The present invention relates to a rotary device and a method of operating a rotary device.

In particular embodiments, the present invention comprises developments of the methods and apparatuses described in the published patent application WO-A-91/06747 and granted patents US-B-6168385 and US-B-6176695 the entire contents of which are hereby incorporated by reference.

Detonation is a process in which a gaseous mixture of a fuel distributed in air or oxygen undergoes oxidation with consequent release of heat in a more rapid manner than that which occurs in flame-induced combustion or deflagration. The detonation is usually started by an ignition of the air/fuel mixture. Detonation of an air/fuel mixture causes the generation of a shock wave, as a result of the expansion of the air/fuel mixture due to the heat generated by the process. During detonation, the shock wave passes through the gaseous mixture (charge gases) travelling at a much greater velocity than is possible for a flame during deflagration and typically at Mach Numbers greater than 1.

It has been demonstrated that detonation can be made to occur in a tube having one end closed and the other open. A charge of fuel and air is introduced to the tube through valves or ports at the closed end where an igniter is located. When the shock wave is initiated due to rapid expansion of the ignited air/fuel mixture at the igniter, it passes down the tube at very high velocity. Significant thru3t is generated as the charge gases exit the open end of the tube at high velocity as a result of the expansion caused by the heat release of detonation. A number of tubes may be arranged so as to form a thrust generation engine in which detonations are made to occur sequentially. See, for example, US-A-5345758 in which such a system is described.

Changes in pressure and density of the charge gases are known to occur during each detonation cycle. Gas density is at a maximum at the front of the advancing shock wave, where thermo-chemical reactions of the air/fuel mixture are initiated. Conversely, in the wake of the shock wave, a rarefaction wave is set up, in which the gas density becomes extremely low. Gas expansion, which results from heat release at the reaction zone, serves to drive the gases out of the open end of the chamber, leaving behind a region of low density or partial vacuum. In the pulse detonation engine, this partial vacuum is used to cause the rapid refilling of the tube with the next charge of air and fuel .

US-A-4741154 discloses a rotary detonation engine. The engine comprises detonation chambers and a number of turbine blades arranged to be driven by the detonated charge of air and fuel mixture received from the detonation chambers. This engine relies on a catherine-wheel effect to drive the rotor. The engine does not enable an efficient conversion of the energy from the detonation into rotary power. Furthermore, the turbine blades are subject to fluctuating forces from the detonation, for which they cannot perform efficient energy conversion and which renders them liable to fatigue fracture.

According to a first aspect of the present invention there is provided a rotary device, comprising: a chamber for receiving a charge of an air/fuel mixture and for oxidising the fuel by detonation; and a rotary expander having a transient chamber of variable volume, the transient chamber being in fluid communication with the detonation chamber during at least part of a cycle of rotation of the rotary expander, the rotary expander being arranged to be driven by expansion of the air/fuel mixture caused by detonation thereof.

The invention provides a rotary device that enables rotary power to be obtained from a detonation process. In contrast to previously disclosed devices used to obtain rotary power from a detonation process, e.g. such as that described in US-A-4741154, in the present invention a rotary expander is provided that provides an efficient means for extracting the power from the expanding gases generated in the rotary device.

The invention provides a rotary device in which energy released from fuel may be converted into shaft power using the rotary expander in a manner, which offers several significant advantages when compared with Otto, Diesel and gas turbine cycle engines. In all of these engines, the fuel oxidation process is initiated only after the fuel-air mixture has been compressed and has therefore already reached temperature and pressure levels which are substantially above ambient. In Otto and Diesel cycle engines, the heat release upon combustion further elevates the temperature and pressure to extremely high Ievel3. This ha3 a number of disadvantages. First, the engine needs to be constructed of materials, which are capable of both withstanding the high thermal and physical stresses and of sealing the gas charge within the combustion chamber. Due to the high thermal and physical stress some thermal and leakage losses are inevitable during this process.

Second, in the case of piston engines, the combustion process is spread over an angle - typically 20 to 90 degrees - about the top dead centre (TDC) position of the piston. This means that the portion of heat release which takes place before TDC, adds to the negative work of compression, which must be recovered during expansion after TDC, before net positive work can be generated on the piston during this half (i.e. compression - combustion - expansion phases) of the Otto and Diesel cycles. The sealing of the charge during this period gives rise to substantial friction as the piston rings seal the gap between piston and cylinder wall. This friction persists also during the induction and exhaust phases of these cycles and constitutes a further loss of internal power in these engines .

In the case of gas turbine engines, the heat release during combustion does not result in a further pressure rise but produces expansion of the gas at the pressure generated by the compressor. However, the work done by the compressor, represents a considerable proportion of the work which is recovered by the expansion turbine system and constitutes considerable negative work which must be overcome before the turbine can deliver a net surplus of power.

The rotary device of the present invention suffers from none of these disadvantages. Little or no work from an external source, such as flywheel inertia, is applied to the working fluid before the fuel is oxidised. Any compression is largely or entirely locally generated in the reaction zone within the working fluid charge as a result of oxidation being achieved by detonation, i.e. by a thermo-chemicalIy derived shock wave. Consequently the pressures and temperatures throughout the engine are much lower than those in piston and gas turbine engines. The lower thermal gradients greatly reduce the potential for thermal losses .

Leakage losses from the working fluid charge can also be kept to extremely low levels without the need for physical or mechanical seals because of the absence of large pressure gradients, thus avoiding the generation of internal friction losses. Thus, the potential energy of the fuel is converted directly into expansion of the working fluid with minimal internal losses . The gas expansion is converted efficiently into shaft power by the rotary expander with minimal losses during the expansion process, thus providing a rotary device of high efficiency through the reduction of internal losses.

According to a second aspect of the present invention there is provided a method of operating a rotary device, the rotary device comprising a detonation chamber in fluid communication wich a transient chamber of a rotary expander, the metzhoά comprising: receiving in the detonation chamber a charge of a gas/fuel mixture; and detonating said mixture to cause expansion of the gas/fuel mixture and thereby drive the rotary expander.

Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows schematically a perspective view of an example of a rotary device according to an embodiment of the present invention;

Figure 2 is a view of the device of Figure 1 with certain components removed for clarity;

Figure 3 is a view of the device of Figure 1 with certain components removed for clarity;

Figures 4A to 4H show rotor end profiles at stages through a cycle for a compressor;

Figures 5A to 5H show rotor end profiles at stages through a cycle for an expander;

Figure 6 shows a section through a port having a grid filter for use in the rotary device in Figure 1;

Figure 7 is a graph showing the stages in a detonation cycle for the rotary device of Figure 1; and

Figure 8 shows schematically a longitudinal section view of an example of a rotary device according to an embodiment of the present invention. Figures 1 to 3 show part views of an example of a rotary device according to an embodiment of the present invention. In the specific example shown, the device comprises a compressor 2, a detonation chamber 4 and an expander 6 arranged within a housing defined by walls (not all shown) . The detonation chamber 4 is contained within a stator cylinder 3 to be described in more detail below. An intermediate wall 10 is provided to separate the compressor and the expander.

Generally, the compressor 2 is arranged to provide a compressed charge of an air/fuel mixture to the detonation chamber 4. Each of the compressor 2 and expander 6 is made up of two rotors (5 and 7 for compressor; 16 and 18 for expander) arranged for counter rotation about parallel axes. In Figure 1, the rotors 16 and 18 of the expander are clearly visible. In Figure 2, the rotors of the expander and the intermediate wall 10 have been removed to provide a clear view of the rotors of the compressor.

The rotors 5, 7, 16 and 18 of both the expander and the compressor are arranged within a housing of which only one end wall 8 and the intermediate wall 10 are shown in Figure 1. Further walls (not shown) are provided so that the rotors and the stator cylinder 3 about which they are arranged to rotate are enclosed.

Openings 12 and 14 are provided in the walls of the housing. The openings 12 and 14 are provided to enable moveable shaped containment walls to be inserted into the rotary device. As will be explained below, the containment walls (shown in section in figures 4A to 4H and 5A to 5H) enable the maximum possible volumes of the transient chambers of each of the compressor and expander to be varied.

In use, once a charge of air/fuel mixture is in the detonation chamber 4 and in a suitably turbulent state, the mixture is ignited. This causes a detonation of the air/fuel mixture and the consequent generation of a supersonic shock wave that propagates through the detonation chamber 4 and into the expander 6. As a result, the gases within the detonation chamber and expander expand causing rotation of the rotors of the expander. The rotary expander is connected to a drive shaft such that rotary power can be drawn from the device.

In more detail, the rotary device shown in Figure 1 comprises a detonation chamber 4 in a stator cylinder having axial ports (not shown in Figure 1) towards either end. The axial ports 20 and 32 can be seen in Figure 3 and in section in Figures 4A to 4H and 5A to 5H. One of the axial ports 20 enables communication between the recess of the recessed rotor of the compressor and the detonation chamber. The other of the axial ports 32 enables communication between the recess of the recessed rotor of the expander and the detonation chamber.

In the example shown, both the compressor and the expander are formed by a respective recess 7 and 18 and lobe 5 and 16 rotor arranged for rotation about respective axes . The rotors of each of the compressor and expander are most preferably of the type described in WO-A- 91/05747, the entire contents of which are hereby incorporated by reference. Referring to the expander 6 that i3 clearly visible in Figure 1, lobed rotor 16 has radial lobes P and Q which are identical in shape and are shaped upon rotation to co-operate with recesses R, S and T within the recessed rotor 18. This serves to define a transient chamber of variable volume between an interacting lobe and recess. As will be explained below, the transient chamber serves to receive expanding gases and extract energy from them.

Referring now to the compressor, a gaseous working fluid, e.g. an air/fuel mixture is provided in the housing surrounding the rotor pair 5 and 7 of the compressor and fills the recesses within the compressor recessed rotor 7. The compression cycle commences when a lobe from the lobed rotor 5 enters one of the recesses of the recessed rotor 7 and entraps a charge of the air/fuel mixture within the transient chamber defined by the co-operating surfaces of a recess of the recessed rotor 7 and a lobe of the lobed rotor 5. The cycle of operation of the rotary device will be described in detail below.

The recessed rotors 7 and 18 of both the compressor and expander have axially central bores 9 and 11. In addition, each recessed rotor 7 and 18 is provided with a passage (shown in Figures 4A to 4H and 5A to 5H) that links the recess or recesses within the rotor to the bore of the rotor. Each of the rotor bores 9 and 11 fits closely adjacent to the outer surface of the stator cylinder 3 within which is defined the detonation chamber 4. This enables each of the ports within the stator cylinder 3 to be in communication with the entrance of the short passages leading to the recess within each of the rotors and consequently to the transient chamber formed between a respective rotor pair, during an appropriate sector of arc of rotation.

The stator cylinder 3 defining the detonation chamber 4 is supported at each end in the two outer walls 8 (other not shown) of the housing which provide close fitting support for the outer end faces of the compressor rotor pair 5 and 7 and for the outer end faces of the expander rotor pair 16 and 18, respectively. End walls are provided to close both ends of the stator cylinder 3 thereby defining the detonation chamber. Preferably, the wall at the compressor end of the detonation chamber 4 provides the location for an igniter such as a spark plug (not shown) or any other suitable means for igniting the charge within the detonation chamber.

Both the compressor and expander rotor pairs (5 and 7; 16 and 18) may be supplied with moveable containment walls (shown in section in Figures 4A to 4H and 5A to 5H) . The moveable containment walls are preferably slideable elements provided to enable variable throughput of a working fluid of the rotary device during its operation. The throughput of working fluid may be varied, for example, in accordance with varying load or in order to maintain constant power delivery with varying altitude in certain applications.

In a preferred embodiment, a grid (described in detail below with reference to Figure S) is fitted in the short passage leading from the transient chamber of the compressor into the detonation charier. The grid is an example of a component suitable for generating micro-scale turbulence in the charge gas as it leaves the compressor transient chamber and enters the detonation chamber. The micro-scale turbulence, whilst producing turbulent eddy structures of very small size in the gas stream, is nevertheless of a very high intensity and produces local mean gas velocities of a high order. This specific form of turbulence is a precursor to the detonation process, which follows shortly afterwards in the detonation chamber.

The turbulence raises the local gas dynamic energy of the air/fuel mixture to a high level so as to produce a high level of potential reactivity which is required for effective detonation of the charge. The grid also affects the entire charge flow, which passes through the passage, thus resulting in good homogeneity of both turbulence and fuel distribution at the micro-level over the whole of the charge, prior to initiation of detonation. Once in the detonation chamber (and possibly also in the expanding transient chamber of the rotary expander) , the charge is ignited thereby causing a detonation. The detonation causes a rapid expansion of the gases, the expansion being used to drive the rotary expander.

Figures 4A to 4H show rotor end profiles at stages through a cycle for a compressor section of the rotary device. It will be understood that the rotary device may operate without a compressor, i.e. the air/fuel mixture being provided directly to the detonation chamber at ambient pressure. Each one of Figures 4A to 4H shows a profile section through the lobed and recessed rotors and a moveable containment wall at a point close to a gas intake end of the rotary device. The containment wall is shaped to engage the first and second rotors to define between the containment wall and the first and second rotor3 the transient chamber, wherein the containment wall is moveable to enable the maximum possible volume of the transient chamber to be varied.

The recessed rotor has a hollow centre which rotates about a close-fitting stator cylinder having a hollow interior defining the detonation chamber. The stator cylinder has a port 20 and each of the recesses of the compressor recessed rotor has a passage 22 for communication with the port 20 in the stator cylinder during a part of the cycle of rotation of the rotor about the stator cylinder. The hollow interior of the stator cylinder serves as a detonation chamber for the rotary device.

Referring to Figure 4A, as the rotors rotate in the directions indicated (lobed rotor clockwise, recessed rotor counter-clockwise) a lobe P and recess R approach each other. Engagement between the lobe P and recess R and moveable containment wall 26 serves to entrap a transient volume J within the moveable wall 26. An end section of the moveable wall is shown. The wall is tapered along the axial length of the rotors. As the wall moves along a path parallel to the axial direction of the rotors, due to the tapered shape of the wall, the maximum possible volume of the transient chamber is varied. This is described in detail in US-B-6176695 the entire contents of which are hereby incorporated by reference. Means such as automatic means for moving the wall 26 as described may¬ be provided.

Referring now to Figure 4B, the fluid contained in the transient volume J is now entrapped and becomes compressed as the rotors continue to rotate.

Referring now to Figure 4C, the transient volume J has been compressed but the fluid remains trapped as the recessed rotor passage 22 has not yet rotated to a position corresponding to the port 20.

In Figure 4D, the transient volume J is now contained entirely by the surfaces of the lobe P and recess R. The leading edge of the recessed rotor passage 22 has now reached the opening edge of the port 20 and fluid flow begins to take place through the port. At this stage, the pressure of the trapped fluid has reached that of the receiver and further rotation of the rotors will result in progressive delivery of the charge of gas compressed within the variable volume chamber between the lobe R and recess P.

In Figure 4Ξ, the leading edge of the recessed rotor passage 22 has now traversed approximately half way across the port 20, thus increasing the variable flow area at the throat of the port 20. In Figure 4F, the recessed rotor passage 22 is now in alignment with the port 20, thus providing maximum flow area for delivery of the charge.

In Figure 4G, the trailing edge of the recessed rotor passage 22 is now approaching the closing edge of the port 20 and the port is starting to close. The remaining transient volume is very small and thus contains a small mass of charge still to be transferred through the port.

Last, in Figure 4H, the transient volume has now been eliminated and only a clearance volume remains between the lobe surface P and that of the recess R. Closure of the port 20 coincides with the completion of the compression action, which occurs when the tip of a lobe reaches the point of minimum radius of the pocket. A new transient volume has now been formed between the next lobe and recess pair. At this stage the entire charge of air/fuel mixture has been compressed and is now stored within the detonation chamber defined by the interior of the stator cylinder and possibly also the transient chamber of the expander.

At some point during the compression cycle explained above with reference to Figures 4A to 4H, a transient chamber is formed between a recess and lobe of the rotors of the expander. The transient chamber increases in volume during a cycle to enable expansion of detonated gases from the charge. In fact, as will be explained below, in a preferred example, the transient chamber receives an amount of compressed charge such that the transient chamber of the expander also functions as a chamber in which detonation occurs. The relative filling of the expander cycle with respect to the compressor and the timing of the detonation and the start of and continuing extent of the expander cycle in relation to the later phases of the compression cycle will be described in detail below. For now, a description of the expander and an expansion cycle will be provided in detail.

Figures 5A to 5H show end profiles at stages through a cycle for an expander of the rotary device. Referring to Figure 5A, a cycle of the expander begins when a lobe surface U and a recess surface W of a pair of engaging rotors pass the point of maximum penetration of the lobe, i.e. as the tip of the lobe passes the point of minimum radiu3 of the recess surface W. At this stage, the leading edge of the recessed rotor passage 30 approaches an opening edge of the port 32 within the stator cylinder 16 to which a pressurised fluid supply has access. Referring to Figure 5B, as the port 32 opens, pressurised fluid passes into the recessed rotor passage 30 and into a newly forming transient volume between the lobe and recess.

Referring to Figure 5C, the port 32 is now fully open, providing maximum flow capacity for the pressurised fluid to pass through into the transient volume defined between lobe surface U and recess surface W. This minimises any pressure differential between that of the fluid supply and that occurring in the transient volume. The pressure of the pressurised fluid acts on the surfaces U of the lobe and W of the recess, thus urging the rotors into further action in the direction of rotation. It is likely that the pressure of the fluid will not be substantial and will not of itself have a significant effect in driving the rotors of the expander. The drive access occurs when the air/fuel mixture contained within stator cylinder 18 and the transient volume in the expander is detonated.

In Figure 5D, a trailing edge of the recessed rotor passage 30 approaches the closing edge of the port 32 which starts to shut off the supply of pressurised fluid to the chamber defined between the lobe and recess.

Referring to Figure 5E, the trailing edge of the recessed rotor passage 30 reaches the closing edge of the port 32, thus closing off the supply of pressurised fluid and isolating the fluid which has already passed into the transient volume. By this stage of the cycle the air/fuel mixture will have detonated causing a shock wave that effectively transfers the entire charge into the expander and causes a rapid expansion of the charge gases that drives rotation of the expander rotors. Simultaneously, a rarefaction wave is formed behind the shock wave. The rarefaction wave creates a depression which will tend to be filled by a subsequent charge of air/fuel mixture entering the detonation and expansion chambers .

As can be seen in Figure 5F, rotation of the rotors causes the transient volume to increase, thus allowing the trapped fluid to expand whilst maintaining some pressure on the surface of the lobe U and recess W and continuing to energise the rotation of the rotors and any shafts to which they may be connected.

Referring to Figure 5G, the transient volume reaches its maximum capacity and the fluid reaches ambient pressure. At this point the fluid ceases to exert any net pressure on the lobe U and recess W surfaces prior to its release to the housing surrounding the rotor pair.

Last, in Figure 5H, the fully expanded fluid is released from the transient volume and may be released to an exhaust system under the natural pumping action of the rotor pair within their housing.

Figure 6 shows a schematic representation of the cross section through an example of a grid as used in the passage between the compressor and the detonation chamber. The grid may be formed of plural elements each having sharp edges. A3 gas flows through spaces between the elements at high velocity, the sharp edges induce substantial micro-scale turbulence of the gas. This is desirable in this context as it ensures that the charge of air/fuel mixture within the detonation chamber has a high level of potential reactivity, which is required for effective detonation of the charge. In the example shown in Figure 6, the grid comprises plural elements of triangular cross-section. As gas passes through spaces between the elements, the sharp edges on the detonation chamber side of the grid cause the gas flow in their close vicinity to be extremely turbulent, thereby ensuring a high level of potential reactivity of the air/fuel mixture.

A description will now be given of the stages in a cycle of operation of the rotary device of Figures 1 to 3. Reference will be made to Figure 7. In the example of the cycle described the rotary device includes a compressor although as explained above this is not always necessary.

Compression begins when the tip of the compressor lobe and the leading edge of the compressor recess are in register with the outer respective edges of the compressor movable containment wall. This coincidence is indicated at zero position on the scale of the angular position of the lobed rotor in Figure 7. A transient compression chamber is formed which is reduced in volume as the compressor rotors continue to rotate.

After 6 degrees of rotation, the charging port begins - 13 -

to open, allowing communication between the compressor transient chamber and the detonation chamber. Air or pre- mixed air/fuel then passes from the transient compressor chamber into the detonation chamber. After a further 20 degrees, the discharge port begins to open, allowing passage of some of the new charge to enter the expander transient chamber. Charging with fresh working fluid then continues for a further 54 degrees, with fresh charge being distributed between the detonation chamber and the slowly enlarging expander transient chamber. As the remaining volume in the compressor transient chamber then reaches zero, the charging port closes and immediately, detonation of the charge is initiated.

The detonation shock wave passes through the entire charge residing in the detonation chamber and through the open discharge port to reach the fresh charge already residing in the expander transient chamber. Immediately behind the shock wave, a rarefaction wave is set up, as the charge remaining in the detonation chamber is expelled from the detonation chamber and into the expander transient chamber by the expansion effect of the detonation process. Here it has immediate effect in urging the further rotation of the expander rotor pair.

20 degrees later, the discharge port closes and the charge, being now effectively contained entirely within the expander transient chamber, expands, giving up its pressure energy which is converted into torque effect on the expander rotors. The expansion continues until the charge is released from the expander transient chamber as the tip of the expander lobed rotor and the leading edge of the expander recessed rotor clear the outer edges of the expander containment wall. At this point, the charge has reached approximately ambient pressure and all the pressure energy generated by the detonation is converted into shaft work.

Immediately after the closure of the discharge port of the detonation chamber, the charging port begins to open to admit fresh charge for the next cycle, compression of which has already begun. Conditions in the detonation chamber at this point are of substantial depression below ambient pressure due to the rarefaction wave established by the detonation process. This means that work being done by the compressor rotors in delivery of the fresh charge is neutralised by virtue of the existence of a negative pressure gradient between the compressor transient chamber and the detonation chamber.

Additional ports (not shown) may be disposed around the periphery of the stator cylinder 3, of similar axial length but reduced in width compared with the port 20 as illustrated. At this stage, these additional ports will be in alignment with the passages 22 in the remaining recesses of the recessed compressor rotor which are not currently in engagement with a lobe. The additional ports will thus allow fresh charge to briefly enter the detonation chamber 4 from the plenum surrounding the compressor rotors while the pressure gradient caused by the rarefaction wave in the detonation chamber 4 exists and before fresh charge is delivered into the detonation chamber 4 from the newly active transient chamber of the compressor rotors. This minimises the work input required for providing the engine with fresh charge and results in a highly efficient engine cycle whose operation results in minimal internal losses of the heat energy released from the fuel contained in the charge.

It is due to the existence of relatively low pressure as a result of the rarefaction wave that the compressor can, in some cases, be unnecessary. In other words, suction caused by the rarefaction wave is sufficient to draw a fresh charge of air/fuel mixture into the detonation chamber.

Figure 8 shows schematically a section view of an example of a rotary device according to a further embodiment of the present invention.

In Figure 8, components common to the embodiment of Figures 1 to 3 are numbered with the same reference numerals. The rotary device of Figure 8 includes radially disposed ports on both the compressor and expander in addition to the axial ports connecting the detonation chamber with the compressor and expander rotor pairs. In an arrangement including radially disposed ports, in addition to or instead of axial ports, a ported disk is provided attached to the delivery end face of one or both of the recessed rotor of each of the rotor pairs. Each disk has one or more ports arranged therein and therefore each of the ports in the disks is located at the delivery end of the rotor recess.

As shown in Figure 8, the rotary device includes a port 34 arranged on an end face of che compressor recess rotor 5. A transfer passage 36 is arranged to provide a route for gases to pass from the transient chamber of the compressor to the detonation chamber 4. Referring to the expaπder, an end face of the expander recess rotor is provided with a port 38 through which the transient chamber of the expander can receive gases from the detonation chamber 4. A transfer passage 40 is arranged to provide a route for gases from the detonation chamber 4 to the transient chamber of the expander via the port 38. Accordingly, in use, in addition to the flow of working gases through the ports 20 and 32 provided in the stator cylinder 3, gases may also be transferred to and from the detonation chamber via the transfer passages 36 and 40 between the respective end faces of the recess rotor 7 of the compressor and the recess rotor 18 of the expander.

The passage 36 which connects the port 34 to the detonation chamber 4 includes turbulence generating means such as a grid, similar in form to that described above with reference to Figure 6. The grid serves to engage the charge gases just prior to entry to the detonation chamber as described above for the axial port arrangement . The ports in the disks of the respective compressor and expander recessed rotors communicate with ports in the corresponding end walls of the rotor housing supporting the compressor and expander rotor pairs. As the rotors rotate, a sliding engagement between the end walls of the housing and the disks arranged on the rotors provides control over the timing of the opening and closing of the ports in the disks. Preferably, for convenience the disks are manufactured as separate components and thereafter are arranged on the end faces of the respective rotors.

With the arrangement shown in Figure 8, in addition to the ports provided in the stator cylinder 3, ports are also provided in appropriate end faces of the rotary device. This enables an increased flow of charge gases to be achieved within the rotary device. It will be appreciated that only axial ports or only radial ports may be provided. In one embodiment, one of the expander and compressor is provided with axial ports and the other with radial ports.

Embodiments of the present invention have been described with particular reference to the examples illustrated. However, it will be appreciated that variations and modifications may be made to the examples described within the scope of the present invention.