One obstacle to constructing an engine or heat pump intended to follow a specified thermodynamic cycle is the common presumption that the working fluid, which may be air or some other gas, gases, or vapours, is contained within some vessel which alters in volume and alternately adopts a higher and lower temperature. The difficulty of achieving said behaviour in practice is one reason which has limited the degree to which ideal thermodynamic cycles have been achieved and which has prevented the practical implementation of certain thermodynamic cycles with any degree of accuracy at all.

Accordingly this invention describes methods of construction of an engine or heat pump intended to cause a working fluid, as described above, to follow any chosen thermodynamic cycle, by separating the thermodynamic cycle desired for the working fluid from that of the containment vessel. Said separation of function is achieved by arranging for the working fluid to be transferred between successive containment spaces, also referred to as cylinders. Said cylinders which have associated pistons are then each only required to operate over a restricted range of the overall thermodynamic cycle.

The effectiveness of operation of any closed cycle heat engine or heat pump is determined by the temperature of the source from which heat is obtained and that of the sink to which excess heat is discharged, the amount of work extracted from or added to the working fluid, and the mass flow rate of the working fluid through the engine or heat pump. All four factors must be matched to ensure that the thermodynamic path followed corresponds as closely as possible to the design cycle.

In a heat engine, increasing the heat input will result in an increase of source temperature unless the mass flow rate is increased to remove the excess heat. The mass flow rate may be increased by allowing the engine to run faster, or by increasing the pressure of the working fluid, within the engine.

Only a proportion of the increased heat flow can be extracted as work, and the balance must be extracted by increased heat flow to the heat sink. Thus an increase of said heat input must be matched by a corresponding increase in the cooling effect. Should the temperatures of the source and sink deviate from the design point, the swept volumes of the cylinders may be incompatible with the new operating conditions to a greater or lesser extent.

Conversely, a decrease of heating effect requires to be accompanied by a reduction in the work output and a reduction in the said cooling effect in order to prevent a drop in source temperature. Pressure reduction may be employed as a means of reducing mass flow through the engine. Alternatively, the said engine may be permitted to rotate more slowly. Altering the pressure within said engine changes the mass of working fluid contained therein.

The values of pressure, volume, and temperature are inextricably linked for any given mass of fluid in equilibrium. For a given engine construction, the swept volumes of each of the cylinders is generally fixed. Consequently, the relationship between the temperature of the source and that of the sink between which said engine operates is fixed.

In one construction of the invention described herein, the swept volumes of each of the cylinders may be adjustable either statically or during operation, to accommodate the chosen curves which are to constitute the thermodynamic cycle. Said variation in swept volume may achieved through known methods such as altering crankshaft throw.

Although cranks have been employed for the purposes of illustration, in the accompanying figures, alternative means of obtaining reciprocation of the pistons may be employed. Said techniques may with advantage employ free pistons.

In an open cycle heat engine a mismatch between heat input, heat output, work and mass flow results in exhaust gases being discharged under conditions which carry away excess energy.

Each cycle receives a fresh charge of working fluid. Consequently initial conditions for the cycle are unaltered and there is no cumulative effect. In contrast, the behaviour of a closed cycle heat engine is influenced by any excess energy which is returned to the start of the cycle, altering the initial conditiohs and aggravating any mismatch. Consequently closed cycle heat engines are more sensitive to changes in operating conditions.

Pressurisation of heat engines is a known method of increasing mass flow rate and hence specific power. In some instances, the crankcase of such an engine may also be pressurised to balance the mean pressure acting on the piston or pistons. Depending on the construction, pressurisation of the said crankcase may serve only to reduce component stresses, or may be required in order for the engine to function. In the present invention, which has several cylinders, each of the pistons experiences a different mean pressure. Thus it is considered advantageous to arrange for the crankcase to be composed of sections which can each be pressurised independently of the others to an appropriate degree.

In another known method of construction of heat engines, pressurisation of the crankcase may be dispensed with, and double acting pistons employed to equalise the working fluid pressures within the working volume. Pairs of pistons acting in opposition may be employed as a means of maintaining balanced forces irrespective of the degree of pressurisation within the engine.

Pistons may be balanced by a number of known means. Pairs of opposed pistons may operate on a single crank, or separate cranks may be geared or otherwise coupled to arrange for the pistons to operate in a suitable phase relationship to one another in a manner which balances pressures. There is no restriction upon the chosen arrangement of said pairs which may be in line, parallel, horizontally opposed or any other suitable arrangement desired by the engine designer. Careful choice of the arrangement may be used to balance inertia forces as well as internal pressures.

Each cylinder in an internal combustion engine generally operates independently of the others.

In contrast, each cylinder in the present invention has been associated with two thermodynamic paths which constitute part of the cycle. Thus each piston operates in conjunction with two others. One advantage of the present construction is that the designer has greater freedom in the choice of materials used for the components of the engine or heat pump.

Another advantage is that each cylinder can be maintained at a temperature appropriate to the portions of the thermodynamic cycle which it services. A further advantage of the present design is that flow is unidirectional, which offers the potential for simplification of any heat exchange components. Another advantage is that dead space can be reduced in comparison to alternative forms of external combustion heat engines or heat pumps. A heat engine or heat pump with a higher compression ratio operates over a greater temperature differential than does one with a relatively lower compression ratio. Said temperature differential requires to be maximised in order to obtain the highest possible thermal efficiency for the driving or driven device. One advantage of reduced dead space is that in comparison to known constructions, a relatively high compression ratio may be achieved in the present invention.

For convenience, the lowest pressure and temperature and the largest volume are regarded as the starting point of the thermodynamic cycle. Any suitable point may be regarded as the start point. Consequently, additional cooling or heating measures in order to correct an excess or deficiency of energy within the working fluid, may be incorporated at any suitable point in the cycle to control the operation of the engine. The extent to which such corrective action may be required, is a measure of the degree to which the engine or pump has deviated from the design cycle, and may represent irreversible energy losses.

In any embodiment of the invention, depending upon whether the construction is to be employed as an engine, a heat pump, or both, any valve gear may be adapted accordingly.

Thus whereas reed valves or similar self acting valves may serve in certain applications and portions of the cycle, mechanically or otherwise directly actuated valves may be employed with advantage at other points in the cycle. In yet other portions of the cycle, no valves may be required. The descriptions given by way of example for a heat engine may be taken to apply to a heat pump by reversing the sequence of operation.

One thermodynamic cycle which may be implemented is sometimes known as the Carnot cycle. The Camot cycle is generally taught in elementary thermodynamics courses to illustrate the limitation on maximum thermal efficiency to which every heat engine is subject. The Camot cycle is reversible, which means that an engine which operates according to the cycle, can be driven in reverse to act as a heat pump. It is commonly stated that a Carnot cycle engine cannot be constructed. Known heat engines employ approximations to ideal thermodynamic cycles which are generally of lower maximum thermal efficiency than the Camot cycle. Engines intended to operate on the thermodynamic cycle sometimes known as the Stirling cycle are an exception in that the maximum thermal efficiency for a regenerative Stirling cycle is equal to that of the Carnot cycle. The present invention may also be applied to implement the thermodynamic cycle sometimes known as the regenerative Stirling cycle. Said cycle is reversible.

Design of regenerators is demanding both from the intellectual perspective and the materials performance requirements. Associated dead space within regenerators imposes limitations on the specific power which known designs of Regenerative Stirling cycle heat engine can achieve. The maximum compression ratio typically attainable with known constructions of Regenerative Stirling engine is in the region of 2: 1.

Accordingly a preferred embodiment of this invention describes one construction of an engine or heat pump intended to cause a working fluid to follow a thermodynamic cycle approximating the Regenerative Stirling cycle in which the regenerator is replaced by a form of heat exchanger. Said heat exchanger permits the regenerative function to be carried out.

Yet another thermodynamic cycle which can be implemented by the present invention comprises one in which the working fluid undergoes one isothermal process, one adiabatic process, and one constant volume process. A constant volume process may also be referred to as an Isochoric process.

Another thermodynamic cycle which can be implemented by the present invention comprises one in which the working fluid undergoes two constant pressure processes and two Isochoric processes. This cycle is sometimes known as the Ericsson cycle.

Another thermodynamic cycle which can be implemented by the present invention comprises one in which the working fluid undergoes two constant volume processes and two adiabatic processes.

The present invention can implement any chosen thermodynamic cycle by arranging for there to be an appropriate number of containment spaces together with the necessary interconnecting elements.

For clarity, in Figures 2,4, 6, and 8, which illustrate preferred embodiments of the invention, four separate crankshafts 15 are shown. Further, according to said illustrations, the crankshafts rotate in the same direction as one another in order to preserve the phase of the pistons. In general, if more than one crankshaft is employed, the direction of rotation of the individual crankshafts is unimportant, provided said crankshafts have been correctly synchronised to achieve the necessary phase relationship for the pistons. For convenience, the cranks may be arranged on a single crankshaft. For the present descriptions, the rotation of the separate crankshafts 15 will be described as though they were as a single crankshaft 15.

A preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: FIGURE 1 is an illustration of the thermodynamic cycle sometimes known as the Carnot cycle.

FIGURE 2 is a diagrammatic representation of the essential components of the new engine or heat pump.

With reference to Figure 1, the Carnot cycle consists of an Isothermal compression 1, followed by an Adiabatic compression 2, then an Isothermal expansion 3 followed by an Adiabatic expansion 4 to complete a cycle. the points 5,6, 7, and 8 on the cycle at which the Isothermal and Adiabatic curves intersect correspond to the working fluid being at specified volumes in the cycle. Once the volume of a given mass of working fluid has been constrained, the pressure and temperature are dependent on one another.

With reference to Figure 2, the proposed construction consists of four pistons and cylinders operating together to comprise a closed cycle. In the present description, a given mass of working fluid is followed as it is described progressing through the cycle There are two such said masses of working fluid, progressing in turn through each portion of the cycle. The swept volumes of the cylinders are different. The pistons in the first 9 and third 11 cylinders operate in phase with each other. The pistons in the second 10 and fourth 12 cylinders operate in phase with each other. The two pairs operate 180 degrees out of phase. The first cylinder 9 is constructed to correspond with point 5 in Figure 1 and is larger than the second cylinder 10 which corresponds with point 6 in Figure 1. The working fluid passes between the first 9 and second 10 cylinders via a heat exchanger 13 of known construction. As the first cylinder 9 is swept to zero volume, the second cylinder 10 is swept to maximum volume. The working fluid is transferred into the second cylinder 10 isothermally because of the transfer of heat through the heat exchanger 13 which is connected to a heat sink. The working fluid now in the second cylinder 10 is at reduced volume having undergone isothermal compression. This corresponds to the working fluid following isothermal 1 from point 5 to point 6 in Figure 1. A suitable valve or valves 16, arranged between the two cylinders 9 and 10 prevents the working fluid returning to the first cylinder 9 during the next half turn of the crankshaft 15. The valve arrangement may with advantage isolate the dead space comprising the heat exchanger region from both cylinders to which it is connected. The working fluid in the second cylinder 10 now undergoes adiabatic compression for the next half turn of the crankshaft 15 as it is transferred into cylinder number three 11 which is smaller than the second cylinder 10. The working fluid now in the third cylinder 11 has been adiabatically compressed by the construction being arranged in order that heat transfer mechanisms to or from the working fluid as it transfers between cylinders two, 10 and three, 11 have been eliminated so far as is practicable. When the working fluid is fully contained within cylinder number three, 11, it is at point 7 in Figure 1 having traversed the Adiabatic curve, 2 from point 6 to point 7 in Figure 1.

As already described, a suitable valve or valves 16 prevent the working fluid from returning to cylinder number two, 10 and may be arranged with advantage to isolate the connecting duct and its dead space from the cylinders to which it is connected.

It is advantageous to arrange the physical disposition of the cylinders to minimise said dead space and also to prevent thermal short circuits which may impair efficiency.

From containment within the third cylinder 11, the working fluid is permitted to pass via a second heat exchanger 14, of known construction, which is arranged to transfer heat to the working fluid from the source, into the fourth cylinder 12. The swept volume of the fourth cylinder 12 is greater than that of the third cylinder 11,-and corresponds to point 8, in Figure 1.

The working fluid therefore expands Isothermally into the fourth cylinder during the third half turn of the crankshaft 15. Similar arrangements to those already described regarding valves 16 may be employed between the cylinders. Finally, the working fluid is returned from the fourth cylinder 12 to the first cylinder 9, the piston of which is 180 degrees out of phase with that in the fourth cylinder 12. The expansion to original volume is once more arranged to be Adiabatic, all mechanisms for heat transfer to or from the working fluid during the transfer having been eliminated so far as possible. This corresponds to the fluid traversing the Adiabatic curve 4 from point 8 to point 5 in Figure 1. This completes the cycle.

With said construction, the interaction between pairs of pistons may be regarded as the process which requires or delivers net work.

The swept volume of each of the cylinders represents the end points of the four phases of the Carnot cycle. Thus having decided which Isothermal curves and which Adiabatic curves are to be used by the engine, the swept volumes are fixed by the intersections of the curves.

A further preferred embodiment of the invention will now be described with reference to the accompanying drawings in which: FIGURE 3 is an illustration of the thermodynamic cycle sometimes known as the Regenerative Stirling cycle.

FIGURE 4 is a diagrammatic representation of the essential components of the new engine or heat pump.

With reference to Figure 3, the Regenerative Stirling cycle consists of an Isothermal compression 1, followed by a constant volume process 2 which is also known as an Isochoric process, then an Isothermal expansion 3 followed by an Isochoric process 4 to complete a cycle. The points 5,6, 7, and 8 on the cycle at which the Isothermal and Isochoric process lines intersect correspond to the working fluid being at specified conditions in the cycle which in turn correspond to containment of the working fluid substantially within one of each of four cylinders described below.

With reference to Figure 4, the proposed construction consists of four pistons and cylinders operating together to comprise a closed cycle. The sequence of operation is similar to that previously described. Refinements and provisions already described have been omitted for clarity. The first cylinder 9 is constructed to correspond with point 5 in Figure 3 and is larger than the second cylinder 10 which corresponds with point 6 in Figure 3. The working fluid passes between the first 9 and second 10 cylinders via a heat exchanger 13 of known construction as previously described coupled to a heat sink. This corresponds to the working fluid following isothermal 1 from point 5 to point 6 in Figure 3. The working fluid in the second cylinder 10 now undergoes an Isochoric process for the next half turn of the crankshaft 15 as it is transferred into cylinder number three 11 which is the same size as the second cylinder 10.

The working fluid now in the third cylinder 11 has undergone an Isochoric process. The construction is arranged to incorporate a heat exchanger 17 arranged to serve as a regenerative element through which the working fluid flows as it transfers between cylinders two, 10 and three, 11. In passing through the said regenerative element, the working fluid derives heat from the working fluid which flows in the opposite direction. Once the working fluid is fully contained within cylinder number three, 11, it is at point 7 in Figure 3 having traversed the Isochoric process line, 2 from point 6 to point 7 in Figure 3.

From containment within the third cylinder 11, the working fluid is permitted to pass via a second heat exchanger 14, of known construction, coupled to the source, into the fourth cylinder 12. The swept volume of the fourth cylinder 12 is greater than that of the third cylinder 11, and corresponds to point 8, in Figure 3. The working fluid therefore expands Isothermally into the fourth cylinder during the third half turn of the crankshaft 15. Finally, the working fluid is returned from the fourth cylinder 12 to the first cylinder 9, the piston of which operates 180 degrees out of phase with that in the fourth cylinder 12. The fourth cylinder 12 has the same swept volume as the first cylinder 9. The transfer to the first cylinder 9 is once more arranged to produce a regenerative Isochoric process to the greatest extent possible, by the working fluid flowing through the said heat exchanger 17. This corresponds to the fluid traversing the Isochoric process line 4 from point 8 to point 5 in Figure 3. This completes the cycle. The present configuration can also implement the Ericsson cycle by altering the heating and cooling arrangements to an appropriate degree.

Similar arrangements to those already described regarding valves 16 may be employed between the cylinders to control the flow of the working fluid. The swept volume of each of the cylinders represents the end points of the four phases of the Regenerative Stirling cycle illustrated in Figure 3. Thus having decided which Isothermal curves and which Isochòric process lines are to be used by the engine, the relative swept volumes are fixed by the intersections of the curves and lines.

With reference to Figure 4, the construction of the regenerating element 17 is such that working fluid may flow from left to right or right to left as it is transferred between cylinder two 10 and cylinder three 11. Similarly, the construction permits a separate flow of working fluid from left to right or right to left as it is transferred between cylinder four 12 and cylinder one 9. The direction of flow depends on whether the machine is used as a driven or a driving device, but the separate flow are always in opposition to one another. The construction of the regenerating element 17 in Figure 4 isolates fluid flow through the lower portion from that through the upper portion. In common with known constructions of regenerator, thermal conductivity from left to right and right to left is minimised by techniques such as interleaving conductors with insulating material or other known methods.

Thermal conductivity between the opposing fluid flows through the regenerating element 17 in Figure 4 is maximised. Consequently, the temperature gradient is greatest across the regenerating element measured left to right but minimal when measured at corresponding sections between the flows. One important advantage of the present invention is that regeneration is achieved without reversal of fluid flow through the regenerating element. The construction of the regenerating element may with advantage be such that the fluid flows are coaxial to one another. A further advantage of the present design is that the regeneration is achieved without the necessity to store heat since the flows of working fluid between cylinder two 10, and cylinder three 11, and that between cylinder four 12, and cylinder one 9, although intermittent, occur in corresponding time intervals.

A further embodiment of the invention will now be described with reference to the accompanying drawings in which: FIGURE 5 is an illustration of a thermodynamic cycle comprising one adiabatic process, one isothermal process, and one Isochoric process.

FIGURE 6 is a diagrammatic representation of the essential components of the new engine or heat pump.

With reference to Figure 5, the cycle consists of an Adiabatic compression 1, then an Isothermal expansion 2 followed by an Isochoric process 3 to complete a cycle. The points 4,5, and 6 on the cycle at which the curves intersect correspond to the working fluid being at specified volumes in the cycle.

With reference to Figure 6, the proposed construction consists of four pistons and cylinders operating together to comprise a closed cycle. The sequence of operation is similar to that previously described. Refinements and provisions already described have been omitted for clarity. The pistons in the first 9 and third 11 cylinders operate in phase with each other. The pistons in the second 10 and fourth 12 cylinders operate in phase with each other. The two pairs operate 180 degrees out of phase. The first cylinder 9 is constructed to correspond with point 4 in Figure 5 and is larger than the second cylinder 10 which corresponds with point 5 in Figure 5. The working fluid passes between the first 9 and second 10 cylinders. The working fluid now in the second cylinder 10 has been adiabatically compressed by the construction being arranged in order that heat transfer mechanisms to or from the working fluid as it transfers between cylinders one, 9 and two, 10 have been eliminated so far as is practicable.

When the working fluid is fully contained within cylinder number two, 10, it is at point 5 in Figure 5 having traversed the Adiabatic curve, 1 from point 4 to point 5 in Figure 5. As the second cylinder 10 is swept to zero volume, the third cylinder 11 is swept to maximum volume.

The working fluid is transferred into the third cylinder 11 isothermally because of the transfer of heat through the heat exchanger 13 which is arranged to transfer energy from a heat source.

The working fluid now in the third cylinder 11 is at increased volume having undergone isothermal expansion. This corresponds to the working fluid following isothermal 2 from point 5 to point 6 in Figure 5. Note that for this construction, the first cylinder 9 is the same size as the third cylinder 11 because the said cylinders correspond to points 4 and 6 respectively on Figure 5, which have been chosen to be the same volume. The working fluid in the third cylinder 11 need not be subjected to any thermodynamic process during the next half turn of the crankshaft 15 as it is transferred into cylinder number four 12 which is the same size as the third cylinder 11. The purpose of this transfer is to synchronise the flow of the working fluid with the motions of the pistons in the cylinders. However, it may with advantage represent an intermediate point such as 7 on the Isochoric process line 3 in Figure 5. In said case, the working fluid would require to undergo cooling during the transfer between the third cylinder 11 and the fourth cylinder 12. To complete the cycle, the working fluid is transferred between the fourth cylinder 12 and the first cylinder 9 through a suitable heat exchanger 14 which is arranged to transfer energy from the working fluid to a heat sink. The thermodynamic process takes place at constant volume because the fourth cylinder 12 is the same size as the first cylinder 9.

A suitable valve or valves 16, are arranged between the cylinders to control the flow of the working fluid as previously described.

A further embodiment of the invention will now be described with reference to the accompanying drawings in which : FIGURE 7 Is an illustration of a thermodynamic cycle comprising two adiabatic processes and two Isochoric processes.

FIGURE 8 Is a diagrammatic representation of the essential components of the new engine or heat pump.

With reference to Figure 7, the cycle consists of an Adiabatic compression 1, followed by an Isochoric rise in pressure 2, then an Adiabatic expansion 3 followed by an Isochoric drop in pressure 4 to complete, a cycle. The points 5,6, 7, and 8 on the cycle at which the Isochoric and Adiabatic curves intersect correspond to the working fluid being at specified volumes in the cycle.

With reference to Figure 8, the proposed construction consists of four pistons and cylinders operating together to comprise a closed cycle. The sequence of operation is similar to that previously described. Refinements and provisions already described have been omitted for clarity. The pistons in the first 9 and third 11 cylinders operate in phase with each other. The pistons in the second 10 and fourth 12 cylinders operate in phase with each other. The two pairs operate 180 degrees out of phase. The first cylinder 9 is constructed to correspond with point 5 in Figure 7 and is larger than the second cylinder 10 which corresponds with point 6 in Figure 7. The working fluid in the first cylinder 9 undergoes adiabatic compression for the first half turn of the crankshaft 15 as it is transferred into cylinder number two 10 which is smaller than the first cylinder 9. The working fluid now in the second cylinder 10 has been adiabatically compressed by the construction being arranged in order that heat transfer mechanisms to or from the workjng fluid as it transfers between cylinders one, 9 and two, 10 have been eliminated so far as is practicable. When the working fluid is fully contained within cylinder number two, 10, it is at point 6 in Figure 7 having traversed the Adiabatic curve, 1 from point 5 to point 6 in Figure 7. The working fluid next passes between the second 10 and third 11 cylinders via a heat exchanger 13 of known construction. As the second cylinder 10 is swept to zero volume, the third cylinder 11 is swept to maximum volume. The working fluid is transferred into the third cylinder 11 Isochorically while heat is added through the heat exchanger 13 which is connected to a heat source, the working fluid now in the third cylinder 11 is at increased pressure having undergone an Isochoric process. This corresponds to the working fluid following the Isochoric line 2 from point 6 to point 7 in Figure 7.

From containment within the third cylinder 11, the working fluid is permitted to expand into the fourth cylinder 12. The transfer is once more arranged to be Adiabatic, all mechanisms for heat transfer to or from the working fluid during the transfer having been eliminated so far as possible. This corresponds to the fluid traversing the Adiabatic curve 3 from point 7 to point 8 in Figure 7. The swept volume of the fourth cylinder 12 is greater than that of the third cylinder 11, and corresponds to point 8, in Figure 7. The working fluid therefore expands Adiabatically into the fourth cylinder duririg the third half turn of the crankshaft 15. Finally, the working fluid is returned from the fourth cylinder 12 to the first cylinder 9, the piston of which is 180 degrees out of phase with that in the fourth cylinder 12. The first cylinder 9 and the fourth cylinder 12 are the same size. The transfer of the working fluid takes place lsochorically via a second heat exchanger 14, of known construction, which extracts heat from the working fluid and results in a drop in pressure until point 5 in Figure 7 is reached once more. This completes the cycle.

A suitable valve or valves 16, are arranged between the cylinders to control the flow of the working fluid as previously described. The temperatures of the heat exchangers do not correspond with one another in the manner described in relation to the Stirling cycle. However, with advantage, a certain amount of regeneration may be achieved by a suitable arrangement in which the heat exchangers 13 and 14 are in sections. Corresponding sections are arranged to transfer energy between the separate fluid flows and other sections are arranged to transfer energy between the fluid flows and the source or sink as appropriate.