinder 13, 14 and whereby pairs of thermodynamic systems 15 are contained within separate expansion and compression spaces 11, 12 connected by conduits 5 as is provided in the present embodiment of the Stirling engine 100 shown in
Another important and valuable benefit of the provided diaphragm embodiment of
Each piston disc 22 and connected components can be of a specific and adjustable mass such that the diaphragm pistons 19 are capable to be tuned to oscillate to the natural frequency of the mass-spring system. The flexible or elastomeric membrane 20 is also capable to provide a spring force which can be adjusted to the natural resonance of the oscillating thermodynamic systems and piston assemblies. Each expansion and compression space 11, 12 can be configured to optimize the swept volume within each space such that the casing walls 1 may preferably be tapered towards the casing end or head, such that the casing may approximately conform to the swept geometry of each said oscillating diaphragm piston 19.
Modifications and improvements may be made to the above embodiments without departing from the scope of the invention. For example, one or more cylinders could be connectable to a source of heat energy or a cooling element, such as a heat sink. Each cylinder may be connectable to a source of heat energy or a cooling element. The engine 100 could be configured to apply heat to the expansion cylinders and/or to apply cooling to the compression cylinders, as is known in the field of Stirling engines.
The cooling element may be connected to a source of cooling fluid. The cooling fluid may be air, ambient air, or the like.
The heat source may be configured to heat the cylinder, or cylinders to which it is connected by a temperature of up to about 1,000 degrees Centigrade, optionally up to about 700 degrees Centigrade, up to about 300 degrees Centigrade, optionally up to about 220 degrees Centigrade, optionally up to about 200 degrees Centigrade, optionally between about 80 degrees Centigrade and about 1,000 degrees Centigrade, optionally between about 80 degrees Centigrade and about 300 degrees Centigrade, optionally between about 100 degrees Centigrade and about 200 degrees Centigrade, optionally at least 600 degrees Centigrade, optionally at least 700 degrees Centigrade.
The engine may be configured to apply a temperature difference between each fluidly connected expansion and compression cylinders of up to 1,000 degrees Centigrade, optionally up to about 800 degrees Centigrade, optionally up to about 750 degrees Centigrade, optionally up to about 500 degrees Centigrade, optionally up to about 300 degrees Centigrade, optionally up to about 200 degrees Centigrade, optionally between about 100 degrees Centigrade and about 200 degrees Centigrade.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2107042.0 | May 2021 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2022/051224 | 5/16/2022 | WO |
