Heat engine

Abstract

A heat engine comprising: an isothermal expansion compartment, at least one adiabatic compartment, and an isothermal compression compartment, wherein each compartment is configured to receive a working fluid; a thermal reservoir for providing thermal energy to working fluid within the isothermal expansion compartment; a thermal store for receiving thermal energy from working fluid within the isothermal compression compartment, and a control unit configured to regulate the movement of working fluid between the compartments, wherein the at least one adiabatic compartment comprises a sealable adiabatic compartment aperture for conveying working fluid between the isothermal expansion compartment and the at least one sealable adiabatic compartment, and the isothermal compression compartment comprises a sealable isothermal compression compartment aperture for conveying working fluid between the at least one adiabatic compartment and the isothermal compression compartment.

Description

[0001] HEAT ENGINE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to improvements in or relating to a heat engine and, more specifically, to a heat engine for incorporating working fluid redistribution steps between different compartments in which different types of expansion and compression take place, thus allowing the heat engine to be more thermodynamically efficient.

[0004] BACKGROUND TO THE INVENTION

[0005] Around half of all energy consumed in the EU is for heating and cooling, with more than 70% of that energy coming from fossil fuels, mostly natural gas. A widely proposed alternative to gas central heating is to use electrically powered heat pumps. However, working specifications of commercially available heat pumps indicate that their efficiencies still typically fall significantly short of that theoretically achievable according to the second law of thermodynamics. Likewise, although the thermodynamic efficiencies of modern power generation or transportation orientated heat engines such as internal combustion engines, gas turbines, and jet engines, are considerably higher than their forebears earlier in the industrial revolution, their efficiencies also still fall materially short of what is theoretically achievable according to the second law of thermodynamics.

[0006] If more efficient heat engine designs could be identified, the cost of generating power could be reduced, energy consumed in e.g. transportation (and other more traditional heat engine uses) could be reduced, heat pumps for residential and commercial space heating could be made more efficient (hence cheaper to run) and less traditional uses for heat engines could become more commercially viable. It is against this background that the present invention has arisen.

[0007] SUMMARY OF THE INVENTION

[0008] According to the present invention there is provided a heat engine comprising: an isothermal expansion compartment, at least one adiabatic compartment, and an isothermal compression compartment, wherein each compartment is configured to receive a working fluid; a thermal reservoir for providing thermal energy to working fluid within the isothermal expansion compartment; a thermal store for receiving thermal energy from working fluid within the isothermal compression compartment, and a control unit configured to regulate the movement of working fluid between the compartments, wherein the at least one adiabatic compartment comprises a sealable adiabatic compartment aperture for conveying working fluid between the isothermal expansion compartment and the at least one sealable adiabatic compartment, and the isothermal compression compartment comprises a sealable isothermal compression compartment aperture for conveying working fluid between the at least one adiabatic compartment and the isothermal compression compartment.

[0009] The use of at least three distinct compartments enables each compartment to be optimised for one or more of the different thermal processes that occur within the heat engine. This may significantly improve the thermodynamic efficiency of the resulting heat engine. For example, in use, an expansion of the working fluid in the isothermal expansion compartment may be a substantially isothermal expansion; a compression of the working fluid in the isothermal compression compartment may be a substantially isothermal compression; and an expansion or compression of the working fluid in the at least one adiabatic compartment may be a substantially adiabatic expansion or compression, respectively.

[0010] The thermal reservoir may be hotter than the thermal store. The thermal reservoir may be a heat source. The thermal store may be a heat sink. However, if the heat engine is reversed, the thermal store may be hotter than the thermal reservoir. The thermal reservoir may be external to the isothermal expansion compartment. The thermal reservoir may be thermally connected to the isothermal expansion compartment. For example, the thermal reservoir may be the external atmosphere, or another external environment. In some embodiments, the thermal reservoir may be a thermal battery. Alternatively, or in addition, the thermal reservoir may be a plurality of chemicals located within the isothermal expansion compartment and suitable for undergoing an exothermic chemical reaction. The thermal reservoir may comprise materials which may undergo an exothermic phase change (e.g. from liquid to solid).

[0011] Similarly, the thermal store may be external to the isothermal compression compartment. The thermal store may be thermally connected to the isothermal compression compartment. For example, the thermal store may be the external atmosphere, or another external environment. In some embodiments, the thermal store may be a thermal battery. Alternatively, or in addition, the thermal store may be a plurality of chemicals located within the isothermal compression compartment and suitable for undergoing an endothermic chemical reaction. The thermal store may comprise materials which may undergo an endothermic phase change (e.g. from solid to liquid).

[0012] Examples of heat engines where exothermic chemical reactions provide energy include internal combustion engines. In this example, the exothermic reaction is the burning of fuel. Another example is the fuel rods in a nuclear power plant. Alternately, or in addition, absorption of light or energetic particles, friction, thermal dissipation, and thermal resistance can be potential heat sources (i.e., thermal reservoirs and / or stores) for heat engines. These may be located within the relevant compartments rather than externally.

[0013] The working fluid may be a gas. For example, the working fluid may be hydrogen, helium and / or air. However, any suitable fluid may be used. In some embodiments, the working fluid may at times be a liquid, such as water. The control unit may be a mechanical control unit. Alternatively, or in addition, the control unit may be an electronic (or electric) control unit.

[0014] The at least one adiabatic compartment may be one compartment that is optimised for adiabatic expansion and adiabatic compression. Alternatively, there may be an adiabatic expansion compartment and a separate adiabatic compression compartment. In some embodiments, the at least one adiabatic compartment comprises a first adiabatic adjustment compartment and a second adiabatic adjustment compartment. Each adiabatic adjustment compartment may be optimised for adiabatic expansion and / or adiabatic compression.

[0015] The sealable adiabatic compartment aperture may be directly connected to the at least one adiabatic compartment and the isothermal expansion compartment. Alternatively, or in addition, the sealable isothermal compression compartment aperture may be directly connected to the isothermal compression compartment and the at least one adiabatic compartment. In this context, "directly connected to" may mean abutting. In other words, the at least one adiabatic compartment may be directly adjacent to the isothermal expansion compartment. Similarly, the at least one adiabatic compartment may be directly adjacent to the isothermal compression compartment. This enables working fluid to be conveyed directly between the at least one adiabatic compartment and each of the isothermal expansion compartment and isothermal compression compartment. This may reduce dead volume between the compartments, wherein 'dead volume' refers to the working fluid remaining within a compartment after a redistribution step (as explained later in this disclosure).

[0016] If the internal volume of a compartment is reduced to zero, the working fluid may be moved entirely into the other compartment(s), thus eliminating dead volume between the compartments. In this application, the internal volume of a compartment is the volume configured to receive the working fluid. Similarly, an internal surface of the compartment is a surface of the compartment configured to restrain the working fluid within the compartment. As such, the working fluid within a given compartment may touch the internal surface(s) of that compartment.

[0017] In some embodiments, at least one additional cycle step may be introduced to mitigate the thermodynamic inefficiency otherwise introduced by the presence of dead volume. The additional cycle step may be a pressure rebalancing step, as described in more detail later in the disclosure. This may be used in embodiments where it is not practical to reduce the internal volume of a compartment to zero.

[0018] Each sealable aperture may be sealed by a door, gate, or valve, for example. Alternatively, or in addition, each sealable aperture may be sealed by a moveable internal surface of one of the compartments to which it provides fluid communication. The moveable internal surface of the compartment may be a surface of a piston, for example. If the aperture is sealed by a valve, the valve may be a cam / follower valve, a rotary value (ported sleeve / face), a solenoid valve, a voice-coil / piezo valve, a butterfly valve or a sleeve valve, for example.

[0019] In some embodiments, each sealable aperture may be only partly sealable rather than wholly sealable. For example, each sealable aperture may be partly sealed by operation of turbines or other features in the aperture that sometimes facilitate flow of working fluid through the aperture but at other times hinder this flow. If partial sealing involves turbines, it may comprise pivotable turbine blades. It may comprise more than one set of turbine blades whose rates of rotation are adjustable.

[0020] Each compartment may have a variable internal volume for receiving the working fluid. The control unit may be configured to regulate the movement of working fluid between the compartments by varying the internal volume of each compartment. This enables the heat engine to generate power or consume power via the following idealised 8-step cycle, wherein the proposed 8-step cycle interposes a redistribution step between each of the 4 steps of a traditional Carnot cycle. This 8-step cycle may be termed the primary cycle.

[0021] Step 1 - isothermal expansion: Whilst the sealable adiabatic compartment aperture is sealed, the internal volume of the isothermal expansion compartment is increased. Simultaneously, thermal energy is transferred from the thermal reservoir to the working fluid within the isothermal expansion compartment to ensure the working fluid within the isothermal expansion compartment remains at a temperature only modestly below the temperature of the thermal reservoir.

[0022] Step 2 - post isothermal expansion adiabatic redistribution: The sealable adiabatic compartment aperture is opened and the internal volume of the isothermal expansion compartment is reduced to zero whilst simultaneously increasing the internal volume of the at least one adiabatic compartment from zero, by the same amount and at same rate as the change in internal volume of the isothermal expansion compartment, such that the entirety of the working fluid is transferred from the isothermal expansion compartment to the at least one adiabatic compartment via the sealable adiabatic compartment aperture without compressing, expanding, or materially changing temperature. Step 3 - post isothermal expansion adiabatic adjustment: Whilst both the sealable adiabatic compartment aperture and the sealable isothermal compression compartment aperture are sealed, the internal volume of the at least one adiabatic compartment is increased or decreased such that the working fluid expands or compresses, respectively, until it is substantially the same temperature as the thermal store.

[0023] Step 4 - isothermal compression redistribution: The sealable isothermal compression compartment aperture is opened and the internal volume of the at least one adiabatic compartment is reduced to zero whilst simultaneously increasing the internal volume of the isothermal compression compartment from zero, by the same amount and at same rate as the change in internal volume of the at least one adiabatic compartment, such that the entirety of the working fluid is transferred from the at least one adiabatic compartment to the isothermal compression compartment via the sealable isothermal compression compartment aperture without compressing, expanding, or materially changing temperature.

[0024] Step 5 - isothermal compression: Whilst the sealable adiabatic compartment aperture is sealed, the internal volume of the isothermal compression compartment is decreased. Simultaneously, thermal energy is transferred from the working fluid within the isothermal compression compartment to the thermal store to ensure the working fluid within the isothermal compression compartment remains at a temperature only modestly above the temperature of the thermal store.

[0025] Step 6 - post isothermal compression adiabatic redistribution: The sealable isothermal compression compartment aperture is opened and the internal volume of the isothermal compression compartment is reduced to zero whilst simultaneously increasing the internal volume of the at least one adiabatic compartment from zero, by the same amount and at same rate as the change in internal volume of the isothermal compression compartment, such that the entirety of the working fluid is transferred from the isothermal compression compartment to the at least one adiabatic compartment via the sealable isothermal compression compartment aperture without compressing, expanding, or materially changing temperature.

[0026] Step 7 - post isothermal compression adiabatic adjustment: Whilst both the sealable adiabatic compartment aperture and the sealable isothermal compression compartment aperture are sealed, the internal volume of the at least one adiabatic compartment is decreased or increased such that the working fluid compresses or expands, respectively, until it is substantially the same temperature as the thermal reservoir. Step 8 - isothermal expansion redistribution: The sealable adiabatic compartment aperture is opened and the internal volume of the at least one adiabatic compartment is reduced to zero whilst simultaneously increasing the internal volume of the isothermal expansion compartment from zero, by the same amount and at same rate as the change in internal volume of the at least one adiabatic compartment, such that the entirety of the working fluid is transferred from the at least one adiabatic compartment to the isothermal expansion compartment via the sealable adiabatic compartment aperture without compressing, expanding, or materially changing temperature.

[0027] A "temperature only modestly below" or a "temperature only modestly above" may be interpreted as within 10% or, more preferably, 5% of the absolute temperature differential between the thermal reservoir and thermal store (or within say 5°C or, more preferably, 2°C if larger). Being "substantially the same temperature" may be interpreted as involving a temperature difference within 75% or, more preferably, 50% of this limit and "without materially changing temperature" may be interpreted as changing by less than 75% or, more preferably, 50% of this limit.

[0028] It is not necessary for each step within the cycle to take the same amount of time. For example, in some embodiments, it may be desirable if the redistribution steps (i.e., steps (2), (4), (6) and (8)) include times when the internal volumes of the relevant compartments are constant. As such, these steps may be longer than the other steps (i.e., steps (1), (3), (5) and (7)). Alternatively, or in addition, the isothermal expansion and / or compression steps may be longer than the post isothermal expansion adiabatic adjustment and the post isothermal compression adiabatic adjustment steps.

[0029] Moreover, the cycle may be repeated. For example, step (8) may be followed by step (1). When the cycle is being repeated many times, the ratio of the change in volume of the working fluid in step (1) to the change in volume of the working fluid in step (5) may be chosen so that each of these changes remains approximately constant over consecutive cycle repeats. For example, the control unit may also regulate the ratio of the change in volume of the working fluid in the isothermal expansion compartment and the isothermal compression compartment. This may also be achieved varying the internal volume of each compartment. In some embodiments, two or more cycles may be implemented in series using different heat engines (or compartments thereof) before a step is repeated within a compartment.

[0030] The 8-step cycle is reversible. It may also be 'started' at any of the steps. As such, within this application, a "heat engine" is interpreted as including both devices used to generate power and consume power. The power generated may be electric power. Power may be generated from heat flowing from a hot source (e.g., the thermal reservoir) to a cold sink (e.g. the thermal store). The consumed power may be mechanical power. The mechanical power may be provided by electrical power. The consumed power may be used to pump heat from a cold source (e.g. the thermal reservoir) to a hot sink (e.g. the thermal store).

[0031] In some embodiments comprising an adiabatic expansion compartment and a separate adiabatic compression compartment, two or more cycles may occur simultaneously within the heat engine. For example, step 1 and step 5 may occur simultaneously. Subsequently, step 2 and step 6 may be occur simultaneously, followed by step 3 and step 7, and then step 4 and step 8. This may increase the engine power.

[0032] Traditional uses of heat engines (including heat engines operating in reverse) include e.g. internal combustion engines (including petrol engines and diesel engines), jet and rocket engines, thermal power stations, external combustion engines, steam engines, steam and gas turbines, firearms, refrigerators, heat pumps, air conditioners, ocean thermal energy conversion systems, evaporation engines, mesoscopic heat engines, steam pumps, cryocoolers etc. Moreover, less traditional uses include high temperature solar thermal power systems and "thermal batteries" (i.e. apparatuses that store electric power by, for example, heating up and / or cooling down well insulated objects using thermodynamically efficient heat pumps, and subsequently converting the stored thermal energy using the same or other thermodynamically efficient heat pumps working in reverse, i.e. working as power generators).

[0033] In some embodiments, it may not be practical to move the entirety of the working fluid between compartments in the redistribution steps (i.e., steps (2), (4), (6) and (8)) of the primary cycle. In such embodiments, the thermodynamic efficiency of the cycle may be reduced because working fluid entering the compartment will subsequently mix with dead volume working fluid at a different pressure and possibly different temperature remaining in the compartment following the next preceding redistribution step involving the compartment. The reduction in thermodynamic efficiency may be larger with the isothermal expansion compartment and the isothermal compression compartment compared to the at least one adiabatic compartment because the surface area to volume ratios of the isothermal compartment may be higher than the corresponding ratios for the at least one adiabatic compartment and hence their practical minimum volumes may be proportionately larger. This source of thermodynamic inefficiency may be mitigated by including at least one pressure rebalancing step within the primary cycle.

[0034] A pressure rebalancing step may occur during (or between) primary cycle steps when the relevant compartment would otherwise not be contributing to the primary cycle. Up to four such steps may be added. For example, at least one of the following four steps may be added to the primary cycle: Step la (applied to the isothermal expansion compartment into which working fluid had been transferred during Step 8); Step 3a (applied to the at least one adiabatic compartment into which working fluid had been transferred during Step 2); Step 5a (applied to the isothermal compression compartment into which working fluid had been transferred during Step 4); and Step 7a (applied to the at least one adiabatic compartment into which working fluid had been transferred during Step 6). For example, Step la may happen during at least one of Steps 3, 4, 5, 6, 7 because the compartment involved with Step la does not contribute to these other steps. In each of Steps la, 3a, 5a and 7a, the internal volume of the compartments involved may be increased or reduced until the pressure and temperature of the dead volume fluid remaining within the compartment substantially equals the pressure and temperature of the working fluid transferred into that compartment in the next primary cycle step. The pressure rebalancing steps may largely reverse the impact on the residual dead volume fluid that was introduced to that fluid in the primary cycle step to which the pressure rebalancing step corresponds.

[0035] Whilst the thermodynamic efficiency of the proposed cycle can closely approximate the thermodynamic efficiency of an ideal Carnot cycle, hence reaching close to the upper limit on this efficiency set by the Second Law of Thermodynamics, even doing so when dead volume is present if appropriate pressure rebalancing steps are incorporated, practical heat engines (including heat engines operating in reverse) can suffer from many other (non-cycle driven) sources of thermodynamic inefficiency. Commercial variants will often also ideally have other features, such as a sufficiently high power to weight ratio, for the purposes to which they are expected to be put.

[0036] Some of these thermodynamic efficiency losses relate to mechanical frictions or potential mechanical vulnerabilities which compartments, pistons and other aspects of the heat engine physical design may mitigate, as disclosed herein.

[0037] For example, each compartment may be elongate. Each compartment may have a circular cross section. Each compartment may be cylindrical. This may maximise structural integrity.

[0038] At least one compartment may comprise a liquid internal surface configured to contain working fluid within the compartment. In this context, a liquid internal surface may be an internal surface of the compartment that is made from a liquid. The liquid internal surface may be a part of the piston. Alternatively, the liquid internal surface may be a side wall and / or end wall of the compartment.

[0039] Each compartment may comprise a moveable piston configured to vary the internal volume of the compartment. The pistons may have various roles, namely: to provide the force to compress the working fluid, to capture power released when the working fluid expands, to move the working fluid between compartments during redistribution steps, and / or to seal the working fluid within each compartment.

[0040] Each piston may comprise an object of fixed shape configured to slide past (or along) compartment walls. Each piston may comprise a seal mechanism attached to the piston where it abuts the compartment walls. This may contain working fluid within the compartment. Friction suffered by these seals may create material thermodynamic efficiency losses. These frictional losses may depend partly on the pressure differentials across the seal, which the seals need to be able to withstand. Seals may contain multiple seal rings. This may reduce seal leakage. Paths that working fluid needs to follow to reach seals or to bleed past them may be elongate (e.g. long and narrow). This may reduce the effective seal leakage rate.

[0041] In some embodiments, pistons and their corresponding compartment walls may comprise a flexible connection therebetween. The flexible connection may be a bellow or diaphragm. For example, the piston and compartment wall may be joined together by the flexible connection. At least one of the piston, wall, and flexible connection may be deformed by movement of a shaft or connector to increase or reduce the volume of the compartment. These may eliminate the need for slidable seals and hence eliminate seal friction thermodynamic efficiency losses. The flexible connection may be a rolling elastomer diaphragm, a PTFE / convoluted diaphragm, a formed bellows or an edge-welded bellows, for example. Sharp corners or excessive stroke distances may be avoided to reduce potential for fatigue. Hard stops at stroke limits and / or anti-pinch rings may be included to prevent folds entering clearances. Elastomeric diaphragms attached to hot walls may be used in conjunction with insulating spacers to avoid overheating.

[0042] Sealable piston arrangements may be combined with a further bellows or diaphragm beyond the sealable piston. This may contain loss of working fluid to the external environment during operation. It may allow approximate equalisation of pressures between the region contained by the sealable piston arrangement and the region outside the sealable piston arrangement but inside the bellows or diaphragm. This may reduce the pressure differentials that the seals may need to withstand and hence may reduce seal friction thermodynamic efficiency losses. It may also be used to avoid exposing an elastomeric diaphragm to a temperature at which it melts.

[0043] Another type of mechanical thermodynamic efficiency loss relates to the motions used and hence to the design of the control unit configured to regulate the movement of working fluid between compartments. These efficiency losses may be greater if parts of the engine suffer sudden jerks or other accelerations. The control unit may be configured to bring each piston to rest at the end of each step. This may be achieved using a single frequency sinusoidal driving mechanism. Alternatively, or in addition, this may be achieved using multiple frequency sinusoidal driving mechanisms that may differ for different pistons. The driving mechanism may have a frequency that is four times that of the cycle as a whole. Bringing each piston to rest at the end of each step may ensure each piston smoothly transitions from moving in one direction to staying at rest during the subsequent step or moving in another, opposing direction during the subsequent step.

[0044] The piston may be a mechanical piston. A mechanical piston may also be a dry piston. Each piston may comprise a piston axis along which it is configured to move. Each piston axis may be parallel. Each piston axis may be aligned vertically (i.e., parallel to the direction of gravity). This may reduce energy losses due to friction.

[0045] In some embodiments, the heat engine may comprise a plurality of rods arranged to oscillate bilinearly in the same direction as the piston axes. The rods may oscillate at a common frequency but with different amplitudes. Each rod may be connected to a rigid frame by a spring. The frame may be fixed at rest. Each rod may also be connected to a common drive bar by a spring. The drive bar may be free to move. As such, the drive bar may be connected to the rigid frame via the plurality of rods. The drive bar may be configured to oscillate in the same axial direction as the pistons and rods.

[0046] The drive bar may be coupled to a linear electric actuator or generator (LEAG). The LEAG may be configured to set the drive bar in approximate bi-linear harmonic motion. Alternatively, or in addition, the LEAG may be configured to slow the drive bar in an approximate bi-linear harmonic manner. The amplitude of vibration of each moving rod may be a constant proportion of the amplitude of vibration of the drive bar. This proportion being dependent on the ratios of the elastic constants of the two springs to which each oscillating rod is affixed. These ratios may be varied such that the rods oscillate with the different amplitudes.

[0047] Movement patterns of pistons that are approximately continuously sinusoidal may be implemented using a traditional rotating shaft approach. For example, one or more pistons may be operably coupled to a shaft. The shaft may be attached to an object. The object may be a rotating object. The object may be a plate. The shaft may comprise one or more lobes configured to control the movement pattern of the piston(s). One end of the shaft may be attached to a fixed point in the object. The other end of the shaft may be constrained to move in a linear direction.

[0048] Within the proposed cycle, it may be desirable for pistons to move during some but not all cycle steps, thus introducing a need for motion to occur only some of the time. Use of a cam-follower mechanism may enable this functionality. For example, the rotatable shaft may comprise a plurality of cams. Cams with appropriately defined shapes attached to the rotating shaft may impart appropriate movements to their followers (i.e. the shaft ends constrained to remain in contact with a rim of the cam).

[0049] In some embodiments, each rod may comprise a rod lock. The rod lock may be configured to lock that particular rod to a piston. As such, during each cycle, each piston may be "locked" to a particular rod. For example, if a piston is at rest during a particular cycle step, it may be "locked" to a particular rod that is held at rest during that cycle step. The rod lock used to lock a particular piston to a particular oscillating (or at rest) rod might be an electromagnetic brake (sometimes also called electromechanical brake) or a mechanically-orientated braking / locking mechanism. The locking and unlocking may be carried out when both the rod and piston are instantaneously at rest. As such, relatively little energy may be needed to switch locks on and off.

[0050] In some embodiments, each piston may comprise a swap mass. Each swap mass may comprise the same mass as the piston to which it corresponds. The swap masses may be used to avoid the rod oscillating with a different frequency when one or two pistons are locked onto it. As such, the lock process might comprise the piston being unlocked from a rest rod and locked to a relevant oscillating rod (or vice versa) with the reverse simultaneously happening to the swap mass associated with that piston.

[0051] Due to energy losses or energy consumption with the heat engine, additional energy may be applied to one or more piston. For example, each piston may be connected to a LEAG. The LEAG may input energy into (or extract energy from) the oscillating system formed by the rods and pistons. In some embodiments, the above piston oscillatory pattern may be implemented using LEAGs attached to the pistons. The heat engine may also comprise control circuitry connected to the LEAGs and configured to create the appropriate amplitude bi-linear harmonic motions described above. Each LEAG may be digital. Each LEAG may be programmable.

[0052] Some mechanical thermodynamic efficiency loss may arise if the heat engine releases work during one part of a cycle only for a substantial proportion or all of this work to be returned to the heat engine at a different point in the cycle. If two or more heat engines are operated in parallel with cycles of equal time length but with a phase difference, some degree of workload balancing (i.e. workload offsetting) may be practical, reducing this thermodynamic efficiency loss. Workload balancing that is purely mechanically implemented may be particularly thermodynamically efficient because the forces created by work released by one piston may be transmitted directly into opposite forces that carry out work on a different piston. In contrast, LEAG mediated workload balancing may require conversion of mechanical work into electrical work and then a separate conversion of electrical work back into mechanical work which may introducing more scope for inefficiencies.

[0053] A disadvantage from a workload balancing perspective of piston movement patterns that are sinusoidal within specified cycle steps is that distances travelled are not in general proportional to the energy added to or subtracted from the working fluid during the time the pistons take to move these distances, i.e. to work done by the relevant components of the heat engine. For example, if a heat engine operates in line with an ideal Carnot cycle interspersed with redistribution steps, the overall energy released in the adiabatic expansion step is equal in magnitude to the energy consumed in the adiabatic compression step. However, if corresponding piston movements are sinusoidal within these steps, one of these will exhibit a peak absolute workflow earlier than half-way through the relevant cycle step whilst the other will exhibit a peak absolute workflow later than half-way through the relevant cycle step.

[0054] Better workload balancing of adiabatic energy flows through time, whilst still bringing both pistons to rest at the start and end of the relevant cycle steps, may be achieved by arranging for two cycles to be happening simultaneously, with the adiabatic expansion step of one coincident in time with the adiabatic compression step of the other. At least one of the piston movement patterns involved may be be non-sinusoidal. For example, instead of each of these piston movements following patterns of the form x(t) = x0+ x±cos(8?rt) for suitable piston-dependent choices of (constant) x0and x±during the relevant cycle step, the movements may follow patterns such as x(t) = x2, where TAis the temperature of the isothermal expansion compartment, Tcis the temperature of the isothermal compression compartment and y is the heat capacity ratio of the working fluid being used. With an ideal gas, this may result in the work flows nearly exactly cancelling out.

[0055] Redistribution cycle steps may be closely workload balanced whatever the selected piston movement pattern. Workload balancing across isothermal cycle steps has more dependent elements. For example, the overall work done across the combination of an isothermal expansion and an isothermal compression step is non-zero because, in the ideal Carnot cycle case, the resulting net work done corresponds to the aggregate work output from the heat engine or work input into it. However, by selecting appropriate movement patterns we may arrange for the two as functions of time to be proportional to each other. If timed appropriately and with enough cycles happening simultaneously with appropriate phase differences, we may also arrange for the aggregate work output or input to behave as a function of time in a manner helpful for its ultimate use. For example, the work output or input may have a time dependency aligned with that characterising sinusoidal alternating current electricity. This may improve the conversion efficiency of mechanical work to (or from) electric power if relevant.

[0056] In some embodiments, non-linear piston movement transformations may be implemented by use of non-circular gears. This may involve using an otherwise crank-connecting rod-crosshead assembly but replacing the input drive with a non-circular gear pair. In some embodiments, non-linear movement transformations may be implemented by use of a radial (disc) cam mounted on a crankshaft.

[0057] In some embodiments, non-linear piston movement transformations may be implemented by use of a plate (such as a cam plate) rather than the previously described shaft (e.g., a cam shaft). For example, a shaft may be attached to a piston and the movement of the end of the shaft not attached to the piston may be constrained to move in a fixed track. The movement path of the piston may comprise a component parallel to the longitudinal axis of the compartment. The fixed track may constrain the end of the shaft not attached to the piston to follow a prescribed path in a flat or cylindrical plate. The plate may be transverse to the longitudinal axis of the compartment. The plate may be moveable. The plate may be moved backwards, forwards, at an angle relative to the fixed track, and / or rotated around an axis that may be parallel to the longitudinal axis of the compartment axis. This may cause the shaft end not attached to the piston and hence the piston (via the shaft) to move relative to its associated compartment according to a pattern that is defined by the interaction of the shapes of the track it is being constrained to follow. There may be a plurality of plates, as described above, each restricting the movement of selected piston shafts.

[0058] The track in each plate may be different. As the shape of the track can be largely arbitrary, a wide range of non-linear piston movement patterns may be introduced by such a mechanism. Roller bearings, magnetic bearings, lubricants or other low friction alternatives such as diamond-like coatings may be used to reduce the frictional efficiency losses incurred by the simultaneous constraining of the shaft end within the tracks. The most appropriate piston movement patterns may depend on operating parameters such as the temperatures of the thermal store and thermal reservoir. If these parameters are expected to change in use, a mechanism may be incorporated that switches the movements assigned to a piston from being derived from one pair of tracks to being derived from a different pair of tracks. If an embodiment uses a cam shaft approach, piston shafts may be shifted between cams to alter movement patterns whilst in use. Non-linear piston movement transformations may also be introduced by use of multi-bar linkages or linkage combinations such as a Stephenson 6- bar linkage, an Atkinson linkage or a combination, for example. These may provide suitable approximations to the desired movement transforms.

[0059] In some embodiments, the piston may be a fluid piston. The fluid piston may be a liquid piston or gas piston. A fluid piston may be generated by injecting a piston fluid into a compartment alongside the working fluid. This may increase the pressure within the compartment. Similarly, by removing the injected piston fluid, the pressure within the compartment can be reduced. The working fluid may be a gas. The piston fluid may comprise water. Although, any immiscible fluids may be used for the working fluid and piston fluid. There may be a moveable barrier between the two fluids. The barrier may be impermeable. The barrier may be shaped so that it can float on the fluid. The barrier may be buoyant. In some embodiments, compression (or expansion) of the working fluid may be made more isothermal by spray cooling (or warming) the working fluid using the fluid piston being pumped into (or out of) the relevant compartment.

[0060] The heat engine may comprise a plurality of tanks. Each tank may be configured to store a fluid. The fluid may be liquid. The liquid may be water. Each compartment may be fluidly connected to a distinct tank. Fluid in the two tanks associated with the isothermal expansion compartment and isothermal compression compartment may be kept in thermal contact with the thermal reservoir and thermal store, respectively. As such, the fluid temperatures in these two tanks may be substantially equal to the temperature of the thermal reservoir and thermal store, respectively.

[0061] Fluid flows between each tank and its corresponding compartment may be controlled by a corresponding turbine. Each turbine may be configured to pump fluid between the tank and the compartment, thus consuming (electric) power. Each turbine may also be configured to be spun by fluid flowing between the tank and the compartment, thus generating (electric) power. Fluid may be pumped into or released out of each compartment separately. It may not be intermingled with fluid pumped into or released out of any other compartment(s). This system may be used to generate the liquid pistons.

[0062] In some embodiments, fluid may be moved between each tank and its corresponding compartment using head pressure within the tank. As such, each tank may be located at a variable height compared to its corresponding compartment. Therefore, raising or lowering the tank (e.g. using a LEAG) may increase or reduce the pressure imparted by the liquid piston, thus reducing, or increasing the volume of the working fluid in the corresponding compartment.

[0063] In some embodiments, a piston may be a hybrid piston. For example, a piston may comprise a solid base plate having a rigid surface that forms an internal surface of the compartment. However, a pump may be used to pump a pumping fluid into (consuming work) or out of (generating power) a part of the compartment that is the opposing side of solid base plate to the working fluid. The side of the solid base plate facing the pumping fluid may be smooth. This may enable the pumping fluid to expand and / or compress in as close to a reversible adiabatic fashion as possible if the pumping fluid is a gas, for example. Consequently, a part of the compartment in which the pumping fluid is located may have a different internal structure to a part of the same compartment in which the working fluid is located.

[0064] The direction of movement in which a piston may move may be linear. However, in some embodiments, the direction of movement in which a piston may move may be curved. Consequently, the compartment may have a specific axis along which it is orientated. If the piston moves along a curved path, the piston sides may be suitably curved to follow the curvature of the compartment within which it moves.

[0065] The sealable adiabatic compartment aperture may be located on an internal surface of the isothermal expansion compartment that opposes the isothermal expansion compartment piston. Alternatively, or in addition, the sealable isothermal compression compartment aperture may be located on an internal surface of the isothermal compression compartment that opposes the isothermal compression compartment piston. This arrangement may reduce radial pressure differentials, thus allowing the use of thinner pistons, which may be used to increase the surface area of each compartment per unit volume. This may make expansions / compressions more isothermal.

[0066] Each moveable piston may have an oval cross-section. As such, each compartment may also have an oval cross-section. An oval cross-section may have minimal impact on the overall structural integrity of the compartment, whilst significantly reducing the risk of the piston twisting within the compartment. This may reduce the risk of jamming or of mechanical failure with the compartment. However, the pistons and compartments may have any corresponding cross-sections, such as circular, elliptical, triangular, and rectangular.

[0067] In some embodiments, each compartment may comprise a guide feature. The guide feature may comprise an indent and a protrusion. The indent and protrusion may be aligned such that the indent is configured to receive the protrusion. As such, the guide feature may also be a meshing feature. One of the indent and the protrusion may be located on the piston, with the other located on an internal surface of the compartment adjacent to the piston. This may reduce (or eliminate) the potential for the piston to rotate within the compartment.

[0068] If the thermal store and thermal reservoir are external to the relevant isothermal compartments, it becomes important to achieve a sufficiently high heat transfer rate between them. The isothermal expansion compartment and the isothermal compression compartment may each comprise a moveable piston having a plurality of protrusions located on a surface of the piston forming an internal surface of the compartment. Each of the isothermal expansion compartment and the isothermal compression compartment may comprise an internal surface opposing the surface of the piston forming an internal surface of the compartment that comprises a plurality of recesses configured to receive the piston protrusions. These protrusions may be the protrusion of the previously described guiding (or meshing) feature.

[0069] In some embodiments, protrusions may protrude from compartment sides with corresponding recesses in the cross-section of the associated piston rather than from compartment and piston ends.

[0070] The protrusions increase the internal surface area of the compartment. More specifically, the use of protrusions increases the rate of heat transfer between the working fluid and the piston and compartment internal surface, as the rate of heat transfer between a fluid and a thermal conductor (e.g., piston and compartment internal surface) is proportional to the surface area of the conductor and is also influenced by the average gap through which the heat flows. This may improve the efficiency of the heat engine. The protrusions may be organised so as to rotate relative to each other. Heat flow may be strongly influenced by the Reynolds number of the working fluid and this depends on the fluid velocity relative to nearby protrusion edges.

[0071] Each protrusion may completely fill its corresponding recess. This reduces dead volume within the system. However, in practice, some clearance between protrusions and their corresponding recesses is likely to be needed. This may avoid them jamming, although as noted above the impact of this dead volume can be mitigated by including additional pressure rebalancing steps. The clearance may be up to 0.1mm, 0.2mm, 0.5mm, 1mm, 2mm or 3mm. The height of the protrusions and recesses may be defined by their length in a direction parallel to the direction of movement of the corresponding piston. The height of each protrusion and its corresponding recess may be at least half the height of the compartment. As such, at least part of the protrusion may always remain within the recess. This may avoid difficulties associated with re-aligning the protrusion with the recess if they are moved too far apart.

[0072] The protrusions and their corresponding recesses may be non-planar (e.g., crinkled, or wavy) along an axis perpendicular to the direction of the movement of the piston. This may increase the surface area of the protrusion and recess, and it may provide greater structural rigidity. Concentric protrusions may comprise one or more concertina features (for example, with tangential folds). The concertina features may have less structural rigidity. In some embodiments, the protrusions and recesses may extend radially away from the central axis of movement of the piston. This may minimise the risk of buckling, in use, and may maximise the scope for a large number of protrusions / recesses, thus surface area, for a compartment having a given cross- sectional area.

[0073] In some embodiments, the protrusions and recesses may have cross-sections that are concentric. The protrusions and recesses may be tapered so that gaps between them become narrower when the compartment is emptier (or smaller). Some of the protrusions and recesses may rotate relative to the compartment or piston or both. The rotation rate of any that are rotating may be largely independent of the positioning of the piston. The rotation may be maintained by a subsidiary electric motor. Rotation may be imparted via a gearing system on a central spindle. The rotation rate of any that are rotating may alter as the piston moves and may slow when the piston is slowed either when the compartment is emptier or when it is fuller or both.

[0074] The heights of the protrusions and recesses may be larger than the distance travelled by the piston. The height to distance ratio may be 150%, 200%, 1000% or more. This may increase the effective surface area of the compartment through which heat may flow to or from the working fluid from or to the compartment or piston walls. Moveable protrusions and recesses may not involve complete circular cross-sections but may involve segments that can flex more easily. This may reduce stresses and hence frictional losses when the moveable protrusions and recesses are moved. Protrusions and recesses may be positioned so that moveable and fixed edges alternate and on at least one abutting side of each the edges are parallel to the direction of movement of the piston. These abutting edges may touch lightly and over a limited area to mitigate frictional losses. For example, this may include placing thin perpendicularly positioned strips of diamond-like coating (such as vapour deposited amorphous carbon that possesses some of the properties of diamond) on each abutting edge or it may include suitable roller or magnetic bearings or lubricants on these edges. Lubricants may be included in these gaps. The Lubricant may reduce the dead volume otherwise introduced by the protrusions. The protrusions may include wicking elements or other capillary features to spread the lubricant more uniformly across the protrusion.

[0075] One set of protrusions may be made of a rigid material with a high thermal conductivity, such as copper. This set may extend from the compartment base or compartment wall. The other set of protrusions may be made of an elastic material that narrows as it is extended. This set may be attached to the compartment base. Alternatively, or in addition, this set may extend from a moveable piston. A relatively small clearance distance may be selected to apply when the compartment is empty, thus reducing dead volume. The clearance may be up to 0.1mm, 0.2mm, 0.5mm, 1mm, 2mm or 3mm. The clearance may then increase as the compartment fills due to the consequential extension of the elastic protrusions.

[0076] Alternatively, or in addition, the isothermal expansion compartment and the isothermal compression compartment may each comprise a porous material configured to increase the internal surface area of the compartment. The porous material may be wire wool, or a concertina-ed material, for example. The concertina-ed material may be metallic. It may take the form of a bellows. The concertina-ed material may comprise one or more spring. Ideally, the volume of the compartment would still be negligible when the working fluid has been fully redistributed to the at least one adiabatic compartment to minimise dead volume. In such embodiments, the effective cross-sectional area of the isothermal compartments could be reduced versus the cross-sectional area required if there was no such porous material present. Conversely, the internal surface(s) of the at least one adiabatic compartment may be smooth. Concertina-ed elements may include features designed to reduce aerodynamic or hydrodynamic resistance when expanded or contracted. These features may be smooth sides and / or hemispherical ends rather than flat ends, for example.

[0077] Each protrusion may comprise a curved tip portion configured to abut an equally curved base portion within a corresponding recess. The curved tip portion may connect directly to the surface of the piston forming an internal surface of the compartment. Consequently, as the piston is moved away from the internal surface of the compartment opposing the surface of the piston forming an internal surface of the compartment end, gaps may immediately open between the protrusions, which may minimise friction as well as potential dead volume. This may also eliminate the need for a second aperture at the piston end of the compartment.

[0078] The width of each protrusion proximal to the surface of the piston forming an internal surface of the compartment may be greater than the width of each protrusion distal to the surface of the piston forming an internal surface of the compartment. As such, each protrusion may be wider at their base end and narrower at their tip end. In other words, the protrusions may be tapered. Consequently, as the piston is moved away from the internal surface of the compartment opposing the surface of the piston forming an internal surface of the compartment end, gaps may immediately open between the protrusions, which may minimise friction as well as potential dead volume. Protrusion taper angles may vary within and between protrusions and one side of a protrusion may be more tapered than the other side.

[0079] In some embodiments, the protrusion(s) may only attach to the piston. The remainder of the compartment when empty of working fluid may be filled with a liquid such as water or oil. Heat may be transferred to or from the working fluid from or to the protrusions. The temperature of the protrusions may be replenished by heat flow to or from them from or to the liquid. The temperature of the liquid may be replenished by heat flow to or from the liquid from or to the compartment or piston walls. This sort of embodiment will however suffer from skin friction thermodynamic efficiency losses as the protrusions move into and out of the liquid.

[0080] A related type of thermodynamic efficiency loss is that arising from skin friction losses suffered by the working fluid as it is moved between or within compartments. Compartment apertures (i.e., internal spaces / voids) configured to receiving the working fluid may be flared with curved edges. This may limit friction otherwise arising at sharp boundaries. Each compartment may have multiple apertures to increase the surface area through which flow may occur.

[0081] At least one of the isothermal expansion compartment and the isothermal compression compartment may comprise a flow channel configured to facilitate an unimpeded flow of working fluid between and / or through the protrusions. The flow channel(s) may be devoid of protrusions (or other methods of increasing surface area). This may reduce skin friction losses from getting the working fluid to regions of the compartment in which the high heat transfer may take place. Each flow channel may have smooth sides. Each flow channel may be wider than the average width of the gaps between the protrusions through which the flow channel passes. For example, each flow channel may be 1.5, 2, 2.5, 3 or more than 3 times as wide as the average width of the gaps between the protrusions through which the flow channel passes. Each flow channel may comprise elongated holes in abutting protrusions that allow unimpeded flow of working fluid therethrough. The working fluid may flow in the fluid channel(s) during some, but not all, of the associated redistribution steps.

[0082] A plurality of flow channels may flow radially outwards from at least one central duct. Whilst inclusion of flow channels increases dead volume, the impact of this dead volume may be modest compared to the impact of the dead volume needed to provide adequate clearance between protrusions and may be mitigated by inclusion of pressure rebalancing cycle steps. Compartment apertures may span much or all the base of a compartment and may involve abutting grids that when closed do not allow fluid flow but when open allow unimpeded fluid flow. Such losses typical scale in proportion to the volume moved and the square of the velocity, hence distance travelled during a given cycle step. Increasing the number of a given type of compartment whilst reducing the size of each one may therefore significantly reduce overall skin friction losses across a given type of compartment whilst leaving overall power output of the heat engine largely unchanged. Each flow channel may be disc-shaped. Each flow channel may be located above the protrusions. For example, the protrusions that would otherwise have been attached to the piston might be separately moveable from the piston. The flow channel may be formed by differentially moving the piston away from the protrusions as the working fluid is moved into or out of the compartment. Alternatively, or in addition, one or more flow channel, or a part thereof, may be in the piston. In some embodiments, there may be corresponding flow channels in the opposing compartment end. Each flow channel may spread out from the central duct.

[0083] In some embodiments, the flow channels may flow out from the central duct into a region in which there are protrusions. The flow channel may flow out neither at the top nor at the bottom of the protrusions but in between. The flow channels may be substantially linear. The flow channels may comprise fractal-like bifurcating structures.

[0084] If the spatial layout of the different compartments is chosen to keep compartments adjacent to ones from which their working fluid comes and to which their working fluid goes, skin friction losses arising from the movement of working fluid between compartments may be reduced. For example, we may have an approximately circular layout in which isothermal expansion and compression compartments alternate on one level and there are adiabatic compartments abutting that are immediately above and / or below the isothermal compartments through which the working fluid flows in between consecutive isothermal compartments. There may be more than one isothermal expansion and more than one isothermal compression compartments in each such approximately circular layout, each one smaller than would be the case if an engine of equivalent power only used one isothermal expansion and one isothermal compression compartment.

[0085] Skin friction flow losses may be asymmetric in relation to the ordering of compartments. In some cases, an adiabatic expansion may be implemented immediately after an isothermal expansion in the same isothermal expansion compartment. This may remove the need for working fluid to flow between two separate compartments. This may reduce the consequential skin friction losses from doing so. However, carrying out an adiabatic expansion in a compartment otherwise optimised for carrying out isothermal expansions may somewhat deplete the heat engine's theoretical adherence to a Carnot-like cycle and may therefore introduce other thermodynamic inefficiencies.

[0086] The length of each protrusion in the direction of movement of the corresponding piston may be at least 50% larger than the distance travelled by the piston as working fluid moves into or out of the compartment. In some embodiments, the length may be at least 75%, 100%, 150%, 200%, 300% or more than 300% larger than the distance travelled by the piston. Each piston may comprise a sealing mechanism abutting the adjacent internal surfaces of the compartment. The sealing mechanism may be a flexible connection, such as a concertina-ed edge, bellow, or diaphragm. Alternatively, or in addition, the sealing mechanism may be lubrication, and / or a plurality of ball bearings. This may be used to prevent working fluid leaking around the (solid) piston ends into other compartments and / or regions of the heat engine. The sealing mechanism may therefore enable the sides of pistons to fit closely to the other internal surfaces (e.g. walls) of the compartment, but not so closely that the pistons are at risk of jamming or of incurring a lot of mechanical friction.

[0087] In some embodiments, the heat engine may comprise a chamber containing the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment. The chamber may be a single continuous void within a structure, such as a housing. The chamber may have a common cross-section along a given axis. For example, the chamber may have a common cross-section along an axis parallel to the direction of movement of one or more pistons within that chamber. If the chamber is a single continuous void, mechanisms for causing movement of a piston within the chamber may be enclosed within the chamber. For example, if piston movement involves a LEAG, this LEAG may be positioned inside the chamber. This may reduce loss of working fluid to the external environment.

[0088] A compartment may be a region within a chamber that is separable from other compartments. Separable compartments may be located within the same chamber and / or in different chambers. There may be just one compartment in a chamber. Alternatively, there may be a plurality of compartments within a chamber.

[0089] For example, a plurality of concentric moveable pistons may be attached to a guiding shaft. The moveable pistons and guiding shaft may be located within a single chamber for compressing and expanding the working fluid. As such, the pistons may compartmentalise the chamber, thus forming the compartments.

[0090] In some embodiments, the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment may each be located in a separate chamber, or within a plurality of chambers. One chamber may comprise two or more compartments. As such, there may be a plurality of different chambers. The chamber may be a toroidal chamber. As such, the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment may be linked in series. Each compartment may be in a fixed location within the chamber. Each compartment may comprise one or more piston. Again, the pistons may compartmentalise the chamber. This enables the cross- sectional characteristics of each compartment to be optimised for the type of expansion or compression taking place therein.

[0091] The chamber may comprise a moveable adiabatic compartment piston located between the isothermal expansion compartment and the at least one adiabatic compartment. The chamber may comprise a moveable isothermal compression compartment piston located between the at least one adiabatic compartment and the isothermal compression compartment. The moveable adiabatic compartment piston may comprise the sealable adiabatic compartment aperture. The moveable isothermal compression compartment piston may comprise the isothermal compression compartment aperture.

[0092] The chamber may comprise a moveable intermediate adiabatic compartment piston for defining an intermediate adiabatic compartment between the isothermal expansion compartment and the at least one adiabatic compartment. The chamber may comprise a moveable intermediate isothermal compression compartment piston for defining an intermediate isothermal compression compartment between the at least one adiabatic compartment and the isothermal compression compartment. The moveable intermediate adiabatic compartment piston may comprise a sealable intermediate adiabatic compartment aperture that is offset from the sealable adiabatic compartment aperture. The moveable intermediate isothermal compression compartment piston may comprise a sealable intermediate isothermal compression compartment aperture that is offset from the sealable isothermal compression compartment aperture.

[0093] The intermediate adiabatic compartment and the intermediate isothermal compression compartment may comprise the same physical properties and / or geometry as the adiabatic compartment. The inclusion of the intermediate adiabatic compartment and the intermediate isothermal compression compartment means that the isothermal expansion compartment and the isothermal compression compartment may not need to alter their internal volume as much.

[0094] The apertures may be offset from each other with respect to an axis parallel to the direction of movement of the pistons. Each piston aperture may be located within a solid base plate of the piston. This base plate may separate two compartments. As such, the base plate of each piston may comprise the surface of the piston forming an internal surface of the compartment within which it is located. However, the surface of the base plate most distal from the surface of the piston forming an internal surface of the compartment within which the piston is located may form an internal surface of the adjacent compartment. As such, the offset nature of two adjacent apertures means that both apertures would be sealed if their corresponding piston base plates were to contact one another (e.g., if the volume of the compartment therebetween was reduced to 0).

[0095] The chamber may comprise a moveable transitional adiabatic compartment piston for defining a transitional adiabatic compartment between the intermediate adiabatic compartment and the at least one adiabatic compartment. The chamber may comprise a moveable transitional isothermal compression compartment piston for defining a transitional isothermal compression compartment between the intermediate isothermal compression compartment and the isothermal compression compartment. The moveable transitional adiabatic compartment piston may comprise a sealable transitional adiabatic compartment aperture that is offset from the sealable intermediate adiabatic compartment aperture. The moveable transitional isothermal compression compartment piston may comprise a sealable transitional isothermal compression compartment aperture that is offset from the sealable intermediate isothermal compression compartment aperture. Again, the apertures may be offset from each other with respect to an axis parallel to the direction of movement of the pistons.

[0096] The transitional adiabatic compartment and the transitional isothermal compression compartment may comprise the same physical properties and / or geometry as the adiabatic compartment. The inclusion of the transitional adiabatic compartment and the transitional isothermal compression compartment may further reduce the amount by which the internal volume of the isothermal expansion compartment and the isothermal compression compartment may need to be varied.

[0097] Each compartment may comprise a moveable rotor configured to vary the internal volume of the compartment. As such, in some embodiments, the heat engine may include features present in a Wankel-like heat engine. In particular, the heat engine may comprise three chambers. Each chamber may comprise a moveable rotor. Each rotor may be configured to rotate with its respective chamber. Each rotor may be substantially triangular. More specifically, each rotor may be in the shape of a Reuleaux triangle. A Reuleaux triangle is a curved triangle with constant width. This shape may be formed from the intersection of three circular disks, each having its centre on the boundary of the other two. As such, each rotor may comprise three sides.

[0098] Each chamber may be substantially oval. More specifically, each chamber may be epitrochoidal. Each rotor may contact the perimeter of a chamber at three locations. As such, each chamber may comprise three compartments separated by the moveable rotor. The moveable rotor may be configured to vary the internal volume of each compartment within the chamber as it rotates. As each rotor completes a full revolution, each compartment within each chamber may undergo two expansions (maximal at the long ends of the substantially oval housing) and two compressions (maximal at the short sides of the substantially oval chamber). The geometry of each rotor and corresponding chamber may be configured such that a working fluid within a compartment undergoes isothermal expansion, adiabatic expansion or compression, isothermal compression, and adiabatic compression or expansion as the rotor completes a full revolution within the chamber.

[0099] The three chambers, each comprising a rotor, may be adjacent to one another. For example, they may be stacked on top of each other. Each chamber may be offset (i.e., rotated about its centre) with respect to the adjacent chamber(s), such that the long side of the substantially oval chambers are angled relative to each other. Each chamber may be offset from an adjacent chamber by up to 120 degrees, 90 degrees, 60 degrees, 45 degrees, or 30 degrees. Each chamber may comprise a plurality of apertures. In particular, each compartment may comprise an aperture.

[0100] A first chamber may comprise the isothermal expansion compartment. A second chamber may comprise the at least one adiabatic compartment. A third chamber may comprise the isothermal compression compartment. As before, the at least one adiabatic compartment comprises a sealable adiabatic compartment aperture for conveying working fluid between the isothermal expansion compartment and the at least one adiabatic compartment, and the isothermal compression compartment comprises a sealable isothermal compression compartment aperture for conveying working fluid between the at least one adiabatic compartment and the isothermal compression compartment.

[0101] Therefore, by suitable choice of timing of opening and closing of these sealable apertures, and by suitable choice of angle offsets between the chambers, working fluid may be transferred between the three chambers. In particular, working fluid may be transferred from the isothermal expansion compartment in the first chamber to the at least one adiabatic compartment in the second chamber, and then from the least one adiabatic compartment in the second chamber to the isothermal compression compartment in the third chamber. Each chamber and / or compartment may comprise a pump configured to pump the working fluid to a compartment within an adjacent chamber. In some embodiments, each chamber and / or rotor may be flexible. This may enable the shapes and hence volumes of the compartments to be adjusted, in use.

[0102] In some embodiments, the heat engine may comprise a toroidal chamber containing the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment. The toroidal chamber may comprise a plurality of adjustable gates configured to separate the compartments and provide at least the sealable adiabatic compartment aperture and the sealable isothermal compression compartment aperture. The toroidal chamber may comprise at least one turbine configured to move working fluid between the compartments. The control unit may be configured to regulate the movement of working fluid between the compartments by opening and closing the gates.

[0103] More specifically, the toroidal chamber may comprise an isothermal expansion compartment, a first adiabatic adjustment compartment, an isothermal compression compartment, and a separate second adiabatic adjustment compartment. The toroidal chamber may comprise at least four gates. For example, the toroidal chamber may comprise an isothermal expansion compartment gate, a first adiabatic adjustment compartment gate, an isothermal compression compartment gate, and a second adiabatic adjustment compartment gate. Each gate, in its closed position, may be configured to seal an aperture. As such, the isothermal expansion compartment gate may be configured to seal the isothermal expansion compartment aperture. The first adiabatic adjustment compartment gate may be configured to seal the first adiabatic adjustment compartment aperture. The isothermal compression compartment gate may be configured to seal the isothermal compression compartment aperture. The second adiabatic adjustment compartment gate may be configured to seal the second adiabatic adjustment compartment aperture.

[0104] However, there may be more than four gates. For example, each compartment may comprise an intermediate and / or transitional gate. These gates may be equivalent to the intermediate and / or transitional pistons previously described. As such, the toroidal chamber may comprise the previously described intermediate and / or transitional compartments located between the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment.

[0105] For example, if all the gates were open and the turbine was rotating at a selected rate, the working fluid may circulate around the toroidal chamber at a "natural" velocity. However, if one gate is sealed at a certain point in time, and the next downstream gate is sealed a little later than implied by this natural velocity, the working fluid trapped in the compartment between the two sealed gates will have been expanded. Here the next downstream gate is the one that the working fluid will next reach as it moves around the toroidal chamber. As such, the compartment containing the expanded fluid may be the isothermal expansion compartment (or an adiabatic expansion compartment). Conversely, if the next downstream gate is sealed a little earlier than implied by this natural velocity, the working fluid trapped in the compartment between the two sealed gates will have been compressed. As such, the compartment containing the compressed fluid may be the isothermal compression compartment (or an adiabatic compression compartment). Finally, if the next downstream gate is sealed in line with this natural velocity, the working fluid trapped in the compartment between the two sealed gates will experience neither expansion nor compression (i.e. will merely undergo redistribution around the toroidal chamber). Therefore, by timing the opening and sealing of consecutive gates appropriately, working fluid within the toroidal chamber may undergo the previously described 8-step cycle.

[0106] In some embodiments, there may be a plurality of turbines. For example, each compartment may comprise a turbine. There may be at least one gate located each side of each turbine. The turbines may be powered by (and / or extracting power using) electrical reluctance motors / generators. The control unit may be configured to switch off each turbine temporarily. This may allow the turbines to "free-wheel" during parts of the cycle, which might reduce potential efficiency losses due to mechanical and other frictions. Each turbine may comprise a plurality of blades. The blades may be located within a housing. The housing may be cylindrical. Therefore, when the turbine was freewheeling, any working fluid remaining within the span of the turbine blades may be kept within the housing, thus rotate around with the blades. This may reduce friction between this rotating working fluid and the non-rotating wall of the chamber surrounding the turbine.

[0107] If each compartment contains several turbines, each with its own gates immediately before and after it (viewed by reference to typical direction of fluid flow), the timing of the opening and closing of these gates may be selected to align the movement of working fluid through the turbine-based heat engine with the movement of working fluid that would occur through a corresponding piston-based heat engine. This may be achieved by identifying how many of these gates need to be open at the same time if the change in volume of a given packet of working fluid were to match the change it would have experienced in a corresponding piston-based heat engine. So, in a formal sense, whatever is feasible with a piston-based variant of the heat engine is also feasible with a turbomachine-based variant of the heat engine.

[0108] Traditionally, turbomachines have been seen as typically more efficient in high performance contexts than positive displacement machines such as piston-based engines (except for automotive purposes where internal combustion engines have typically been preferred). For example, jet engines and gas turbines have mostly displaced other types of heat engine over time for their targeted purposes. However, with the heat engine described in this application, and particularly when heat energy is being delivered externally to or from the heat engine, this traditional preference may not apply.

[0109] Both turbomachine and positive displacement machine variants then face the challenge of delivering working fluid into heat exchange mechanisms that have potentially narrow channels that are subject to skin friction losses. In addition turbomachine variants may need many different turbines to work efficiently, so may be very complicated to make, and may need to be run at speeds that may incur high skin friction losses to avoid the aerofoils in their turbines stalling (or may need gating arrangements as above, in which stalling is intentionally introduced but only when gates on either side of the turbines are closed). If dead volume efficiency losses are otherwise material, turbomachinebased variants may need pressure rebalancing features akin to those explained above for piston-based variants. However, with turbomachine-based variants, such pressure rebalancing features may need an additional set of turbines running in the opposite direction to the main set of turbines, further adding to the complexity of a turbomachine variant compared to a corresponding positive displacement machine variant.

[0110] In some embodiments, the heat engine may comprise an energy regeneration mechanism configured to temporarily store energy produced within one or more compartment for use elsewhere within the heat engine and / or at a later time. The stored energy may be re-used, at a later time, within the compartment in which it was generated. Alternatively, or in addition, the stored energy may be used within another compartment.

[0111] The energy regeneration mechanism may comprise a mechanical regeneration mechanism. For example, the energy regeneration mechanism may comprise a mechanical spring. The mechanical spring may temporarily store energy released within a compartment during one heat engine cycle step and return it back to the heat engine during a different cycle step. Alternatively, or in addition, the energy regeneration mechanism may comprise a spinning flywheel. Moreover, in some embodiments, the energy regeneration mechanism may comprise a rigid connection between two or more pistons. The rigid connection may transfer energy generated within one compartment directly to a piston within another compartment. As such, the rigid connection may be a direct rigid connection.

[0112] Alternatively, or in addition, the rigid connection may comprise a rigid lever connection. The rigid lever connection may comprise two arms connected by a pivot about which they may rotate. Each arm may be connected to a piston or a rotor. This may enable the power or work output by one piston or rotor and / or provided to another piston or rotor to be adjusted based on the positioning of the arms relative to their pivot point.

[0113] Alternatively, or in addition, the energy regeneration mechanism may comprise an electrical regeneration mechanism. The electrical regeneration mechanism may comprise a LEAG. The LEAG may be bi-directional. Each piston may be connected to a LEAG. The LEAGs may be connected via an electrical circuit. The LEAGs may be connected such that that power generated by one LEAG within one compartment during one part of the cycle is temporarily transferred to another LEAG at the same or other parts of the cycle.

[0114] The electrical circuit may be configured to supply additional energy to one or more piston or rotor when it needs to do work, and to generate energy from one or more piston or rotor when it needs to release work. As such, the energy regeneration mechanism may provide additional energy to the heat engine and / or remove excess energy from within the heat engine.

[0115] Energy may be temporarily stored in one or more capacitor. The net electrical energy input into the heat engine (if it is being used as a heat pump) or withdrawn from the heat engine (if it is being used as a power generator) may be smoothed out over a full cycle.

[0116] In some embodiments, at least part of the piston or rotor may comprise a ferromagnetic material. Conversely, the compartment may be substantially non-magnetic. This may enable the piston or rotor to be manipulated (e.g., along a trajectory aligned with the direction of movement of the piston) by an external LEAG. This may be used in embodiments comprising a plurality of pistons located within a toroidal chamber.

[0117] These energy regeneration mechanisms are not mutually exclusive. Any combination of the above features may be used. In some embodiments, each compartment comprises an energy regeneration mechanism. Each energy regeneration mechanisms may be configured to provide and / or receive energy from at least one other energy regeneration mechanism. The plurality of connected energy regeneration mechanisms may form an energy regeneration system.

[0118] In some embodiments, the energy regeneration mechanism (or system) may comprise a motor. The motor may be configured to provide additional energy to the heat engine. For example, the motor may be connected to the LEAG (or any other previously disclosed energy regeneration mechanism feature). Alternatively, or in addition, the energy regeneration mechanism (or system) may comprise a generator and / or battery. The generator and / or battery may be configured to receive additional energy produced by the heat engine.

[0119] The heat engine may comprise a control module configured to regulate the energy regeneration mechanism. The control module may be a mechanical control module. For example, the control module may comprise a gear mechanism. The gear mechanism may be configured to regulate movement of the energy regeneration mechanism. Alternatively, the control module may comprise a locking mechanism. The locking mechanism may be configured to restrict movement of the energy regeneration mechanism. The control module may regulate the energy regeneration mechanism based on an output from one or more sensor. The one or more sensors may comprise a temperature sensor. At least one sensor may be configured to measure the temperature of the thermal reservoir. At least one sensor may be configured to measure the temperature of the thermal store. The control module may adjust the magnitudes of the isothermal expansion, the isothermal compression, the adiabatic expansion and / or the adiabatic compression if the temperature of the thermal reservoir and / or the temperature of the thermal store changes.

[0120] In some embodiments, the control module may be an electrical control module. The electrical control module may comprise one or more sensor. The sensor may be a temperature sensor. The control module may be configured to programme an electrical regeneration mechanism. More specifically, the control module may be configured to programme an electrical regeneration mechanism based on one or more temperature sensor readings. At least one sensor may be configured to measure the temperature of the thermal reservoir. At least one sensor may be configured to measure the temperature of the thermal store.

[0121] In some embodiments, the control unit may regulate the movement of working fluid between the compartments based on the output from the one or more sensor. For example, the control unit may vary the internal volumes of the compartments based on the output from the one or more sensor. This may be achieved with and / or without the presence of an energy regeneration mechanism.

[0122] In some embodiments, the control module configured to regulate the energy regeneration mechanism may be the control unit configured to regulate the movement of working fluid between the compartments.

[0123] The at least one adiabatic compartment may comprise a first adiabatic adjustment compartment and a second adiabatic adjustment compartment. Each of the first adiabatic adjustment compartment and the second adiabatic adjustment compartment may be configured to receive working fluid. The first adiabatic adjustment compartment may comprise a sealable first adiabatic adjustment compartment aperture for conveying working fluid between the isothermal expansion compartment and the first adiabatic adjustment compartment. The second adiabatic adjustment compartment may comprise a sealable second adiabatic adjustment aperture for conveying working fluid between the isothermal compression compartment and the second adiabatic adjustment compartment.

[0124] The previously disclosed sealable adiabatic compartment aperture for conveying working fluid between the isothermal expansion compartment and the at least one adiabatic compartment may be the sealable first adiabatic adjustment compartment aperture. Moreover, the isothermal expansion compartment may comprise a sealable isothermal expansion compartment aperture for conveying working fluid between the second adiabatic adjustment compartment and the isothermal expansion compartment.

[0125] The working fluid may therefore cycle through the isothermal expansion compartment, the first adiabatic adjustment compartment, the isothermal compression compartment, and the second adiabatic adjustment compartment in turn, and in either direction. This may enable quicker fluid flow through the heat engine, thus increasing power / heat output.

[0126] The first adiabatic adjustment compartment and the second adiabatic adjustment compartment may each have a variable internal volume for receiving working fluid. The first adiabatic adjustment compartment may comprise a sealable first adiabatic adjustment compartment aperture for conveying working fluid between the isothermal expansion compartment and the first adiabatic adjustment compartment. The sealable isothermal compression compartment aperture may be configured to convey working fluid between the first adiabatic adjustment compartment and the isothermal compression compartment. The second adiabatic adjustment compartment may comprise a sealable second adiabatic adjustment compartment aperture for conveying working fluid between the isothermal compression compartment and the second adiabatic adjustment compartment. The isothermal compression compartment may comprise a sealable isothermal compression compartment aperture for conveying working fluid between the second adiabatic adjustment compartment and the isothermal compression compartment.

[0127] In other words, each aperture may convey working fluid in either direction. Consequently, the sealable first adiabatic adjustment compartment aperture may convey working fluid from the isothermal expansion compartment to the first adiabatic adjustment compartment and / or from the first adiabatic adjustment compartment to the isothermal expansion compartment. Similarly, the sealable isothermal compression compartment aperture may be configured to convey working fluid from the first adiabatic adjustment compartment to the isothermal compression compartment and / or from the isothermal compression compartment to the first adiabatic adjustment compartment. The sealable second adiabatic adjustment compartment aperture may convey working fluid from the isothermal compression compartment to the second adiabatic adjustment compartment and / or from the second adiabatic adjustment compartment to the isothermal compression compartment. The sealable isothermal compression compartment aperture may convey working fluid from the second adiabatic adjustment compartment to the isothermal compression compartment and / or from the isothermal compression compartment to the second adiabatic adjustment compartment. The sealable first adiabatic adjustment compartment aperture may be directly connected to the isothermal expansion compartment. The sealable isothermal compression compartment aperture may be directly connected to the first adiabatic adjustment compartment. The sealable second adiabatic adjustment compartment aperture may be directly connected to the isothermal compression compartment. The sealable isothermal expansion compartment aperture may be directly connected to the second adiabatic adjustment compartment.

[0128] In other words, the first adiabatic adjustment compartment may be between and directly adjacent to the isothermal expansion compartment and the isothermal compression compartment. Similarly, the second adiabatic adjustment compartment may be between and directly adjacent to the isothermal compression compartment and the isothermal expansion compartment.

[0129] The average thermal conductivities of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment may be higher than the average thermal conductivities of their respective external surfaces. For example, the average thermal conductivities of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment may be up to 10, 50, 100, 500, 1000, or more than 1000 times higher than the average thermal conductivities of their respective external surfaces.

[0130] The material of the internal and / or external surfaces of each compartment may be varied to control the average thermal conductivity thereof. For example, the isothermal expansion compartment and / or the isothermal compression compartment may comprise a highly thermally conductive internal lining. The lining may be a metal. Alternatively, or in addition, the isothermal expansion compartment and / or the isothermal compression compartment may be wrapped in insulation.

[0131] In some embodiments, each internal surface of the isothermal expansion and / or isothermal compression compartment has a higher thermal conductivity than its corresponding external surface. This may increase desirable heat flow between the internal surface(s) of the compartment and the working fluid therein, whilst reducing unwanted heat flows between the external surface(s) and the surrounding environment. At least one internal surface with each compartment may be a surface of a piston.

[0132] If a fluid piston is present, the corresponding compartment(s) may comprise a parting medium configured to separate the fluid piston and the working fluid within each isothermal compartment. The fluid element of a fluid piston may then in effect become part of the drive mechanism through which motion is imparted to or by such pistons. The parting medium may have a higher thermal conductivity than the liquid piston. Alternatively, or in addition, the parting medium may comprise a surface area that is greater than the cross-sectional area of the compartment within which it is located.

[0133] In some embodiments, the isothermal expansion compartment, the isothermal compression compartment and / or the at least one adiabatic compartment may be located within a vacuum or a gas-filled housing kept at low pressure. This may (further) reduce unwanted heat flows between the external surface(s) of these compartments and their surrounding environment. This may also contain loss of working fluid to the external environment and / or reduce unwanted expansions or compressions of gases present in the embodiment that are not working fluid.

[0134] The average thermal conductivity of the internal surfaces of the at least one adiabatic compartment may be lower than the average thermal conductivity of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment. This may reduce undesirable heat flow between the internal surface(s) of the at least one adiabatic compartment and the working fluid therein. More specifically, and if present, the average thermal conductivity of the internal surfaces of the first adiabatic adjustment compartment and the second adiabatic adjustment compartment may be lower than the average thermal conductivity of the internal surfaces of the isothermal expansion and isothermal compression compartments. The material of the internal surfaces of each compartment may be varied to control the average thermal conductivity thereof. At least one internal surface with each compartment may be a surface of a piston.

[0135] In some embodiments, the average thermal conductivities of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment may be up to 10, 50, 100, 500, 1000, or more than 1000 times higher than the average thermal conductivity of the internal surfaces of the at least one adiabatic compartment. For example, the isothermal compartment may be made of metal. Their internal surfaces may have average thermal conductivities of 20 - 400 W / mK. Conversely, the adiabatic compartments may be made of plastic. Their internal surfaces may have average thermal conductivities of 0.1 - 0.5 W / mK.

[0136] Similarly, the average thermal conductivity of the internal surfaces of the transitional adiabatic compartment and / or of the intermediate adiabatic compartment may be lower than the average thermal conductivity of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment.

[0137] The internal surface areas of the isothermal expansion compartment and the isothermal compression compartment may be greater than the internal surface area of the at least one adiabatic compartment. More specifically, and if present, the internal surface areas of the isothermal expansion compartment and the isothermal compression compartment may be greater than the internal surface areas of the first adiabatic adjustment compartment and the second adiabatic adjustment compartment.

[0138] According to the present invention, there is also provided a system comprising a plurality of heat engines. Each heat engine may be as previously described. Each heat engine may be phased differently, to smooth the overall power input or output of the system. Working fluid may cycle through each heat engine, in turn, before returning to the first heat engine in the cycle. This process may be repeated any number of times.

[0139] Moreover, in use, the working fluid may undergo a potentially significant change in temperature whilst traversing the relevant adiabatic compartment(s) resulting in one end of the adiabatic compartment being meaningfully colder than the other. This may lead to undesired thermal expansions or contractions, which may cause the pistons in such compartments to fit less well in different parts of the compartment. The system may comprise a plurality of heat engines placed in series between an eventual thermal reservoir and an eventual thermal source. The eventual thermal reservoir may be the thermal reservoir of the first heat engine within the series of heat engines. The eventual thermal store may be the thermal store of the last heat engine within the series of heat engines. If present, each intermediate heat engine within the series may comprise an intermediate thermal reservoir and thermal store. The thermal store of each heat engine may be connected to the thermal reservoir of the heat engine next in the series. This may be used to reduce the temperature differential between the different ends of the at least one adiabatic compartment within each heat engine. This may reduce the practical impact of such thermal expansions or contractions.

[0140] In some embodiments, the sides of the at least one adiabatic compartment may be made of compressible material. The at least one adiabatic compartment may comprise one or more band(s) around its outside. The bands may be concentric. The one or more band may be selectively tightened or loosened. For example, they may be tightened or loosened depending on the temperatures of the thermal reservoir and the thermal store. This may be used to make the piston in the compartment fit more snugly within the compartment.

[0141] There is also provided a method of operating the heat engine. The method may comprise the steps of: (a) sealing a working fluid within the isothermal expansion compartment; (b) isothermally expanding the working fluid within the isothermal expansion compartment to produce an isothermally expanded working fluid; (c) moving the isothermally expanded working fluid from the isothermal expansion compartment to the at least one adiabatic compartment; (d) sealing the isothermally expanded working fluid within the at least one adiabatic compartment; (e) adiabatically adjusting the volume of the isothermally expanded working fluid within the at least one adiabatic compartment to produce a first adiabatically adjusted working fluid; (f) moving the first adiabatically adjusted working fluid from the at least one adiabatic compartment to the isothermal compression compartment; (g) sealing the adiabatically expanded working fluid within the isothermal compression compartment; (h) isothermally compressing the first adiabatically adjusted working fluid within the isothermal compression compartment to produce an isothermally compressed working fluid; (i) moving the isothermally compressed working fluid from the isothermal compression compartment to the at least one adiabatic compartment; (j) sealing the isothermally compressed working fluid within the at least one adiabatic compartment; (k) adiabatically adjusting the volume of the isothermally compressed working fluid within the at least one adiabatic compartment to produce a second adiabatically adjusted working fluid; (I) and moving the second adiabatically adjusted working fluid from the at least one adiabatic compartment to the isothermal expansion compartment.

[0142] The second adiabatically adjusted working fluid moved from the at least one adiabatic compartment to the isothermal expansion compartment may be the working fluid sealed within the isothermal expansion compartment. As such, the method may repeat, or cycle around. The method steps (a) to (I) may form the previously described primary cycle.

[0143] The method may comprise transferring thermal energy from the thermal reservoir to the working fluid within the isothermal expansion compartment. The method may comprise transferring thermal energy from the working fluid within the isothermal compression compartment to the thermal store.

[0144] The isothermally expanded working fluid may be moved from the isothermal expansion compartment to the at least one adiabatic compartment via the sealable adiabatic compartment aperture. More specifically, in some embodiments, the isothermally expanded working fluid may be moved from the isothermal expansion compartment to the first adiabatic adjustment compartment via the sealable first adiabatic adjustment compartment aperture.

[0145] The first adiabatically adjusted working fluid may be moved from the at least one adiabatic compartment to the isothermal compression compartment via the sealable isothermal compartment aperture. More specifically, in some embodiments, the first adiabatically adjusted working fluid may be moved from the first adiabatic adjustment compartment to the isothermal compression compartment via the sealable isothermal compression compartment aperture.

[0146] The isothermally compressed working fluid may be moved from the isothermal compression compartment to the at least one adiabatic compartment via the sealable isothermal compression compartment aperture. Alternatively, in some embodiments, the isothermally compressed working fluid may be moved from the isothermal compression compartment to the second adiabatic adjustment compartment via the sealable second adiabatic adjustment compartment aperture.

[0147] The second adiabatically adjusted working fluid may be moved from the at least one adiabatic compartment to the isothermal expansion compartment via the sealable adiabatic compartment aperture. Alternatively, in some embodiments, the second adiabatically adjusted working fluid may be moved from the second adiabatic adjustment compartment to the isothermal expansion compartment via the sealable isothermal expansion compartment aperture.

[0148] The method may comprise changing the rate of change of volume of the isothermal expansion compartment, the isothermal compression compartment, and / or the at least one adiabatic compartment smoothly over steps b., c., e., f., h., i., k., and / or I. The rate of change of volume of the isothermal expansion compartment, the isothermal compression compartment, and / or the at least one adiabatic compartment may be zero at the beginning and / or end of steps b., c., e., f., h., i., k., and / or I.

[0149] The method may comprise at least one of the following additional steps: (m) compressing the working fluid remaining in the isothermal expansion compartment after step (c) during a time when this compartment is not otherwise involved in steps (a) to (I); (n) expanding the working fluid remaining in the at least one adiabatic compartment after step (f) if in step (e) the working fluid had been compressed, or compressing it if in step (e) the working fluid had been expanded, during a time when this compartment is not otherwise involved in steps (a) to (I); (o) expanding the working fluid remaining in the isothermal compression compartment after step (i) during a time when this compartment is not otherwise involved in steps (a) to (I); (p) compressing the working fluid remaining in the at least one adiabatic compartment after step (I) if in step (k) the working fluid had been expanded, or expanding it if in step (k) the working fluid had been compressed, during a time when this compartment is not otherwise involved in steps (a) to (I).

[0150] The working fluid remaining in the isothermal expansion compartment after step (c), the at least one adiabatic compartment after step (f), the isothermal compression compartment after step (i), and / or the at least one adiabatic compartment after step (I) may be dead volume working fluid.

[0151] The additional steps, (m) to (p) may be in addition to the primary cycle. The additional steps (m) to (p) may be pressure rebalancing steps. This may address the practical presence of dead volume within compartments. The adverse thermodynamic efficiency impact of dead volume may be mitigated the most if the relevant expansion or compression ratio is the inverse of the compression or expansion ratio that the working fluid underwent during the corresponding step (b), (e), (h) or (k). However, use of other expansion or compression ratios may still reduce the negative efficiency impact of dead volume.

[0152] In some embodiments, the method may comprise the additional requirement that the rate of change of volume of the compartments are brought to zero at the beginning and end of steps when the compartment is involved in the method. This may reduce the mechanical frictions otherwise suffered by the engine.

[0153] For example, the rate of change of volume of the isothermal expansion compartment, the isothermal compression compartment, and the at least one adiabatic compartment may be zero at the beginning and end of steps m., n., o. and / or p.

[0154] If the heat engine comprises two adiabatic compartments each comprising a moveable piston configured to vary the internal volume of the corresponding compartment, the work done as a function of time by the piston of one adiabatic compartment may be equal in magnitude at all times but opposite in sign to the work done by the piston of a different adiabatic compartment. This may be controlled by the control unit.

[0155] In some embodiments, the aggregate work output as a function of time by the heat engine or work input to the heat engine as a function of time may be aligned with a pre-selected power profile as a function of time for the end use or end source of this work. Alternatively, or in addition, the aggregate work output as a function of time by the heat engine or work input to the heat engine as a function of time is that of a sinusoidal alternating electric current. Again, this may be controlled by the control unit.

[0156] For example, in some embodiments, it may be desirable for the control unit regulating the movement of working fluid between compartments to be configured so that instantaneous (within cycle step) workload balancing of adiabatic steps is introduced and / or overall power output (or input) exhibits a time dependency that aligns with the purpose to which that power will be put (or provided). For electric power output or input, this may align with the power profile of sinusoidal alternating electrical current.

[0157] It may also be desirable for the spatial layout of the compartments to facilitate segregation between hotter and cooler regions of the heat engine. Such segregation reduces conductive heat transfer between high and low temperature zones, simplifies the routing of thermal interfaces (e.g. heat exchangers or insulation panels), and allows shared manifolding for groups of similar-temperature compartments.

[0158] In some embodiments, several groups of three or four compartments each forming a complete thermodynamic cycle (i.e., heat engine) may be combined into a single modular block. Each block may be arranged so that the isothermal expansion chambers are positioned outwardly and the isothermal compression chambers inwardly relative to a central mechanical drive axis (or vice versa). The arrangement may form radial, polygonal, or annular configurations that naturally concentrate hotter regions around a peripheral thermal reservoir and colder regions near a central thermal store.

[0159] Compartments may be fluidly connected via ducts. The ducts between compartments may be singlesided. The ducts may comprise an inlet and outlet port located at the base of each compartment. There may be a plurality of interconnected ducts. The interconnecting ducts may be routed beneath the compartment plane. This approach may simplify mechanical packaging and access to valve actuation hardware, but typically results in longer ducts and greater pressure losses.

[0160] A central-plane ducting arrangement may instead be employed, wherein opposing compartments are positioned back-to-back and ducts share a common mid-plane. This configuration may shorten intercompartment flow paths and reduce redistribution dead-volume. It may also simplify sealing interfaces between hot and cold zones.

[0161] Multiple modular blocks may be positioned side-by-side to achieve the desired power output. They may instead be positioned in stacked planes. They may instead be positioned in radial arrays about a common crankshaft or drive axis. Thermal insulation may be incorporated between hot and cold blocks to minimise cross-conduction.

[0162] In some embodiments, the control unit may be configured to impart non-sinusoidal piston displacement profiles. The non-sinusoidal motion may be produced by a non-circular gearing mechanisms The non-sinusoidal motion may be produced by a rotating cam-plate or profiled disc having shaped grooves or cam tracks engaged by follower pins attached to each piston shaft. The groove geometry may be designed to provide the desired displacement-to-crank-angle relationship. The groove geometry may be adjustable through interchangeable cam-plates or radial-offset mechanisms. This may accommodate different hot-to-cold temperature ratios or operating frequencies.

[0163] In some embodiments, one or more camshafts comprising lobes of specified profile may be used to drive followers connected to the piston shafts. The camshafts may also include secondary lobes to actuate aperture valves. A fixed or adjustable phase relationship between piston movement and valve opening sequences may be maintained. Lever or linkage systems may optionally interconnect adjacent pistons or opposed pairs of pistons. This may equalise mechanical load and smooth cyclic torque variations.

[0164] In some embodiments, lever pivot points may themselves be driven by cam followers. This may enable load balancing to occur dynamically within each thermodynamic cycle.

[0165] Any of these mechanical control systems may incorporate friction-reduction elements, such as rolling or magnetic bearings, and / or may be enclosed in a lubricated or sealed cavity shared with the workingfluid containment structure.

[0166] The invention will now be further and more particularly described, by way of example only, with reference to the accompanying drawings.

[0167] FIGURES

[0168] Figure 1 shows a heat engine comprising an isothermal expansion compartment, an adiabatic compartment, and an isothermal compression compartment each located within a separate chamber.

[0169] Figure 2 shows a heat engine comprising a separate first adiabatic adjustment compartment and second adiabatic adjustment compartment;

[0170] Figure 3 shows a heat engine comprising an isothermal expansion compartment, an adiabatic compartment, and an isothermal compression compartment each located within a single chamber.

[0171] Figure 4 shows the heat engine of figure 3, further comprising a transitional adiabatic compartment and a transitional isothermal compression compartment.

[0172] Figure 5 shows a heat engine comprising an isothermal expansion compartment, a first adiabatic adjustment compartment, an isothermal compression compartment, and a second adiabatic adjustment compartment all being located within a single toroidal chamber.

[0173] Figures 6A and 6B shows a moveable piston having a protrusion located on a surface of the piston forming an internal surface of the isothermal expansion compartment or isothermal compression compartment.

[0174] Figure 7 shows a stylised piston positioning with constant velocity movements. Figure 8 shows a quasi-sinusoidal piston movement starting and ending each cycle step at rest.

[0175] Figure 9 shows the work done by each piston in aggregate with piston movements as per Figure 8.

[0176] Figure 10 shows a spring arrangement configured to create sinusoidal piston movements having different amplitudes but the same frequency.

[0177] Figure 11 shows a heat engine comprising a plurality of fluid pistons.

[0178] Figure 12 shows a non-sinusoidal piston movement pattern starting and ending each cycle step at rest that is adapted from the one in Figure 8.

[0179] Figure 13 shows the work done by each piston in aggregate with piston movements as per Figure 12.

[0180] Figure 14 shows how constraining a shaft end to follow two prescribed tracks or paths that are moving relative to each other can be used to impart non-sinusoidal motion to the shaft end and hence by appropriate choice of tracks or paths may be used to implement a movement pattern in line with Figure 12.

[0181] Figure 15 shows a half cross-section of the inside of a largely axially symmetric isothermal compartment that may have a high surface area to volume ratio.

[0182] Figure 16(a) to (i) shows a multi-compartment heat engine including a mechanical control unit arrangement able to impart non-sinusoidal piston movement patterns such as those in Figure 12.

[0183] DETAILED DESCRIPTION

[0184] Figure 1 shows a heat engine 100 according to the present invention. The heat engine 100 comprises an isothermal expansion compartment 110, an adiabatic compartment 120, and an isothermal compression compartment 130. Each compartment 110, 120, 130 has a variable internal volume for receiving the working fluid. The isothermal expansion compartment 110 is located within an isothermal expansion chamber 112. The adiabatic compartment 120 is located within an adiabatic chamber 122. The isothermal compression compartment 130 is located within an isothermal compression chamber 132.

[0185] The heat engine 100 also comprises a thermal reservoir 140 for providing thermal energy to working fluid within the isothermal expansion compartment 110 and a thermal store 150 for receiving thermal energy from working fluid within the isothermal compression compartment 130. The adiabatic compartment 120 comprises a sealable adiabatic compartment aperture 121 for conveying working fluid between the isothermal expansion compartment 110 and the adiabatic compartment 120. The isothermal compression compartment 130 comprises a sealable isothermal compression compartment aperture 131 for conveying working fluid between the adiabatic compartment 120 and the isothermal compression compartment 130. The sealable adiabatic compartment aperture 121 is directly connected to the isothermal expansion compartment 110 and the adiabatic compartment 120. Similarly, the sealable isothermal compression compartment aperture 131 is directly connected to the adiabatic compartment 120 and the isothermal compression compartment 130.

[0186] Each compartment 110, 120, 130 comprises a moveable piston 115, 125, 135 configured to vary the internal volume of the compartment. More specifically, the isothermal expansion compartment 110 comprises a moveable isothermal expansion compartment piston 115; the adiabatic compartment 120 comprises a moveable adiabatic compartment piston 125; and the isothermal compression compartment 130 comprises a moveable isothermal compression compartment piston 135.

[0187] A control unit (not shown in the accompanying drawings) is configured to regulate the movement of working fluid between the compartments. More specifically, the control unit is configured to regulate the movement of working fluid between the compartments by varying the internal volume of each compartment.

[0188] In figure 1, working fluid can flow between a given isothermal compartment and the adiabatic compartment if the piston in that isothermal compartment is not at its rightmost extent and if the piston in the adiabatic compartment is not at its leftmost extent as viewed in this Figure. However, when one or other piston is pushed up to the relevant compartment end, this plugs the aperture, thus stopping any flow of working fluid between the compartments. The relevant aperture is designed so that if both pistons are pushed up to the relevant chamber end, each compartment has zero volume. By moving the pistons in the three chambers in a suitable manner we can therefore arrange for the whole of the working fluid to move to or from the adiabatic compartment from either of the two isothermal compartments (thus eliminating dead volume), and we can also arrange for the working fluid to be expanded or compressed in any of the three compartments.

[0189] Figure 2 shows an alternative heat engine 200 according to the present invention. This heat engine 200 comprises many of the same features as the heat engine 100 of figure 1, as indicated by the corresponding reference numerals. However, in figure 2, the adiabatic compartment comprises a first adiabatic adjustment compartment 170 and a second adiabatic adjustment compartment 180. Both the first adiabatic adjustment compartment 170 and the second adiabatic adjustment compartment 180 comprise a variable internal volume configured to receive working fluid. The first adiabatic adjustment compartment 170 is located within a first adiabatic adjustment chamber 172. The second adiabatic adjustment compartment 170 is located within a second adiabatic adjustment chamber 182.

[0190] The first adiabatic adjustment compartment 170 comprises a sealable first adiabatic adjustment compartment aperture 171 for conveying working fluid between the isothermal expansion compartment 110 and the first adiabatic adjustment compartment 170. The isothermal compression compartment 130 comprises a sealable isothermal compression compartment aperture 131 for conveying working fluid between the first adiabatic adjustment compartment 170 and the isothermal compression compartment 130. The second adiabatic adjustment compartment 180 comprises a sealable second adiabatic adjustment compartment aperture 181 for conveying working fluid between the isothermal compression compartment 130 and the second adiabatic adjustment compartment 180. The isothermal expansion compartment 110 comprises a sealable isothermal expansion compartment aperture 111 for conveying working fluid between the second adiabatic adjustment compartment 180 and the isothermal expansion compartment 110.

[0191] The sealable first adiabatic adjustment compartment aperture 171 is directly connected to the isothermal expansion compartment 110 and the first adiabatic adjustment compartment 170. The sealable isothermal compression compartment aperture 131 is directly connected to the first adiabatic adjustment compartment 170 and the isothermal compression compartment 130. The sealable second adiabatic adjustment compartment aperture 181 is directly connected to the isothermal compression compartment 130 and the second adiabatic adjustment compartment 180. The sealable isothermal expansion compartment aperture 111 is directly connected to the second adiabatic adjustment compartment 180 and the isothermal expansion compartment 110.

[0192] The first adiabatic adjustment compartment 170 comprises a moveable first adiabatic adjustment compartment piston 175. The second adiabatic adjustment compartment 180 comprises a moveable second adiabatic adjustment compartment piston 185. Each of the moveable first adiabatic adjustment compartment piston 175 and the moveable second adiabatic adjustment compartment piston 185 are configured to vary the internal volume of their respective compartment.

[0193] Figure 3 shows a heat engine 300 according to the present invention. This heat engine 300 comprises many of the same features as the heat engine 100 of figure 1, as indicated by the corresponding reference numerals. However, in figure 3, the isothermal expansion compartment 110, the adiabatic compartment 120, and the isothermal compression compartment 130 are all located within a single chamber 190.

[0194] The chamber 190 comprises a moveable adiabatic compartment piston 125 located between the isothermal expansion compartment 110 and the adiabatic compartment 120, and a moveable isothermal compression compartment piston 135 located between the adiabatic compartment 120 and the isothermal compression compartment 130. The moveable adiabatic compartment piston 125 comprises the sealable adiabatic compartment aperture 121, and the moveable isothermal compression compartment piston 135 comprises the isothermal compression compartment aperture 131.

[0195] The chamber 190 also comprises a moveable intermediate adiabatic compartment piston 194 for defining an intermediate adiabatic compartment 193 between the isothermal expansion compartment 110 and the adiabatic compartment 120, and a moveable intermediate isothermal compression compartment piston 196 for defining an intermediate isothermal compression compartment 197 between the adiabatic compartment 120 and the isothermal compression compartment 130. The intermediate adiabatic compartment 193 and the intermediate isothermal compression compartment 197 may each comprise the same physical properties as the adiabatic compartment 120.

[0196] The moveable intermediate adiabatic compartment piston 194 comprises a sealable intermediate adiabatic compartment aperture 192 that is offset from the sealable adiabatic compartment aperture 121. The sealable intermediate adiabatic compartment aperture 192 is configured to convey working fluid between the isothermal expansion compartment 110 and the intermediate adiabatic compartment 193. As such, the sealable adiabatic compartment aperture 121 may be configured to convey working fluid between the intermediate adiabatic compartment 193 and the adiabatic compartment 120.

[0197] The moveable intermediate isothermal compression compartment piston 196 comprises a sealable intermediate isothermal compression compartment aperture 198 that is offset from the sealable isothermal compression compartment aperture 131. The sealable intermediate isothermal compression compartment aperture 198 is configured to convey working fluid between the adiabatic compartment 120 and the intermediate isothermal compression compartment 197. As such, the sealable isothermal compression compartment aperture 131 may be configured to convey working fluid between the intermediate isothermal compression compartment 197 and the isothermal compression compartment 130. In figure 3, the pistons have non-overlapping (i.e., off-set) apertures so that some piston positions allow the working fluid to flow between consecutive compartments, whilst other positions prohibit such flow.

[0198] Figure 4 shows a heat engine 400 according to the present invention. This heat engine 400 comprises many of the same features as the heat engine 300 of figure 3, as indicated by the corresponding reference numerals. However, in figure 4, the chamber 190 further comprises a transitional adiabatic compartment 204 and a transitional isothermal compression compartment 209.

[0199] In particular, the chamber 190 comprises a moveable transitional adiabatic compartment piston 203 for defining a transitional adiabatic compartment 204 between the intermediate adiabatic compartment 193 and the adiabatic compartment 120. The chamber 190 also comprises a moveable transitional isothermal compression compartment piston 208 for defining a transitional isothermal compression compartment 209 between the intermediate isothermal compression compartment 197 and the isothermal compression compartment 130. The transitional adiabatic compartment 204 and the transitional isothermal compression compartment 209 may each comprise the same physical properties as the adiabatic compartment 120.

[0200] The moveable transitional adiabatic compartment piston 203 comprises a sealable transitional adiabatic compartment aperture 202 that is offset from the sealable intermediate adiabatic compartment aperture 192. The sealable transitional adiabatic compartment aperture 202 is also offset from the sealable adiabatic compartment aperture 121. The sealable transitional adiabatic compartment aperture 202 is configured to convey working fluid between the intermediate adiabatic compartment 193 and the transitional adiabatic compartment 204. As such, the sealable adiabatic compartment aperture 121 may be configured to convey working fluid between the transitional adiabatic compartment 204 and the adiabatic compartment 120.

[0201] The moveable transitional isothermal compression compartment piston 208 comprises a sealable transitional isothermal compression compartment aperture 207 that is offset from the sealable intermediate isothermal compression compartment aperture 198. The sealable transitional isothermal compression compartment aperture 207 is also offset from the sealable isothermal compression compartment aperture 131. The sealable transitional isothermal compression compartment aperture 207 is configured to convey working fluid between the intermediate isothermal compression compartment 197 and the transitional isothermal compression compartment 209. As such, the sealable isothermal compression compartment aperture 131 may be configured to convey working fluid between transitional isothermal compression compartment 209 and the isothermal compression compartment 130.

[0202] Again, in figure 4, the pistons have non-overlapping (i.e., off-set) apertures so that some piston positions allow the working fluid to flow between consecutive compartments, whilst other positions prohibit such flow. The inclusion of two additional pistons (compared to figure 3) means that the pistons abutting the isothermal compartments do not need to move as far, since the ends of the adiabatic compartment can be plugged using the remaining 4 pistons.

[0203] Figure 5 shows a heat engine comprising an isothermal expansion compartment 110, a first adiabatic adjustment compartment 170, an isothermal compression compartment 130, and a second adiabatic adjustment compartment 180 all being located within a single toroidal chamber 501. As such, the compartments 110, 170, 130, 180 may be linked in series.

[0204] The toroidal chamber comprises a plurality of adjustable gates 510, 570, 530, 580 configured to separate the compartments 110, 170, 130, 180. The adjustable gates 510, 570, 530, 580, provide the sealable first adiabatic adjustment compartment aperture 171, the sealable isothermal compression compartment aperture 131, the sealable second adiabatic adjustment compartment aperture 181, and the sealable isothermal expansion compartment aperture 111.

[0205] The toroidal chamber 501 further comprises at least one turbine 520 configured to move working fluid between the compartments 110, 170, 130, 180. However, there may be a plurality of turbines. For example, each compartment 110, 170, 130, 180 may comprise a turbine. The control unit (not shown in the accompanying drawing) is configured to regulate the movement of working fluid between the compartments by controlling / timing the opening and closing of the gates.

[0206] Alternatively, in some embodiments, each adjustable gate 510, 570, 530, 580 may be replaced or supplemented with at least one moveable piston which when appropriately positioned provide sealable apertures between compartments. For example, there may be a moveable first adiabatic adjustment piston and a moveable first intermediate adiabatic adjustment piston separating the isothermal expansion compartment 110 and the first adiabatic adjustment compartment 170; a moveable isothermal compression compartment piston and a moveable intermediate isothermal compression compartment piston separating the first adiabatic adjustment compartment 170 and the isothermal compression compartment 130; a moveable second adiabatic adjustment compartment piston and a moveable second intermediate adiabatic adjustment compartment piston separating the isothermal compression compartment 130 and the second adiabatic adjustment compartment 180; and a moveable isothermal expansion compartment piston and a moveable intermediate isothermal expansion compartment piston separating the second adiabatic adjustment compartment 180 and the isothermal expansion compartment 110. As before, the moveable pistons may provide the sealable apertures between the compartments 110, 170, 130, 180.

[0207] Figures 6A and 6B show a moveable piston 135, 115 having a protrusion 601 located on a surface of the piston forming an internal surface 610 of the isothermal expansion compartment 110 or an internal surface 630 the isothermal compression compartment 130. Each of the isothermal expansion compartment 110 and the isothermal compression compartment 130 may comprise an internal surface 611, 631 opposing the surface of the piston comprising a plurality of recesses 610, 630 configured to receive the piston protrusions.

[0208] As shown in figures 6A and 6B, the protrusion 601 comprises a curved tip portion 650 configured to abut an equally curved base portion 651 within a corresponding recess 652. The curved tip portion 650 connects directly to the surface of the piston forming an internal surface of the compartment at position X. The width of each protrusion proximal to the surface of the piston forming an internal surface of the compartment is greater than the width of each protrusion distal to the surface of the piston forming an internal surface of the compartment.

[0209] Figure 6A shows the curved tip portion 650 of the piston 135, 115 retracted away from the curved base portion 651 of the compartment 110, 130. Conversely, figure 6B shows the curved tip portion 650 of the piston 135, 115 nearly touching the curved base portion 651 of the compartment 110, 130. As such, the internal volume of the chamber 110, 130 in figure 6A is larger than the internal volume of the chamber 110, 130 in figure 6B. Each piston 135, 115 may comprise a plurality of protrusions 601. As such, the compartments compartment 110, 130 may comprise a plurality of corresponding recesses 652.

[0210] Figure 7 shows a stylised piston positioning (with constant velocity movements). This chart shows (for a selected thermal reservoir and thermal store temperature pair and a selected type of working fluid) movements in pistons as per Figure 1 that would optimise the thermodynamic efficiency of the heat engine, assuming that the pistons move at constant velocity whenever they are moving. Here XI, X2 and X3 are the pistons in the isothermal expansion compartment 110, the adiabatic compartment 120, and the isothermal compression compartment 130, respectively.

[0211] Figure 8 shows a quasi-sinusoidal piston movement starting and ending each cycle step at rest. In contrast with figure 7, this chart shows (for a selected thermal reservoir and thermal store temperature pair and a selected type of working fluid) desirable piston movements for the pistons in Figure 1, but now assuming that the pistons follow sinusoidal trajectories within each of the identified 8 cycle steps.

[0212] Figure 9 shows the work done by each piston in aggregate with piston movements as per figure 8. This chart shows the work done by each piston (when not moving in tandem with another piston) if they follow the movements indicated in Figure 8.

[0213] Figure 10 shows a spring arrangement configured to create sinusoidal piston movements having different amplitudes but the same frequency. In particular, the heat engine comprises a plurality of rods 1010 arranged to oscillate bi-linearly in the same direction as the piston axes. Each rod is connected to a rigid frame 1020 by a spring 1030. The frame may be fixed relative to the rods 1010 and springs 1030. Each rod 1010 may also be connected to a common drive bar 1040 by a spring 1060. The drive bar may be free to move relative to the frame 1020 and configured to oscillate in the same axial direction as the rods 1010. Consequently, a single drive bar 1040 that has a displacement that moves sinusoidally may drive similarly phased sinusoidal motions, but of different amplitudes in several subsidiary drive rods 1010.

[0214] Figure 11 shows a heat engine 1100 according to the present invention. This heat engine 1100 comprises many of the same features as the heat engine 100 of figure 1, as indicated by the corresponding reference numerals. However, in figure 11, each of the isothermal expansion compartment 110, the adiabatic compartment 120, and the isothermal compression compartment 130 comprise a fluid piston 1115, 1125, 1135, respectively.

[0215] In figure 11, the compartments 110, 120, 130 are placed apart. However, in some embodiments, the compartments may be directly adjacent to each other such that the adiabatic compartment aperture 121 is directly connected to the isothermal expansion compartment 110 and the adiabatic compartment 120. Similarly, the sealable isothermal compression compartment aperture 131 may then be directly connected to the adiabatic compartment 120 and the isothermal compression compartment 130.

[0216] In figure 11, each compartment 110, 120, 130 comprises a moveable fluid piston 1115, 1125, 1135 configured to vary the internal volume of the compartment. More specifically, the isothermal expansion compartment 110 comprises a moveable isothermal expansion compartment fluid piston 1115; the adiabatic compartment 120 comprises a moveable adiabatic compartment fluid piston 1125; and the isothermal compression compartment 130 comprises a moveable isothermal compression compartment fluid piston 1135. In use, pumping fluid may be pumped (e.g. by turbines) between the three chambers 112, 122, 132 and their associated chamber 1112, 1122, 1132 to increase or reduce the amount of pumping fluid in the corresponding compartment, hence compressing, expanding, or redistributing the working fluid depending on whether the sealable apertures 121, 131 between the compartments are closed (expansion or compression) or open (redistribution). When redistributing, the combined volume of pumping fluid in the two compartments between which the working fluid is being moved would be kept (near) constant.

[0217] Figure 12 shows a non-sinusoidal piston movement pattern starting and ending each cycle step at rest that is adapted from the one in Figure 8. Whilst visually quite similar to figure 8, the differences are sufficient to position the peak work done in each isothermal and adiabatic step mid-way within each step. As with figure 8, an ideal cycle is postulated, making it unnecessary to incorporate pressure rebalancing.

[0218] Figure 13 shows the work done by each piston in aggregate with piston movements as per Figure 12. This chart shows the work done by each piston (when not moving in tandem with another piston) if they follow the movements indicated in Figure 12. The exhibited workload balancing is better than in Figure 9. For example, if two otherwise identical cycles happen simultaneously but suitably out of phase, the adiabatic workloads of one can exactly cancel out the adiabatic workloads of the other.

[0219] Figure 14 shows how constraining a shaft end to follow prescribed tracks that are moving relative to each other can be used to impart non-sinusoidal motion to the shaft end and hence by appropriate choice of tracks may be used to implement a movement pattern in line with Figure 12. In this layout, one plate, say plate 1 14051, is fixed and the other, say plate 2 14052, and is moving. Each plate includes a track (e.g. 14101) that pairs with a track (e.g. 14IO2) in the other plate 1405. The two plates 14051, 14052 move relative to each other, here potentially oscillating sinusoidally horizontally, with three different time points Tl, T2 and T3 shown at which the overlaps between the plates 14051, 14052 are different. A pin or other object connected to a shaft that is linked to a piston is located so that it is constrained to stay in both a track in plate 1 14101 and the corresponding track in plate 2 14102. Its motion will then follow the pattern characterised by how the location of the point corresponding to the overlap between of the two tracks changes as plate 2 moves. If the fixed plate track is vertical (so a straight line), the pin will then move vertically up and down through time according to a movement pattern driven by the shape of the track in the moving plate (and by how this plate moves through time relative to the fixed plate). If the shape of the track in the moving plate is curved, it is possible to introduce a wide variety of non-linear transformations to the piston movement pattern that would otherwise have applied to the piston to which the shaft is connected. Figure 15 shows a half cross-section of the inside of a largely axially symmetric isothermal compartment that may have a high surface area to volume ratio. In this embodiment, in which some protrusions may rotate relative to others, A is a solid compartment rim wall and bottom wall, B is a solid rotating part, C is a solid non-rotating part that moves up and down to implement the desired working fluid expansion / contraction, D is a spindle (which may move up and down to open and close the aperture, E). F is a stator and G a rotor of the engine maintaining the rotation of some protrusions versus others, H are suitable bearings to keep the rotor appropriately positioned in line with the compartment axis, / are channels that facilitate working fluid flowing into and out of the gaps between the fins. J and K are seals stopping the working fluid flowing past C.

[0220] Figure 16 (a) to (i) shows a multi-compartment heat engine including a mechanical control unit arrangement able to impart non-sinusoidal piston movement patterns such as those in Figure 12. In this embodiment, a plurality of isothermal expansion compartments 901 and isothermal compression compartments 902 are positioned in an approximately circular arrangement, with the isothermal expansion compartments towards the outside of the arrangement and the isothermal compression compartments towards the inside of the arrangement so that there is spatial segregation of hot and cold regions within the heat engine. A plurality of first adiabatic compartments 911 and second adiabatic compartments 912 are positioned abutting and below the isothermal expansion compartments 901 and isothermal compression compartments 902 in the manner indicated looking from above in figure 16 (a) and obliquely in figure 16 (b). Working fluid flows from the isothermal expansion compartment 901 to the first adiabatic compartment 911 to the isothermal compression compartment 902 to the second adiabatic compartment 912 to the isothermal expansion compartment 901 etc. around each group of four connected compartments. The dimensions of the compartments 901, 902, 911 and 912 are selected based on whether the working fluid will be expanded or compressed in the relevant compartment.

[0221] In between abutting compartments there are openable apertures 921 (the control mechanisms for which are not shown). There is also a plurality of shafts 922 that each connect at one end to an isothermal compartment 901, 902. There is also a plurality of shafts 923 that each connect at one end to an adiabatic compartment 911, 912. The shafts 922, 923 pass through fixed plates 935 and 934 which constrain the shafts 922, 923 to move only vertically. Fixed to the shafts 922, 923 are pins 931a, 931b, 931c, ... that are constrained to move within tracks 933a, 933b, 933c, ... in a rotating plate 932. The positioning of each track in the plate 932 is chosen to impart the desired movement pattern for the compartment to which it is attached. The tracks 933a, 933b, 933c, ... may include friction reducing elements such as roller bearings, low friction coatings or magnetic bearings as may the holes through which the shafts 922, 923 pass within the fixed plates 934 and 935. The axis of the rotating plate 932 forms a drive shaft 936 through which power is extracted from or inserted into the heat engine. The openable apertures 921 are positioned in the fixed compartment ends 943. The cross-sections of the openable apertures 921 are illustrated as circular in this figure but may be non-circular (e.g. double arc shaped) to increase their area. The moveable ends 924 may be solid piston plates with seals around the compartment rims to which the shafts are attached. They may comprise elastomeric diaphragms to which the shafts 922, 923 are attached to mitigate seal friction losses. The diaphragms may be implemented as either a stand-alone solution or in combination with further solid piston plates that aim to protect the elastomeric diaphragms from e.g. melting.

[0222] In the isothermal compartments 901, 902 there are some protrusions 941 from the fixed compartment ends and some protrusions 942 from the moveable compartment ends. The two types of protrusions 941, 942 may alternate as shown in figures 16 (c) and (d). Ducts from the two apertures 921 lead to a central duct 944. The protrusions 941, 942 may be tapered to reduce the risk of jamming.

[0223] The duct 944 may be tapered as per figure 16 (e). The end of the shaft 922 may be positioned so that the duct is mostly full of the shaft when the shaft 922 is at its lowest extent. Extending out from the central duct may be flow channels 945. These flow channels may be fractal-like, bifurcating and getting successively narrower further away from the central duct. This may allow working fluid to better reach the whole compartment whilst suffering reduced skin friction.

[0224] As the protrusions 942 will move during use, the flow channels 945 may be mapped out principally in the fixed protrusions 941 by incorporating appropriately positioned and appropriately sized smooth sided holes 951, 952a, 952b in these protrusions as per figure 16 (f). The holes 951, 952a, 952b may be of different sizes. If there are several holes at different heights in the protrusion then these holes 952a, 952b may be aligned vertically. Corresponding holes may be included in the moveable protrusions 942 that may in part align with ones in the adjacent fixed protrusions 941. The holes in the moveable protrusions 953, 954 may be elongated relative to corresponding holes in 941 as per figure 16 (g). This may increase the proportion of time during relevant redistribution steps when flow through the flow channels mapped out in the fixed protrusion 941 is unimpeded as it travels through the movable protrusion 942.

[0225] Not shown are monitoring and control mechanisms that may be present to monitor working fluid pressures and temperatures. They may also add or bleed off working fluid should this be necessary. Also not shown are any potential gearing mechanisms for adjusting the tracks 933a, 933b, 933c, ... that may be desirable to incorporate if the heat engine is expected to encounter different temperature ratios between the thermal store and the thermal reservoir whilst in use.

[0226] Instead of or in addition to the rotating plate 932 (or 'cam plate') arrangement shown in figure 16 (b), cam follower mechanisms linked to one or more cam shafts as per figure 16 (h) may be used to impart appropriate motion to the pistons. For example, a plurality of cams 961 and 962 may be attached to a camshaft 971 and configured to impart appropriate motion to the pistons 924 via followers connected to relevant piston shafts 922, 923. Aperture valve actuation (not shown) may be implemented using similar cam follower mechanisms.

[0227] In figure 16 (a), the piston shafts 922, 923 are positioned in a 4 x 4 grid, so four linked camshafts 971 may be used to drive all 16 pistons.

[0228] Lever mechanisms as shown in figure 16 (i) may link individual nearby pairs of compartments, 912, 911 to facilitate mechanical workload balancing of these compartments. Motion may be imparted to the lever pivot point 981 by connecting it to a camshaft 971 via a cam follower mechanism. This may impart within cycle step workload balancing of the pistons to which the lever mechanism is attached.

[0229] The entire heat engine may be encased in a single closed chamber (not shown).This may contain loss of working fluid to the external environment.

[0230] Various further aspects and embodiments of the present invention will be apparent to those skilled in the art in view of the present disclosure, "and / or" where used herein is to be taken as specific disclosure of each of the two specified features or components with or without the other. For example, "A and / or B" is to be taken as specific disclosure of each of (i) A, (ii) B and (iii) A and B, just as if each is set out individually herein.

[0231] Unless context dictates otherwise, the descriptions and definitions of the features set out above are not limited to any particular aspect or embodiment of the invention and apply equally to all aspects and embodiments that are described. It will further be appreciated by those skilled in the art that although the invention has been described by way of example with reference to several embodiments, it is not limited to the disclosed embodiments and that alternative embodiments could be constructed without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A heat engine comprising: an isothermal expansion compartment, at least one adiabatic compartment, and an isothermal compression compartment, wherein each compartment is configured to receive a working fluid; a thermal reservoir for providing thermal energy to working fluid within the isothermal expansion compartment; a thermal store for receiving thermal energy from working fluid within the isothermal compression compartment, and a control unit configured to regulate the movement of working fluid between the compartments, wherein the at least one adiabatic compartment comprises a sealable adiabatic compartment aperture for conveying working fluid between the isothermal expansion compartment and the at least one adiabatic compartment, and the isothermal compression compartment comprises a sealable isothermal compression compartment aperture for conveying working fluid between the at least one adiabatic compartment and the isothermal compression compartment.

2. The heat engine according to claim 1, wherein the sealable adiabatic compartment aperture is directly connected to the at least one adiabatic compartment and the isothermal expansion compartment, and / or the sealable isothermal compression compartment aperture is directly connected to the isothermal compression compartment and the at least one adiabatic compartment.

3. The heat engine according to claim 1 or 2, wherein each compartment has a variable internal volume for receiving the working fluid, and wherein the control unit is configured to regulate the movement of working fluid between the compartments by varying the internal volume of each compartment.

4. The heat engine according to any preceding claim, wherein at least one compartment comprises a liquid internal surface configured to contain working fluid within the compartment.

5. The heat engine according to any preceding claim, wherein each compartment comprises a moveable piston configured to vary the internal volume of the compartment.

6. The heat engine according to claim 5, wherein each moveable piston has an oval cross-section.

7. The heat engine according to any preceding claim, wherein the isothermal expansion compartment and the isothermal compression compartment each comprise a moveable piston having a plurality of protrusions located on a surface of the piston forming an internal surface of the compartment, and wherein each compartment comprises an internal surface opposing the surface of the piston forming an internal surface of the compartment that comprises a plurality of recesses configured to receive the piston protrusions.

8. The heat engine according to claim?, wherein each protrusion comprises a curved tip portion configured to abut an equally curved base portion within a corresponding recess, and wherein the curved tip portion connects directly to the surface of the piston forming an internal surface of the compartment.

9. The heat engine according to claim 7 or 8, wherein the width of each protrusion proximal to the surface of the piston forming an internal surface of the compartment is greater than the width of each protrusion distal to the surface of the piston forming an internal surface of the compartment.

10. The heat engine according to any of claims 7 to 9, wherein the length of each protrusion in the direction of movement of the corresponding piston is at least 50% larger than the distance travelled by the piston as working fluid moves into or out of the compartment.

11. The heat engine according to any of claims 7 to 10, wherein at least one of the isothermal expansion compartment and the isothermal compression compartment comprises a flow channel configured to facilitate an unimpeded flow of working fluid between and / or through the protrusions.

12. The heat engine according to any of claims 5 to 11, wherein each piston comprises a sealing mechanism abutting the adjacent internal surfaces of the compartment.

13. The heat engine according to claim 4, wherein the moveable piston is a liquid piston.

14. The heat engine according to any preceding claim, comprising a chamber containing the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment.

15. The heat engine according to claim 14, wherein the chamber is a toroidal chamber.

16. The heat engine according to claim 14 or 15, wherein the chamber comprises: a moveable adiabatic compartment piston located between the isothermal expansion compartment and the at least one adiabatic compartment; and a moveable isothermal compression compartment piston located between the at least one adiabatic compartment and the isothermal compression compartment, wherein the moveable adiabatic compartment piston comprises the sealable adiabatic compartment aperture, and the moveable isothermal compression compartment piston comprises the isothermal compression compartment aperture.

17. The heat engine according to claim 16, wherein the chamber comprises: a moveable intermediate adiabatic compartment piston for defining an intermediate adiabatic compartment between the isothermal expansion compartment and the at least one adiabatic compartment, and a moveable intermediate isothermal compression compartment piston for defining an intermediate isothermal compression compartment between the at least one adiabatic compartment and the isothermal compression compartment, wherein the moveable intermediate adiabatic compartment piston comprises a sealable intermediate adiabatic compartment aperture that is offset from the sealable adiabaticcompartment aperture, and the moveable intermediate isothermal compression compartment piston comprises a sealable intermediate isothermal compression compartment aperture that is offset from the sealable isothermal compression compartment aperture.

18. The heat engine according to claim 17, wherein the chamber comprises: a moveable transitional adiabatic compartment piston for defining a transitional adiabatic compartment between the intermediate adiabatic compartment and the at least one adiabatic compartment, and a moveable transitional isothermal compression compartment piston for defining a transitional isothermal compression compartment between the intermediate isothermal compression compartment and the isothermal compression compartment, wherein the moveable transitional adiabatic compartment piston comprises a sealable transitional adiabatic compartment aperture that is offset from the sealable intermediate adiabatic compartment aperture, and the moveable transitional isothermal compression compartment piston comprises a sealable transitional isothermal compression compartment aperture that is offset from the sealable intermediate isothermal compression compartment aperture.

19. The heat engine according to any of claims 1 to 3, wherein each compartment comprises a moveable rotor configured to vary the internal volume of the compartment.

20. The heat engine according to any of claims 1 to 3, further comprising a toroidal chamber containing the isothermal expansion compartment, the at least one adiabatic compartment, and the isothermal compression compartment, wherein the toroidal chamber comprises a plurality of adjustable gates configured to separate the compartments and provide at least the sealable adiabatic compartment aperture and the sealable isothermal compression compartment aperture, wherein the toroidal chamber further comprises at least one turbine configured to move working fluid between the compartments, and wherein the control unitis configured to regulate the movement of working fluid between the compartments by opening and closing the gates.

21. The heat engine according to any preceding claim, further comprising an energy regeneration mechanism configured to temporarily store energy produced within one or more compartment for use elsewhere within the heat engine and / or at a later time.

22. The heat engine according to claim 21, further comprising a control module configured to regulate the energy regeneration mechanism.

23. The heat engine according to any preceding claim, wherein the at least one adiabatic compartment comprises a first adiabatic adjustment compartment and a second adiabatic adjustment compartment, each configured to receive working fluid, wherein the first adiabatic adjustment compartment comprises a sealable first adiabatic adjustment compartment aperture for conveying working fluid between the isothermal expansion compartment and the first adiabatic adjustment compartment, and wherein the second adiabatic adjustment compartment comprises a sealable second adiabatic adjustment compartment aperture for conveying working fluid between the isothermal compression compartment and the second adiabatic adjustment compartment.

24. The heat engine according to any preceding claim, wherein the average thermal conductivities of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment are higher than the average thermal conductivities of their respective external surfaces.

25. The heat engine according to any preceding claim, wherein the average thermal conductivity of the internal surfaces of the at least one adiabatic compartment is lower than the average thermal conductivity of the internal surfaces of the isothermal expansion compartment and the isothermal compression compartment.

26. The heat engine according to any preceding claim, wherein the internal surface areas of the isothermal expansion compartment and the isothermal compression compartment are greater than the internal surface area of the at least one adiabatic compartment.

27. A system comprising a plurality of heat engines according to any preceding claim.

28. A method of operating the heat engine according to any of claims 1 to 27, the method comprising the steps of: a. sealing a working fluid within the isothermal expansion compartment; b. isothermally expanding the working fluid within the isothermal expansion compartment to produce an isothermally expanded working fluid; c. moving the isothermally expanded working fluid from the isothermal expansion compartment to the at least one adiabatic compartment; d. sealing the isothermally expanded working fluid within the at least one adiabatic compartment; e. adiabatically adjusting the volume of the isothermally expanded working fluid within the at least one adiabatic compartment to produce a first adiabatically adjusted working fluid; f. moving the first adiabatically adjusted working fluid from the at least one adiabatic compartment to the isothermal compression compartment; g. sealing the adiabatically expanded working fluid within the isothermal compression compartment; h. isothermally compressing the first adiabatically adjusted working fluid within the isothermal compression compartment to produce an isothermally compressed working fluid; i. moving the isothermally compressed working fluid from the isothermal compression compartment to the at least one adiabatic compartment; j. sealing the isothermally compressed working fluid within the at least one adiabatic compartment;k. adiabatically adjusting the volume of the isothermally compressed working fluid within the at least one adiabatic compartment to produce a second adiabatically adjusted working fluid; and l. moving the second adiabatically adjusted working fluid from the at least one adiabatic compartment to the isothermal expansion compartment.

29. The method according to claim 28, wherein the rate of change of volume of the isothermal expansion compartment, the isothermal compression compartment, and the at least one adiabatic compartment is zero at the beginning and end of steps b., c., e., f., h., i., k., and I.

30. The method according to claim 28 or 29, further comprising at least one of the following additional steps: m. compressing the working fluid remaining in the isothermal expansion compartment after step (c) during a time when this compartment is not otherwise involved in steps (a) to (I); n. expanding the working fluid remaining in the at least one adiabatic compartment after step (f) if in step (e) the working fluid had been compressed, or compressing it if in step (e) the working fluid had been expanded, during a time when this compartment is not otherwise involved in steps (a) to (I); o. expanding the working fluid remaining in the isothermal compression compartment after step (i) during a time when this compartment is not otherwise involved in steps (a) to (I); p. compressing the working fluid remaining in the at least one adiabatic compartment after step (I) if in step (k) the working fluid had been expanded, or expanding it if in step (k) the working fluid had been compressed, during a time when this compartment is not otherwise involved in steps (a) to (I).

31. The method according to claim 28 or 29, wherein the rate of change of volume of the isothermal expansion compartment, the isothermal compression compartment, and the at least one adiabatic compartment is zero at the beginning and end of steps m., n., o. and / or p.

32. The method according to any of claims 28 to 31, wherein the heat engine comprises two adiabatic compartments each comprising a moveable piston configured to vary the internal volume of the corresponding compartment, and wherein the work done as a function of time by the piston of one adiabatic compartment is equal in magnitude at all times but opposite in sign to the work done by the piston of a different adiabatic compartment.

33. The method according to any of claims 28 to 32, wherein the aggregate work output as a function of time by the heat engine or work input to the heat engine as a function of time is aligned with a pre-selected power profile as a function of time for the end use or end source of this work.

34. The heat engine according to any of claims 28 to 32, wherein the aggregate work output as a function of time by the heat engine or work input to the heat engine as a function of time is that of a sinusoidal alternating electric current.

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