GB2598032A

GB2598032A - Engine cylinder

Info

Publication number: GB2598032A
Application number: GB2109159.0A
Authority: GB
Inventors: Richardson Beal Peter
Original assignee: Brayton Cycle Developments Ltd; Brayton Cycle Dev Ltd
Current assignee: Brayton Cycle Developments Ltd; Brayton Cycle Dev Ltd
Priority date: 2021-06-25
Filing date: 2021-06-25
Publication date: 2022-02-16
Anticipated expiration: 2041-06-25
Also published as: WO2022269263A1; GB202109159D0; GB2598032B

Abstract

An engine cylinder 10 comprises a cylinder bore defined by an interior wall 14, and a piston 16 arranged for reciprocation within the cylinder bore. The piston body 16 comprises a piston end 20 and the engine cylinder comprises a cylinder end 22, so that a chamber 24 is defined between the cylinder end 22, the piston end 20 and the interior wall 14. The engine cylinder further comprises at least one valve 26 for inlet and/or outlet of fluid to/from the chamber 24. An air bearing is formed between the piston body 16, 18 and the interior wall 14 of the cylinder bore; and the air bearing is supplied by a flow of air which passes through an interior region 40 of said piston body 16. The bearing air may be supplied via a passage 42 in the piston rod 28, and there may be a further air bearing between the piston rod 28 and a support 46. The piston rod 28 may be connected to a crankshaft by a crosshead.

Description

Engine Cylinder

FIELD OF THE INVENTION

The present invention relates to an engine cylinder, and to an engine including one or more engine cylinders.

BACKGROUND OF THE INVENTION

Reciprocating piston engines are well known and have a wide range of applications in different industrial sectors. There are various types of reciprocating piston engines such as two, four or six stroke engines with spark or compression ignition. Alternative reciprocating piston engines such as the Brayton Cycle Engine disclosed in GB2511652A are also known. Such a Brayton Cycle Engine, as originally introduced by George Brayton in 1872, is known to operate at higher efficiency than spark or compression ignition engines. Furthermore, such a Brayton Cycle Engine can operate with any source of fuel or heat exchanger, such that it can operate with reduced emissions (e.g. using heat from solar power where available, and hydrogen fuel otherwise).

Regardless of the specific reciprocating piston engine type, there is a need to provide a means for lubricating the interface between the piston and the cylinder bore in which the piston reciprocates. Traditionally, such lubrication has been achieved via oil which needs to then be filtered and cooled.

Similarly, there is a need to cool the components of a reciprocating engine (e.g. the piston and intake/exhaust valves) to prevent expansion which could inhibit movement of these components and cause damage to the engine. Traditionally, such cooling has been achieved by a flow of coolant through the engine.

The present invention seeks to overcome, or at least mitigate, one or more problems of

the prior art.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an engine cylinder is provided, the engine cylinder comprising a cylinder bore defined by an interior wall and a piston having a piston body arranged for reciprocation within the cylinder bore; wherein the cylinder is configured such that, in use, an air bearing is formed between the piston body and the interior wall of the cylinder bore; and wherein the air bearing is supplied by a flow of air which passes through an interior region of said piston body.

Having an air bearing supplied by a flow of air which passes through an interior region of the piston body allows the piston body to be supported and/or lubricated by the air bearing across its whole range of movement within the cylinder bore. In other words, the air bearing moves with the piston body, which ensures the piston body is optimally supported and/or lubricated as it reciprocates.

Such an air bearing also provides a seal between the piston body and the interior wall, which reduces or removes the need for additional sealing components such as 0-rings.

Such an air bearing also provides a means of cooling the interior wall of the cylinder bore.

In exemplary embodiments, the piston body comprises a piston end and the cylinder comprises a cylinder end, wherein a chamber is defined between the cylinder end, the piston end and the interior wall.

In exemplary embodiments, the engine cylinder further comprises at least one valve for inlet and/or outlet of fluid to/from the chamber.

In exemplary embodiments, the chamber is configured to contain hot and/or high pressure gas (e.g. gas from a combustion or heat exchanging process).

In exemplary embodiments, said flow of air is cooled prior to passing through the interior region of said piston body.

Cooling the flow of air prior to passing through the interior region (i.e. before being supplied between the piston body and the interior wall of the cylinder bore) improves the cooling properties of the air bearing.

In exemplary embodiments, the piston body comprises an outer radial surface having one or more outlets arranged adjacent the interior wall of the cylinder bore for outflow of air from the interior region of the piston body to said air bearing.

In exemplary embodiments, the interior region of the piston body comprises one or more interior passageways in fluid communication with said one or more outlets.

Such an arrangement of one or more outlets in fluid communication with one or more interior passageways has been found to be effective for providing an air bearing between the piston body and the interior wall of the cylinder bore.

In exemplary embodiments, the one or more outlets comprise a plurality of outlets distributed circumferentially around the outer radial surface.

Having a plurality of outlets distributed circumferentially provides effective support and/or lubrication around the entire circumference of the piston body.

In exemplary embodiments, the one or more outlets comprise a plurality of first outlets distributed circumferentially around the outer radial surface and a plurality of second outlets distributed circumferentially around the outer radial surface, wherein the plurality of first outlets are spaced from the plurality of second outlets in an axial direction of the cylinder bore; optionally, wherein the plurality of first outlets are of different size, shape or configuration to the plurality of second outlets.

Having such a plurality of first outlets spaced from a plurality of second outlets in an axial direction provides effective support and/or lubrication around the entire circumference and along a longitudinal length of the piston body.

In exemplary embodiments, the plurality of first outlets are circumferentially offset from the plurality of second outlets; optionally, wherein each second outlet is equidistant from two first outlets and/or wherein each first outlet is equidistant from two second outlets.

Having the first outlets circumferentially offset from the second outlets reduces the circumferential interval between outlets, which improves the support and/or lubrication of the air bearing around the circumference of the piston body.

In exemplary embodiments, each first outlet defines a passageway with a longitudinal axis perpendicular to the interior wall of the cylinder bore; and/or wherein each second outlet defines a passageway with a longitudinal axis angled relative to the interior wall of the cylinder bore; optionally, wherein each second outlet defines a passageway with a longitudinal axis arranged at an angle in the range of 30 to 60 degrees relative to the interior wall of the cylinder bore; optionally, wherein each second outlet defines a passageway with a longitudinal axis arranged at an angle of around 45 degrees relative to the interior wall of the cylinder bore.

Such an arrangement of first and second outlets has been found to be particularly effective for supporting and/or lubricating the piston body as it moves within the cylinder bore.

In exemplary embodiments, the first outlets are located at a first distance from the piston end and the second outlets are located at a second distance from the piston end; and wherein the second distance is less than the first distance.

In exemplary embodiments, the piston further comprises a piston rod having a first rod end coupled to the piston body and a second rod end for coupling to a crankshaft in order to drive the piston body in a reciprocating motion within the cylinder bore.

Such a piston rod provides a simple means for moving the piston within the cylinder bore.

In exemplary embodiments, the piston rod comprises one or more interior passageways in fluid communication with the one or more outlets via one or more interior passageways of the piston body.

Having one or more interior passageways in the piston rod in fluid communication with the one or more outlets provides a simple means for supplying air through the piston to the outlets for supporting and/or lubricating the piston body.

In exemplary embodiments, the piston rod comprises one or more inlets in fluid communication with the one or more interior passageways of the piston rod for inflow of air to said interior passageways.

Such inlets provide a simple means for supplying air to the air bearing via the interior passageways and one or more outlets.

In exemplary embodiments, the engine cylinder further comprises a support formation for supporting the piston rod, wherein the engine cylinder is configured so that, in use, a second air bearing is formed between the piston rod and the support formation.

Such a support formation ensures that the piston rod (and thus the piston body) stay properly aligned within the cylinder bore.

Having a second air bearing between the piston rod and the support formation ensures that the piston rod is supported and/or lubricated as the piston rod reciprocates within the support formation.

In exemplary embodiments, the support formation comprises an annular groove for receiving a flow of air, wherein the annular groove is located adjacent the piston rod.

Such an annular groove provides a simple means of providing an air bearing between the support formation and the piston rod. Furthermore, the groove being annular ensures that the second air bearing is provided around an entire circumference of the piston rod.

In exemplary embodiments, the piston is axially movable between a first piston position proximal the cylinder end to a second piston position distal the cylinder end, and wherein the annular groove extends axially such that the annular groove is in continual fluid communication with one or more inlets of the piston rod as the piston reciprocates between the first piston position and the second piston position.

Such an arrangement provides a simple means of supplying air from the annular groove of the support formation via the one or more inlets to the interior passageways of the piston rod/body and out of the one or more outlets of the piston body. In other words, such an arrangement provides an effective inlet for the air bearing supplied by a flow of air which passes through an interior region of the piston.

In exemplary embodiments, the piston body comprises one or more heat pipes for cooling at least a portion of the piston body.

It will be understood that each heat pipe is configured to transfer heat from a hot interface to a cold interface through a cycle of vaporisation of liquid at the hot interface and condensation of said liquid at the cold interface, releasing latent heat.

Having one or more heat pipes allows the temperature of the piston body to be controlled. This prevents excessive expansion of the piston body which could inhibit the performance of the air bearing between the piston body and the interior wall of the cylinder bore, and/or inhibit movement of the piston body within the cylinder bore.

In exemplary embodiments, each heat pipe comprises a hot interface proximal the chamber and a cold interface distal the chamber; and wherein the cold interface is located proximal said flow of air through the interior region of the piston body; optionally, wherein each heat pipe is provided within one or more interior passageways of the interior region.

Having a cold interface located proximal said flow of air through the interior region of the piston body allows heat transferred along the heat pipe from the hot interface to the cold interface to be transferred to the flow of air. In other words, this arrangement facilitates cooling of the portion of the piston body proximal the chamber by the flow of air.

According to a second aspect of the invention an engine cylinder is provided, the engine cylinder comprising a cylinder bore defined by an interior wall and a piston body arranged for reciprocation within the cylinder bore, wherein the piston body comprises one or more piston heat pipes for cooling at least a portion of the piston body.

Having one or more heat pipes allows the temperature of the piston body to be controlled. This prevents excessive expansion of the piston body which could inhibit movement of the piston body within the cylinder bore.

In exemplary embodiments, the piston body comprises a piston end and the engine cylinder comprises a cylinder end, wherein the engine cylinder further comprises a chamber defined between the cylinder end, the piston end and the interior wall.

In exemplary embodiments, each heat pipe comprises a hot interface proximal the chamber and a cold interface distal the chamber; optionally, wherein the cold interface is located proximal a flow of air.

Having a hot face proximal the chamber and a cold interface distal the chamber allows the portion of the piston body proximal the chamber to be cooled by transfer of heat to a cooler portion of the piston.

Having the cold interface proximal a flow of air provides a means for transferring heat away from the cold interface of the heat pipe (i.e. heat is transferred to the flow of air).

In exemplary embodiments, the piston body comprises a plurality of piston heat pipes arranged in an array.

Having a plurality of heat pipes arranged in an array provides effective cooling across a wider area of the piston body than would be possible with a single heat pipe.

In exemplary embodiments, the piston body comprises a longitudinal axis and wherein the plurality of piston heat pipes are distributed radially and/or circumferentially with respect to said longitudinal axis; optionally, wherein the plurality of piston heat pipes are arranged in two or more concentric arrays.

Such an arrangement of heat pipes provides effective cooling across a wide area of the piston body.

In exemplary embodiments, the engine cylinder further comprises at least one valve having a valve body, for inlet and/or outlet of fluid to/from the chamber, the valve comprising a valve body.

In exemplary embodiments, the or each valve is a poppet valve comprising a valve body having a head portion and a stem portion coupled to the head portion, and wherein the valve body comprises one or more valve heat pipes which extend from a hot interface at the head portion at least partially along the stem portion to a cold interface; optionally, wherein the engine cylinder comprises a stem support for supporting the stem portion of the or each valve, wherein the engine cylinder is configured such that, in use, an air bearing is formed between the stem support and the stem portion of the valve; and/or optionally, wherein the engine cylinder further comprises a cooling air flow passageway adjacent to the valve stem; optionally, wherein said cooling air flow passageway is provided proximal the cold interface of the valve heat pipe.

It will be understood that each valve heat pipe is configured to transfer heat from the hot interface to the cold interface through a cycle of vaporisation of liquid at the hot interface and condensation of said liquid at the cold interface, releasing latent heat.

Having one or more heat pipes allows the temperature of the valve body to be controlled. This prevents excessive expansion of the valve body which could inhibit opening/closing of the valve.

According to a third aspect of the invention an engine cylinder is provided, the engine cylinder comprising a cylinder bore defined by an interior wall and a piston body arranged for reciprocation within the cylinder bore, wherein the piston body comprises a piston end and the engine cylinder comprises a cylinder end, wherein the engine cylinder further comprises a chamber defined between the cylinder end, the piston end and the interior wall; wherein the engine cylinder further comprises at least one valve having a valve body for inlet and/or outlet of fluid to/from the chamber; and wherein the valve body comprises one or more valve heat pipes for cooling at least a portion of the valve body.

In exemplary embodiments, the or each valve is a poppet valve comprising a valve body having a head portion and a stem portion coupled to the head portion.

In exemplary embodiments, the one or more valve heat pipes extend from a hot interface at the head portion at least partially along the stem portion to a cold interface.

In exemplary embodiments, the engine cylinder comprises a stem support for supporting the stem portion of the or each valve, wherein the engine cylinder is configured such that, in use, an air bearing is formed between the stem support and the stem portion of the 30 valve.

Having an air bearing between the stem support and the stem portion provides two functions of lubricating/supporting the valve stem whilst also providing a flow of air proximal the stem portion for removing heat from the heat pipe.

In exemplary embodiments, the engine cylinder further comprises a cooling air flow passageway adjacent to the valve stem; optionally, wherein said cooling air flow passageway is provided proximal the cold interface of the valve heat pipe.

Having such a cooling air flow passageway provides an effective means for removing heat from the cold interface of the heat pipe, by transfer of heat to air flowing through the cooling air passageway.

According to a fourth aspect of the invention an engine is provided, the engine comprising one or more engine cylinders according to any preceding claim.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a cross-sectional view of an engine cylinder according to an embodiment; Figure 2 is a plan view of a piston body for an engine cylinder according to an embodiment; Figure 3 is a cross-sectional view of a piston body for an engine cylinder according to an embodiment; and Figure 4 is a cross-sectional view of a valve for an engine cylinder according to an embodiment.

DETAILED DESCRIPTION

Referring firstly to Figure 1, an engine cylinder according to an embodiment is indicated at 10. The engine cylinder 10 has a cylinder bore 12 defined by an interior wall 14. The engine cylinder 10 also has a piston 16 having a piston body 18 arranged for reciprocation within the cylinder bore 12.

The piston body 18 has a piston end 20 and the cylinder has a cylinder end 22. A chamber 24 is defined between the cylinder end 22, the piston end 20 and the interior wall 14. The chamber 24 is configured to contain hot and/or high pressure gas (e.g. gas from a combustion process). In the illustrated embodiment, the engine cylinder 10 is part of a Brayton Cycle Engine in which the hot and/or high pressure gas is input to the chamber 24 from a separate combustor and/or heat exchanger external to the engine cylinder 10. In alternative embodiments, combustion takes place within the chamber 24 instead of, or in addition to, the separate combustor/heat exchanger.

It will be understood that the volume of the chamber 24 varies depending on the position of the piston end 20 within the cylinder bore 12. For example, Figure 1 shows the piston end 20 proximal the cylinder end 22, whereas the dotted lines 18A illustrate where the piston body 18 would be at an opposite end of the reciprocal motion (i.e. when the piston body 18 is positioned distal the cylinder end 22). It will be therefore understood that the volume of the chamber 24 increases as the piston end 20 is moved away from the cylinder end 22.

The engine cylinder 10 includes at least one valve 26 for inlet and/or outlet of fluid to/from the chamber 24. For example, two or four valves 26 may be provided depending on the type of engine. In the illustrated embodiment, the engine cylinder 10 is a four stroke cylinder with four valves 26 (e.g. a Brayton Cycle Engine as described in GB2511652A).

In particular, the valves 26 include a charge air intake valve, a compressed charge air outlet valve, a hot gas inlet valve (for input of hot and high pressure gas from said external combustor or heat exchanger) and an exhaust valve. It will be understood that in such an engine charge air enters the chamber 24 via the charge air intake valve on the first stroke, compressed charge air leaves the chamber 24 via the compressed charge air outlet valve on the second stroke (for heating in an external combustor and/or heat exchanger), hot and high pressure gas (from the external combustor/heat exchanger) is input to the chamber 24 via the hot gas inlet valve on the third stroke, and gas is expelled via the exhaust valve on the fourth stroke.

In alternative embodiments (e.g. spark ignition or compressed ignition engines), the engine cylinder 10 only has two valves 26 (e.g. an intake valve and an exhaust valve).

In alternative embodiments, the engine cylinder 10 is a two stroke cylinder or a six stroke cylinder.

The piston 16 has a piston rod 28 with a first rod end 30 coupled to the piston body 18 and a second rod end 32 coupled to a crankshaft (not shown) in order to drive the piston body 18 in a reciprocating motion within the cylinder bore 12. It will be understood that the piston rod 28 may be coupled to the crankshaft via a crosshead arrangement or any other suitable known coupling mechanism.

As will be described in more detail below, the engine cylinder 10 is configured such that, in use, an air bearing is formed between the piston body 18 and the interior wall 14 of the cylinder bore 12. The air bearing is supplied by a flow of air which passes through an interior region 34 of the piston body 18. Having an air bearing supplied by a flow of air which passes through an interior region 34 of the piston body 18 allows the piston body 18 to be supported and/or lubricated by the air bearing across its whole range of movement within the cylinder bore 12. In other words, the air bearing moves with the piston body 18, which ensures the piston body 18 is optimally supported and/or lubricated as it reciprocates. Such an air bearing also provides a seal between the piston body 18 and the interior wall 14, which reduces or removes the need for additional sealing components such as 0-rings. Such an air bearing also provides a means of cooling the interior wall 14 of the cylinder bore 12.

Referring still to Figure 1, the piston body 18 has an outer radial surface 36 with a plurality of outlets 38A, 38B arranged adjacent the interior wall 14 of the cylinder bore 12 for outflow of air from the interior region 34 of the piston body 18 to the air bearing.

In the illustrated embodiment, the interior region 34 of the piston body 18 has an annular interior passageway 40 in fluid communication with the outlets 38A, 38B. In alternative embodiments, a plurality of interior passageways (e.g. one interior passageway per outlet) are provided through the interior region 34.

In the illustrated embodiment, the outlets 38A, 38B are distributed circumferentially around the outer radial surface 36, which provides effective support and/or lubrication around the entire circumference of the piston body 18.

In the illustrated embodiment, there is a group of first outlets 38A distributed circumferentially around the outer radial surface 36 and a group of second outlets 38B distributed circumferentially around the outer radial surface 36. The first outlets 38A are spaced from the second outlets 38B in an axial direction of the cylinder bore 12 (i.e. in the direction of axis A). In other words, the first outlets 38A are located at a first distance from the piston end 20 and the second outlets 38B are located at a second distance from the piston end 20, the second distance being less than the first distance. This arrangement of first and second outlets 38A, 38B provides effective support and/or lubrication around the entire circumference and along a longitudinal length of the piston body 18.

In some embodiments, the first outlets 38A are of different size, shape or configuration to the second outlets 38B. For example, in the illustrated embodiment each first outlet 38A defines a passageway with a longitudinal axis perpendicular to the interior wall 14 of the cylinder bore 12, whereas each second outlet 38B defines a passageway with a longitudinal axis angled relative to the interior wall 14 of the cylinder bore 12 (e.g. at an angle of 45 degrees relative to the interior wall 14 in the illustrated embodiment, or 30 to 60 degrees in alternative exemplary embodiments). Such an arrangement of first and second outlets 38A, 386 has been found to be particularly effective for supporting and/or lubricating the piston body 18 as it moves within the cylinder bore 12.

In exemplary embodiments, the first outlets 38A are circumferentially offset from the second outlets 386. For example, each second outlet 386 may be equidistant from two first outlets 38A and/or each first outlet 38A may be equidistant from two second outlets 385. Having the first outlets 38A circumferentially offset from the second outlets 385 reduces the circumferential interval between outlets 38A, 386, which improves the support and/or lubrication of the air bearing around the circumference of the piston body 18.

In alternative embodiments, only a single group of outlets are provided. For example, the piston body 18 of Figure 3 includes a single group of outlets 38A distributed circumferentially around the outer radial surface 36.

Referring again to Figure 1, the piston rod 28 has an interior passageway 42 in fluid communication with the outlets 38A, 386 via the interior passageway 40 of the piston body 18. In alternative embodiments, a plurality of interior passageways 42 may be provided through the piston rod 28 (e.g. one interior passageway per outlet 38A, 385).

The piston rod 28 also has a plurality of inlets 44 in fluid communication with the interior passageway 42 of the piston rod 28 for inflow of air to the interior passageways 40, 42. In alternative embodiments, only a single inlet 44 is provided.

The engine cylinder 10 also has a support formation 46 for supporting the piston rod 28.

Such a support formation 46 ensures that the piston rod 28 (and thus the piston body 18) stay properly aligned within the cylinder bore 12.

The engine cylinder 10 is configured so that, in use, a second air bearing is formed between the piston rod 28 and the support formation 46. In alternative embodiments, a different bearing type is provided between the piston rod 28 and the support formation 46 (e.g. a lubricated plain bearing).

In the illustrated embodiment, the support formation 46 has an annular groove 48 for receiving a flow of air. The annular groove 48 is located adjacent the piston rod 28. Such an annular groove 48 provides a simple means of providing an air bearing between the support formation 46 and the piston rod 28. Furthermore, the groove 48 being annular ensures that the second air bearing is provided around an entire circumference of the piston rod 28.

As has been described above, the piston 16 is axially movable between a first piston position proximal the cylinder end 22 to a second piston position distal the cylinder end 22. The annular groove 48 extends axially such that the annular groove 48 is in continual fluid communication with the inlets 44 of the piston rod 28 as the piston 16 reciprocates between the first piston position and the second piston position. Such an arrangement provides a simple means of supplying air from the annular groove 48 of the support formation 46 via the one or more inlets 44 to the interior passageways 40, 42 of the piston rod/body and out of the one or more outlets 38A, 38B of the piston body 18.

To complete the air flow path, an air channel 50 is provided between the annular groove 48 and an external air source (not shown), such as an air pump or compressor. In other words, air flows from the external air source, through air channel 50, around annular groove 48, through inlets 44, through interior passageway 42, through interior passageway 40, and out through the outlets 38A, 38B.

It will be understood that as well as supplying the air bearing between the piston body 18 and the interior wall 14, the flow of air through air channel 50, annular groove 48, inlets 44, and interior passageways 42, 40 also cools the piston body 18 and piston rod 28 by transfer of heat to said flow of air.

In exemplary embodiments, the flow of air supplied by the external air source is cooled prior to entering air channel 50. This improves the cooling properties of the air bearing.

Referring now to Figures 1 and 2, the piston body 18 has a plurality of heat pipes 52A, 52B, 52C, 52D for cooling a portion of the piston body 18 proximal the piston end 20 (i.e. a "crown" of the piston 16). It will be understood that each heat pipe 52A, 52B, 52C, 52D is configured to transfer heat from a hot interface 54A to a cold interface 54B through a cycle of vaporisation of liquid at the hot interface 54A and condensation of said liquid at the cold interface 54B, releasing latent heat. Such heat pipes 52A, 52B, 52C, 52D allow the temperature of the piston body 18 to be controlled. This prevents excessive expansion of the piston body 18 which could inhibit the performance of the air bearing between the piston body 18 and the interior wall 14 of the cylinder bore, and/or inhibit movement of the piston body within the cylinder bore.

In the illustrated embodiment, each hot interface 54A is located proximal the chamber 24 and each cold interface 54B is located distal the chamber 24 (i.e. within the interior region 34 of the piston body 18). The cold interface 54B is located proximal the flow of air through the interior region 34 (i.e. through interior passageway 40). Having cold interfaces 546 located proximal said flow of air allows heat transferred along the heat pipes 52A, 52B, 52C, 52D from the hot interfaces 54A to the cold interfaces 54B to be transferred to the flow of air. In other words, this arrangement facilitates cooling of the portion of the piston body 18 proximal the chamber 24 by the flow of air.

Referring to Figure 2, potential locations of the heat pipes 52A, 526, 52C, 52D are illustrated in plan view. A central heat pipe 52A is provided at a centre point (i.e. on a longitudinal axis) of the piston body 18. Surrounding the central pipe 52A are three concentric arrays 526, 52C, 52D of heat pipes. The heat pipes of the concentric arrays 526, 52C, 52C are distributed radially and circumferentially with respect to a longitudinal axis of the piston body 18.

In alternative embodiments, a different array of heat pipes may be provided in the piston body 18. For example, while Figure 2 shows 24 heat pipes per concentric array 526, 52C, 52D a greater or smaller number of heat pipes may be provided. Similarly, one or more of the concentric arrays 52B, 52C, 52D may be removed (e.g. the inner array 52B). In alternative embodiments, the heat pipes are distributed in an asymmetric arrangement across the crown of the piston body 18.

Regardless of the particular arrangement of heat pipes 52A, 526, 52C, 52D, the plurality of heat pipes provide effective cooling across a wide area of the piston body 18.

It will also be understood that the length of heat pipes 52A, 526, 52C, 52D may also vary.

For example, the dotted lines shown in Figures 1 and 3 depict potential different length/positions of the heat pipes.

In the embodiments illustrated in Figures 1 and 3, the piston body 18 is formed in a two part structure. In particular, the piston body 18 is formed of a crown portion 55 and a skirt portion 56 connected together (e.g. via weld bead 58, or other suitable means). Having such a two part construction provides a simple way of constructing the interior passageway 40 of the piston body (e.g. by casting or machining part of the interior passageway 40 into the facing sides of the crown portion 54 and skirt portion 56.

While the piston body of Figure 3 shows a weld bead 58 which protrudes beyond the outer radial surface 36, it will be understood that such a weld bead 58 would be machined to give a smooth outer radial surface 36 (as shown in Figure 1) prior to use.

In alternative embodiments, the piston body 18 is produced as a single piece (i.e. the crown portion 54 and skirt portion 56 are integrally formed). For example, the piston body 18 may be produced via 3D printing, or the interior passageway 40 may be machined from a solid piston body 18.

In the illustrated embodiments, the piston rod 28 and the skirt portion 56 are produced as a single piece (i.e. they are integrally formed). In alternative embodiments, the piston rod 28 and skirt portion 56 are produced as separate pieces and are welded or otherwise secured together.

Referring now to Figures 1 and 4, each valve 26 is a poppet valve with a valve body 60 having a head portion 62 and a stem portion 64 coupled to the head portion 62. The valve 26 also includes a valve seat 66 and the valve body 60 is moveable relative to the valve seat 66 such that the valve is closed when the head portion 62 is in contact with the valve seat 66, and the valve is open when the head portion 62 is spaced apart from the valve seat 66. It will be understood that the valve body 60 is biased towards the closed position by a spring 68 and is periodically urged towards the open position against the force of the spring 68 by a cam or other actuating member (e.g. an electronic control means).

At least one of the valves 26 has a valve heat pipe 70 which extends from a hot interface 72A at the head portion 62 at least partially along the stem portion 64 to a cold interface 72B (as depicted in Figure 4). In some embodiments, all of the valves 26 have such a heat pipe structure. In alternative embodiments, some of the valves 26 have such a heat pipe structure (e.g. inlet and exhaust valves) while other valves 26 have a different construction.

It will be understood that each valve heat pipe 70 is configured to transfer heat from the hot interface 72A to the cold interface 72B through a cycle of vaporisation of liquid at the hot interface and condensation of said liquid at the cold interface, releasing latent heat.

Having one or more heat pipes 70 allows the temperature of the valve body 60 to be controlled. This prevents excessive expansion of the valve body 60 which could inhibit opening/closing of the valve 26.

In the valve 26 illustrated in Figure 4, the engine cylinder 10 has a cooling air flow passageway 74 adjacent to the stem portion 64. In particular, the cooling air flow passageway 74 is provided proximal the cold interface 72B of the valve heat pipe 70. Having such a cooling air flow passageway 74 provides an effective means for removing heat from the cold interface 72B of the heat pipe 70, by transfer of heat to air flowing through the cooling air passageway 74.

The cooling air flow passageway 74 is in fluid communication with an air supply channel 76 coupled to an external air source (e.g. an air pump or compressor).

In exemplary embodiments, the flow of air supplied by the external air source is cooled prior to entering air supply channel 76. This improves the cooling properties of the cooling air flow passageway 74 (e.g. in comparison to a system in which ambient air is used).

In the valve 26 illustrated in Figure 4, the engine cylinder 10 has a stem support 78 for supporting the stem portion 64. The engine cylinder 10 is configured such that, in use, an air bearing is formed between the stem support 78 and the stem portion 64 of the valve 26.

In particular, the stem support 78 includes an annular chamber 80 in fluid communication with the air supply channel 76. In this way, air flowing along the air supply channel 76 and around the annular chamber 80 acts as an air bearing for support and/or lubrication of the stem portion 64.

In the illustrated embodiment, the air supply channel 76 has two branches 76A, 76B for supplying the cooling air flow passageway 74 and annular chamber 80 respectively. In alternative embodiments, two separate air supply channels are provided.

In alternative embodiments, the cooling air flow passageway 74 is omitted and instead the air flow through annular chamber 80 is used to transfer heat from the heat pipe 70 (as well as support and/or lubricate the stem portion 64).

In alternative embodiments, the or each valve 26 is a sleeve valve or rotary valve.

While Figures 1 to 4 only illustrate an engine cylinder or parts thereof, it will be understood that an engine including one or more of the described engine cylinders 10 can be constructed. It will also be understood that such an engine may include other standard engine components which are not depicted in the figures, such as fuel injectors, spark plugs, cam shafts, crank shafts etc. In particular, the engine cylinder 10 of the illustrated embodiment is configured for use in a Brayton Cycle Engine in which hot and/or high pressure gas is input to the chamber 24 from a separate combustor or heat exchanger external to the engine cylinder 10 (e.g. as described in GB2511652A).

Although the invention has been described in relation to one or more embodiments, it will be appreciated that various changes or modifications can be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. An engine cylinder comprising a cylinder bore defined by an interior wall and a piston having a piston body arranged for reciprocation within the cylinder bore; wherein the piston body comprises a piston end and the engine cylinder comprises a cylinder end, wherein the engine cylinder further comprises a chamber defined between the cylinder end, the piston end and the interior wall; wherein the engine cylinder further comprises at least one valve for inlet and/or outlet of fluid to/from the chamber; wherein the engine cylinder is configured such that, in use, an air bearing is formed below the chamber between the piston body and the interior wall of the cylinder bore; and wherein the air bearing is supplied by a flow of air which passes through an interior region of said piston body.
2. An engine cylinder according to claim 1, wherein the piston body comprises an outer radial surface having one or more outlets arranged adjacent the interior wall of the cylinder bore for outflow of air from the interior region of the piston body to said air bearing.
3. An engine cylinder according to claim 2, wherein the interior region of the piston body comprises one or more interior passageways in fluid communication with said one or more outlets.
4. An engine cylinder according to claim 2 or 3, wherein the one or more outlets comprise a plurality of outlets distributed circumferentially around the outer radial surface.
5. An engine cylinder according to claim 4, wherein the one or more outlets comprise a plurality of first outlets distributed circumferentially around the outer radial surface and a plurality of second outlets distributed circumferentially around the outer radial surface, wherein the plurality of first outlets are spaced from the plurality of second outlets in an axial direction of the cylinder bore; optionally, wherein the plurality of first outlets are of different size, shape or configuration to the plurality of second outlets.
6. An engine cylinder according to claim 5, wherein the plurality of first outlets are circumferentially offset from the plurality of second outlets; optionally, wherein each second outlet is equidistant from two first outlets and/or wherein each first outlet is equidistant from two second outlets.
7. An engine cylinder according to claim 5 or 6, wherein each first outlet defines a passageway with a longitudinal axis perpendicular to the interior wall of the cylinder bore; and/or wherein each second outlet defines a passageway with a longitudinal axis angled relative to the interior wall of the cylinder bore; optionally, wherein each second outlet defines a passageway with a longitudinal axis arranged at an angle in the range of 30 to 60 degrees relative to the interior wall of the cylinder bore; optionally, wherein each second outlet defines a passageway with a longitudinal axis arranged at an angle of around 45 degrees relative to the interior wall of the cylinder bore.
8. An engine cylinder according to any of claims 5 to 7, wherein the first outlets are located at a first distance from the piston end and the second outlets are located at a second distance from the piston end; and wherein the second distance is less than the first distance.
9. An engine cylinder according to any of claims 2 to 8, wherein the piston further comprises a piston rod having a first rod end coupled to the piston body and a second rod end for coupling to a crankshaft in order to drive the piston body in a reciprocating motion within the cylinder bore.
10. An engine cylinder according to claim 9, wherein the piston rod comprises one or more interior passageways in fluid communication with the one or more outlets via one or more interior passageways of the piston body.
11. An engine cylinder according to claim 10, wherein the piston rod comprises one or more inlets in fluid communication with the one or more interior passageways of the piston rod for inflow of air to said interior passageways.
12. An engine cylinder according to any of claims 9 to 11, further comprising a support formation for supporting the piston rod, wherein the engine cylinder is configured so that, in use, a second air bearing is formed between the piston rod and the support formation.
13. An engine cylinder according to claim 12, wherein the support formation comprises an annular groove for receiving a flow of air, wherein the annular groove is located adjacent the piston rod.
14. An engine cylinder according to claim 13, wherein the piston is axially movable between a first piston position proximal the cylinder end to a second piston position distal the cylinder end, and wherein the annular groove extends axially such that the annular groove is in continual fluid communication with one or more inlets of the piston rod as the piston reciprocates between the first piston position and the second piston position.
15. An engine cylinder according to any preceding claim, wherein the piston body comprises one or more heat pipes for cooling at least a portion of the piston body.
16. An engine cylinder according to claim 15, wherein each heat pipe comprises a hot interface proximal the chamber and a cold interface distal the chamber; and wherein the cold interface is located proximal said flow of air through the interior region of the piston body; optionally, wherein each heat pipe is provided within one or more interior passageways of the interior region.
17. An engine cylinder comprising a cylinder bore defined by an interior wall and a piston body arranged for reciprocation within the cylinder bore, wherein the piston body comprises a piston end and the engine cylinder comprises a cylinder end, wherein the engine cylinder further comprises a chamber defined between the cylinder end, the piston end and the interior wall; wherein the engine cylinder further comprises at least one valve for inlet and/or outlet of fluid to/from the chamber; and wherein the piston body comprises one or more piston heat pipes for cooling at least a portion of the piston body.
18. An engine cylinder according to claim 17, wherein each heat pipe comprises a hot interface proximal the chamber and a cold interface distal the chamber; optionally, wherein the cold interface is located proximal a flow of air.
19. An engine cylinder according to claim 17 or 18, wherein the piston body comprises a plurality of piston heat pipes arranged in an array.
20. An engine cylinder according to claim 19, wherein the piston body comprises a longitudinal axis and wherein the plurality of piston heat pipes are distributed radially and/or circumferentially with respect to said longitudinal axis; optionally, wherein the plurality of piston heat pipes are arranged in two or more concentric arrays.
21. An engine cylinder according to any preceding claim, wherein the or each valve is a poppet valve comprising a valve body having a head portion and a stem portion coupled to the head portion, and wherein the valve body comprises one or more valve heat pipes which extend from a hot interface at the head portion at least partially along the stem portion to a cold interface; optionally, wherein the engine cylinder comprises a stem support for supporting the stem portion of the or each valve, wherein the engine cylinder is configured such that, in use, an air bearing is formed between the stem support and the stem portion of the valve; and/or optionally, wherein the engine cylinder further comprises a cooling air flow passageway adjacent to the valve stem; optionally, wherein said cooling air flow passageway is provided proximal the cold interface of the valve heat pipe.
22. An engine cylinder comprising a cylinder bore defined by an interior wall and a piston body arranged for reciprocation within the cylinder bore, wherein the piston body comprises a piston end and the engine cylinder comprises a cylinder end, wherein the engine cylinder further comprises a chamber defined between the cylinder end, the piston end and the interior wall; wherein the engine cylinder further comprises at least one valve having a valve body for inlet and/or outlet of fluid to/from the chamber; wherein the or each valve is a poppet valve comprising a valve body having a head portion and a stem portion coupled to the head portion; and wherein the valve body comprises one or more valve heat pipes for cooling at least a portion of the valve body, which extend from a hot interface at the head portion at least partially along the stem portion to a cold interface.
23. An engine cylinder according to claim 22, wherein the engine cylinder comprises a stem support for supporting the stem portion of the or each valve, wherein the engine cylinder is configured such that, in use, an air bearing is formed between the stem support and the stem portion of the valve.
24. An engine cylinder according to claim 22 or 23, wherein the engine cylinder further comprises a cooling air flow passageway adjacent to the valve stem; optionally, wherein said cooling air flow passageway is provided proximal the cold interface of the valve heat pipe.
25. An engine comprising one or more engine cylinders according to any preceding claim.