NL2024831B1 - Energy transfer apparatus and associated methods - Google Patents

Abstract

Thermal energy conversion apparatus for converting heat energy. The thermal energy apparatus comprises a closed-circuit cyclic engine in the form of a ß Stirling engine. A heater head comprising a working fluid. A ceramic cylinder is connected to the heater head, the cylinder having a cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head. A displacer is mounted in the chamber for reciprocating movement by the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion. A thermal regenerator is provided, with the heater head in fluid communication with each of the thermal regenerator and the cylinder chamber.

Description

ENERGY TRANSFER APPARATUS AND ASSOCIATED METHODS

TECHNICAL FIELD This disclosure concerns energy transfer apparatus and associated methods. For example, the disclosure concerns thermal or heat engines for converting heat energy. In particular, but not exclusively, examples of the disclosure concern Stirling engines able to operate at very high temperature differentials.

BACKGROUND A heat engine operating a Stirling cycle operates by converting heat energy, which flows between zones of different temperatures, into useful work. A typical Stirling engine uses the heat energy to drive a coordinated and reciprocating motion of a set of pistons. The motion of the pistons then drives machinery or a generator. The moving pistons are enclosed in a housing, and are coupled mechanically, usually by one or more axles or pushrods to external components, thus driving external machinery. High efficiency in such an arrangement requires that the housing is sealed in an airtight fashion. A seal failure leads to the failure of the engine. The principle underlying the Stirling cycle engine is the mechanical realization of the Stirling thermodynamic cycle: isovolumetric heating of a gas within a cylinder, isothermal expansion of the gas (during which work is performed by driving a piston), isovolumetric cooling, and isothermal compression). Stirling cycle engine efficiency is related to the Carnot efficiency, which is governed by the ratio of maximum working fluid temperature relative to the minimum fluid temperature. As the lower working fluid temperature is typically governed by the temperature of the cooling source, often ambient or surrounding air or water temperature, the key to increased efficiency resides in the application of as high as possible working temperatures. At the same time, Stirling engines are also operated at high internal pressures to optimize the power output for a given engine size, usually operating at internal pressures of from 50 to 200 atmospheres. The maximum working temperature of presently known Stirling engines is limited by the used materials, such as high strength stainless steel alloys, which need to maintain their strength at high temperature and under high pressures. As the heat in Stirling engines is transferred through the containment materials to the working fluid, these materials are thin to maximize the heat transfer rates. The combination of high pressure and temperature differentials and thin materials has limited commercially used Stirling engines to maximum temperatures below 750°C to 800°C.

It may be an object of one or more aspects, examples, embodiments, or claims of the present disclosure to at least mitigate or ameliorate one or more problems associated with the prior art, such as described herein or elsewhere.

SUMMARY According to a first aspect there is provided a thermal energy conversion apparatus for converting heat energy. The thermal energy apparatus may comprise a thermal engine. The thermal engine may comprise a closed-circuit cyclic engine. The thermal engine may comprise a regenerative heat engine, such as a closed-cycle regenerative heat engine. The thermal engine may comprise a gaseous working fluid, such as air or a component/s thereof. The gaseous working fluid may be permanently gaseous, such as throughout every entire cycle of the thermal engine. The thermal engine may comprise a Stirling engine. The Stirling engine may comprise a B Stirling engine. The Stirling engine may comprise a single cylinder. The single cylinder may comprise a hot end and a cold end, relative to each other. The Stirling engine may comprise a high temperature differential engine. For example, the single cylinder may comprise a temperature differential of up to 1000°C or more, such as between the cold end and the hot end. The temperature differential may comprise a total temperature differential between an input to and an output from the thermal energy conversion apparatus. The temperature differential may comprise more than 500°C; optionally more than 600°C; optionally more than 700°C or more than 800°C. The thermal energy conversion apparatus may be for converting energy from heat to another form of energy. The thermal energy conversion apparatus may be for converting heat energy to mechanical energy. The thermal energy conversion apparatus may be for converting heat energy to electrical energy. The thermal energy conversion apparatus may comprise an electrical generator. The apparatus may comprise a heater. The heater may be configured to transfer heat to the apparatus, such as from an external heat source. The heater may comprise a heater head. The apparatus may comprise a cylinder. The cylinder may comprise both compression and expansion cycles. The cylinder may comprise a chamber. The chamber may be configured for both compression and expansion cycles. The cylinder may comprise a hot end and a cold end. The hot end may be relatively hotter than the cold end, such as on average generally comprising a higher temperature. The hot end of the cylinder may comprise a hot end chamber portion. The hot end chamber portion may be configured for compression and expansion cycles. The hot end may comprise an expansion cycle and a compression cycle. The cold end of the cylinder may comprise a cold end chamber portion. The cold end chamber portion may be configured for compression and expansion cycles. The hot end chamber portion and the cold end chamber portion may be in fluid communication. The hot end chamber portion and the cold end chamber portion may be in fluid communication within the cylinder.

The apparatus may comprise a displacer. The displacer may be movable relative to the cylinder. The displacer may separate the hot end chamber portion from the cold end chamber portion. The displacer may be movable within the cylinder to displace fluid within and/or to/from the cylinder. The displacer may separate the chamber into the hot end chamber portion and the cold end chamber portion. The displacer may divide the cylinder in cyclic alternation into an expansion chamber and a compression chamber. The respective volumes of the expansion and compression chambers may vary with the direction of movement of the displacer. The displacer may displace the working fluid in the chamber by axial movement of the displacer within the cylinder. The displacer may cyclically compress and expand the volume of each chamber portion such that the working fluid is cyclically compressed and expanded in each of the hot end and cold end chamber portions. The displacer may drive the pressure differential between the expansion and compression chambers. The displacer may divide the cylinder into a relatively cooler portion and a relatively hotter portion, such as dividing the hot end from cold end. Alternatively, the displacer may sealingly divide the cylinder into a relatively cooler portion and a relatively hotter portion. Accordingly, the displacer may comprise a displacer piston. The displacer may comprise a tight interference, or close fit with the cylinder wall. The chamber portions may be in fluid communication with each other. The expansion and compression chambers may be in fluid communication with each other. The respective portions, such as the expansion and compression chambers, may be in fluid communication with each other via one or more fluid passages outside or at an exterior of the cylinder. Additionally, or alternatively, the portions may be in fluid communication with each other within the cylinder, such as through or around the displacer. The displacer may comprise a loose fit with the cylinder wall.

The apparatus may comprise a piston. The piston may comprise a power piston. The piston may be driven by the expansion and/or compression cycles in the cylinder. The piston may convert thermal energy to mechanical energy. The piston may move axially within the cylinder. The piston may be drawn into the cylinder chamber by compression, such as during a compression cycle/s in the hot and/or cold chamber portion/s of the cylinder. The piston may be extended in the cylinder chamber by expansion, such as during an expansion cycle/s in the hot and/or cold chamber portion/s.

The piston may comprise a tight interference, or close fit with the cylinder wall. The piston may be in sealing engagement with the cylinder wall. The piston may comprise a seal, such as an annular sealing portion for contacting the cylinder wall. The piston may comprise a piston head. The piston head may comprise the seal.

The apparatus may comprise a power drive member. The power drive member be connected to the power piston. The power drive member may be for transferring work from the power piston, such as to a flywheel, generator, solenoid, linear generator, drive system, or the like. The power drive member may comprise a drive shaft, such as a drive crank.

The piston may be connected to the displacer. The piston may be linked to the displacer. The piston may be mechanically linked to the displacer via one or more of: a wheel, such as flywheel or the like; a linkage, a linkage assembly; a connector assembly. A displacer drive rod for driving the displacer may pass through the power piston, such as centrally through the power piston. The displacer drive rod may be in reciprocating sealing engagement with the power piston. The displacer piston may be driven or powered by the power piston, such as directly or indirectly (e.g. via the wheel, such as flywheel or the like; the linkage; the linkage assembly; and/or the connector assembly).

The apparatus may comprise a heat exchanger. The heat exchanger may comprise a thermal regenerator. The heat exchanger may be for transferring heat between the working fluid and a portion of the apparatus. The portion of the apparatus may comprise the cylinder, such as the expansion chamber. The portion of the thermodynamic cycle may comprise a movement of the displacer, such as stroke, or portion thereof, of the displacer. The heat exchanger may be for at least partially temporarily storing heat, such as between cycles. Accordingly, the heat exchanger may be for transferring heat between cycles, or portions thereof, of the thermodynamic cycle, such as between a compression cycle or phase and an expansion cycle or phase. The heat exchanger may be in fluid communication with the heater of the apparatus. The heat exchanger may be in fluid communication with a heat sink or cooler of the apparatus.

The apparatus may comprise a heat sink. The heat sink may comprise a cooler. The cooler may be configured to passively cool the working fluid. The cooler may be configured to actively cool the working fluid. The cooler may be configured to extract heat from the working fluid. The cooler may be configured to redirect heat extracted from the working fluid to another portion of the apparatus. The cooler may be configured to transfer heat to the other portion of the apparatus. The cooler may be configured to transfer heat to outside the apparatus. The cooler may be configured to transfer heat to an external environment, such as an atmospheric environment. The cooler may be configured to indirectly transfer heat to the external environment. Additionally, or alternatively, the cooler may be configured to directly transfer heat to the external environment. 5

REGENERATOR The apparatus may comprise one or more regenerator/s. A component in Stirling engines which may be important to the maximum performance is the regenerator. The regenerator may be configured to heat and cool the working fluid for each cycle of the engine, which may be up to 100's of times per second. For example, the working fluid may be cyclically heated and cooled around 25 times per second. Previous regenerators typically comprise densely packed fine metal mesh screens. These fine screens may be sufficient to provide high heat transfer rates. However, the present inventors have established that such screens exhibit a significant pressure drop as the working fluid, such as Helium, Hydrogen, or air, is pressed through the mesh at relatively high speeds. The efficiency of a Stirling engine equipped with such screens is hence limited. Other previous regenerators have used random metal matrix materials and felt with steel filaments oriented perpendicular to the flow direction. However, the present applicant has established that there are significant pressure drops associated with use of those materials. The present disclosure may also provide a regenerator for a high temperature differential Stirling cycle engine which overcomes the limitations and shortcomings of the prior art, such as described in further detail below. According to an aspect, there is provided the thermal regenerator of the present disclosure. The thermal regenerator may comprise a fluid channel for flow of the working fluid, such as flow of the working fluid between the chambers or hot and cold portions or ends of the cylinder. The fluid channel may be configured to prevent or at least mitigate a pressure differential along the length of the fluid channel. The fluid channel may provide an unobstructed flowpath for the working fluid. The fluid channel may comprise a constant cross-sectional area along its length, such as along its entire length. The fluid channel may comprise a constant cross-section along its length. The fluid channel may comprise a constant cross-sectional shape along its length. Each fluid channel may comprise a constant cross-sectional shape along its length such that the working fluid may flow along or through the fluid channel without obstruction. The fluid channel may comprise a continuous fluid channel of constant cross-section along its length to minimise or prevent a pressure differential, such as pressure drop, along the length of the fluid channel.

The thermal regenerator may comprise a plurality of fluid channels.

In at least some examples, at least some of the fluid channels may be in fluid communication with each other.

For example, adjacent fluid channels may interconnect.

In at least some examples, the thermal regenerator may effective comprise only a single or only a pair of flow paths.

The pair of flow paths may comprise an inner flowpath and an outer flowpath, such as separated by a thickness of a regenerator element.

The/each flow path may comprise a multitude of fluid channels.

Additionally, or alternatively, at least some of the fluid channels may be fluidly isolated from each other.

For example, the fluid channels may be separated by a portion/s of the regenerator and/or a seal and/or additional member/s.

Each of the plurality of fluid channels may comprise a similar cross-section, such as a similar cross-sectional area and/or shape.

The cross-sectional shape may comprise a teardrop shape.

The teardrop may be open at its pointed end, such as open into to fluidly connect the fluid channel to other fluid channels, such as the pointed ends of laterally- arranged other fluid channels.

The fluid channels may be arranged in alternating orientations.

For example, each alternate teardrop shape may have its pointed end directed towards a similar direction, such as either inwardly or outwardly.

Inwardly oriented fluid channels may be interspersed with outwardly oriented fluid channels.

In at least some examples, each of the inwardly-oriented fluid channels comprises a same first cross-section; and each of the outwardly-oriented fluid channels comprises a same second cross-section.

The thermal regenerator may comprise a heat transfer element.

The heat transfer element may comprise a regenerator element.

The regenerator element may comprise or define the fluid channels.

The regenerator may be formed from a sheet material.

The regenerator may comprise a sheet material of uniform thickness.

The regenerator element may comprise a single sheet.

The single sheet may be formed so as to define the plurality of fluid channels.

The single sheet may be formed into an annular shape.

The annularly-shaped single sheet may comprise a greater surface area than a single sheet cylinder at either a maximum or minimum diameter corresponding to the annular shape of the regenerator element.

The annularly-shaped single sheet’s greater surface area may be a factor greater than a single sheet cylinder at the maximum and/or minimum diameter corresponding to the annular shape of the regenerator element.

The factor may be two; optionally at least three; optionally four or more; optionally five or more.

Accordingly, in at least some examples the annularly-shaped sheet’s surface area may be a factor of three greater than a single sheet cylinder at the maximum and/or minimum diameter corresponding to the annular shape of the regenerator element.

The provision of a relatively greater surface area may allow a greater heat transfer between the regenerator and the working fluid flowing through the regenerator (such as compared to a reduced surface area). The single sheet may comprise a corrugated sheet.

The corrugations of the corrugated sheet may define the plurality of fluid channels.

The sheet material may define a corrugated cylindrical shape when assembled.

The corrugations may run in a longitudinal direction, such as parallel to a longitudinal axis of the cylinder.

In comparison to alternative means to provide an increased surface area, such as the provision of mesh or filamentous regenerator elements, the provision of the corrugated regenerator element provides an improved flow, such as with less or no pressure drop along the flowpath through or along the regenerator element.

In some examples, the respective ends of the sheet material may be unjoined, such as loosely meeting, so as to enclose an inner volume, such as an inner roughly cylindrical volume within the sheet material.

In other examples, the respective ends of the corrugated sheet material may be connected, such as mechanically joined, so as to enclose the inner volume, such as the inner roughly cylindrical volume within the annularly formed sheet material.

According to a further aspect, there is provided a heat transfer element for a heat exchanger.

The heat transfer element may comprise any or all of the features of any heat transfer element of any other aspect, example, embodiment or claim.

The heat transfer element may comprise any or all of the features of the thermal regenerator described herein.

According to a further aspect, there is provided a method of manufacturing a heat transfer element.

The heat transfer element may comprise the heat transfer element, such as the regenerator element, of any other aspect, embodiment, example or claim.

The method may comprise providing a sheet material with corrugations.

The method may comprise passing the sheet material through a pair of interengaging forming elements.

The pair of interengaging forming elements may comprise two intercalating cog-wheels.

The method may comprise passing the sheet material through the pair of interengaging forming elements to form the corrugations in the sheet material, for providing the fluid channels.

The method may comprise embossing a thin sheet of metal to form a pattern of spaced discrete embossments that protrude a uniform amount from the surface of the sheet.

The method may comprise wrapping the embossed sheet about a longitudinal axis into an annulus such that individual sheets are spaced apart by the embossments.

The method may comprise locating the embossments to provide parallel axial flow paths and unobstructed continuous annular channels for the working fluid of the heat engine that minimize pressure losses and maximize heat transfer.

Accordingly, the regenerator may provide a better heat transfer to and/or from the fluid passing through the regenerator; such as relative to previous regenerators and/or regenerators without such unobstructed continuous annular channels.

The method may comprise installing layers of foil of approximately uniform thickness in a generally cylindrical space.

The method may comprise cutting a piece of foil to a length such that a distance between axial edges of the piece of foil are cut approximately equal to three times the circumference of the inner surface of the generally cylindrical space to be defined by the annular shape.

The method may comprise embossing the cut foil by running the foil between the two intercalating cog-wheels such that the axial edges are overlapping.

The method may comprise inserting the embossed foil into the generally cylindrical space to form the annular regenerator element.

The thermal regenerator may comprise a plurality of regenerator elements.

The plurality of regenerator elements may be arranged in series.

The plurality of regenerator elements may be arranged in series such that each fluid channel of a first regenerator element is in series with corresponding fluid channels of a second regenerator element.

Accordingly the working fluid may flow from the fluid channels of the first regenerator element into corresponding channels of the second regenerator element {or vice versa, such as during a reverse cycle). The first and second regenerator elements may be similar, such as at least of similar cross-sectional shape and/or dimension perpendicular to the direction of flow.

The plurality of regenerator elements may be arranged end-to-end.

Each regenerator element may be configured to provide a rapid heat transfer.

Each regenerator element may be configured to withstand extreme cycle temperature fluctuations The provision of the plurality of regenerator elements may enable each regenerator element to be exposed to a reduced temperature fluctuation.

For example, the provision of the plurality of regenerator elements may enable a reduced temperature differential across the/each regenerator element in comparison to a single regenerator element in the regenerator.

For example, where the regenerator is exposed to or configured to provide a temperature differential in a fluid of up to 1000°C, rather than a single regenerator element being exposed to a temperature differential across the single regenerator element of up to 1000°C, each regenerator element may be exposed to a reduced temperature differential.

For example, the regenerator may be configured to limit each regenerator element to a fraction of the total temperature differential, such as little as a third of the total temperature differential where three regenerator elements are provided in series.

Accordingly, where the regenerator is configured to receive a fluid with a high temperature (e.g. of 1000°C) and output the fluid with a low temperature (e.g. 80°C), none of the individual regenerator elements are exposed to both the high temperature and the low temperature.

The regenerator may be configured to provide a stepped or phased temperature differential.

For example, each of the regenerator elements may be configured to provide a sequential, phased reduction in the temperature.

Where each regenerator element is of similar properties, such as dimensions (e.g. axial length), each regenerator may provide a similar reduction in temperature.

For example, each regenerator element may provide a proportion of the total reduction in temperature corresponding to The thermal regenerator may comprise a heat shield or reflector.

The heat shield or reflector may comprise a baffle.

The heat shield or reflector may comprise a radiation heat shield or reflector.

The heat shield or reflector may be configured to reflect and/or deflect heat.

The heat shield or reflector may be configured to minimise a change in flow.

The heat shield or reflector may be configured to minimise redirection of flow.

The heat shield or reflector may be configured to reflect and/or deflect heat away from a direction of flow of fluid through the regenerator.

The heat shield or reflector may be configured to absorb heat from the fluid flowing through the regenerator.

The heat shield or reflector may be configured to reduce transmission of heat out of the regenerator element.

The heat shield or reflector may be configured to allow flow out of and/or into the regenerator element.

The heat shield or reflector may be configured to prevent or at least mitigate a pressure drop across the heat shield or reflector.

The heat shield or reflector may provide a deviation to the flow.

The heat shield or reflector may comprise a similar or same cross- sectional area as the flowpaths through the regenerator.

The heat shield or reflector may comprise a cross-sectional flowpath area perpendicular to flow of the working fluid, wherein the heat shield or reflector’s total cross-sectional flowpath area is at least the same as the total cross-sectional area of all of the fluid channels in the regenerator.

The heat shield or reflector may be configured to reduce transmission of heat from the regenerator element.

The heat shield or reflector may be configured to reduce transmission of heat radiation from the regenerator element.

The heat shield or reflector may comprise a thermal reflector.

The heat shield or reflector may comprise a thermal insulator.

The heat shield or reflector may comprise a ceramic.

The heat shield or reflector may comprise a ring.

The heat shield may be located at an axial end/s of the/each regenerator element/s.

The thermal regenerator may be provided as a module or unit, such as a cartridge.

An inner cylindrical wall may define an inner portion of an annular regenerator.

An outer cylindrical wall may define an outer portion of the annular regenerator.

The regenerator may comprise a device for maintaining the plurality of annular sheets spaced substantially in a parallel arrangement.

The device may comprise the heat shield or reflector.

The device may comprise one or more ceramic fastening rings shaped to obstruct direct heat radiation.

In at least some example, the fastening ring may be the heat shield or reflector.

The device may be configured such that the regenerator elements are stacked with channels essentially parallel to the direction of the fluid flow.

The rings may be arranged such that channels formed by the sheet material are aligned axially to minimize disruption to flow of the fluid and to maintain continuous annular channels.

In at least some examples, the thermal regenerator comprises at least one element comprising a corrugated sheet material provided in an annular configuration positioned such that the working fluid passes through the channels formed in the corrugated sheet when forced by the movement of the displacement piston in the cylinder for transferring heat between the fluid moving through the channels and the inside and outside wall with a minimal pressure drop in the fluid.

In at least some examples, the sheet material is essentially formed from metal.

The sheet material may comprise a foil.

The metal may comprise stainless steel, or a nickel alloy.

The metal may comprise an average thickness of from 0.1 to 1mm.

The sheet material may comprise a uniform thickness, such as along its axial length and/or around its circumference.

The sheet material may comprise the uniform thickness prior to and/or after formation of the channels.

The thickness of the sheet material may be sufficient to store energy so as to allow transfer energy between cycles.

For example, the thickness of the sheet material, such as combined with a thermal property/ies, of the sheet material, may be such so as to store as much energy as possible transferable from the working fluid passing through the regenerator in a/each cycle.

The thickness of the sheet material may be determined in dependence on at least one of: a rate of flow of working fluid; a thermal property of the working fluid, such as a (specific) heat capacity; an amount, such as a mass and/or volume of working fluid; and a surface area of the sheet material.

In at least some examples, there is provided a multi-channel thermal regenerator for a Stirling cycle heat engine, comprising a corrugated sheet material provided in an annular configuration positioned such that the working fluid is passing through the channels formed in the corrugated sheet when forced by the movement of the displacer in the cylinder chamber for transferring heat between the fluid moving through the channels and the inside and outside wall with a minimal pressure drop in the fluid.

The thermal regenerator may comprise a cavity. The cavity may be an annular cavity located around the cylinder chamber/s. Accordingly the cavity may be located radially outward of the cylinder chamber/s. In at least some examples, the cavity may be located in the cylinder wall. The cavity may comprise an inner wall at an inner diameter and an outer wall at an outer diameter. The cavity may be defined by a double-walled cylinder.

The inner and/or outer wall/s may comprise a ceramic. The cavity may be defined by an inner cylinder form and an outer cylinder form. The ceramic cylinders may be arranged such that channels formed by the sheet material are aligned axially to minimize disruption to flow of the fluid and to maintain continuous annular channels. There may be provided a device for maintaining the plurality of annular sheets spaced substantially in a parallel arrangement. The device may comprise a ceramic cylinder with an end portion shaped as to obstruct a direct heat radiation but permitting fluid flow.

The regenerator may comprise a regenerator cartridge, formed of regenerator element/s and device/s, such as the ceramic cylinder/s for housing the regenerator element/s. The inner side of the regenerator may act as a cylinder wall for the displacer. The regenerator cartridge may comprise an inner sleeve, an outer sleeve in spaced parallel arrangement from the inner sleeve with the sheets being disposed therebetween, and a base member connected between the inner sleeve and outer sleeve at one end of both sleeves.

The plurality of regenerator elements may be axially arranged. The plurality of regenerator elements may be arranged such that the working fluid flows sequentially through the regenerators. The regenerator may comprise the heat shield or reflector. In at least some examples, the regenerator may comprise at least a pair of heat shield or reflectors, a first heat shield or reflector arranged at a first end of the regenerator and a second heat shield or reflector arranged at a second end of the regenerator. Each regenerator element may be arranged with a heat shield or reflector at each axial end of the regenerator element. In at least some examples, the regenerator comprises a plurality of axially-arranged regenerator elements with a heat shield or reflector arranged between each adjacent pair of regenerator elements; and optionally a heat shield or reflector at one or both axial ends of the regenerator.

According to a further aspect, there is provided a heat shield or reflector for a heat exchanger, such as the heat shield or reflector of any other aspect, example, claim or embodiment.

According to a further aspect, there is provided a method of manufacturing a thermal regenerator, such as the thermal regenerator of any other aspect, example, claim or embodiment. The method may comprise assembling the regenerator element/s into the cavity in or adjacent the cylinder. The method may comprise assembling the heat shield/s or reflector/s into or adjacent the cavity, such as axially arranged relative to the regenerator element/s. The method may comprise assembling the plurality of regenerator elements and heat shields or reflectors, wherein the heat shields or reflectors function as fasteners to hold the regenerator elements in aligned position/s within the annular cavity.

HEATER HEAD According to an aspect, there is provided the heater head of the present disclosure. The heater head may comprise the working fluid. The heater head may be in fluid communication with the thermal regenerator. The heater head may be in fluid communication with the cylinder chamber. The heater head may be in fluid communication with each of the thermal regenerator and the cylinder chamber. The cylinder chamber may be in fluid communication with the thermal regenerator via the heater head. The chamber may be in fluid communication with the working fluid heatable by the heater head.

The heater head may comprise a plurality of fluid conduits containing the working fluid. Each of the plurality of fluid conduits may be arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

The heater head may comprise at least one first aperture for fluid communication of the working fluid with the cylinder chamber. The heater head may comprise at least one second aperture for fluid communication with the thermal regenerator.

The first aperture and the second aperture may be separated by a seal of the seal assembly. Each fluid conduit may comprise two ends, a first end for communication with the cylinder chamber and a second end for communication with the thermal regenerator. Each first end may comprise a first aperture and each second end may comprise a second aperture.

The plurality of first apertures may be in fluid communication at an interface between the heater head and the cylinder. The plurality of first apertures may be in fluid communication with each other via the cylinder. The plurality of second apertures may be in fluid communication at the interface between the heater head and the regenerator. The plurality of first apertures and the plurality of second apertures may alternate functioning as respective inlets and outlets with a change in cycles of the thermal Stirling cycle engine, such that a direction of fluid flow of the working fluid in each of the fluid conduits reverses. For example, the first apertures may function as outlets from the heater head during an expansion phase or cycle of the relatively hotter portion of the chamber. Accordingly, the heater head may supply heated working fluid to the cylinder chamber via the first apertures during the expansion phase or cycle, propelled by the displacer moving in a direction away from the first apertures. Similarly, the heater head may receive working fluid from the cylinder chamber via the first apertures during a retraction phase or cycle, such as when the displacer is moving towards the first apertures.

The plurality of fluid conduits may be defined by a plurality of thermally conductive tubes.

The thermally conductive tubes may each be of constant cross-section along their lengths to minimise a pressure differential along each respective tube. Each of the tubes may comprise a wall of uniform thickness along its length and around its circumference. The tubular wall may be cylindrical in shape, at least in cross-section.

The fluid conduits may be configured to operate at a temperature in excess of 500°C .

The fluid conduits may be configured to operate at a temperature in excess, of 600°C ; optionally 700°C; optionally 800°C ; optionally 1000°C. The plurality of tubes may be manufactured from an essentially pure metal able to sustain the tubular geometry and shape at an operating temperature in a range of from 850 to 1400 °C. There may be an operating temperature range, such as between at least 800°C to 900°C.

The plurality of heater tubes may be rotationally symmetric about their centre axes. The heater tubes may be spaced parallel with respect to one another. The heater tubes may be spaced at a distance and shape that during heating up or cooling down of the heater head, the tubes are in direct contact with a temperature of 500°C or more, such as an input operating temperature in the range of from 850 to 1400 °C.

The heater head may comprise a heater head manifold. The heater tubes may be positioned in a staggered, annular or partially concentric array and form a toroidal shape. Each of the plurality of first apertures may be located at a different diameter than each of the plurality of second apertures. Accordingly, an annular seal may be provided between the plurality of first apertures and the plurality of second apertures, thereby preventing passage of the working fluid between the first and second apertures — other than via the heater tubes, or the cylinder and regenerator. The plurality of second apertures may be located towards an outer diameter of the manifold. The plurality of first apertures may be located towards a radial centre of the manifold. The plurality of first apertures may be located at a smaller distance from the radial centre of the manifold than the plurality of second apertures.

The heater manifold may be formed, such as cast, from a single superalloy metallic material, or from an essentially pure metal, able to sustain the geometry and shape at an operating temperature in the range of from 850 to 1400 °C.

The plurality of first apertures may be perpendicular to a central longitudinal axis of the ceramic cylinder such that each of the plurality of heater tubes provides a continuous linear flow path between the ceramic cylinder and a first tube portion of each fluid conduit adjacent the respective first apertures.

Each heater tube may comprise such a first tube portion that extends parallel to the longitudinal axis at an inner diameter, then curves around with at least a minimum bend radius to a second tube portion transverse, such as perpendicular, to the first tube portion. The second portion may extend the tube laterally away from the central longitudinal axis. The heater tube may curve around a second bend with at least a minimum bend radius to a third tube portion. The third tube portion may be transverse, such as perpendicular, to the second tube portion.

Each third tube portion may extend to the respective second aperture. The second aperture may be at a smaller diameter than a maximum diameter of the tube relative to the central longitudinal axis, such as a diameter of the second bend relative to the central longitudinal axis of the cylinder. The heater head may comprise a central longitudinal axis coincident with the central longitudinal axis of the cylinder.

|In at least some examples, the heater head may be configured to transmit heat energy to the working fluid. The heat may be transferred indirectly, such as via the wall/s of the fluid conduit/s. The heater head may be configured to transfer heat by radiation. The heater head may comprise a compartment, such as a compartment for housing the plurality of fluid conduits. The compartment may be configured to transfer heat to the fluid conduits, such as by radiation. Accordingly, the heater head may comprise a compartment for transferring heat from an exterior of the heater head, such as a compartment contained within a sealed outer housing of the heater head. The sealed outer housing of the heater head may be heated by an external heat source, such as an external heat source adjacent or encasing the heater head. Heat may be transferred via the compartment through each fluid conduit’s outer wall to the working fluid within each heater tube. The compartment may comprise a vacuum. Accordingly, the plurality of fluid conduits may be heated in the heater head in a vacuum, such as at least predominantly by radiation. Alternatively, the compartment may comprise an enclosed fluid. The enclosed fluid may be contained by the sealed outer housing, with the enclosed fluid being sealingly separated from the working fluid by the fluid conduit’s outer wall. The enclosed fluid may comprise an inert fluid, such as inert gas (e.g. nitrogen, argon, or the like). The enclosed fluid may comprise a liquid. In at least some examples, the fluid may comprise a salt, such as molten salt/s. The tubes may comprise single-wall tubes. The enclosed fluid may comprise an inert fluid, such as nitrogen. The enclosed fluid may not be actively pumped. For example, there may be no driven flow in a heater head housing chamber comprising the enclosed fluid. The compartment in the heater head may be passive, such as comprising the vacuum or a passive fluid. The working fluid in the fluid conduits in the heater head may be driven such as by movement of a stroke of the displacer and/or the power piston.

HEATER HEAD CONNECTION According to an aspect, there is provided the heater head connection of the present disclosure. In at least some examples, there is provided a thermal Stirling cycle engine wherein the ceramic cylinder and the heater head are connected and sealed by a resilient and elastic gas-tight seal assembly. The seal assembly may comprise a lumen. The outer wall may compressively and gas-tightly be disposed between the head and cylinder components. The inner lumen may comprise an inert gas at an elevated pressure. Accordingly, there may be provided a thermal Stirling cycle engine comprising: a heater head comprising a working fluid; a ceramic cylinder connected to the heater head, the cylinder having a cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head; a displacer mounted in the chamber for reciprocatingly displacing the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; wherein the ceramic cylinder and the heater head are connected and sealed by a gas- tight seal assembly comprising a lumen; wherein the lumen is compressively and gas- tightly disposed between the head and cylinder components, and wherein the lumen comprises an inert gas.

The seal assembly may be for containing the working fluid within the engine. The seal assembly may be for sealingly separating one or more portion/s of the engine. The lumen may be formed as an annular channel, with the heater head defining a first annular portion of the annular channel and the ceramic cylinder defines a second annular portion of the annular channel. The lumen may be sealed by pressure of the heater head against the cylinder, such as by mechanically fastening the heater head to the cylinder. The seal assembly may be resilient. The seal assembly may be elastic. The inert gas may be at an elevated pressure. The inert gas may be pressurised. The inert gas may be formed and pressurised by a thermal reaction on heating, such as initial heating of the heater head, the gas being derived from a non-gaseous composition applied to a portion of the lumen prior to sealing of the lumen. The gas may be a vapour generated by heating a liquid, paste or other solid applied to the lumen, the heating occurring at or preferably below an operating temperature of Stirling engine at the lumen. The engine may comprise a fastener for securing the heater head to the cylinder. The fastener may be configured to accommodate mechanical and thermal differences between the heater head and the ceramic cylinder under operating conditions to prevent axial movement therebetween. The fastener may be configured to be self-tightening. The fastener may be configured to increase a securement force as temperature increases. The fastener may be configured to utilise a difference in thermal expansion properties between the heater head and the cylinder to increase a clamping force securing the heater head and cylinder together.

The fastener may comprise a circlip formed of temperature resistant metal. The circlip may comprise a part-ring shaped body. The two ends of the circlip may comprise a pair of integrally co-operative legs. The circlip may secure the heater head axially relative to the ceramic cylinder. The circlip may be configured to prevent relative axial movement between the heater head and the ceramic cylinder. The circlip may be configured to accommodate mechanical and thermal differences between the heater head and the ceramic cylinder under operating conditions to prevent axial movement therebetween. The circlip may comprise a hollow circlip defining a lumen. The lumen may be sealed at each end of the circlip. The circlip may provide a circumferential securement. The circlip may provide a circumferential securement between a portion of the heater head radially outside a portion of the cylinder. The inert gas may be formed and pressurised by a thermal reaction on heating, such as initial heating of the heater head, the gas being derived from a non-gaseous composition applied to a portion of the lumen prior to sealing of the lumen. The gas may be a vapour generated by heating a liquid, paste or other solid applied to the lumen, the heating occurring at or preferably below an operating temperature of Stirling engine at the lumen.

The heater head may be in fluid communication with each of the thermal regenerator and the cylinder chamber. The cylinder chamber may be in fluid communication with the thermal regenerator via the heater head. Accordingly, the heater head connection may provide respective fluid-tight communications of the working fluid between each of the thermal regenerator and the heater head and the cylinder chamber and the heater head. The heater head may comprise at least one first aperture for fluid communication of the working fluid with the cylinder chamber. The heater head may comprise at least one second aperture for fluid communication with the thermal regenerator. The first aperture and the second aperture may be separated by a seal of the seal assembly. The seal may comprise an annular seal disposed between the first aperture at an inner diameter and the second aperture at an outer diameter. The assembly may comprise a further seal, the further seal being an outer annular seal disposed at a greater diameter than the second aperture. The seal and the further seal may be arranged in a same plane. The same plane may be perpendicular to a longitudinal axis of the cylinder. The heater head may comprise a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit. Each fluid conduit may comprise two ends, a first end for communication with the cylinder chamber and a second end for communication with the thermal regenerator. Each first end may comprise a first aperture and each second end may comprise a second aperture. The thermal regenerator may be an annular thermal regenerator disposed around an exterior of the cylinder chamber. Accordingly, the head connection may provide annular fluid connections via the second apertures between the heater head and the thermal regenerator. The plurality of first apertures may be in fluid communication at an interface between the heater head and the cylinder. The plurality of second apertures may be in fluid communication at the interface between the heater head and the cylinder. The interface may comprise a planar axial interface, such as between respective end axial faces of the heater head and the cylinder.

CERAMIC PARTS According to an aspect, there is provided a thermal Stirling cycle engine wherein at least two of the cylindrical wall and the displacer each may comprise a respective ceramic material, and wherein the respective ceramic material of each of the two is a dissimilar ceramic material.

Accordingly, there may be provided a thermal Stirling cycle engine comprising: a heater head; a cylinder connected to the heater head, the cylinder having a cylindrical wall forming a chamber, and containing a working fluid heatable by the heater head, a displacer mounted in the chamber for reciprocatingly moving the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; and a displacer drive rod for driving the displacer, wherein at least two of the cylindrical wall, the displacer and the displacer drive rod each may comprise a respective ceramic material, and wherein the respective ceramic material of each of the two is a dissimilar ceramic material.

The engine may operate as an energy convertor, such as converting thermal energy to mechanical energy. The mechanical energy may be further converted, such as to electrical energy.

The brittleness and low heat expansion of ceramic materials vis-a-vis that of metal components have previously precluded consideration and implementation of ceramic materials in such dynamic high temperature applications. The brittleness and low heat expansion of ceramics may appear counterintuitive for such application as herein disclosed. However, the present Applicants have developed arrangements whereby such very properties of ceramic can be utilised; even in combination with metal components.

The cylindrical wall and the displacer may comprise the respective ceramic material. Each of the cylindrical wall, the displacer and the drive rod may comprise a ceramic material. At least two of the ceramic materials may be a dissimilar ceramic material. Two of the cylindrical wall, the displacer or the drive rod may comprise a similar ceramic material.

The cylindrical wall and the displacer may comprise dissimilar ceramic materials, the cylindrical wall comprising a first ceramic material and the displacer comprising a second ceramic material, the second ceramic material being different from the first ceramic material.

A portion of the displacer may comprise the ceramic material, the portion being at a maximum diameter of the displacer, the maximum diameter portion of the displacer being contactable with the cylindrical wall. The portion may comprise a disc, such as with a circular cross-section. In at least some embodiments, the portion may comprise an annular portion.

The materials of the cylindrical wall and the displacer portion may be selected in dependence on each other to provide a friction coefficient sufficiently low at operation temperature to reduce energy loss.

The surface properties of the cylindrical wall and displacer portion may be selected in dependence on each other to reduce wear.

The ceramic materials may comprise compositions having very low thermal conductivity. The respective ceramic materials may have comparable heat expansion properties. For example, each of the respective ceramic materials may have a thermal expansion coefficient below a threshold/s. Accordingly, heat expansion of the ceramic material/s within the operating temperature range/s of the engine may be contained such that interference between the respective parts or components is mitigated or maintained at a sufficiently low level. Accordingly, the respective ceramic materials, such as of relatively moving parts or components, may respond to heat similarly such that contact forces at or between the respective ceramic materials is maintained across the operating temperature range. For example, the contact forces may be minimal, or even negligible, throughout operation of the engine.

The material for the cylinder, piston and drive rod may be chosen from refractory materials exhibiting a small thermal expansion and conduction coefficients; and a sufficiently high compression strength.

The material for the drive rod may be selected at least in partial dependence on the material's bending strength. The drive rod may comprise a hollow drive rod. The drive rod may comprise a reinforced drive rod.

The ceramic material may comprise a metal oxide carbide, nitride or silicide, wherein the metal is selected from the group consisting of aluminum, boron, magnesium, calcium; a transition metal, such as chromium, iron, nickel, nickel, niobium, titanium; yttrium, zirconium, or a mixture thereof, preferably least one of alumina, titania, chromium oxide, zirconia; aluminum nitride, titanium nitride, calcium nitride , silicon nitride; titanium carbide tungsten carbide, silicon carbide, and mixtures thereof.

The ceramic materials may be selected from the group consisting of magnesium oxide, yttrium oxide, aluminum oxide, aluminum nitride, silicon carbide, boron nitride, silicon nitride, boron carbide, silicon oxide, magnesium aluminate spinel, titanium carbide, titanium nitride, zirconium silicon oxide, and combinations thereof.

The displacer and cylinder may be dimensioned such that at operating temperature the displacer and cylindrical wall have a minimal friction therebetween.

The thermal Stirling cycle engine may comprise a Beta configuration, further comprising a power piston for phased synchronized reciprocating motion in the same axial directions as the displacer. The displacer and the power piston may each be connected to a drive system, the displacer drive rod passing through the power piston to connect the displacer to the drive system. The drive rod may comprise the ceramic material to accommodate a temperature differential along a length of the drive rod, such as from a displacer head to a distal end through the power piston. The drive rod end may be exposed to one or more of. a temperature in the relatively hotter portion of the cylinder chamber; a temperature in the relatively cooler portion of the cylinder chamber; and a coldest temperature below the power piston.

The drive system may further comprise one or more adjustable linkages to vary a phase angle between the displacer piston and the power piston.

The drive system may further comprise a connector assembly connecting the displacer for driving the displacer in the cylinder and for providing an adjustment of phase shift between the piston and the displacer.. The engine may further comprise a reciprocating member for moving the power piston in the cylinder towards the displacer in a compression stroke and away from the displacer in an expansion stroke, and providing a first dwell in a predetermined limited range of power piston movement near the beginning of the compression stroke of the power piston and providing a second dwell in the range of power piston movement near the beginning of the expansion stroke of the power piston, wherein the first dwell is longer than the second dwell. The engine may further comprise a means co-operable with the connector assembly and the reciprocating member for coordinating the reciprocating cycles of displacer and power piston so that the beginning of the piston expansion stroke occurs intermediately after the displacer stroke in the other direction, whereby heated working fluid is drawn into the cylinder during the expansion stroke.

The means co-operable with the connector assembly may adjustably coordinate the reciprocating cycles of the displacer and power piston, whereby cooled fluid is drawn into the cylinder during the first dwell and such that the piston is in its compression stroke during the longer dwell of the displacer.

The means co-operable with the connector assembly means may cause the power piston expansion stroke to occur simultaneously with a major portion of displacer movement in one direction, whereby the power piston is in an expansion stroke during introduction of heated working fluid into the cylinder.

HEAT SOURCE According to an aspect, there is provided an energy conversion apparatus for converting heat energy. The energy conversion apparatus may comprise a thermal Stirling cycle engine comprising a cylinder with a working fluid and a heater head for supplying heat to the working fluid. The energy conversion apparatus may comprise a heat source for supplying heat to the heater head. The heat source may comprise at least one of: a solid state heat source; and a liquid state heat source. The solid state heat source may be configured to be heated to a temperature of at least 850°C.

The heat source may be heated by solar energy, such as directly via a solar collector. The heat source may comprise a solar collector, and/or any component thereof, such as described in WO2015/097829 and/or in WO2009/002168, the contents of each being herein incorporated. The heat source may be heated indirectly, such as from one or more of: photovoltaic; wind; any other electric power source, such as from an electrical grid. The heat source may comprise a heat sink for transferring heat to working fluid in the heater head, the working fluid in the heater head may be in fluid communication with the working fluid in the cylinder.

The heat source may comprise a material with a specific heat capacity of at least around 400 J/(kg-K); optionally at least around 1000 J/{kg:K).

The heat source may be encased in or by an insulator, the insulator having a thermal conductivity of less than 3W/(m-K); optionally less than about 1.5W/(m-K).

The heat source may comprise a concrete. The heat source may comprise a ceramic. The heat source may be heatable to temperatures in a range of 850°C to 1400°C.

The thermal Stirling cycle engine may comprise a high temperature differential Beta configuration Stirling engine, with the cylinder fluidly connected to the heater head, the cylinder having a ceramic cylindrical wall defining a chamber for housing a reciprocating displacer, the displacer dividing the chamber into a hotter portion and a cooler portion, the cooler portion may be cooled by a cooling device.

The heater head may be mounted at or towards a core of the heat source and the cooling device may be mounted or directed away from the core.

The heater head may comprise the working fluid within one or more sealed conduits for circulating the working fluid within the heater head to receive heat from the heat source.

The one or more sealed conduits may be arranged to receive heat indirectly from the heat source.

The heat may be transferred from the heat source via radiation, such as at least predominantly by radiation. The heat may be transferred from the heat source via the compartment in the heater head. The heat may be transferred from the heat source via an inert fluid in the heater head. The inert fluid may be fluidly sealed from the working fluid. The heat may be transferred from the inert fluid through one or more tubular walls defining the one or more sealed conduits to the working fluid.

The energy conversion apparatus may be configured to function as an electrical generator for providing electrical energy.

The energy conversion apparatus may be configured to control operation of the thermal Stirling cycle engine to match electrical energy demand, the thermal Stirling cycle engine may be effectively instantaneously switched on and/or off.

The energy conversion apparatus may be configured to provide electricity supply for commercial use, such as for industrial use and/or to a grid or network.

The energy conversion apparatus may be stationary to provide in situ electrical energy as an output.

Alternatively, the energy conversion apparatus may comprise a mobile apparatus to provide a mobile electrical energy output, such as to provide power to a mode of transport.

The energy conversion apparatus may comprise a plurality of thermal Stirling cycle engines, each engine arranged to be heated by the heat source.

The energy conversion apparatus may further comprise a control system, wherein the control system may be arranged to adapt operation of each of the plurality of thermal Stirling cycle engines in dependence on a demand for output from the apparatus.

According to a further aspect there is provided a method of converting heat energy. The method may comprise heating a heat source of an energy conversion apparatus to a temperature of at least 850°C. The method may comprise transferring heat from the heat source to a heater head of a thermal Stirling cycle engine comprised in the energy conversion apparatus. The method may comprise supplying heat from the heater head to a working fluid in a cylinder of the thermal Stirling cycle engine comprised in the energy conversion apparatus.

HIGH TEMPERATURE DIFFERENTIAL ENGINE According to an aspect, there is provided a thermal Stirling cycle engine high temperature differential beta configuration, wherein the thermal Stirling cycle engine is configured to operate at a temperature of at least, optionally in excess of, 850°C.

Accordingly, in at least some examples, there may be provided a thermal Stirling cycle engine comprising: a heater head comprising a working fluid; a ceramic cylinder connected to the heater head, the cylinder having a ceramic cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head; a displacer mounted in the chamber for reciprocatingly moving the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; a thermal regenerator; a cooling device; wherein the heater head is in fluid communication with each of the thermal regenerator and the cylinder chamber; and the cooling device is in fluid communication with each of the thermal regenerator and the cylinder chamber; the relatively hotter portion of the cylinder chamber being in fluid communication with the thermal regenerator via the heater head; and the relatively cooler portion of the cylinder chamber being in fluid communication with the thermal regenerator via the cooling device; and wherein the thermal Stirling cycle engine comprises a high temperature differential beta configuration, the thermal Stirling cycle engine being configured to operate at a temperature in excess of 850°C.

The thermal Stirling cycle engine may be configured to operate with a maximum temperature in a range of from 850°C to 1400°C.

The thermal Stirling cycle engine may be configured to provide an efficiency of at least 45%. The thermal Stirling cycle engine may be configured to accommodate a temperature differential in the working fluid of 850°C or more.

The cooling device and/or the thermal regenerator may be configured to cool the working fluid to a temperature at least 850°C less than a maximum temperature of the working fluid, such as that of the working fluid passing from the heater head to the cylinder.

The heater head may be configured to heat the working fluid by and/or to at least 850°C. The heater head may comprise a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

A heat source may be provided for supplying heat to the heater head, wherein the heat source may comprise a solid state heat source, the solid state heat source being configured to be heated to a temperature of at least 850°C.

The cooling device may comprise a plurality of fluid conduits fluidly connecting the relatively cooler portion of the cylinder to the regenerator.

Each of the plurality of fluid conduits may comprise an aperture in a cylinder wall of the relatively cooler portion.

The plurality of apertures may be located in a non-ceramic cylinder wall portion, the non- ceramic cylinder wall portion being axially distal to the heater head.

The power piston may be located in the relatively cooler portion and the plurality of apertures may be arranged circumferentially in the cylinder wall at an axial location of the relatively cooler portion that is not traversed by the power piston. The drive rod from the displacer may pass through the power piston to a drive system.

According to a further aspect there are provided at least some examples of a power plant, comprising the apparatus, such as the Stirling engine/s, of any other aspect, example, embodiment or claim.

According to a further aspect there is provided a method of manufacturing an apparatus, such as a Stirling engine, or component thereof, according to any other aspect, embodiment, example or claim. The method may comprise additive printing, 3D printing. The method may comprise transferring manufacturing instructions, such as to or from a computer (e.g. vie internet, e-mail, file transfer, web or the like). In at least some examples, the method may comprise printing at least some of the components of the apparatus. For example, the method may comprise printing any or all of the ceramic components, such as of the cylinder, chamber, thermal regenerator housing, displacer head, drive rod, or the like. The components or apparatus may be supplied in a final-use configuration.

According to an aspect, there is provided a kit or array of apparatuses or devices. The kit may comprise the apparatus of any other aspect.

According to an aspect, there is provided a system comprising a controller according to an aspect, claim, embodiment or example of this disclosure, or a system arranged to perform a method according to an aspect, claim, embodiment or example of this disclosure.

According to an aspect, there is provided computer software which, when executed by a processing means, is arranged to perform a method according to aspect, claim, embodiment or example of this disclosure. The computer software may be stored on a computer readable medium. The computer software may be tangibly stored on a computer readable medium. The computer readable medium may be non-transitory. For example, the computer software may be for manufacturing the apparatus, such as for 3D printing a component thereof.

Any controller or controllers described herein may suitably comprise a control unit or computational device having one or more electronic processors. Thus, the system may comprise a single control unit or electronic controller or alternatively different functions of the controller may be embodied in, or hosted in, different control units or controllers. As used herein the term “controller” or “control unit” will be understood to include both a single control unit or controller and a plurality of control units or controllers collectively operating to provide any stated control functionality. In at least some examples, the controller is for regulating output from the one or more thermal Stirling cycle engines.

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

The invention includes one or more corresponding aspects, embodiments or features in isolation or in various combinations whether or not specifically stated (including claimed) in that combination or in isolation. For example, it will readily be appreciated that features recited as optional with respect to the first aspect may be additionally applicable with respect to the other aspects without the need to explicitly and unnecessarily list those various combinations and permutations here (e.g. the apparatus or device of one aspect may comprise features of any other aspect). Optional features as recited in respect of a method may be additionally applicable to an apparatus or device; and vice versa. In addition, corresponding means for performing one or more of the discussed functions are also within the present disclosure. The above summary is intended to be merely exemplary and non-limiting. Various respective aspects and features of the present disclosure are defined in the appended claims. It may be an aim of certain embodiments of the present disclosure to solve, mitigate or obviate, at least partly, at least one of the problems and/or disadvantages associated with the prior art. Certain embodiments may aim to provide at least one of the advantages described herein. Non-exhaustive examples of the present disclosure are provided in the below non- limiting clauses, which are distinct from the claims appended later in this disclosure:

REGENERATOR CLAUSES

1. A thermal regenerator for a Stirling engine, the thermal regenerator comprising a plurality of fluid channels for flow of a working fluid, the fluid channels providing an unobstructed flowpath for the working fluid so as to mitigate a pressure differential along the length of the fluid channels, wherein the thermal regenerator comprises a regenerator element, the regenerator element being formed from a corrugated sheet material, the sheet material formed into an annular shape to define the regenerator element with the corrugations defining the fluid channels, the corrugations running parallel to a longitudinal axis perpendicular to the annular shape.

2. The thermal regenerator of clause 1, wherein each fluid channel comprises a constant cross-section along its length to minimise a pressure drop along the length of the fluid channel.

3. The thermal regenerator of clause 1 or 2, wherein each fluid channel comprises a continuous fluid channel of constant cross-sectional shape along its length such that the working fluid can flow through the fluid channel without obstruction.

4. The thermal regenerator of any preceding clause, wherein at least some of the fluid channels are in fluid communication with each other.

5. The thermal regenerator of any preceding clause, wherein each of the plurality of fluid channels comprises a similar cross-section.

6. The thermal regenerator of clause 5, wherein the cross-section comprises a teardrop shape.

7. The thermal regenerator of any preceding clause, wherein the sheet material comprises a sheet material of uniform thickness.

8. The thermal regenerator of clause 7, wherein the regenerator element comprises a single sheet of stainless steel, or a nickel alloy, with an average thickness of from 0.1mm to 1mm.

9. The thermal regenerator of any preceding clause, wherein the annularly-shaped sheet comprises a greater surface area than a single sheet cylinder at either a maximum or minimum diameter corresponding to the annular shape of the regenerator element, with the annularly-shaped single sheet’s greater surface area may be a factor greater than a single sheet cylinder at the maximum and/or minimum diameter corresponding to the annular shape of the regenerator element.

10. The thermal regenerator of any preceding clause, wherein the corrugated sheet material is formed from a sheet with a length of approximately three times a cylindrical circumference of the annular shape.

11. The thermal regenerator of any preceding clause, wherein the thermal regenerator comprises a plurality of regenerator elements, the plurality of regenerator elements being arranged in series end-to-end such that each fluid channel of a first regenerator element is in series with corresponding fluid channels of a second regenerator element.

12. The thermal regenerator of clause 11, wherein the regenerator is configured to limit each regenerator element to a fraction of the total temperature differential across the thermal regenerator.

13. The thermal regenerator of any preceding clause, the thermal regenerator further comprising a radiation heat shield configured to reflect and/or deflect heat, wherein the heat shield is configured to minimise a change in flow.

14. The thermal regenerator of clause 13, wherein the heat shield is configured to mitigate a pressure drop across the heat shield; and wherein the heat shield comprises a similar cross-sectional area as the flowpaths through the regenerator element/s.

15. The thermal regenerator of clause 13 or 14, wherein the heat shield comprises a ceramic ring for fastening or aligning the regenerator element/s.

16. The thermal regenerator of clause 15, wherein the regenerator comprises a plurality of axially arranged regenerator elements such that the working fluid flows sequentially through the regenerators; and wherein each regenerator element is arranged with a heat shield at each axial end of the regenerator element such that a heat shield is arranged between each adjacent pair of regenerator elements and a heat shield is arranged at both axial ends of the regenerator.

17. The thermal regenerator of any preceding clause, wherein the thermal regenerator comprises an annular cavity for location around a Stirling engine cylinder chamber, the cavity comprising an inner wall at an inner diameter and an outer wall at an outer diameter, the walls comprising a ceramic; and wherein the regenerator element/s is housed in the cavity.

18. The thermal regenerator element of any preceding clause, the thermal regenerator element being for a thermal regenerator for a Stirling engine.

19. A method of manufacturing the thermal regenerator element of clause 18, the method comprising providing a sheet material with corrugations by passing the sheet material through a pair of interengaging forming elements, the pair of interengaging forming elements comprising two intercalating cog-wheels, to form the corrugations in the sheet material to provide the fluid channels.

20. The method of clause 19, wherein the method comprises embossing a thin sheet of metal to form a pattern of spaced discrete embossments that protrude a uniform amount from the surface of the sheet; wrapping the embossed sheet about a longitudinal axis into an annulus and locating the embossments to provide parallel axial fluid channels and unobstructed continuous flow paths.

21. The heat shield of any of clauses 13 to 16, the heat shield being for a thermal regenerator for a Stirling engine.

22. A method of manufacturing a thermal regenerator for a Stirling engine, the method comprising assembling a plurality of regenerator elements into an annular cavity adjacent a cylinder; and assembling a plurality of heat shields into or adjacent the cavity, axially arranged relative to the regenerator elements such that the heat shields function as fasteners to hold the regenerator elements in aligned positions within the annular cavity.

23. A thermal Stirling cycle engine comprising the thermal regenerator of clause 18 and optionally the heat shield of clause 21.

HEAD CLAUSES

1. A thermal Stirling cycle engine comprising: a heater head comprising a working fluid; a ceramic cylinder connected to the heater head, the cylinder having a cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head; a displacer mounted in the chamber for reciprocating movement by the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; a thermal regenerator, wherein the heater head is in fluid communication with each of the thermal regenerator and the cylinder chamber; and the cylinder chamber is in fluid communication with the thermal regenerator via the heater head; and wherein the heater head comprises a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

2. The thermal Stirling cycle engine clause 1, wherein the heater head comprises at least one first aperture for fluid communication of the working fluid with the cylinder chamber; and at least one second aperture for fluid communication with the thermal regenerator.

3. The thermal Stirling cycle engine of clause 2, wherein the first aperture and the second aperture are separated by a seal of the seal assembly.

4. The thermal Stirling cycle engine of clause 3, wherein each fluid conduit comprises two ends, a first end for communication with the cylinder chamber and a second end for communication with the thermal regenerator; and wherein each first end comprises a first aperture and each second end comprises a second aperture.

5. The thermal Stirling cycle engine of clause 4, wherein the plurality of first apertures are in fluid communication at an interface between the heater head and the cylinder; and the plurality of second apertures are in fluid communication at the interface between the heater head and the cylinder.

6. The thermal Stirling cycle engine of clause 4 or 5, wherein the plurality of first apertures and the plurality of second apertures alternate functioning as respective inlets and outlets with a change in cycles of the thermal Stirling cycle engine, such that a direction of fluid flow of the working fluid in each of the fluid conduits reverses.

7. The thermal Stirling cycle engine of any preceding clause, wherein the plurality of fluid conduits are defined by a plurality of thermally conductive tubes, the thermally conductive tubes each being of constant cross-section along their lengths to minimise a pressure differential along each respective tube.

8. The thermal Stirling cycle engine of clause 7, wherein the plurality of tubes are manufactured from an essentially pure metal able to sustain the tubular geometry and shape at an operating temperature in a range of from 850 to 1400 °C.

9. The thermal Stirling cycle engine according to clause 7 or 8, wherein the plurality of heater tubes are rotationally symmetric about their center axes, and wherein the heater tubes are spaced parallel with respect to one another, and at a distance and shape that during heating up or cooling down of the heater head, the tubes are in direct contact up to a temperature of 850°C or more.

10. The thermal Stirling cycle engine according to any of clauses 7 to 9, wherein the heater head comprises a heater head manifold, wherein the heater tubes are positioned in a staggered, annular or partially concentric array and form a toroidal shape, wherein the plurality of second apertures are located towards an outer diameter of the manifold, and the plurality of first apertures are located towards a radial centre of the manifold.

11. The thermal Stirling cycle engine according to clause 10, wherein the heater manifold is formed, such as cast, 3D-printed or machined from a single superalloy metallic material, or from an essentially pure metal, able to sustain the geometry and shape at an operating temperature in the range of from 850 to 1400 °C.

12. The thermal Stirling cycle engine according to any of clauses 7 to 11, wherein the plurality of first apertures are perpendicular to a central longitudinal axis of the ceramic cylinder such that each of the plurality of heater tubes provides a continuous linear flow path between the ceramic cylinder and a first tube portion of each fluid conduit adjacent the respective first apertures.

13. The thermal Stirling cycle engine according to clause 12, wherein each heater tube comprises the first tube portion that extends parallel to the longitudinal axis at an inner diameter, curves around with at least a minimum bend radius to a second tube portion transverse, such as perpendicular, to the first tube portion, the second portion extending the tube laterally away from the central longitudinal axis, the heater tube curving around a second bend with at least a minimum bend radius to a third tube portion, the third tube portion being transverse, such as perpendicular, to the second tube portion.

14. The thermal Stirling cycle engine according to clause 13, wherein each third tube portion extends to the respective second aperture, the second aperture optionally being at a smaller diameter than a maximum diameter relative to the central longitudinal axis of the second bend.

15. The thermal Stirling cycle engine of any of clauses 7 to 14, wherein the heater head comprises a sealed compartment for transferring heat from an exterior of the heater head, such as a sealed outer housing of the heater head, through each tube to the working fluid within each heater tube.

16. The thermal Stirling cycle engine of clause 15, wherein the heater head compartment comprises a vacuum.

17. The thermal Stirling cycle engine of clause 15, wherein the heater head compartment comprises an enclosed fluid, the enclosed fluid being sealingly separated from the working fluid.

18. The thermal Stirling cycle engine of any preceding clause, wherein the heater head is heated from a solid state heat source encasing the heater head.

19. The thermal Stirling cycle engine of any preceding clause, wherein the thermal regenerator is an annular thermal regenerator disposed around an exterior of the cylinder chamber.

HEAD CONNECTION CLAUSES

1. A thermal Stirling cycle engine comprising: a heater head comprising a working fluid; a ceramic cylinder connected to the heater head, the cylinder having a cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head;

a displacer mounted in the chamber for reciprocatingly displacing the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; wherein the ceramic cylinder and the heater head are connected and sealed by a gas- tight seal assembly comprising a lumen; wherein the lumen is compressively and gas- tightly disposed between the head and cylinder components, and wherein the lumen comprises an inert gas.

2. The thermal Stirling cycle engine according to clause 1, wherein the lumen is formed as an annular channel, with the heater head defining a first annular portion of the annular channel and the ceramic cylinder defines a second annular portion of the annular channel.

3. The thermal Stirling cycle engine according to clause 1 or 2, wherein the inert gas is pressurised.

4. The thermal Stirling cycle engine according to any preceding clause, wherein the inert gas is formed and pressurised by a thermal reaction on heating, such as initial heating of the heater head, the gas being derived from a non-gaseous composition applied to a portion of the lumen prior to sealing of the lumen.

5. The thermal Stirling cycle engine according to any preceding clause, wherein the lumen is sealed by pressure of the heater head against the cylinder, such as by mechanically fastening the heater head to the cylinder.

6. The thermal Stirling cycle engine of any preceding clause, further comprising a thermal regenerator, wherein the heater head is in fluid communication with each of the thermal regenerator and the cylinder chamber; and the cylinder chamber is in fluid communication with the thermal regenerator via the heater head.

7. The thermal Stirling cycle engine of clause 6, wherein the heater head comprises at least one first aperture for fluid communication of the working fluid with the cylinder chamber; and at least one second aperture for fluid communication with the thermal regenerator, wherein the first aperture and the second aperture are separated by a seal of the seal assembly, the seal comprising the inert gas.

8. The thermal Stirling cycle engine of clause 7, wherein the seal comprises an annular seal disposed between the first aperture at an inner diameter and the second aperture at an outer diameter.

9. The thermal Stirling cycle engine of clause 7 or 8, wherein the seal assembly comprises a further seal, the further seal being an outer annular seal disposed at a greater diameter than the second aperture; and the further seal comprising the inert gas.

10. The thermal Stirling cycle engine of clause 9, wherein the seal and the further seal are arranged in a same plane, the same plane being perpendicular to a longitudinal axis of the cylinder.

11. The thermal Stirling cycle engine of any of clauses 6 to 10, wherein the thermal regenerator is an annular thermal regenerator disposed around an exterior of the cylinder chamber.

12. The thermal Stirling cycle engine of any of clauses 6 to 11, wherein the heater head comprises a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

13. The thermal Stirling cycle engine of clause 12, wherein each fluid conduit comprises two ends, a first end for communication with the cylinder chamber and a second end for communication with the thermal regenerator; and wherein each first end comprises a first aperture and each second end comprises a second aperture.

14. The thermal Stirling cycle engine of clause 13, wherein the plurality of first apertures are in fluid communication at an interface between the heater head and the cylinder; and the plurality of second apertures are in fluid communication at the interface between the heater head and the cylinder.

15. The thermal Stirling cycle engine according to any preceding clause, wherein a securement of the heater head to the cylinder is provided by a fastener, wherein the fastener is configured to accommadate a difference in thermal expansion of the heater head and the cylinder at an operating temperature or over an operating temperature range of the engine.

16. The thermal Stirling cycle engine according to clause 15, wherein the fastener comprises a circlip, the circlip being formed of temperature resistant metal and comprising a partially-ring shaped body where the ends comprise a pair of integrally co-operative legs.

17. The thermal Stirling cycle engine of clause 16, wherein the circlip secures the heater head axially relative to the ceramic cylinder, the circlip being configured to accommodate mechanical and thermal differences between the heater head and the ceramic cylinder under operating conditions to prevent axial movement therebetween.

CERAMIC PARTS CLAUSES

1. A thermal Stirling cycle engine comprising: a heater head; a cylinder connected to the heater head, the cylinder having a cylindrical wall forming a chamber, and containing a working fluid heatable by the heater head; a displacer mounted in the chamber for reciprocatingly moving the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; and a displacer drive rod for driving the displacer; wherein at least two of the cylindrical wall, the displacer or the displacer drive rod each comprises a respective ceramic material; and wherein the respective ceramic material of each of the two is a dissimilar ceramic material.

2. The thermal Stirling cycle engine of clause 1, wherein each of the cylindrical wall, the displacer and the displacer drive rod comprises a ceramic material; and wherein at least two of the ceramic materials is a dissimilar ceramic material.

3. The thermal Stirling cycle engine of clause 1 or 2, wherein two of the cylindrical wall, the displacer or the displacer drive rod comprises a similar ceramic material.

4. The thermal Stirling cycle engine of any preceding clause, wherein the cylindrical wall and the displacer comprise dissimilar ceramic materials, the cylindrical wall comprising a first ceramic material and the displacer comprising a second ceramic material, the second ceramic material being different from the first ceramic material.

5. The thermal Stirling cycle engine of any preceding clause, wherein a portion of the displacer comprises the ceramic material, the portion being at a maximum diameter of the displacer, the maximum diameter portion of the displacer being contactable with the cylindrical wall.

6. The thermal Stirling cycle engine according to clause 5, wherein the materials of the cylindrical wall and displacer portion are selected in dependence on each other to provide a friction coefficient sufficiently low at operation temperature to reduce energy loss.

7. The thermal Stirling cycle engine according to clause 5 or 6, wherein the surface properties of the cylindrical wall and displacer portion are selected in dependence on each other to reduce wear.

8. The thermal Stirling cycle engine of any preceding clause, wherein the ceramic materials comprise compositions having very low thermal conductivity.

9. The thermal Stirling cycle engine of any preceding clause, wherein the material for the cylinder, piston and displacer drive rod are chosen from refractory materials exhibiting a small thermal expansion and conduction coefficients and a sufficiently high compression strength.

10. The thermal Stirling cycle engine of any preceding clause, wherein a material for the displacer drive rod is selected at least in partial dependence on the material's bending strength.

11. The thermal Stirling cycle engine of any preceding clause, wherein the displacer drive rod comprises a hollow displacer drive rod.

12. The thermal Stirling cycle engine of any preceding clause, wherein the displacer drive rod comprises a reinforced displacer drive rod.

13. The thermal Stirling cycle engine of any preceding clause, wherein the ceramic material comprises a metal oxide carbide, nitride or silicide, wherein the metal is selected from the group consisting of aluminum, boron, magnesium, calcium; a transition metal, such as chromium, iron, nickel, nickel, niobium, titanium; yttrium, zirconium, or a mixture thereof, preferably least one of alumina, titania, chromium oxide, zirconia; aluminum nitride, titanium nitride, calcium nitride , silicon nitride; titanium carbide tungsten carbide, silicon carbide, and mixtures thereof.

14. The thermal Stirling cycle engine of any preceding clause, wherein the ceramic materials are selected from the group consisting of magnesium oxide, yttrium oxide, aluminum oxide, aluminum nitride, silicon carbide, boron nitride, silicon nitride, boron carbide, silicon oxide, magnesium aluminate spinel, titanium carbide, titanium nitride, zirconium silicon oxide, and combinations thereof.

15. The thermal Stirling cycle engine of any preceding clause, wherein the displacer and cylinder are dimensioned such that at operating temperature the displacer and cylindrical wall have a minimal friction therebetween.

16. The thermal Stirling cycle engine of any preceding clause, wherein the thermal Stirling cycle engine comprises a Beta configuration, further comprising a power piston for phased synchronized reciprocating motion in the same axial directions as the displacer, the displacer and the power piston each being connected to a drive system, the displacer drive rod passing through the power piston to connect the displacer to the drive system.

17. The thermal Stirling cycle engine according to clause 16, wherein the drive system further comprises one or more adjustable linkages to vary a phase angle between the displacer piston and the power piston.

18. The thermal Stirling cycle engine according to clause 17, wherein the drive system further comprises a connector assembly connecting the displacer for driving the displacer in the cylinder; the engine further comprising a means co- operable with the connector assembly for coordinating the reciprocating cycles of displacer and power piston so that the beginning of the piston expansion stroke occurs intermediately after the displacer stroke in the other direction, whereby heated working fluid is drawn into the cylinder during the expansion stroke.

19. The thermal Stirling cycle engine according to clause 18, wherein the means co- operable with the connector assembly adjustably coordinates the reciprocating cycles of the displacer and power piston, whereby cooled fluid is drawn into the cylinder during the first dwell and such that the piston is in its compression stroke during the longer dwell of the displacer.

20. The thermal Stirling cycle engine according to clause 18 or 19, wherein the means co-operable with the connector assembly means causes the power piston expansion stroke to occur simultaneously with a major portion of displacer movement in one direction, whereby the power piston is in an expansion stroke during introduction of heated working fluid into the cylinder.

HIGH TEMPERATURE DIFFERENTIAL CLAUSES

1. A thermal Stirling cycle engine comprising: a heater head comprising a working fluid; a ceramic cylinder connected to the heater head, the cylinder having a ceramic cylindrical wall defining a chamber, the chamber being in fluid communication with the working fluid heatable by the heater head; a displacer mounted in the chamber for reciprocating movement by the working fluid, the displacer dividing the chamber into a relatively hotter portion and a relatively cooler portion; a thermal regenerator; a cooling device;

wherein the heater head is in fluid communication with each of the thermal regenerator and the cylinder chamber; and the cooling device is in fluid communication with each of the thermal regenerator and the cylinder chamber; the relatively hotter portion of the cylinder chamber being in fluid communication with the thermal regenerator via the heater head; and the relatively cooler portion of the cylinder chamber being in fluid communication with the thermal regenerator via the cooling device; and wherein the thermal Stirling cycle engine comprises a high temperature differential beta configuration, the thermal Stirling cycle engine being configured to operate at a temperature in excess of 850°C.

2. The thermal Stirling cycle engine of clause 1, wherein the thermal Stirling cycle engine is configured to operate with a maximum temperature in a range of from 850°C to 1400°C.

3. The thermal Stirling cycle engine of clause 1 or clause 2, where the thermal Stirling cycle engine is configured to provide an efficiency of at least 45%.

4. The thermal Stirling cycle engine of any preceding clause, wherein the thermal Stirling cycle engine is configured to accommodate a temperature differential in the working fluid of 850°C or more.

5. The thermal Stirling cycle engine of clause 4, wherein the cooling device and/or the thermal regenerator are configured to cool the working fluid to a temperature at least 850°C less than that of the working fluid passing from the heater head to the cylinder.

6. The thermal Stirling cycle engine of clause 4 or 5, wherein the heater head is configured to heat the working fluid by at least 850°C.

7. The thermal Stirling cycle engine of any preceding clause, wherein the heater head comprises a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

8. The thermal Stirling cycle engine of any preceding clause, wherein a heat source is provided for supplying heat to the heater head, wherein the heat source comprises a solid state heat source, the solid state heat source being configured to be heated to a temperature of at least 850°C.

9. The thermal Stirling cycle engine of any preceding clause, wherein the cooling device comprises a plurality of fluid conduits fluidly connecting the relatively cooler portion of the cylinder to the regenerator.

10. The thermal Stirling cycle engine of clause 9, wherein each of the plurality of fluid conduits comprises an aperture in a cylinder wall of the relatively cooler portion.

11. The thermal Stirling cycle engine of clause 10, wherein the plurality of apertures are located in a non-ceramic cylinder wall portion, the non-ceramic cylinder wall portion being axially distal to the heater head.

12. The thermal Stirling cycle engine of clause 10 or 11, wherein a power piston is located in the relatively cooler portion and the plurality of apertures are arranged circumferentially in the cylinder wall at an axial location of the relatively cooler portion that is not traversed by the power piston.

13. The thermal Stirling cycle engine of clause 12, wherein a displacer drive rod from the displacer passes through the power piston to a drive system.

14. The thermal Stirling cycle engine of clause 13, wherein at least two of the cylindrical wall, the displacer or the displacer drive rod each comprises a respective ceramic material, and wherein the respective ceramic material of each of the two is a dissimilar ceramic material.

15. The thermal Stirling cycle engine of clause 14, wherein the cylindrical wall and the displacer comprise dissimilar ceramic materials, the cylindrical wall comprising a first ceramic material and the displacer comprising a second ceramic material, the second ceramic material being different from the first ceramic material.

16. The thermal Stirling cycle engine of any preceding clause, wherein the thermal regenerator is an annular thermal regenerator disposed around an exterior of the cylinder chamber.

17. The thermal Stirling cycle engine of clause 16, the heater head comprises at least one first aperture for fluid communication of the working fluid axially with the cylinder chamber; and at least one second aperture for fluid communication with the thermal regenerator, the first aperture and the second aperture being separated by a seal of the seal assembly.

18. The thermal Stirling cycle engine of any preceding clause, wherein heat is transferred to the working fluid in the heater head via an inert fluid in the heater head, the inert fluid being fluidly sealed within the heater head from the working fluid, the heat being transferred from the inert fluid through one or more tubular walls to the working fluid.

19. The thermal Stirling cycle engine of any preceding clause, wherein the thermal Stirling cycle engine is configured to function as an electrical generator for providing electrical energy.

20. The thermal Stirling cycle engine of clause 19, wherein the operation of the thermal Stirling cycle engine is controllable to match electrical energy demand, the thermal Stirling cycle engine being effectively instantaneously switched on and/or off.

21. The thermal Stirling cycle engine of any preceding clause, wherein the thermal Stirling cycle engine is configured to provide electricity supply for commercial use, such as for industrial use and/or to a grid or network.

22. The thermal Stirling cycle engine of any preceding clause, wherein the thermal Stirling cycle engine is stationary to provide in situ electrical energy as an output.

23. The thermal Stirling cycle engine of any of clauses 1 to 21, wherein the apparatus comprises a mobile apparatus to provide a mobile electrical energy output, such as to provide power to a mode of transport.

24. An energy conversion apparatus comprising a plurality of the thermal Stirling cycle engines of any preceding clause.

SOLID OR LIQUID STATE CLAUSES

1. An energy conversion apparatus for converting heat energy, the energy conversion apparatus comprising a thermal Stirling cycle engine comprising a cylinder with a working fluid and a heater head for supplying heat to the working fluid; a heat source for supplying heat to the heater head, wherein the heat source comprises at least one of: a solid state heat source; and a liquid state heat source; and wherein the heat source is configured to be heated to a temperature of at least 850°C.

2. The energy conversion apparatus of clause 1, wherein the heat source is heated by solar energy, such as directly via a solar collector.

3. The energy conversion apparatus of clause 1, wherein the heat source is heated indirectly, such as from one or more of. photovoltaic; wind; any other electric power source, such as from an electrical grid.

4. The energy conversion apparatus of any preceding clause, wherein the heat source comprises a heat sink for transferring heat to working fluid in the heater head, the working fluid in the heater head being in fluid communication with the working fluid in the cylinder.

5. The energy conversion apparatus of any preceding clause, wherein the heat source comprises a material with a specific heat capacity of at least around 400 J/(kg-K}; optionally at least around 1000 J/(kg-K).

6. The energy conversion apparatus of any preceding clause, wherein the heat source is encased in or by an insulator, the insulator having a thermal conductivity of less than 3W/(m-K); optionally less than about 1.5W/(m-K).

7. The energy conversion apparatus of any preceding clause, wherein the solid state heat source comprises a concrete.

8. The energy conversion apparatus of any preceding clause, wherein the solid state heat source comprises a ceramic.

9. The energy conversion apparatus of any preceding clause, wherein the heat source is heatable to temperatures in a range of 850°C to 1400°C.

10. The energy conversion apparatus of any preceding clause, wherein the thermal Stirling cycle engine comprises a high temperature differential Beta configuration Stirling engine, with the cylinder fluidly connected to the heater head, the cylinder having a ceramic cylindrical wall defining a chamber for housing a reciprocating displacer, the displacer dividing the chamber into a hotter portion and a cooler portion, the cooler portion being cooled by a cooling device.

11. The energy conversion apparatus of clause 10, wherein the heater head is mounted at or towards a core of the heat source and the cooling device is mounted or directed away from the core.

12. The energy conversion apparatus of any preceding clause, wherein the heater head comprises the working fluid within one or more sealed conduits for circulating the working fluid within the heater head to receive heat from the solid state heat source.

13. The energy conversion apparatus of clause 12, wherein the one or more sealed conduits are arranged to receive heat indirectly from the heat source.

14. The energy conversion apparatus of clause 13, wherein heat is transferred from the heat source via an inert fluid in the heater head, the inert fluid being fluidly sealed from the working fluid, the heat being transferred from the inert fluid through one or more tubular walls defining the one or more sealed conduits to the working fluid.

15. The energy conversion apparatus of any preceding clause, wherein the apparatus is configured to function as an electrical generator for providing electrical energy.

16. The energy conversion apparatus of clause 15, wherein the apparatus is configured to control operation of the thermal Stirling cycle engine to match electrical energy demand, the thermal Stirling cycle engine being effectively instantaneously switched on and/or off.

17. The energy conversion apparatus of any preceding clause, wherein the apparatus is configured to provide electricity supply for commercial use, such as for industrial use and/or to a grid or network.

18. The energy conversion apparatus of any preceding clause, wherein the apparatus is stationary to provide in situ electrical energy as an output.

19. The energy conversion apparatus of any of clauses 1 to 17, wherein the apparatus comprises a mobile apparatus to provide a mobile electrical energy output, such as to provide power to a mode of transport.

20. The energy conversion apparatus of any preceding clause, wherein the apparatus comprises a plurality of thermal Stirling cycle engines, each engine arranged to be heated by the solid state heat source.

21. The energy conversion apparatus of clause 20, further comprising a control system, wherein the control system is arranged to adapt operation of each of the plurality of thermal Stirling cycle engines in dependence on a demand for output from the apparatus.

22. A method of converting heat energy, the method comprising: heating a heat source of an energy conversion apparatus to a temperature of at least 850°C; transferring heat from the heat source to a heater head of a thermal Stirling cycle engine comprised in the energy conversion apparatus; and supplying heat from the heater head to a working fluid in a cylinder of the thermal Stirling cycle engine comprised in the energy conversion apparatus; wherein the heat source is at least one of: a solid state heat source; a liquid state heat source.

BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: FIG. 1 is a longitudinal vertical cross-sectional view showing the overall arrangement for a Stirling engine according to the disclosure. FIG. 2 is a perspective view of a regenerator element shown without inner and outer sleeves to expose the surface of the element.

Fig. 2a is a perspective view of the regenerator element of Fig.2 housed in a portion of a cylinder assembly. Fig. 2b is a cross-sectional view of the regenerator element and cylinder housing portion of Fig. 2a. FIG. 3 is a schematic illustration of a top plan view of the regenerator.

FIG. 4 is a detailed view of a portion of FIG. 3. FIG. 5 is a three-quarters isometric view of the heater head. FIG. 6 is a top plan view of the heater head. FIG. 7 is a detail vertical cross-sectional view showing the heater head of the Stirling engine of FIG. 1.

FIG. 8 is a detail vertical cross-sectional view showing the heater head connection of the Stirling engine of FIG. 1. FIG. 9 is a side view of the displacer of the of the Stirling engine of FIG. 1. FIG. 10 is a vertical cross-sectional view of the displacer. FIG. 11 is a detail vertical cross-sectional view of the head of the displacer.

FIG. 12 is a vertical cross-sectional view of the cooling device of the Stirling engine of FIG. 1. Fig. 13 shows an example of a heater head assembly.

DETAILED DESCRIPTION Inthe following description of the invention, the components are illustrated and described in a vertical orientation with the cylinder located above the lower housing. Terms such as upper, lower, above and below are used to describe the relative positions of components and are not intended to indicate a quality or locational requirement since the cylinder can be ariented in any position relative to the housing and crankshaft.

In the B-line up of the Stirling Cycle engines, a work piston and a displacer piston are reciprocably mounted typically in the same cylinder. The displacer piston movement in one direction in the cylinder fills the cylinder with cool gas, referred to also as the working fluid, and displacer movement in the other direction in the cylinder filling the cylinder with heated working fluid.

In engine mode of operation, a heater head connected to the cylinder is heated, and a regenerator through which the working fluid is pumped by the displacer piston, is utilized to cool the working fluid when the displacer moves in the one direction, and heat the working fluid passing through it when the displacer moves in the other direction. The work piston is operatively connected to a crankshaft by means of a conventional connecting rod to drive the crankshaft when hot working fluid is drawn into the cylinder and its expansive forces move the piston in its power stroke. The displacer piston is connected to a crankshaft, by connection in conventional manner by a connecting rod, and operates in timed relation with the piston crankshaft to cause the working fluid to be drawn into the cylinder in a manner to drive the piston and its crankshaft. Since the external heating of the working fluid in the heater head may be accomplished on a continuous basis, irrespective of the displacer and piston position in the cylinder, and is not confined to the cylinder in which the displacer and work pistons move, the operation of the engine can be essentially pollution free, can use any fuel, is quiet in operation, does not require a timed ignition system and may therefore even be adapted to solar power operation.

Despite advantages, and notwithstanding considerable developmental effort by the industry, the Stirling engine has not found widespread use due to relatively low specific power rates. According to one example of the present invention, the hot zone of the chamber is heated by energy from a heat source, and a cooling system maintains the cold zone at a lower temperature than the hot zone. A cooling fluid may be drawn from a reservoir of cooling fluid. Referring to Figure 1, components of a Stirling engine 12 having a heater head assembly 14; a power piston 16 that drives an output crankshaft 20, and a displacer 18 are illustrated. A working fluid, preferably an inert gas, is contained in a cylinder assembly 22 above the power piston 16 and is shuttled through heat transfer tubing 24 and a thermal regenerator 26 by the action of the displacer 18. A portion of a cylinder 36 surrounds the regenerator 26. The cylinder 28 here comprises an inner shell 38 and an outer shell 36. The upper portion 30 of the cylinder 28 is connected to the head assembly 14, whereby the connection is fastened via a metal circlip 32. In other examples (not shown), alternative fastening is provided, such as with an alternative self-tightening, thermally-compensating fastener. The circlip 32, or alternative fastener, is configured to accommodate a relative difference in expansion of the heater head 14 and the cylinder

28. The regenerator 26 preferably comprises a series of annular rings 34 of corrugated heat resistant material, such as shown in Figure 2, disposed between a cylinder outer shell 36 and an inner shell 38 and situated in cartridges that form a cylinder surrounding the piston and defining the inner chamber of the cylinder. An example of such a cartridge arrangement is shown in Figures 2a and 2b, wherein the regenerator element 34 is sandwiched between an inner cylindrical wall and an outer cylindrical wall, with both walls being ceramic in this particular embodiment. The displacer 18 is essentially cylindrical and is concentrically positioned within the cylinder chamber 40 of the cylindrical housing between the heater head 14 and a cooling device 42. The heater head 14 is concentrically positioned with the cylindrical housing 28 and aligned with the chamber 40 along the central axis 44. In at least one embodiment, the heater head 14 itself is a physically separate component which is affixed to the cylindrical housing 28 by a cylindrical flange interface 46 between the heater head 14 and the cylindrical housing 28. A sealing assembly 48 pattern is radially spaced out from the cylinder axis on the cylindrical flange interface 46, by which the heater head 14 may be affixed in order to attach to the cylindrical housing 28 in a gas tight manner.

The cylindrical housing 28 further preferably comprises an annular coolant chamber 50 and a working fluid chamber 52. The cooling device 42 is positioned around a chamber portion housing the power piston 16.

The present Stirling cycle engine 12 preferably is heated by thermal energy obtained by direct or indirect sustainable heat, e. g. sunlight. Ideally, the heater head portion 14 of the Stirling engine 12 is operated at a temperature of, for example, of above 1000°C, more preferably of from 500°C to 1400 °C, more preferably of from 600°C to about 2000°C.

Previous commercially available Stirling engines (not shown) usually cannot operate at the upper end of these ranges due to mechanical failure of the materials used in the heater head and regenerator and piston assemblies. Applicants now have designed a Stirling cycle engine 12 that is able withstand such temperatures and pressures. In at least one example, this is achieved by combining a heater head assembly 14 according to the present disclosure with ceramic cylinders 36 and 38, displacer 18 and drive rod 54, and a regenerator 26 according to this disclosure, whereby the heater head 14 and regenerator 26 are connected and sealed by a resilient and elastic gas-tight seal assembly 48 comprising a rigid housing with an outer wall forming a lumen; wherein the lumen compressively and gas-tightly is disposed between the head 14 and cylinder 28 components, and wherein the lumen comprises an inert gas at an elevated pressure. Preferably, the engine 12 comprises a fastener, such as a circlip 32 formed of temperature resistant metal and comprising a part-ring shaped body part having one end turned inwardly at such that if forms a coiled structure, whereby the ends form a pair of integrally co-operative legs. Accordingly there is provided a thermal energy conversion apparatus 10 for converting heat energy. The thermal energy apparatus 10 comprises a thermal engine 12. The thermal engine 12 comprises a closed-circuit cyclic engine 12. The thermal engine 12 comprises a regenerative heat engine, such as a closed-cycle regenerative heat engine

12. The thermal engine 12 comprises a gaseous working fluid, such as air or a component/s thereof. The gaseous working fluid is permanently gaseous, such as throughout every entire cycle of the thermal engine 12. The thermal engine 12 comprises a Stirling engine 12. The Stirling engine 12 comprises a RR Stirling engine 12. The Stirling engine 12 comprises a single cylinder assembly 22. The single cylinder assembly 22 comprises a hot end 23 and a cold end 25, relative to each other. The Stirling engine 12 comprises a high temperature differential engine 12. For example, the single cylinder assembly 22 comprises a temperature differential of up to 1000°C or more, such as between the cold end 25 and the hot end 23. The thermal energy conversion apparatus 10 is for converting energy from heat to another form of energy. The thermal energy conversion apparatus 10 is for converting heat energy to mechanical energy. The thermal energy conversion apparatus 10 is for converting heat energy to electrical energy. The thermal energy conversion apparatus 10 comprises an electrical generator. The apparatus 10 comprises a heater. The heater is configured to transfer heat to the engine, such as from an external heat source. The heater comprises a heater head 14.

The apparatus 10 comprises a cylinder assembly 22. The cylinder assembly 22 comprises a hot end 23 and a cold end 25. The hot end 25 comprises a hot end chamber 41; and the cold end comprises a cold end chamber 43; each chamber hosing working fluid within the cylinder assembly 22. The hot end 23 and cold end 25 are in fluid communication via the thermal regenerator 26. The apparatus 10 comprises a displacer 18. The displacer 18 is movable relative to the cylinder assembly 22. The displacer 18 divides the cylinder assembly 22 into the hot end 23 and the cold end 25. The respective volumes of the chambers 41, 43 vary with the movement of the displacer 18. Change in the volume and/or pressure of the chambers 41,43 is driven by the movement of the displacer 18. The displacer 18 cyclically subjects each of the chambers 41, 43 to expansion and compression. The displacer 18 here is driven by the displacer driverod 54, which in turn is driven by the crankshaft 86, which in turn is driven by a wheel (not shown), the wheel in turn being driven by crankshafts 82, 84 powered by the power piston 16. The displacer 18 divides the cylinder assembly 22 into a relatively cooler portion and a relatively hotter portion. Here, the displacer 18 comprises a displacer piston. The displacer 18 comprises a close fit with the cylinder assembly 22 wall. In other examples (not shown), the displacer 18 may seal against the cylinder wall. The respective portions in the cylinder comprising the working fluid, such as the hot end and cold end chamber portions 41, 43, are in fluid communication with each other via one or more fluid passages 52 in the co-annular space between the ceramic cylinders 36 and 38. As shown in more detail in Figures 9, 10 and 11, the apparatus 10 comprises a drive rod

54. The drive rod 54 is connected to the displacer 18. The drive rod 54 is for transferring work from a crankshaft for driving the displacer 18.

The apparatus 10 comprises the power piston 16. The piston is mechanically linked to the displacer 18 via one or more of! a wheel, such as flywheel or the like; a linkage; a linkage assembly; a connector assembly (not all shown). The drive rod 54 of the displacer 18 passes through the power piston 16, here centrally through the power piston

16. The displacer 18 drive rod 54 is in reciprocating sealing engagement with the power piston 16.

The apparatus 10 comprises a heat exchanger in the form of the thermal regenerator 26.

The thermal regenerator 26 is for at least partially temporarily storing heat, such as between cycles. Accordingly, the heat exchanger is for transferring heat between cycles, or portions thereof, of the thermodynamic cycle, such as between a compression cycle or phase and an expansion cycle or phase. The thermal regenerator can transfer heat between the working fluid and a portion of the apparatus 10. The portion of the apparatus 10 can comprise the cylinder assembly 22, such as the hot end chamber portion. The portion of the thermodynamic cycle comprises a movement of the displacer 18, such as stroke, or portion thereof, of the displacer 18. The thermal regenerator 26 is in fluid communication with the heater 14 of the apparatus 10. The thermal regenerator 26 is in fluid communication with the cooling device 42.

The apparatus 10 comprises a heat sink. The heat sink comprises the cooling device 42. The cooler 42 is configured to passively cool the working fluid. The cooler 42 is configured to extract heat from the working fluid. The cooler 42 is configured to redirect heat extracted from the working fluid to another portion of the apparatus 10. The cooler 42 is configured to transfer heat to outside the engine 12. In at least some examples, the cooler 42 is configured to transfer heat to an external environment, such as an atmospheric environment (not shown). The cooler 42 can be configured to indirectly transfer heat to the external environment.

Figures 2, 3 and 4 show a regenerator element 34 of the thermal regenerator 26 of the present disclosure. The thermal regenerator 26 comprises a fluid channel 27 for flow of the working fluid, such as flow of the working fluid between the chambers 41, 43 or hot and cold portions or ends 23, 25 of the cylinder assembly 22. The fluid channel 27 is configured to prevent or at least mitigate a pressure differential along the length of the fluid channel 27. The fluid channel 27 provides an unobstructed flowpath for the working fluid.

The fluid channel 27 comprises a constant cross-sectional area along its entire length, the cross-section of the regenerator element 26 defining the fluid channels 27 being shown in Figures 3 and 4. The fluid channel 27 comprises a constant cross-section along its length. The fluid channel 27 comprises a constant cross-sectional shape along its length. Each fluid channel 27 comprises a constant cross-sectional shape along its length such that the working fluid may flow along or through the fluid channel 27 without obstruction. The fluid channel 27 comprises a continuous fluid channel 27 of constant cross-section along its length to minimise or prevent a pressure differential, such as pressure drop, along the length of the fluid channel.

The thermal regenerator 26 comprises a plurality of fluid channels 27. In at least some examples, at least some of the fluid channels 27 are in fluid communication with each other. For example, as shown her, adjacent fluid channels 27 interconnect. In at least some examples, the thermal regenerator 26 effectively comprise only a single or only a pair of flow paths. The pair of flow paths comprises an inner annular flowpath and an outer annular flowpath, such as separated by a thickness of the regenerator element 34. The/each flow path comprises a multitude of fluid channels 27. In other examples, at least some of the fluid channels 27 are fluidly isolated from each other. For example, the fluid channels 27 may be separated by a portion/s of the regenerator 26 and/or a seal and/or additional member/s. Each of the plurality of fluid channels 27 comprises a similar cross-section, such as a similar cross-sectional area and/or shape. The cross-sectional shape comprises a teardrop shape. The teardrop is open at its pointed end, such as open into to fluidly connect the fluid channel 27 to other fluid channels 27, such as the pointed ends of laterally-arranged other fluid channels 27. The fluid channels 27 are arranged in alternating orientations. For example, each alternate teardrop shape has its pointed end directed towards a similar direction, such as either inwardly or outwardly. Inwardly oriented fluid channels 27 are interspersed with outwardly oriented fluid channels 27. Here, each of the inwardly-oriented fluid channels 27 comprises a same first cross- section; and each of the outwardly-oriented fluid channels 27 comprises a same second cross-section. The thermal regenerator 26 comprises a regenerator element 34 comprises or define the fluid channels 27. The regenerator element 34 is formed from a sheet material. The regenerator element 34 comprises a single sheet material of uniform thickness. The single sheet is formed so as to define the plurality of fluid channels 27. The single sheet is formed into an annular shape.

The annularly-shaped single sheet comprises a greater surface area than a single sheet cylinder at either a maximum or minimum diameter corresponding to the annular shape of the regenerator element 34. The annularly-shaped single sheet’s greater surface area is a factor greater than a single sheet cylinder (not shown) at the maximum and/or minimum diameter corresponding to the annular shape of the regenerator element 34. The factor her is about three.

Accordingly, in at least some examples the annularly-shaped sheet’s surface area is a factor of three greater than a single sheet cylinder at the maximum and/or minimum diameter corresponding to the annular shape of the regenerator element 34. The provision of a relatively greater surface area allows a greater heat transfer between the regenerator 26 and the working fluid flowing through the regenerator 26 (such as compared to a reduced surface area). The single sheet comprises a corrugated sheet.

The corrugations of the corrugated sheet define the plurality of fluid channels 27. The sheet material defines a corrugated cylindrical shape when assembled, as shown in Figure 2. The corrugations run in a longitudinal direction, parallel to the 44 longitudinal axis of the cylinder assembly 22. In comparison to alternative means to provide an increased surface area, such as the provision of mesh or filamentous regenerator elements, the provision of the corrugated regenerator element 34 provides an improved flow, such as with less or no pressure drop along the flowpath through or along the regenerator element 34. In some examples, the respective ends of the sheet material are unjoined, such as loosely meeting, so as to enclose an inner volume, such as an inner roughly cylindrical volume within the sheet material.

In other examples, the respective ends of the corrugated sheet material are connected, such as mechanically joined, so as to enclose the inner volume, such as the inner roughly cylindrical volume within the annularly formed sheet material.

Although not shown, it will be appreciated that the regenerator element 34 of Figure 2 can be formed by a method of manufacturing comprising providing a sheet material with corrugations.

The method comprises passing the sheet material through a pair of interengaging forming elements.

The pair of interengaging forming elements comprises two intercalating cog-wheels.

The method comprises passing the sheet material through the pair of interengaging forming elements to form the corrugations in the sheet material, for providing the fluid channels 27.

The method comprises embossing a thin sheet of metal to form a pattern of spaced discrete embossments that protrude a uniform amount from the surface of the sheet.

The method comprises wrapping the embossed sheet about a longitudinal axis 44 into an annulus such that individual sheets are spaced apart by the embossments.

The method comprises locating the embossments to provide parallel axial flow paths and unobstructed continuous annular channels for the working fluid of the heat engine 12 that minimize pressure losses and maximize heat transfer.

The method comprises installing layers of foil of approximately uniform thickness in a generally cylindrical space 52. The method comprises cutting a piece of foil to a length such that a distance between axial edges of the piece of foil are cut approximately equal to three times the circumference of the inner surface of the generally cylindrical space to be defined by the annular shape.

The method comprises embossing the cut foil by running the foil between the two intercalating cog-wheels such that the axial edges are overlapping.

The method comprises inserting the embossed foil into the generally cylindrical space 52 to form the annular regenerator element 34. The thermal regenerator 26 comprises a plurality of regenerator elements 34. The plurality of regenerator elements 34 are arranged in series such that each fluid channel 27 of a first regenerator element 34 is in series with corresponding fluid channels 27 of a second regenerator element 34. Accordingly the working fluid may flow from the fluid channels 27 of the first regenerator element 34 into corresponding channels of the second regenerator element 34 (or vice versa, such as during a reverse cycle). Figure 1 shows a series of four regenerator elements 34 stacked in the cylinder cavity 52, each second regenerator element 34 being similar, such as at least of similar cross-sectional shape and/or dimension perpendicular to the direction of flow (e.g. as shown in Figures 2, 3 and 4). The plurality of regenerator elements 34 is arranged end-to-end.

Each regenerator element 34 is configured to provide a rapid heat transfer.

Each regenerator element 34 is configured to withstand extreme cycle temperature fluctuations The provision of the plurality of regenerator elements 34 enables each regenerator element 34 to be exposed to a reduced temperature fluctuation.

For example, the provision of the plurality of regenerator elements 34 enables a reduced temperature differential across the/each regenerator element 34 in comparison to a single regenerator element 34 in the regenerator 26. For example, where the regenerator 26 is exposed to or configured to provide a temperature differential in a fluid of up to 1000°C, rather than a single regenerator element 34 being exposed to a temperature differential across the single regenerator element 34 of up to 1000°C, each regenerator element 34 is exposed to a reduced temperature differential. For example, the regenerator 26 is configured to limit each regenerator element 34 to a fraction of the total temperature differential, such as little as a third, or her a quarter, of the total temperature differential where four or more regenerator elements 34 are provided in series. Accordingly, where the regenerator 26 is configured to receive a fluid with a high temperature (e.g. of 1000°C) and output the fluid with a low temperature (e.g. 80°C), none of the individual regenerator elements 34 are exposed to both the high temperature and the low temperature.

The thermal regenerator 26 comprises a heat shield or reflector 35. The heat shield or reflector 35 comprises a baffle. The heat shield or reflector 35 comprises a radiation heat shield or reflector 35 configured to reflect and/or deflect heat. The heat shield or reflector 35 is configured to minimise a change or redirection of flow of the working fluid flowing through the regenerator 26. The heat shield or reflector 35 is configured to reflect and/or deflect heat away from a direction of flow of fluid through the regenerator 26. The heat shield or reflector 35 is configured to reduce transmission of heat out of the regenerator element 34. The heat shield or reflector 35 is configured to allow flow out of and/or into the regenerator element 34. The heat shield or reflector 35 is configured to prevent or at least mitigate a pressure drop across the heat shield or reflector 35. The heat shield or reflector 35 comprises a similar or same cross-sectional area as the flowpaths through the regenerator 26. The heat shield or reflector 35 comprises a cross-sectional flowpath area perpendicular to flow of the working fluid, wherein the heat shield or reflector’s total cross-sectional flowpath area is at least the same as the total cross-sectional area of all of the fluid channels 27 in the regenerator 26. The heat shield or reflector 35 is configured to reduce transmission of heat from the regenerator element 34. Here, the heat shield or reflector 35 comprises a ceramic reflector.

The regenerator 26 comprises a device for maintaining the plurality of annular sheets spaced substantially in a parallel arrangement. Here, the device comprises the heat shield or reflector 35, which is a ceramic fastening ring shaped to obstruct direct heat radiation. As shown in Figure 1, the device is configured such that the regenerator elements 34 are stacked with channels essentially parallel to the direction of the fluid flow. The ring-shaped heat shields 35 are arranged such that channels formed by the sheet material are aligned axially to minimize disruption to flow of the fluid and to maintain continuous annular channels.

Accordingly, in at least some examples, the thermal regenerator 26 comprises at least one element comprising a corrugated sheet material provided in an annular configuration positioned such that the working fluid is passing through the channels formed in the corrugated sheet when forced by the movement of the displacement piston 18 in the piston chamber 40 for transferring heat between the fluid moving through the channels and the inside and outside wall with a minimal pressure drop in the fluid. In at least some examples, the sheet material is essentially formed from metal. The sheet material comprises a foil. The metal comprises stainless steel, or a nickel alloy. The metal comprises an average thickness of from 0.1mm to 1mm. In at least some examples, the metal comprises a uniform thickness in the range from 0.1mm to 1mm, with a tolerance or deviation of at most +/- 10%; optionally 5%; optionally 1%; optionally 0.1% or less. For example, the sheet material may comprise a uniform thickness of 0.2mm with a maximum deviation of 0.001mm.

In at least some examples, there is provided a multi-channel thermal regenerator 26 for a Stirling cycle heat engine, comprising a corrugated sheet material provided in an annular configuration positioned such that the working fluid is passing through the channels formed in the corrugated sheet when forced by the movement of the displacer 18 in the chamber 40 for transferring heat between the fluid moving through the channels and the inside and outside wall with a minimal pressure drop in the fluid. The thermal regenerator 26 comprises a cavity 52. The cavity 52 is an annular cavity located around the cylinder assembly 22 chambers 41, 43. Accordingly the cavity 52 is located radially outward of the cylinder assembly 22 chambers 41, 43. Here, the cavity 52 is located in the cylinder assembly 22 wall. The cavity 52 comprises an inner wall at an inner diameter and an outer wall at an outer diameter. As such, the cavity 52 is defined by a double-walled cylinder assembly 22. Her, the inner and outer walls comprise a same ceramic. The ceramic cylinder assembly 22 is arranged such that channels 27 formed by the sheet material are aligned axially to minimize disruption to flow of the fluid and to maintain continuous annular channels. In some examples, the regenerator 26 comprises a regenerator cartridge, formed of regenerator elements 34 and the ceramic cylinder assembly 22 for housing the regenerator elements 34. The inner side of the regenerator 26 may act as a cylinder wall for the displacer 18. The regenerator 26 cartridge comprises an inner sleeve, an outer sleeve in spaced parallel arrangement from the inner sleeve with the sheets being disposed therebetween, and a base member connected between the inner sleeve and outer sleeve at one end of both sleeves. The plurality of regenerator elements 34 is axially arranged such that the working fluid flows sequentially through the regenerator elements 34. The regenerator 26 comprises a first heat shield or reflector 35 arranged at a first end of the regenerator 26 and a second heat shield or reflector 35 arranged at a second end of the regenerator 26. As shown in Figure 1, each regenerator element 34 is arranged with a heat shield or reflector 35 at each axial end of the regenerator element 34. Accordingly, the regenerator 26 comprises a plurality of axially-arranged regenerator element 34s with a heat shield or reflector 35 arranged between each adjacent pair of regenerator element 34s; and also a heat shield or reflector 35 at each axial end of the regenerator 26. Figures 5, 6 and 7 show the heater head 14 of the present disclosure. The heater head 14 comprises the working fluid. The heater head 14 is in fluid communication with the thermal regenerator 26. The heater head 14 is in fluid communication with the cylinder assembly 22 chamber 40. The heater head 14 is in fluid communication with each of the thermal regenerator 26 and the cylinder assembly 22 chamber 40. The cylinder assembly 22 chamber 40 is in fluid communication with the thermal regenerator 26 via the heater head 14. The chamber 40 is in fluid communication with the working fluid heatable by the heater head 14. The heater head 14 comprises a plurality of fluid conduits containing the working fluid. Each of the plurality of fluid conduits is arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit. The heater head 14 comprises a plurality of first apertures 60 for fluid communication of the working fluid with the cylinder chamber 40. The heater head 14 comprises a plurality of second apertures 62 for fluid communication with the thermal regenerator 26. The first apertures 80 and the second apertures 62 are separated by a seal of the seal assembly. Each fluid conduit comprises two ends, a first end for communication with the cylinder chamber 40 and a second end for communication with the thermal regenerator 26. Each first end comprises a first aperture 60 and each second end comprises a second aperture

62. The plurality of first apertures 60 is in fluid communication at an interface between the heater head 14 and the cylinder assembly 22. The plurality of second apertures 62 is in fluid communication at the interface between the heater head 14 and the cylinder assembly 22. The plurality of first apertures 60 and the plurality of second apertures 62 alternate functioning as respective inlets and outlets with a change in cycles of the thermal Stirling cycle engine, such that a direction of fluid flow of the working fluid in each of the fluid conduits reverses. For example, the first apertures 60 function as outlets from the heater head 14 during an expansion phase or cycle of the relatively hotter portion 23 of the chamber 40. Accordingly, the heater head 14 supplies heated working fluid to the cylinder chamber 40 via the first apertures 60 during the expansion phase or cycle, propelled by the displacer 18 in a direction away from the first apertures 60, and away from the heater head 14. Similarly, the heater head 14 receives working fluid from the cylinder chamber 40 via the first apertures 60 during a retraction phase or cycle, such as when the displacer 18 is moving towards the first apertures 60.

The plurality of fluid conduits is defined by a plurality of thermally conductive tubes 24. The thermally conductive tubes 24 are each be of constant cross-section along their lengths to minimise a pressure differential along each respective tube 24. Each of the tubes 24 comprises a wall of uniform thickness along its length and around its circumference. The tubular wall is cylindrical in shape, at least in cross-section. The plurality of tubes 24 is manufactured from an essentially pure metal able to sustain the tubular geometry and shape at an operating temperature in a range of from 850 to 1400 °C. The plurality of heater tubes 24 are rotationally symmetric about their centre axes. As shown in Figures 5, 6 and 7, the heater tubes 24 are spaced parallel with respect to one another. The heater tubes 24 are spaced at a distance and shape that during heating up or cooling down of the heater head 14, the tubes 24 are in direct contact up to a temperature in an operating range of 850°C to 1400°C . The heater head 14 comprises a heater head manifold 84. The heater tubes 24 are positioned in a staggered, annular or partially concentric array and form a toroidal shape. The plurality of second apertures 62 are located towards an outer diameter of the manifold 64. The plurality of first apertures 60 are located towards a radial centre of the manifold 64. The heater manifold 64 is formed, cast, 3D-printed or machined, from a single superalloy metallic material, or from an essentially pure metal, able to sustain the geometry and shape at an operating temperature in the range of from 850 to 1400 °C.

The plurality of first apertures 60 are perpendicular to the central longitudinal axis 44 of the ceramic cylinder assembly 22 such that each of the plurality of heater tubes 24 provides a continuous linear flow path between the ceramic cylinder assembly 22 and a first tube portion 66 of each fluid conduit adjacent the respective first apertures.

Each heater tube 24 comprises such a first tube portion 66 that extends parallel to the longitudinal axis 44 at an inner diameter, then curves around with at least a minimum bend radius to a second tube 68 portion transverse, here perpendicular, to the first tube portion 66. The second portion 68 extends the tube 24 laterally away from the central longitudinal axis 44. The heater tube 24 curves around a second bend with at least a minimum bend radius to a third tube portion 70. The third tube portion 70 is transverse, here perpendicular, to the second tube portion 68. Here, each third tube portion 70 extends to the respective second aperture 62, the second aperture 62 being at a smaller diameter than a maximum diameter of the tube 24 relative to the central longitudinal axis 44, such as a diameter of the second bend relative to the central longitudinal axis 44 of the cylinder assembly 22. The heater head 14 comprises a central longitudinal axis coincident with the central longitudinal axis 44 of the cylinder assembly 22. The heater head 14 comprises an enclosed compartment (not shown) for transferring heat from an exterior of the heater head 14, such as a sealed outer housing (not shown) of the heater head 14. The sealed outer housing of the heater head 14 is heated by an external heat source, such as an external heat source adjacent or encasing the heater head 14. The sealed outer housing of the heater head is heated by radiation; and optionally by conduction. In examples where the enclosed compartment comprises a vacuum, heat is transferred through the compartment from the sealed outer housing by radiation. Heat is transferred via the enclosed compartment through each tube’s 24 outer wall to the working fluid within each heater tube 24, the vacuum being sealingly separated from the working fluid by the tube’s 24 outer wall. The tubes 24 comprises single-wall tubes 24. In some examples, rather than a vacuum in the enclosed compartment, a fluid is provided, such as a gas and/or a liquid. in some examples, the enclosed fluid comprises an inert fluid, such as nitrogen. The enclosed fluid is not actively pumped. For example, there is no driven flow in the heater head 14 housing compartment comprising the enclosed fluid (or the vacuum). The working fluid in the fluid conduits in the heater head 14 is driven by movement of a stroke of the displacer 18.

Figure 8 shows the heater head 14 connection of the present disclosure. The ceramic cylinder assembly 22 and the heater head 14 are connected and sealed by a resilient and elastic gas-tight seal assembly 48. The seal assembly 48 comprises a rigid housing with an outer wall forming an inner lumen. The outer wall may compressively and gas- tightly be disposed between the head 14 and cylinder assembly 22 components. The inner lumen comprises an inert gas at an elevated pressure.

Accordingly, there is provided a thermal Stirling cycle engine 12 comprising: a heater head 14 comprising a working fluid; a ceramic cylinder assembly 22 connected to the heater head 14, the cylinder assembly 22 having a cylindrical wall defining a chamber 40, the chamber 40 being in fluid communication with the working fluid heatable by the heater head 14; a displacer 18 mounted in the chamber 40 for reciprocatingly moving the working fluid, the displacer 18 dividing the chamber 40 into a relatively hotter portion and a relatively cooler portion; wherein the ceramic cylinder assembly 22 and the heater head 14 are connected and sealed by a resilient and elastic gas-tight seal assembly comprising a rigid housing with an outer wall forming an inner lumen; wherein the outer wall compressively and gas-tightly is disposed between the head 14 and cylinder assembly 22 components, and wherein the inner lumen comprises an inert gas at an elevated pressure. The seal assembly 38 comprises a circlip 32 formed of temperature resistant metal. The circlip 32 comprises a part-ring shaped body. The two ends of the circlip 32 comprise a pair of integrally co-operative legs. The circlip 32 secures the heater head 14 axially relative to the outer ceramic cylinder 36. The circlip 32 is configured to prevent relative axial movement between the heater head 14 and the outer ceramic cylinder 36. The circlip 32 is configured to accommodate mechanical and thermal differences between the heater head 14 and the outer ceramic cylinder 36 under operating conditions to prevent axial movement therebetween. The circlip 32 may provide a circumferential securement. The circlip 32 provides a circumferential securement between a portion of the heater head 14 radially outside a portion of the outer ceramic cylinder 36. Here the circlip 32 is positioned in corresponding circumferential grooves of the heater manifold 64 and the cylinder 36 The heater head 14 is in fluid communication with each of the thermal regenerator 26 and the cylinder chamber 40. The cylinder chamber 40 is in fluid communication with the thermal regenerator 26 via the heater head 14. Accordingly, the heater head 14 connection provides respective fluid-tight communications of the working fluid between each of the thermal regenerator 26 and the heater head 14; and the cylinder chamber 40 and the heater head 14.

The heater head 14 comprises at least one first aperture for fluid communication of the working fluid with the cylinder assembly 22 chamber 40. The heater head 14 comprises at least one second aperture for fluid communication with the thermal regenerator 26. The first aperture and the second aperture are separated by the first seal 49 of the seal assembly 48. The seal 49 comprises an annular seal disposed between the first aperture 60 at an inner diameter and the second aperture 62 at an outer diameter. The seal assembly 48 comprises a further seal 51, the further seal being an outer annular seal disposed at a greater diameter than the second aperture 62. The seal 49 and the further seal 51 are arranged in a same plane. The same plane is perpendicular to the longitudinal axis 44 of the cylinder assembly 22. The seal 49 and further seal 51 comprise lumens between the heater head 14 and the cylinder assembly 22. The respective annular lumens are defined by annular channel portions in each of the heater head 14 and the cylinder assembly 22. The lumen is filled with an inert gas. The inert gas is formed and pressurised by a thermal reaction on heating, such as initial operational heating of the heater head 14, the gas being derived from a non-gaseous composition applied to a portion of the lumen prior to sealing of the lumen. The gas is a vapour generated by heating a liquid, paste or other solid applied to the lumen, the heating occurring at or preferably below an operating temperature of Stirling engine 12 at the lumen.

The heater head 14 comprises a plurality of fluid conduits containing the working fluid, each of the plurality of fluid conduits being arranged for simultaneous parallel fluid flow of the working fluid to allow heating of the working fluid along the respective length of each fluid conduit.

The thermal regenerator 26 is an annular thermal regenerator 26 disposed around an exterior of the cylinder chamber 40. Accordingly, the head 14 connection provides annular fluid connections via the second apertures 62 between the heater head 14 and the thermal regenerator 26.

The plurality of first apertures is in fluid communication at an interface between the heater head 14 and the cylinder assembly 22. The plurality of second apertures is in fluid communication at the interface between the heater head 14 and the regenerator 26. The interface comprises a planar axial interface, between respective end axial faces of the heater head 14 and the cylinder assembly 22. Figures 9, 10 and 11 show the displacer 18 of the example of the present disclosure. At least two of: the cylindrical wall 28 the displacer 18 or the drive rod 54 each comprises a respective ceramic material.

The respective ceramic material of each of the two is a dissimilar ceramic material.

Here, each of the cylindrical wall, the displacer 18 and the drive rod 54 comprises a ceramic material.

At least two of the ceramic materials is a dissimilar ceramic material.

In this example, the cylindrical wall and the displacer 18 comprise dissimilar ceramic materials, the cylindrical wall comprising a first ceramic material and the displacer 18 comprising a second ceramic material, the second ceramic material being different from the first ceramic material.

As shown in detail in Figure 11, a partion 80 of the displacer 18 comprises the ceramic material, the portion 80 being at a maximum diameter of the displacer 18, the maximum diameter portion of the displacer 18 being contactable with the cylindrical wall.

The portion 80 here comprises an annular disc.

The materials of the cylindrical wall and the displacer portion 80 have been selected in dependence on each other to provide a friction coefficient sufficiently low at operation temperature to reduce energy loss.

The surface properties of the cylindrical wall and displacer portion 80 have been selected in dependence on each other to reduce wear.

Both ceramic materials comprise compositions having very low thermal conductivity.

The material for the cylinder assembly 22, displacer portion 80 and drive rod 54 have been chosen from refractory materials exhibiting a small thermal expansion and conduction coefficients; and a sufficiently high compression strength.

The material for the drive rod 54 has been selected at least in partial dependence on the material's bending strength.

The drive rod 54 comprises a hollow drive rod 54. The displacer 18 and cylinder assembly 22 are dimensioned such that at operating temperature the displacer 18 and cylindrical wall have a minimal friction therebetween.

The example ceramic materials here for cylinder assembly 22 and drive rod 54 comprise zirconium oxide, or compositions comprising thereof.

The example ceramic material for the displacer portion 80 comprises alumina.

In other examples, other materials, such as other ceramic materials are used.

The thermal Stirling cycle engine 12 comprises a Beta configuration, comprising the power piston 16 for phased synchronized reciprocating motion in the same axial directions as the displacer 18. The displacer 18 and the power piston 18 are each connected to a drive system, the displacer 18 drive rod 54 passing through the power piston 16 to connect the displacer 18 to the drive system.

The displacer drive rod 54 comprises the ceramic material to accommodate a temperature differential along a length of the displacer drive rod 54, such as from a displacer 18 head 14 to a distal end through the power piston 16. The displacer drive rod 54 ends here are exposed to a temperature in the relatively hotter portion 23 of the cylinder chamber 40; and a coldest temperature below the power piston 16.

The drive system further comprises one or more adjustable linkages 82, 84, 86 to vary a phase angle between the displacer 18 piston and the power piston 16, if desired. Here, the crankshaft 20 driven by the power piston 16 comprises a pair 82, 84 of the linkages.

The drive system further comprises a connector assembly connecting the displacer 18 for driving the displacer 18 in the cylinder assembly 22 and for providing a longer first dwell within a given range of displacer 18 movement near the end of the displacer 18 travel in one direction than a second dwell in the given range in the opposite direction.

The engine 12 may further comprise a reciprocating member for moving the power piston 16 in the cylinder assembly 22 towards the displacer 18 in a compression stroke and away from the displacer 18 in an expansion stroke, and providing a first dwell in a predetermined limited range of power piston 16 movement near the beginning of the compression stroke of the power piston 16 and providing a second dwell in the range of power piston 16 movement near the beginning of the expansion stroke of the power piston 16, wherein the first dwell is longer than the second dwell. The engine 12 may further comprise a means co-operable with the connector assembly and the reciprocating member for coordinating the reciprocating cycles of displacer 18 and power piston 16 so that the beginning of the piston expansion stroke occurs intermediately after the displacer 18 stroke in the other direction, whereby heated working fluid is drawn into the cylinder assembly 22 during the expansion stroke.

The means co-operable with the connector assembly may adjustably coordinate the reciprocating cycles of the displacer 18 and power piston 16, whereby cooled fluid is drawn into the cylinder assembly 22 during the first dwell and such that the piston is in its compression stroke during the longer dwell of the displacer 18.

The means co-operable with the connector assembly means may cause the power piston 16 expansion stroke to occur simultaneously with a major portion of displacer 18 movement in one direction, whereby the power piston 16 is in an expansion stroke during introduction of heated working fluid into the cylinder assembly 22.

As shown in Figure 12, the cooling device 42 comprises a plurality of fluid conduits 90 fluidly connecting the relatively cooler portion 25 of the cylinder assembly 22 to the regenerator 26. Each of the plurality of fluid conduits 90 comprises a first aperture 92 in a cylinder wall of the relatively cooler portion. It will be appreciated that the conduits 90 terminate at slightly different heights here, providing the two circumferential rows of first apertures 92 shown in Figure 12. The plurality of first apertures 92 of the cooling device is located in a non-ceramic cylinder wall portion, the non-ceramic cylinder wall portion being axially distal to the heater head 14. The power piston 16 is located in the relatively cooler partion 25 and the plurality of first cooling device apertures 92 is arranged circumferentially in the cylinder wall at an axial location of the relatively cooler portion that is not traversed by the power piston 16. A plurality of cooling device second apertures 94 provides axial communication of the working fluid between the cooling device 52 and the thermal regenerator 26. The displacer drive rod 54 from the displacer 18 passes through the power piston 16 to the drive system. The thermal Stirling cycle engine 12 is configured to accommodate a temperature differential in the working fluid of 850°C or more. The combination of the cooling device 42 and the thermal regenerator 26 are configured to cool the working fluid to a temperature at least 850°C less than a maximum temperature of the working fluid, such as that of the working fluid passing from the heater head 14 to the cylinder assembly 22. The heater head 14 is configured to heat the working fluid by and to at least 850°C. The thermal Stirling cycle engine 12 is configured to operate with a maximum temperature in a range of from 850°C to 1400°C. The thermal Stirling cycle engine 12 is configured to provide an efficiency of at least 45%. It will be appreciated that there is hereby provided an energy conversion apparatus 10 comprising the thermal Stirling cycle engine 12 comprising the cylinder assembly 22 with the working fluid and the heater head 14 for supplying heat to the working fluid. The energy conversion apparatus 10 comprises a heat source (not shown) for supplying heat to the heater head 14. In at least one example, the heat source comprises a solid state heat source configured to be heated to a temperature of at least 850°C. The solid state heat source is heated either directly such as via a solar collector or indirectly by solar energy, such as photovoltaic energy, or wind power or any other electrical energy source. In at least one example, the heat source comprises a solar collector, and/or any component thereof, such as described in WO2015/097629 and/or in WO2009/002188, the contents of each being herein incorporated. The solid state heat source comprises a heat sink for transferring heat to working fluid in the heater head 14, the working fluid in the heater head 14 being in fluid communication with the working fluid in the cylinder assembly 22. The solid state heat source comprises a material with a specific heat capacity of at least around 400 J/(kg-K); optionally at least around 1000 J/(kg:K}. The solid state heat source comprises an insulator to encase at least the heater head 14, the insulator having a thermal conductivity of less than 3W/(m-K); optionally less than about

1.5W/(m-K). The solid state heat source can comprise a ceramic and/or a concrete. The solid state heat source is heatable to temperatures in a range of 850°C to 1400°C.

The example of the thermal Stirling cycle engine 12 here comprises a high temperature differential Beta configuration Stirling engine, with the cylinder assembly 22 fluidly connected to the heater head 14, the cylinder assembly 22 having a ceramic cylindrical wall defining a chamber 40 for housing a reciprocating displacer 18, the displacer 18 dividing the chamber 40 into the hotter portion 41 and the cooler portion 43, the cooler portion 43 cooled by the cooling device 42, as shown in Figure 12. Although not shown, it will be appreciated that the heater head 14 is mounted at or towards a core of the solid state heat source and the cooling device 42 is mounted or directed away from the core.

The heater head 14 comprises the working fluid within the sealed conduits 24 for circulating the working fluid within the heater head 14 to receive heat indirectly from the solid state heat source.

The heat is transferred from the solid state heat source via thermal heat radiation, direct heat conduction or via an inert fluid in the heater head 14. The inert fluid is fluidly sealed from the working fluid, the inert fluid being housed in a heater head housing (not shown). The heat is transferred from the inert fluid through the tubular walls defining the sealed conduits 24, to the working fluid.

The energy conversion apparatus 10 comprising the thermal Stirling cycle engine 12 is configured to function as an electrical generator for providing electrical energy.

The energy conversion apparatus 10 is configured to control operation of the thermal Stirling cycle engine 12 to match electrical energy demand, the thermal Stirling cycle engine 12 being effectively instantaneously switched on and/or off.

The energy conversion apparatus 10 is configured to provide electricity supply for commercial use, such as for industrial use and to a grid or network.

The energy conversion apparatus 10 is stationary to provide in situ electrical energy as an output.

In other examples, the energy conversion apparatus 10 comprises a mobile apparatus to provide a mobile electrical energy output, such as to provide power to a mode of transport.

In at least some examples, the energy conversion apparatus 10 comprises a plurality of thermal Stirling cycle engines 12, each engine 12 arranged to be heated by the solid state heat source.

Such energy conversion apparatus 10 may further comprise a control system, wherein the control system is arranged to adapt operation of each of the plurality of thermal Stirling cycle engines 12 in dependence on a demand for output from the apparatus 10. Figure 13 illustrates an example of a heater head assembly 114, generally similar to that 14 shown in Figure 8. For brevity, not all features common to both figures is repeated here; however like features are denoted by like reference numerals incremented by 100. Accordingly, the heater head assembly 114 portion shown in Figure 13 comprises a heater head manifold 164, generally similar to that 64 shown in Figure 8. Likewise,

annular seals 149 and 151 are also provided.

In the example shown in Figure 13, rather than a circlip 32, an annular ring 132b is provided to assist in maintaining an integrity of the heater head assembly 114. The annular ring 132b here comprises an intermediate ring, positioned here between a fixing ring 132c and a flange or lip of the cylinder 136. The fixing ring 132c has an interengaging profile 135a for engaging a corresponding interengaging profile 135b of the heater head manifold 164. As shown here, the interengaging profiles 135a, 135b comprise screwthreads, allowing the fixing ring 132¢ to be screwedly fastened to the heater head manifold 164. The annular ring 132b is effectively a fastening nut.

Accordingly, the heater head manifold 164 can be fixed to the cylinder 136 of the assembly 114. The intermediate annular ring 132b can function as a buffer, washer or support.

The annular ring 132b here is positioned axially between the fixing ring 132c and the flange of the cylinder 136. The annular ring 132b is configured to provide a pretension between the cylinder 136 and the fixing.

As shown here, the annular ring 132b is configured to provide an axial tension (and pretension) between the flange of the cylinder 136 and the fixing ring 132c when fully assembled.

As shown here, the annular ring 132b is configured to provide a radial axial tension (and pretension)

between the cylinder 136 and the heater head manifold 164 when fully assembled.

As shown here, the annular ring 132b has a higher linear thermal expansion coefficient than the heater head manifold 164. The annular ring 132b has a higher linear thermal expansion coefficient than the cylinder 136. The annular ring 132b has a higher linear thermal expansion coefficient than the fixing ring 132c.

The annular ring 132b is configured to compensate for differences in thermal expansion in use of the components of the heater head assembly 114. In the example shown here, the fixing ring 132c comprises a material with a same thermal expansion property as the heater head manifold 164. Accordingly, the fixing ring 132c and the heater head manifold are configured to expand (and contract) similarly during use.

Accordingly, the screwed connection therebetween is maintained during use.

Indeed, similar thermal expansion of male & female parts of screw fitting can enhance the screw fitting in use.

The annular ring 132b is configured to have a higher linear thermal expansion coefficient than the cylinder 136. The annular ring 132b is configured to increase force exerted on the assembly 114 as temperature increases.

Accordingly, the annular ring 132b is configured to increase fastening forces of the assembly, such as with increasing temperature and pressure within the assembly 114. The annular ring 132b in this example comprises a manganese steel with a thermal coefficient of around 23 x107® per °C.

In other embodiments, other annular ring materials may be used, such as steel from the type 300 series (e.g. type 316 stainless steel). As shown here, the cylinder 136 comprises a zirconia with a coefficient of around 10.2 x107° per °C. The heater head manifold 164 and the fixing ring 132c both comprise an Inconel 600 with a thermal coefficient of around

16.8x107® per °C. Accordingly, the annular ring 132b expands with heat more and exerts force on the cylinder 136 and on the heater head manifold 164 and the fixing ring 132c — thereby pressurising the connection therebetween. Here, the proportions of the annular ring 132b result in a greater axial expansion than radial expansion when heated — desirably pressurising the Zirconia cylinder flange axially against the Inconel 600 heater head manifold 164 when heated. This ensures the integrity of the axially-located sealrings 149, 151 in use. It will be appreciated that, for clarity, not all features {such as the heat transfer tubing 24) has been shown in Figure 13. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope or spirit of the invention. For example, it will be appreciated that the Stirling engine may be provided in alternative orientations and/or configurations. It will be appreciated that any of the aforementioned apparatus may have other functions in addition to the mentioned functions, and that these functions may be performed by the same apparatus. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope or spirit of the invention.

For example, it will be appreciated that although shown here in a vertical arrangement, the apparatus may be mounted in other orientations, such as tilted or horizontal.

Claims (20)

CONCLUSIONS A thermal Stirling cycle engine comprising: a heater head; a cylinder connected to the heater head, the cylinder including a cylindrical wall forming a chamber and containing a working fluid that can be heated by the heater head; a mover mounted in the chamber for reciprocating the working fluid, the mover dividing the chamber into a relatively hotter portion and a relatively cooler portion; and a mover drive rod for driving the mover; wherein at least two of the cylindrical wall, the mover, or the mover drive rod each comprise a respective ceramic material; and wherein the respective ceramic material of each of the two is a different ceramic material. The thermal Stirling cycle engine of claim 1, wherein each of the cylindrical wall, the displacer, and the displacer drive rod comprises a ceramic material; and wherein at least two of the ceramics are different ceramics. The thermal Stirling cycle engine of claim 1 or 2, wherein two of the cylindrical wall, the displacer, or the displacer drive rod comprise a similar ceramic material. A thermal Stirling cycle engine according to any one of the preceding claims, wherein the cylindrical wall and the displacer comprise different ceramics, the cylindrical wall comprises a first ceramic, and the displacer comprises a second ceramic, wherein the second ceramic is different of the first ceramic material. A thermal Stirling cycle engine as claimed in any preceding claim wherein a portion of the displacer comprises the ceramic material, the portion being at a maximum diameter of the displacer, the portion of the displacer at the maximum diameter being able to contact with the cylindrical wall. A thermal Stirling cycle engine according to claim 5, wherein the materials of the cylindrical wall and of the part of the displacer are selected in function of each other to provide a coefficient of friction sufficiently low at the operating temperature, so as to reduce energy losses . A thermal Stirling cycle engine according to claim 5 or 6, wherein the surface properties of the cylindrical wall and of the part of the displacer are selected in function of each other, in order to reduce any wear. A thermal Stirling cycle engine as claimed in any preceding claim, wherein the ceramic materials comprise compositions with very low thermal conductivities. A thermal Stirling cycle engine according to any one of the preceding claims, wherein the material of the cylinder, of the piston, and of the displacement drive rod are selected from heat-resistant materials which exhibit a small thermal expansion and limited conductivity coefficients, as well as a sufficiently high compressive strength. A thermal Stirling cycle engine according to any one of the preceding claims, wherein a material of the displacer drive rod is selected at least as a function of the bending strength of the material. A thermal Stirling cycle engine according to any one of the preceding claims, wherein the displacer drive rod comprises a hollow displacer drive rod. A thermal Stirling cycle engine according to any one of the preceding claims, wherein the mover drive rod comprises a reinforced mover drive rod. The thermal Stirling cycle engine of any preceding claim, wherein the ceramic material comprises a metal oxide carbide, nitride, or silicide, wherein the metal is selected from the group consisting of aluminum, boron, magnesium, calcium; a transition metal such as chromium, iron, nickel, nickel, niobium, titanium, yttrium, zirconium, or a mixture of the foregoing, preferably at least one of aluminum oxide, titanium oxide, chromium oxide, zirconium oxide; aluminum nitride, titanium nitride, calcium nitride, silicon nitride; titanium carbide, tungsten carbide, silicon carbide, and mixtures of the foregoing. The thermal Stirling cycle engine of any preceding claim, wherein the ceramics are selected from the group consisting of magnesium oxide, yttrium oxide, aluminum oxide, aluminum nitride, silicon carbide, boron nitride, silicon nitride, boron carbide, silicon oxide, magnesium aluminate spinel, titanium carbide, titanium nitride, zirconium silicon oxide, and combinations of the foregoing. A thermal Stirling cycle engine according to any one of the preceding claims, wherein the displacer and the cylinder are dimensioned in such a way that, at an operating temperature, the displacer and the cylindrical wall exhibit a minimum mutual coefficient of friction. A thermal Stirling cycle engine according to any preceding claim, wherein the thermal Stirling cycle engine is in beta configuration, and further comprises a power piston for phased, synchronized, reciprocating motion in the same axial directions. as the mover, wherein the mover and the power piston are each connected to a drive system, wherein the mover drive rod passes through the power piston to connect the mover to the drive system. The thermal Stirling cycle engine of claim 16, wherein the drive system further comprises one or more adjustable rod mechanisms to vary a phase angle between the displacer piston and the power piston. The thermal Stirling cycle engine of claim 17, wherein the drive system further comprises a connector assembly for connection to the displacer to drive the displacer in the cylinder; the engine further comprising means cooperating with the connector assembly to coordinate the reciprocating cycles of the displacer and of the power piston, in such a way that the start of the expansion stroke of the piston immediately after the stroke of the mover occurs in the other direction, drawing heated working fluid into the cylinder during the expansion stroke. The thermal Stirling cycle engine of claim 18, wherein the means co-operating with the connector assembly adjustably coordinates the reciprocating cycles of the displacer and of the power piston, drawing cooled fluid into the cylinder during said operation. first interval, in such a way that the piston is in the compression stroke during the longer interval of the displacer. A thermal Stirling cycle engine as claimed in claim 18 or 19, wherein the means cooperating with the connector assembly causes the expansion stroke of the power piston to occur simultaneously with a major part of the movement of the displacer in one direction, wherein the power piston has an expansion stroke. performs during the introduction of heated working fluid into the cylinder,