GB2610667A

GB2610667A - Pressure vessel, use and method of manufacture

Info

Publication number: GB2610667A
Application number: GB2203659.4A
Authority: GB
Inventors: Martin John Kemp Ronald
Original assignee: XCIENCE Ltd
Current assignee: XCIENCE Ltd
Priority date: 2021-09-09
Filing date: 2022-03-16
Publication date: 2023-03-15
Anticipated expiration: 2042-03-16
Also published as: GB202203659D0; GB2610667B

Abstract

A pressure vessel, comprising: a sandwich structure arranged comprising: two or more skin layers 102, 104, 210; and one or more filler layers, each filler layer 208 being arranged between two of the skin layers. In some embodiments, the filler layer is formed of a foam, corrugated structure or lattice structure. The pressure vessel maybe used in a vehicle to store fuel

Description

PRESSURE VESSEL USE AND METHOD OF MANUFACTURE

Field of the invention

The present invention relates to a pressure vessel, in particular, to a pressure vessel for storing fluids under pressure for transport applications.

Background

In recent years, hydrogen, biogas, and liquid ammonia have emerged as promising renewable energy source candidates. In particular, in the transportation industry, where they offer improved refuelling times and reduced weight over existing battery technologies. Portable power generation is an additional area of development.

Hydrogen can be stored in the solid state using adsorbing or absorbing materials, in the liquid state at cryogenic temperatures (and at pressure), or in the gaseous state at high pressure (the IS014687-2 and I5012619-1:2014 define a gauge pressure of 700bar). Ammonia is generally stored in the liquid state. It may however also be stored as a gas.

Fig. 1A shows a conventional Type IV pressure vessel 100 known in the prior art. The pressure vessel 100 comprises an inner liner 102 (shown in dashed lines) overwrapped by an outer skin 104. The inner liner 102 of the pressure vessel defines a volume 106 in which fluid is contained (e.g., a liquid or a gas). Fig. 1B is a sectional view along AA', illustrating the double-wall structure in the conventional pressure vessel 100. The inner liner 102 is non-structural and serves as a barrier to contain the gas; whereas, the outer skin 104 is structural and serves to withstand the internal overpressure. Conventionally, the pressure vessels 100 are capped at each end with respective hemispherical shells (not shown).

In industry, pressure vessels of the configuration illustrated in Fig. 1A and 1B, are denoted "Type III" or "Type IV". In type III pressure vessels, the inner liner 102 is metallic-based (e.g., an aluminium alloy) and the outer skin 104 is typically a diagonally wrapped fibre-reinforced composite. In Type IV cylinders, the inner liner 102 is a thermoplastic and the outer skin 104 is typically a fibre-reinforced composite. The outer skin 104 in each may instead be metallic. Such fibre-reinforced overwrap layers are normally made using a filament winding process, which is generally applicable only to simple geometries, such as cylinders, spheres and tori. These cylindrical shaped pressure vessels are cumbersome to handle, have a tendency to roll and are relatively inefficient at filling space. These properties are undesirable for use in mobile and transportation applications, such as in road, rail, marine and airborne vehicles. Another pressure vessel variant is the Type V cylinder, which consists of a single outer skin, typically a fibre-reinforced composite. Type V pressure vessels therefore do not include a (thermoplastic) inner liner.

Fluid storage efficiency, especially in the transportation sector, is crucial. There is a need for a pressure vessel with improved volumetric efficiency (quantity of fluid stored per unit volume) and/or gravimetric efficiency (quantity of fluid stored per unit mass).

Summary of the Invention

It is an object of the present invention to provide a new and useful pressure vessel.

The invention provides a pressure vessel, comprising: a sandwich structure comprising: two or more skin layers; and one or more filler layers, each filler layer being arranged between two of the skin layers.

The pressure vessel may further comprise an inner liner, wherein the sandwich structure is arranged around the inner liner and at least partially covering it.

The sandwich structure may completely cover the inner liner.

Each of the one or more filler layers may comprise at least one of: a foam; a corrugated structure; and/or a lattice structure.

The thickness of at least one of the one or more filler layers may be non-uniform (i.e., not constant), or, uniform (i.e., constant).

The external shape of the outermost filler layer may be corrugated and the external shape of the pressure vessel is corrugated. This shape may be particularly stable to rolling.

The inner liner may be tubular in shape.

The strength of at least one of the one or more filler layers may vary spatially depending on the shape of the inner liner (which, through its shape, defines a spatially varying stress-strain profile). The one or more filler layers may be stronger in regions of higher stress-strain. In an example, the variation in strength is achieved through a variation in filler layer density. That is, at least one of the one or more filler layers may have a density that varies spatially around the periphery of the innermost skin. More specifically, the density of at least one of the one or more filler layers may increase close to the edges of the pressure vessel, and/or increases close to the centre line of each face of the pressure vessel.

The shape of the pressure vessel may be any one of: an ellipsoid (e.g., a pill, or oblate spheroid), a cuboid or a rectangular cuboid. Cuboids are intended to cover cuboidal shape with and without rounded corners and/or edges. Ellipsoidal pressure vessels would be advantageous where improved aerodynamic properties is required, for instance, on a drone. The shape of the pressure vessel can be achieved through variation in the thickness of the sandwich structure around the periphery of the innermost skin. The shape of the pressure vessel may be optimised for a given application.

In some examples, the inner liner is shaped to conform to a predetermined space, or optimised in shape to facilitate manufacturing (e.g., having appropriate radii of curvature to allow filament winding), and the thickness of the sandwich structure is uniform.

The inner liner may comprise at least one substantially planar side, which allows stacking. The sandwich structure may be arranged at least on this substantially planar side. In some examples, the sandwich structure is applied completely around said inner liner.

The inner liner may comprise an internal network structure to further reinforce the pressure vessel.

The pressure vessel may be comprised from an assembly of inner liner sections. In particular, at least one inner liner section and at least two cap sections joined together with one another.

Each of the one or more skin layers may comprise a resin-infused fibre cloth, filament wound reinforced composite, aluminium alloy, titanium alloy, or other metallic alloy.

Each of the one or more filler layers may be comprised from an aerogel (e.g., based on silica or other material), an aramid material, phenolic resin, aluminium alloy or titanium alloy(or other metallic alloy), polyurethane, polyetherimide, polymethyacrylamide, wood or combinations thereof. Other polymeric, metallic, ceramic or biomaterial materials are possible. The fillers may be structural and/or thermally insulating, such that the sandwich structure provide both mechanical reinforcement and thermal insulation.

In a second aspect, there is provided use of the pressure vessel described above in a vehicle to store fuel. The fuel may be liquid ammonia, gaseous ammonia, liquid hydrogen or gaseous hydrogen, liquid or gaseous methane, biogas, natural gas, propane, derivatives of the above, or any other fluid..

In a third aspect, there is provided a method for manufacturing the pressure vessel described above, comprising: applying a first skin around a surface based on the external shape of the surface; applying a filler layer onto the first skin; applying a second skin around the filler layer based on the external shape of the filler layer. The surface may form an inner liner of the pressure vessel, which is prepared in advance.

The first and second skin may be applied using filament winding if the external shape of the surface (e.g., inner liner) and the external shape of the filler layer are respectively tubular, toroidal, ellipsoidal, oblate spheroid, or spherical; otherwise, the first and second skin are applied using at least one of the following: braiding or knitting of a fabric, infusing of the braiding or knitting with resin and curing of the resin infused braiding or knitting; compression moulding of a woven resin pre-impregnated fabric and curing of the resin pre-impregnated fabric; automated fibre placement, and/or hot pressing of a woven resin pre-impregnated fabric onto the inner liner and curing.

In a fourth aspect, there is provided a method of manufacturing a (metallic) pressure vessel, as described above, the method comprising: arranging a metallic filler layer between a metallic first skin and a metallic second skin, wherein one or more spacers are arranged between each opposing side of the filler layer to separate the metallic filler in those regions from said skins; supplying a gas between the first and second skin at a pressure and temperature at which: the filler layer superplastically deforms, and diffusion bonds to the first and second skins in regions of contact with said skins.

The pressure vessel according to the third and fourth aspect may be fabricated by assembling and sealingly joining two halves of the pressure vessel together. Each half of the pressure vessel may be sealingly joined together by any of one: welding of the first and second skins; or diffusion bonding of the first and second skins. The pressure vessels may be sealingly joined by welding, adhesive bonding and the like.

The pressure vessel described herein may have one or more of the following advantages: * Improved volumetric efficiency (compared to conventional pressure vessels) through high pressure operation; * Improved gravimetric efficiency (compared to conventional pressure vessels) through high pressure operation; * The opportunity to design non-standard (conformal) external pressure vessel shapes to more efficiently fill space; * Improved scalability for manufacturing larger pressure vessels (the sectional approach); and * The provision of a thermally insulating, mechanically reinforcing layer in the overwrap.

Brief Description of the Drawings

Some embodiments of the invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1A and 1B show an exemplary pressure vessel known in the prior art; Figure 2 shows a cross-sectional view of a pressure vessel with a reinforced overwrap.

Figure 3 shows a cross-sectional view of a reinforced overwrap.

Figure 4A and 4B show simulated displacement and stress results for a hexagon-incross-section pressure vessel, when internally over-pressurised.

Figure 5 shows a cross-sectional view of a reinforced overwrap with spatially varying reinforcement.

Figure 6 shows a cross-sectional view of a pressure vessel with a corrugated exterior.

Figure 7A and 7B show a top and end view of a substantially planar pressure vessel. Figure 8A shows a top-view of a substantially planar pressure vessel with reinforced overwrap.

Figure 8B shows an end view of a substantially planar pressure vessel with reinforced overwrap.

Figure 9A and 9B show a sectional inner liner.

Figure 10A to 10D show internal network structures.

Figure 11 shows an internal network structure.

Figure 12 shows a schematic illustration of an assembly from which a sandwich structure, formed by a superplastic and diffusion bonding process, is made.

Detailed Description of Preferred Embodiments

Conventionally, the thickness of the outer skin 104 is set according to the gauge pressure in Type III, Type IV, or Type V pressure vessels. With larger gauge pressures, thicker outer skins 104 are required to avoid failure/bursting. Problems with this approach include: * Material costs of the outer skin material (e.g., carbon fibre composite) are high; * it is relatively difficult to apply thick layers of the outer skin 104 onto the pressure vessel liner 102; and * increasing the outer skin 104 thickness generally decreases the gravimetric and/or volumetric storage efficiency of the pressure vessel.

The present invention provides a pressure vessel, which at least partially solves the

aforementioned problems in the prior art.

Figure. 2 shows a pressure vessel 200 according to Figure. 1A and Figure. 1B, further comprising a filler layer 208 and outermost layer 210 arranged around outer skin 104. It will be understood that, although the skin 104 is referred to as an outer skin 104 (as in a conventional Type IV pressure vessel), the outer skin 104 may also be described as an inner skin, given that the sandwich structure 212 described herein comprises at least one further skin 306, 210. The outer skin 104 and outermost layer 210 may comprise substantially the same material. The filler layer 208 is arranged around the outer skin 104 and the outermost layer 210 is arranged around the filler layer 208. It will be understood that the outermost layer 210 refers to the outermost skin of the pressure vessel. The outer skin 104, filler layer 208 and outermost layer 210 form a "sandwich structure" 212. With that in mind, the filler layer 208 may be referred to as the "core" of the sandwich structure. The sandwich structure is also referred to herein as a reinforced overwrap. In some examples, the outermost layer 210 may be substantially similar in shape to the inner liner 102. In other examples, the shape of the outermost layer 210 and inner liner 102 may differ.

It should be appreciated that the pressure vessel 200 in any of the examples described herein may be linerless (i.e., it may be a Type V pressure vessel). . If the pressure vessel is, for example, Type IV, the pressure vessel will comprise an inner liner 102 and the "sandwich structure" 212 is arranged around the inner liner. In a linerless pressure vessel, the outer skin 104 of a conventional Type IV pressure vessel (Figure 1A, B) may be referred to as an inner skin. Nanomaterial additives may be added to one or more layers in the sandwich structure 212 in a linerless pressure vessel 200. These additives prevent gas egress from the pressure vessel (i.e., they increase the impermeability of the sandwich structure to gas), such that the functionality of the inner liner 102 is still provided.

It is envisaged that the pressure vessel 200 can be used to store hydrogen, but other fluids may be stored, for example, nitrogen, oxygen, natural gas, ammonia, biogas, methane gas, liquid hydrogen, liquid nitrogen, liquid nitrogen, liquid natural gas, liquid ammonia, liquid methane or liquid biogas. The fluid may be stored at high pressure, such as 300bar, 350bar, 500bar or 700bar. The term "fluid" includes liquids and gases.

The thickness of the filler layer 208 in the sandwich structure 212 is preferably, although not necessarily, greater than the outermost layer 210 and outer skin 104. During internal over-pressurisation, the outermost layer 210 and outer skin 104 provide the majority of support against in-plane and bending loads, whereas the filler layer 208 provides support against shear loads and helps to transmit the loads between layers 210, 104 effectively.

An advantage of the sandwich structure 212 is its improved flexural stiffness compared to a single laminate sheet of equal weight. Preferably, but not necessarily, the filler layer 208 is light-weight, such that flexural stiffness is enhanced without significant increase in weight. The filler layer 208 may also generally be less dense than the outermost layer 210 and outer skin 104. Layers 104, 210 may be referred to as "skins" because: they are generally thinner compared to the filler layer; and/or they substantially cover a neighbouring layer (e.g., outer skin 104 covers inner liner 102; outermost skin 210 covers filler layer 208).

The outermost layer 210 and outer skin 104 may comprise a relatively stiff material (compared with the filler layer 208). For example: a filament-wound fibre reinforced composite (FRC), or a resin-infused fibre cloth. The filament may comprise carbon fibre (e.g., pitch-based, or polyacrylonitrile (PAN-based) carbon fibre, or T1000), glass, aramid or boron fibres. The resins may comprise any of epoxies, cyanate esters, polyurethane, polyester, vinyl ester, phenolics, furans or thermoplastics such as, polyamides or polypropylene. In other examples, the outermost layer 210 and outer skin 104 are metallic-based (e.g., an aluminium or titanium alloy).

In order for the filler layer 208 to be less dense than the outer skin 104 and outermost layer 210, the filler layer 208 may be comprised from a less dense material than layers 104, 210 and/or the filler layer may adopt an (more) open-structure. Example structures include: a honeycomb (or other lattice) structure; a corrugated structure; and/or a foam.

In specific examples, the filler layer 208 comprises: * a honeycomb (or other lattice) structure of an aramid material (for example, Nomex (RTM)), a phenolic resin, a ceramic such as silica aerogel, or a metal such as a titanium or aluminium alloy; * a corrugated core of an aluminium alloy (or other metallic alloy); * a metallic foam (e.g., an aluminium alloy), a polyurethane foam, a Pcylyetherimide (PE) foam, a microporous foam of silica, glass or polymer aerogel, or a foam of Polymethylacrylamide (PMI, e.g., Rohacell (RTM)); or * biomaterial, such as wood (e.g., balsa).

Turning now to Figure 3, the sandwich structure 300 may comprise more than one filler layer 308, an outermost layer 210, an outer skin 104 and one or more intermediate layers 306 arranged between the outermost layer 210 and outer skin 104, alternating with the filler layers 308. The intermediate layer 306 is a skin, like the outer skin 104 and outermost layer 210. The sandwich structure 300 may therefore constitute a stack of the sandwich structures 212 (also referred to herein as a "multi-stack" 212) shown in Figure 2, without duplication of the "intermediate" layers 306. The increased number of intermediate layers 306 increases the flexural strength of the sandwich structure 300 (at the expense of additional weight). Such sandwich structures 300 may find use in high pressure vessels (700bar gauge pressure or more). The intermediate layer may also be a filament-wound fibre reinforced composite (FRC), or a resin-infused fibre cloth, as set out above.

Referring now to Figure 4A, the radial deformation of a pressure vessel 400, with hexagonal cross-section, is shown, when internally over-pressurised. The original "hexagonal" shape of the pressure vessel, prior to over-pressurisation, is shown for clarification. The results were calculated via a finite element analysis (FEA) simulation tool. The results show that along each edge 408, the radial deformation is in the negative sense (i.e., net deformation inwardly towards the axial centre of the pressure vessel 400), whereas along the centre line (parallel to the longitudinal axis of the pressure vessel 400) of each face, the radial deformation is in the positive sense (i.e., net deformation outwardly away from the axial centre of the pressure vessel 400). The radial deformation varies continuously between each edge and centre line. Pressure vessels 400 having a non-circular cross-section (or non-spherical shape) have a tendency to "bow out" into a more-circular shape, when they are internally over-pressurised.

Figure 4B shows the Von Mises stress corresponding to the radial deformations shown in Figure 4A. The stresses were also calculated using a FEA tool. The results show that the Von Mises stress is greatest along each edge 408 and along the centre line of each face of the pressure vessel 400. These maxima correspond with the maximum positive and negative radial deformations shown in Figure 4A. The Von Mises stress varies continuously between these maxima. The teaching of these results applies to other pressure vessels of non-circular cross-section (for example, square, rectangular etc.), as the skilled reader would appreciate.

It has been shown that stress and strain are non-uniform in non-circular cross-sectioned pressure vessels. Correspondingly, it is desirable for the sandwich structure 212, 300 to provide corresponding non-uniform reinforcement (around the pressure vessel), such that the pressure vessel is preferentially reinforced in regions of higher stress and strain. For example, to preferentially reinforce the pressure vessel 400 along its edges/corners 408 or along the centre line of each face, as taught in Figure 4A and 4B.

The use of non-circular cross-sectioned pressure vessels is primarily (although not exclusively) motivated by using space more efficiently. For example, pressure vessels can be designed with a shape that conforms in shape to a predetermined space during operation. This is especially important in the transportation industry, where available space to store fluids (such as fuels) is at a premium. As has already been noted, conventional cylindrical pressure vessels require external supports (e.g., holders) to prevent rolling, which is undesirable. Conversely, a pressure vessel of hexagonal or cubic cross-section would have a reduced tendency to roll and such external supports (e.g., holders) would not be required.

Figure 5 shows a square-in-cross-section pressure vessel 500, comprising an inner liner 102, an outer skin 104 arranged on the inner liner 102, a filler layer 208, 308 arranged around the outer skin 104 and an outermost layer 210 arranged around the filler layer 208, 308. In some examples, the pressure vessel 500 is linerless. As the skilled reader would appreciate, the pressure vessel 500 may have a different shape in cross-section to a square and the sandwich structure shown 212 may instead be the more complex structure 300. In the example shown, the filler layer 208 is a foam, which define a plurality of bubbles 502. The foam may either be open cell or closed cell. As a simplification, the plurality of bubbles 502 are shown across only a single side of the pressure vessel 500. In reality, they would extend around the periphery of the innermost outer skin 104, as the skilled reader would appreciate.

As shown, the size of the bubbles varies around the periphery of the outer skin 104 so as to define a spatial variation in bubble (volume) density. Referring back to Figure 4A and 4B, the magnitude of stress and strain for a square-in-cross-section pressure vessel 500 is largest along each edge (i.e., corners) and along the centre line of each face, and smallest between them. Correspondingly, the bubble size may be smallest close to each corner/edge or centre line of each face, and largest between them. In this way, structurally redundant material in the filler layer 208, 308 can be removed, thereby reducing weight and saving on materials cost, without generating a "weak" link for failure in the pressure vessel.

As the skilled reader would appreciate, a spatial variation in bubble (volume) density can be achieved in a number of different ways. For example, the size of the bubble may be changed to generate the variation, and/or the number density of bubbles can be changed to generate the variation.

Furthermore, the concept of removing structurally redundant material in the filler layer extends to, not only foams, but also to other filler layer structures, for example, to corrugated core and honeycomb (lattice) structures. In those examples, the pressure vessel could be preferentially reinforced through a spatial variation in the spacing of ridges and their thickness (for corrugated structures) and a spatial variation in the volume or number density of struts in the lattice structure. More generally, these variations lead to a spatial variation in (mass) density of the filler layer 208, 308.

As has already been mentioned, conventional pressure vessels, which are cylindrical or spherical in shape, are disadvantageous because they have a tendency to roll. External supports (e.g., holders) are therefore required to prevent them this occurring. These external supports do not provide structural reinforcement to the pressure vessel.

Referring to Figure 6, a pressure vessel 600 with a corrugated exterior shape is shown.

The pressure vessel 600 comprises an inner liner 102, an outer skin 104, and a filler layer 208, 308 of non-uniform (or non-constant) thickness and outermost layer 210 arranged on the outer skin 104 to form a sandwich structure 212. In some examples, the pressure vessel 600 is linerless. In the example shown, the filler layer 208, 308 and outermost layer 210 have a corrugated shape (defined by the non-uniform thickness of the filler layer 208, 308). For the avoidance of doubt, the filler layer itself may comprise a corrugated structure (not shown in Figure 6), as well as any of the other structures (e.g., honeycomb, lattice, foam etc.) set out above. Preferably, the ridges in the corrugation are sufficiently spaced and of sufficient height to improve the stability of the pressure vessel 600 against rolling. In this way, instead of using an external holder to prevent rolling, which does not provide structural reinforcement, the reinforcing sandwich structure 212 can be shaped to achieve the same effect as well as provide an improvement in the pressure vessel's flexural strength. The filler layer 208, 308 preferably, although not necessarily, covers the entire peripheral edge of the outer skin 104. The sandwich structure 212 in Figure 6 has a thickness which varies around the periphery of the outer skin 104, or, inner liner 102. In another specific example, the outer skin 104 or intermediate layer 306 may be corrugated, and the outermost skin 210 is non-corrugated (e.g., tubular).

The filler layer 208, 308, being an open light-weight structure, may be a good thermal insulator. Polymeric filler layers 208, 308 may be particularly thermally insulating. The filler layer 208, 308 in the sandwich structure may therefore have a secondary function of improving thermal insulation, thereby reducing heating of the pressure vessel, which often store fluids in the liquid state below that of ambient conditions. Better thermal insulation requires less sophisticated, cheap and less bulky thermal management and cooling equipment. Such considerations are particularly important for hydrogen and/or ammonia storing pressure vessels.

In the transportation industry, a substantially planar pressure vessel may be particularly advantageous in terms of storage. For example, a planar pressure vessel could be located beneath the vehicle or in other unconventional locations, rather than the more traditional storage locations which are used to locate other equipment (e.g., the engine). Moreover, a substantially planar pressure vessel is stackable. An assembly of planar pressure vessels may therefore be packed efficiently in space.

Figure 7A shows an end-view of a substantially planar pressure vessel 700. A substantially planar pressure vessel 700 refers to a pressure vessel, which has at least one, substantially planar side. A surface (e.g., a side of the pressure vessel) may be described as substantially planar, if, the maximum angular difference between any two surface normal defined by any two points on the surface, is less than 60 degrees, preferably less than 30 degrees, more preferably less than 10 degrees. The planar pressure vessel 700 may include the inner liner 102 and sandwich structure 212, 300 shown in Figure 2 and 3, which are not shown for clarity. In some examples, the pressure vessel 700 is linerless. In this example, the sandwich structure 212, 300 has constant thickness. The inner liner 102 and planar pressure vessel 700 therefore have the same shape. In other examples (e.g., as shown in Figure 8B), the inner liner 102 and planar pressure vessel 700 have different shape by varying the thickness of the sandwich structure 212, 300 around the periphery of the inner liner 102. In this way, the outer shape of the pressure vessel 700 may be customisable to different operational needs.

In an example, the x end 710 of inner liner may have a radius of curvature, r1, and the y end 720 may have a radius of curvature, 12, where r2 is greater than n. The z end, shown in Figure 7B, may have a radius of curvature, r3 which varies along direction x between a maximum r3, max and ri. r3 may be less than or greater than r2. Equally, the x end and y end may also have variable radius. In a specific example, ri is 30mm to 100mm, preferably 30mm to 75mm, more preferably 30 to 50mm; r2 is around 300mm to 1000mm, preferably, 400mm to 800mm, more preferably 400mm to 600mm and r3 varies between r1 and around 200mm, preferably 150mm, more preferably 100mm. In a specific example, the xz side of the inner liner 102 may be planar, such that r3 is constant and the pressure vessel/ inner liner are symmetric. In those examples, r3 is around 30mm to 200mm. In some examples, the pressure vessel 700 is ellipsoidal, with principal radii, r1, r2 and r3 having a range as defined above. In a specific example, the pressure vessel 700 could be circular in cross section in any given plane (e.g., in the x-z plane if ri=r3).. For a linerless pressure vessel 700, references to the dimensions of the inner liner should be interpreted as the dimensions of the inner skin 104 of the sandwich structure (referred to as outer skin 104).

In an assembled sectional pressure vessel 900 (refer to Figure 9A), the z-end of the assembled sectional pressure vessel (i.e., the end caps 906) may have a variable radius. However, the y-end and x-end of the assembled sectional pressure vessel 900, which include interlocking portions 908, 910, have a constant radius (i.e., such that they can be formed through assembly of inner liner sections 902, 904, 906). In a specific example, the assembled sectional pressure vessel could be ellipsoidal in shape (i.e., like a pill or oblate spheroid), as has been described above.

An ellipsoidal shaped pressure vessel (sectional or otherwise) would have improved aerodynamic properties compared to a cuboidal pressure vessel. Such shaped pressure vessels may therefore be useful in use cases where the pressure vessel is airborne, such as a pressure vessel containing fuel for a drone.

For a pressure vessel comprising an outer skin 104, intermediate layer 306 and/or outermost layer 108 formed by filament winding, it is preferable (although not essential) that the radii of the inner liner 102 are optimised in size to facilitate filament winding. The ranges provided above for the inner liner 102 are particularly well-suited for filament winding. The ranges may be changed, depending on the manufacturing process, to optimise ease of fabrication.

Referring back to Figure 4, the planar pressure vessel 700, when internally over-pressurised, will have a tendency to deform into a more-circular shape by bowing outwardly in the y direction and, to an extent, inwardly in the x and z directions.

The planar pressure vessel 700 may therefore be preferentially reinforced with a sandwich structure 212, 300 arranged to prevent deflection in the y direction (i.e., arranged on the xz side of the pressure vessel, shown in Figure 7B). The remaining xy and yz sides being reinforced with an outer skin 104 only. This reduces material cost (of the expensive outer skin 104) and reduces the weight of the pressure vessel (compared to a structure having a sandwich structure 212, 300 around the entirety of the pressure vessel). In another example, the planar pressure vessel 700 may include the sandwich structure 212, 300 around all/each side, as shown in Figure 2 and Figure 8B.

Referring now to Figure 8A, the weight and material cost of the pressure vessel 700 may be reduced further by partially covering the xz side of the inner liner 102 with a sandwich structure 212, 300 comprising a filler layer 208, 308, outer skin 104 and outermost layer 210. The remainder of the xz side of the inner liner 102 may instead be covered with an outer skin 104 only. In an example, the outer skin 104 covering the remainder of the xz side of the inner liner may have non-uniform thickness to define a substantially corrugated shape. In the specific example shown, the filler layer 208, 308 and outermost layer 210 may form a "cross" (cruciform) against the remainder of the xz side of the inner liner 102 having a coverage of outer skin 104 only. This is a "sculpted topology". The cross may be formed by filament winding by control of the winding angles, compression moulding of a composite laminate, or other fibre placement techniques.

As has already been noted, the substantially planar pressure vessel 700 may, instead of having a sandwich structure 212, 300 of constant thickness, comprise a sandwich structure 212, 300 having a thickness that varies around the periphery of the inner liner 102. As the thickness of the sandwich structure 212, 300 is controllable, the shape of the outer surface of the pressure vessel 700 is customisable. For example, if the pressure vessel 700 is used for storing fuel in a vehicle, and the space available for it in the vehicle is cuboidal, the thickness of the sandwich structure 212, 300 around the inner liner 102, may be adapted accordingly to create that shape. To an extent, the shape of the inner liner 102 is also determined based on the method of forming the outer skin 104.

For example, and as has been described above, the inner liner 102 may be shaped to allow easier placement of the outer skin via filament winding. The shape of the substantially planar pressure vessel 700 may, for example, be any one of: a cube, a rectangular cuboid, ellipsoidal, oblate spheroid, a triangular prism, or other prismatic shape. Other shapes are possible. The edges and/or corners of the planar pressure vessel 700 may be rounded to reduce stress concentrations.

Figure 8B shows a schematic illustration of a substantially planar pressure vessel 700 having a (rectangular) cuboidal shape. Other shapes are possible. The edges and corners of the pressure vessel 700 are rounded to reduce stress concentrations. For clarity, the thickness of the outer skin 104 and outermost layer 210 are not shown: they are represented as single, thick line.. As has already been mentioned, it should be appreciated that in some embodiments the inner liner 102 is optional (i.e., the pressure vessel 700 could be a linerless Type V pressure vessel, with the conventional outer skin 104 being replaced with the sandwich structure described above). For illustrative purposes only, two different forms of filler layer 708a, 708b are shown: a foam 708a, comprising a plurality of bubbles 502, and a lattice structure 708b, comprising a plurality of struts 722. This should not be viewed as limiting. Other types of filler layer, as described above, are equally applicable. The inner liner 102 may be similar/same in size and shape to the inner liner of Figure 7A and 7B. In other examples, the inner liner may be tubular, cylindrical, spherical or any other shape, as the skilled reader would appreciate.

In an example, the substantially planar pressure vessel 700 shown in Figure 8B is fabricated in two (symmetrical) halves, assembled and joined together by adhesive bonding, welding and the like. Alternatively, the sandwich structure 212 may be manufactured "net-shape" using additive manufacturing techniques (e.g., 3D printing).

As shown in Figure 4A and 4B, an inner liner 102 of non-circular cross section, when over-pressurised, induces a spatially varying stress/strain profile in the inner liner 102.

Accordingly, dependent on the cross-sectional shape of the inner liner (and hence the induced stress/strain profile within it), the structure of the filler layer may be adapted to optimise the strength of the pressure vessel 700. That is, the filler layer 708a, 708b around the inner liner 102 may be preferentially stronger (i.e., greater reinforcement) in areas of higher stress/strain; especially, in regions of tension. The structure of the filler layer 708a, 708b may therefore be adapted to ensure appropriate structural reinforcement in those regions. As an example, the foam 708a may comprise smaller and/or less "bubbles" in higher stress/strain regions and larger bubbles elsewhere; or, the lattice structure 708b may comprise more closely spaced struts 722, interconnected struts (not shown), and/or thicker struts in regions of higher stress/strain.

In some examples, the inner liner 102 of the pressure vessel may comprise its own reinforcement -an internal network structure. The internal network structure provides support to the inner liner 102 (and in turn the outer skin 104, filler layer 208, 308 and outermost layer 210) by transferring loads into the internal network structure. The internal network structure is therefore in contact or integrally formed with the inner liner. The internal network structure may be any one or more of: * a periodic structure, for example: o a Bravais lattice, e.g., diamond cubic, triclinic, monoclinic, orthorhombic, tetragonal, trigonal and hexagonal (primitive, base-centred, body-centred and face-centred variations) disposed within the inner liner and integrally formed to it; * a non-periodic structure, for example: o a fractal structure; a a graded structure with increased reinforcement (e.g., via contact) with regions of highest stress/strain, as for example shown in Figure 10A-D; * one or more holes located in the inner liner wall, as shown in Figure 11; and/or * a foam (open or closed cell).

The non-periodic structures may be topology optimised using finite element simulation tools.

As provided in further detail below, the internal network structure may be comprised from a polymer, a metal and the like. The internal network structure may be made through additive manufacturing routes (e.g., 3D printing) or through the assembly of inner liner sections.

Other suitable internal network structures can be found in GB2598737, which are incorporated herein by reference.

In some examples, the inner liner of the pressure vessel is sectional, such that the size and (to an extent) shape of the pressure vessel (which, in some examples follows the shape of the inner liner) may be varied according to operation requirements. In general, the size of the sectional inner liner may be in the range 50 to 2000mm and the shape of the inner liner can be, for example, configured to fit an arbitrary space in a vehicle, or, configured in shape to allow stackable arrangements.

Referring to Figure 9A, the sectional inner liner comprises a plurality of interlocking inner liner sections 902, 904, 906 connected with one another. There are three types of inner liner section: a central section 902; a cap section 906; and an intermediate section 904.

Each of these inner liner sections 902, 904, 906 comprises at least one interlocking portion 908, 910, which is configured to engage with a complementary interlocking portion 908, 910 of an adjacent inner liner section 902, 904, 906, such that inner liner sections 902, 904, 906 can be mated with one another. In an example, the complementary interlocking portions 908, 910 respectively comprise complimentary collars/flanges portions that interlock. Other examples include tongue and groove, or teeth arrangements, or any other latching mechanism, as the skilled person would appreciate. More generally, the interlocking portions 908, 910 can either be described as "male" type or "female" type.

The central and intermediate inner liner sections 902, 904 comprise two opposing open ends, whereas the cap section 906 comprises an open-end and a closed-end. The closed-end defines one of the sectional inner liner faces 912. The central liner section 902 may comprise the same type of interlocking portion 908, 910 (i.6., male-male or female-female) at each of its open-ends. The intermediate inner liner section 904 comprises opposite (or complementary) types of interlocking portion 908, 910 (i.e., female-male or male-female) at each of its open-ends. The cap section 906 comprises a single interlocking portion 908, 910 (i.e., male or female) located at its open-end.

Hence, a sectional inner liner 900 may be constructed from a central inner section 902, two cap sections 906 and, optionally, one or more intermediate inner liner sections 904.

Each inner liner section 902, 904, 906 comprises an internal network structure, which may be any of the structures described above. However, it should be appreciated that these internal network structures are not intended to be limiting in any way and are provided as illustrative examples only. The specific internal network structure used in the sectional inner liner may be determined by optimisation based on operational requirements (e.g., the size and shape that the "conformal" pressure vessel conforms with).

In an alternative exemplary sectional inner liner 920, as shown in FIG. 9B, the central and intermediate inner liner sections 902, 904 are adjoined in a plane containing the longitudinal direction of the pressure vessel. In this alternative example, the pressure vessel additionally comprises two further end caps sections 914, which comprise, which adjoin an adjacent intermediate inner liner section 904 and the end cap sections 906, to form a closed sectional inner liner 920.

Compared to conventional cylindrical or spherical pressure vessel designs, non-circular cross-sections (such as the rounded-square cross-section shown in FIG. 9A) are able to store a larger volume of fluid. Improvements in volumetric and/or gravimetric energy density efficiencies are therefore possible provided the fractional increase in efficiency is not outweighed by any decrease in strength associated with the non-round shape.

As has already been outlined above, a reinforcing sandwich structure disposed around the inner liner 102 may provide improved flexural strength to a non-circular cross-section pressure vessel. Likewise, and in combination, the internal network structure, provided within each inner liner section 902,904 may also provide additional structural support for the same purpose.

Turning to FIG. 10A and FIG. 10B, a cross-sectional view of an inner liner section 902, 904 is shown, comprising an internal network structure 1000, 1010. In FIG. 10A, the internal network structure 1000 comprises a first set of support members 1014, comprising a plurality of first support members 1004. Each support member 1004 extends across one of the internal corners 1008 of the inner liner surface 102. The internal corners 1008 are equivalent to a corner edge in three dimensions and references to corners elsewhere in the description should be interpreted accordingly. The first set of support members 1014 therefore constrain each of the faces 1002 of the inner liner section 902, 904, which has the effect of reducing their tendency to bow outwards (as shown in FIG. 4A, 4B). The first set of support members 1014 therefore serve to reduce or distribute the stress and strain from each of the faces 1002 of the inner liner to the internal network structure (in particular, from the centre of each face 1502). The stress and strain are therefore distributed over a larger area, which reduces stress concentrations, premature failure and enables higher storage pressures within the pressure vessel In the example shown in FIG. 10A, the inner liner is square in cross-section and the corner-extending support members 1004 are arranged at 45 degrees relative to each face 1002. More generally, the corner-extending support members 1504 may be arranged at an angle equal to half the internal angle of the inner liner surface 202, relative to each face 1002.

In FIG 10B, the internal network structure 1010 comprises: a first set of support members 1014 as shown in FIG. 10A; and a second set of support members 1016, comprising a plurality of second support members 1006. Each support member 1006 extends between two first support members 1004, which extend across adjacent corners 1008 of the inner liner.

The second set of support members 1016 therefore constrain the first support members 1004, thereby reducing their tendency to bow outwards (in a similar way to shown in FIG. 4A, 4B). In turn, the first set of support members constrain faces 1002 of the inner liner.

In this way, stress and strain may be effectively distributed from the inner liner face 1002 to a larger area of internal network structure 1010. Hence, stress concentrations can be reduced further, enabling even higher storage pressures and the potential for improved gravimetric storage efficiencies.

On the other hand, including further support members to the internal network structures reduces the total volume within which fluid may be stored under pressure. There is an optimisation to the number of support member sets, which maximises the gravimetric efficiency of the sectional pressure vessel.

FIG. 10C shows a longitudinal cross section (containing the central longitudinal axis of the pressure vessel 900) of an optimised internal structure for an inner liner section. The inner liner section comprises interlocking portions 908, 910 and an internal network structure 1020. As shown, the cross section of the internal network structure 1020 is constant along the longitudinal axis of the inner liner section. That is, the internal network structure 1020 could be readily extruded using a die or injection moulded using a split tool.

FIG. 10D shows a transverse cross section of an optimised internal network structure 1020 for an inner liner section. The optimised internal network structure 1020 comprises: a first set of support members 1014, comprising a plurality of first support members 1004, wherein each support member 1004 extends across one of the internal corners 1008 of the inner liner surface 102; a second set of support members 1016, comprising a plurality of second support members 1006a, 1006b, wherein each support member 1006a, 1006b extends between two first support members 1504 that extend across adjacent corners 1008 of the inner liner; a third set of support members 1018, comprising a plurality of third support members 1008, wherein each support member 1008 extends between two adjacent second support members 1006b and forms a square; a fourth set of support members 1022, comprising a plurality of fourth support members 1012, wherein each support member 1012 extends in a radial direction between the centre of each face 1002 of the inner liner section and a vertex of the square formed by the third set of support members 1018. Optionally, the support member 1012 may bisect one or more of the second support members 1006a, 1006b; and a fifth set of support members 1024, comprising a plurality of fifth support members 1014, wherein each support member 1014 extends in a radial direction between the internal corner 1008 of the inner liner and one or more of the first support members 1004. Optionally, the support member 1014 may bisect one or more of the first support members 1004.

In the example shown in FIG. 10D, the third set of support members 1018 form a square, with its vertices 1024 pointing towards the centre of each face 1002 of the inner liner section. More generally, if the shape of the outer surface 202 of the inner liner section is axially symmetric, then the shape formed by the third set of support members 1018 may be substantially similar to the shape defined by the outer surface 102 of the inner liner section.

The fourth and fifth set of support members 1022, 1024 provide radial support to the second and first set of support members respectively. As has already been noted, the first 1004 and second support members 1006a, 1006b have a tendency to bow outwards (although this tendency is reduced by the second set of support members and third set of support members respectively). For the first and second support members 1004, 1006a, 1006b to bow outwardly, the radially extending support members 1012, 1014 must be compressed. Hence the fourth and fifth set of support members 1022, 1024 constrain the second and first set of support members respectively to reduce the maximum stress in the first and second set of support members 1014, 1016. In this way, the stress and strain are distributed more evenly over a larger area.

Referring now to FIG. 11, an alternative internal network structure 1100 is shown. The internal network structure 1100 is integrally formed within a thickness of the inner liner wall 1102. The internal network structure comprises an inner liner wall 1102 of variable thickness. More particularly, the inner liner wall 1102 is thickest along the corner edges 1108 and thinnest along the centre of each of the inner liner section faces and varying monotonically in-between. The internal network structure 1100 comprises one or more holes 1106, which are located along each corner edge of the inner liner section. The one or more holes 1106 may be partially circumferential.

The (sectional) inner liner may comprise a thermoplastic or thermoset polymer. For example, high density polyethylene (HDPE), polyaryletherketone (PAEK), polyether ether ketone (PEEK), nylon (e.g., PA6 PA12), an epoxy, or a blend thereof The (sectional) inner liner may instead in metallic (e.g., an aluminium or titanium alloy).

In some examples, the internal network structure of the (sectional) inner liner may comprise additives. These additives, or fillers, may be functional and/or structural. In an example, nano-fillers such as graphene, carbon fibre (e.g., in the form of short, "chopped" fibres), and/or carbon nano-tubes are added to improve the stiffness and yield stress of the internal structure. The filler layer 208, 308 of the sandwich structure 212, 300 may also comprise these additives. In some examples, the internal network structure may comprise additives of lightweight metals such as Aluminium, or aluminium alloys, titanium or titanium alloys, or ceramics e.g. alumina. In this way, the internal network structure may comprise a polymer-metal composite or a polymer-ceramic composite. As described above, in some examples, a gradient in stiffness can be engineered by varying the stiffness of the support members 208, 502. One option for generating this varying stiffness is to vary the volume or mass fraction of this structural additive. In other examples, the internal network structure 204, 500, 1500, 1510, 1520 may be a lightweight metal or ceramic. A non-exhaustive list of possible metals includes aluminium and aluminium and titanium alloys. A non-exhaustive list of possible ceramics includes alumina.

An inner liner 102 without an internal network structure may be manufactured using rotational moulding. Rotational moulding may be used to form inner liners of any (realistic) shape (e.g., cubic, rectangular, hexagonal cross-sectioned inner liners).

In other examples, hydrogen absorbing, or adsorbing additives can be added to the internal network structure 204, 500, 800, 900, 1000, 1100, 1200, 1500, 1510, 1520. In this way, the effective volume 206 for containing pressurised gas can be increased. In response to a pressure drop, these hydrogen absorbing/adsorbing additives are configured to controllably release hydrogen.

The inner liner sections 902, 904, 906 (with internal network structures) may be manufactured by additive manufacturing, injection moulding or casting. One or more valve ports may be added to each inner liner end section 906, using manufacturing techniques known to the skilled person The filler layers 208, 308 may also be manufactured by additive manufacturing.

The exact choice of additive manufacturing is at least partially dependent on the material selection of the inner liner 200. A non-exhaustive list includes: stereolithography methods (Vat photopolymerisation), material jetting, binder jetting, powder bed fusion (Direct metal laser sintering (DMLS), selective laser sintering (SLS), selective laser melting (SLM), multi jet fusion (MJF), electron beam melting (EBM)), filament extrusion processes (fused deposition modelling (FDM). A non-exhaustive list of net-shaped manufacturing methods includes injection moulding, lost-wax casting or investment casting.

In some examples, the (sectional) inner liner with internal network structure may be manufactured using injection moulding. This mode of manufacture may be particularly advantageous for large internal network structures where additive manufacturing routes are impractical, or time consuming. A large internal network structure is one comprising dimensions greater than 500mm. The sectional inner liner sections 902, 904, 906 may also be produced by injection moulding. In particular, using split moulding techniques.

In some examples, the intermediate and/or central inner liner sections may be formed by extrusion or compression moulding. The interlocking portions 908, 910 may then be produced by any subtractive manufacturing technique known to the skilled person.

The internal network structures may be produced by selectively removing material, rather than through additive manufacturing routes. Such subtractive manufacturing methods include CNC (computer numeric control) of drills, lathes, and the like.

In some examples, the internal network structure is a foam. The foam may be manufactured by a foaming process route, which results in an open celled structure. The foaming process route may include a foaming agent. For polymeric materials, the foaming agent may be a chemical agent. The chemical agent may be used both to synthesis the polymer and to generate gas as a by-product in the reaction. In other examples, the foaming agent may comprise an inert gas such as Argon. In the latter, the local flow rate of the gas may be controlled spatially to generate regions of increasing or decreasing bubble density, such that the foam density varies from low density, or larger bubble diameters, at the core and decreases close to the inner liner outer surface 202 to produce progressively smaller bubbles. Similarly, the filler layer 208, 308 foams and a spatial variation in bubble density, as for example shown in Figure 5, may be manufactured in a similar manner.

In the sectional inner liner approach, the manufactured inner liner sections 902, 904, 906 are joined by mating complementary interlocking portions 908, 910 and sealing using adhesive bonding or welding. Adhesive bonding is applicable to both polymer-based and metal-based inner liner sections. Welding is applicable for metallic inner liner sections. Other joining methods known to the skilled person are also applicable.

The outer skin 104 may be formed by filament winding, providing the shape of the inner liner allows (for example, it has a tubular, cylindrical or close to cylindrical shape). The filler layer 208, 308 would be bonded onto the outer skin 104 (or intermediate layer 306) via an appropriate adhesive or resin. The wind angle and tension can be controlled using appropriate machinery known to the skilled person. Automated fibre placement may also be used to apply the overwrap. Options include: filament wound dry fibre/tape preform for resin impregnation, or thermoplastic towpreg or pre-impregnated fibre/tape towpreg.

If the shape of the inner liner 102 or filler layer 208, 308 is complex (i.e., not cylindrical or close to cylindrical in shape), the inner skin 104, intermediate layers 306 and outermost layer 210 may instead be provided by: * braiding a fabric onto the inner liner using, infusing the braiding with resin and curing; * knitting a fabric onto the inner liner, infusing the knitting with resin and curing; or * compression moulding or hot pressing (optionally vacuum assisted, especially with thermoplastic inner liners 102) of a woven resin pre-impregnated fabric onto the inner liner and curing. Ends of the fabric for the outer skin 104 and outermost layer 210 may for example be adhesive bonded together to seal off the filler layer 208, 308, using an autoclave.

As the inner liner 102 may be a thermoplastic, the resin infusion may be vacuum assisted. Alternatively, low temperature cure thermoset resins may be used (i.e., with cure temperatures less than the melting point (or glass transition temperature) of the thermoplastic.

As shown above, the outer skin 104 may follow the same shape as the inner liner 102, whereas the intermediate layers 306 and outermost layer 210 may not (because the filler layer 208, 308) may have variable thickness. In these examples, the outer skin 104 may be fabricated using filament winding methods and the intermediate layers 306 and outermost layer 210 by braiding/knitting.

The sandwich structure 212, 300 may alternatively be formed by a superplasfic forming and diffusion bonding process, provided the outer skin 104, any intermediate layer(s) 306, outermost layer 210 and one or more filler layers 208, 308 are metallic (e.g., an aluminium or titanium alloy). The filler layers 208, 308 preferably exhibit superplasficity and allow for diffusion bonding with the outer skin 104, intermediate layer 306, and outermost layer 210, as appropriate. The diffusion bonding takes place where no stop-off layer has been applied. The sandwich structure with a corrugated core may therefore be manufactured in-situ. An inner liner 102 is optional in these examples.

Referring now to Figure 12, a schematic illustration of an assembly 1200, from which a sandwich structure 212 formed by a superplastic and diffusion bonding process, is shown. The assembly 1200 comprises: at least two skin layers 102, 210; 102, 306; 104, 210; 104, 306 with a metallic filler layer 208, 308 disposed therebetween, and one or more "stop-off' layers (or spacers) 1202 arranged between each opposing side of the filler layer 208, 308 and the respective outer skin 104/ outermost layer 210 / inner liner 102 / intermediate layer 306. In the process, the metallic filler layer 208, 308 is arranged between the outer skin 104 and outermost layer 210 (or intermediate layer 306 if the sandwich structure is a "multi-stack" 212) to form the assembly 1200. In a specific example, the stop-off layers in the assembly 1200 are equally spaced and arranged to alternate between each of the opposing sides of the filler layer 208, 308. Other arrangements and spacing are possible, as the skilled reader would appreciate. Thereafter, the layers 104, 210, 208, 308, 306 are heated, such that the filler layer 208, 308 selectively bonds with the outer skin 104 / outermost layer 210 / inner liner 102 / intermediate layer 306 through diffusion bonding. The "stop-off' layer 1202 prevents diffusion bonding and, as such, allows the provision of selective diffusion bonding to take place. In an example, the "stop-off' layer 1202 is a ceramic. Either concurrently or sequentially with this heating, a gas (such as, Argon) is supplied at pressure between the outer skin 104 and outermost layer 210, causing the layers 104, 210 to expand away from one another. The conditions of pressure and temperature are such that the filler layer 208, 308 (and other layers) deform superplastically. A sandwich structure 212 comprising a corrugated filler layer 208, 308 is therefore formed. The sandwich structure 212 may also be a "multi-stack" structure. In such examples, there is more than one filler layer 208, 308 as would be understood with reference to Figure 3. For the avoidance of doubt, if the inner liner 102 is metallic, the inner liner 102 may replace outer skin 104 in the formation of the sandwich structure 212. In this process, the shape of the pressure vessel may also be controlled. For example, into a cuboidal, spherical, ellipsoidal (e.g., oblate spheroid) shape.

During manufacture of the inner liner by injection moulding or additive manufacturing, a metallic valve port, such as a polar boss for a gas inlet/outlet, may be included by over-moulding, insert moulding, welding or adhesive bonding.

One or more valves can be integrated into the end sections 906 of the pressure vessel. In the sectional approach, the one or more valves may be moulded-in with the end sections 906 during injection moulding. Alternatively, the one or more valves can be fitted prior to or after the overwrapping step stage, using methods known to the skilled person.

The contained fluid in the pressure vessel may be hydrogen, nitrogen, oxygen, methane, natural gas, ammonia, biogas, liquid hydrogen, liquid nitrogen, liquid nitrogen, liquid natural gas, liquid ammonia, liquid methane, or liquid biogas.

A summary of exemplary pressure vessel configurations, which have been described in detail above, is shown in Table 1 (below).

LINER SANDWICH

CONSTRUCTION

No liner Thermoplastic Inner liner 102 Inner Filler core layer 208 Outer (linerless) inner liner 102 with internal skin skin 210 network 104 structure

Y Y N N

Y Y y y

Y Y Y Y

(") (") (") Y Y Y TABLE 1: Options for Design Configurations (Y=selected; N=not selected; (*) = any one of) Any of the pressure vessels described may be fabricated in two (symmetric) halves, which are assembled together by via adhesive bonding, welding, diffusion bonding, or other joining method. In particular, this approach may be used when preparing a metallic pressure vessel by the superplastic and diffusion bonding process described above' The invention has been described in detail with reference to the exemplary embodiments; modifications may be made without departing from the scope of the invention as defined by the claims. Each feature disclosed or illustrated in the present specification may be incorporated in the invention, whether alone or in any appropriate combination with any other feature disclosed or illustrated herein.

Claims

CLAIMS: 1 4. 5. 6 7.A pressure vessel, comprising: a sandwich structure comprising: two or more skin layers; and one or more filler layers, each filler layer being arranged between two of the skin layers.
The pressure vessel according to claim 1, further comprising an inner liner, wherein the sandwich structure is arranged around the inner liner and at least partially covering it.
The pressure vessel according to claim 1 or 2 wherein each of the one or more filler layers comprises at least one of: a foam; a corrugated structure; and/or a lattice structure.
The pressure vessel according to any of claims 1 to 3, wherein the thickness of at least one of the one or more filler layers is non-uniform.
The pressure vessel according to any of claims 1 to 4, wherein the thickness of at least one of the one or more filler layers is uniform.
The pressure vessel according to any preceding claim, wherein the external shape of the outermost filler layer is corrugated and the external shape of the pressure vessel is corrugated.
The pressure vessel according to any of claims 2 to 6, wherein the inner liner is tubular in shape.
The pressure vessel according to any preceding claim, wherein at least one of the one or more filler layers has a density that varies spatially around the periphery of the innermost skin such that the strength of the sandwich structure correspondingly varies around said periphery of said skin.
9 The pressure vessel according to any preceding claim, wherein the density of at least one of the one or more filler layers increases close to the edges of the pressure vessel, and/or increases close to the centre line of each face of the pressure vessel.
10. The pressure vessel according to any one of claims 2 to 9, wherein the inner liner comprises at least one substantially planar side, and the sandwich structure is arranged on said at least one substantially planar side of the inner liner.
11 The pressure vessel according to any one of claims 2 to 5 and 7 to 10, wherein the external shape of the pressure vessel is any one of a cuboid, ellipsoid, oblate spheroid, or a rectangular cuboid, and wherein, the thickness of the sandwich structure, arranged around the inner liner, varies around the periphery of the inner liner to define said external shape.
12. The pressure vessel according to claim 10, wherein the thickness of the sandwich structure is uniform.
13. The pressure vessel according to any one of claims 2 to 12 wherein the inner liner comprises an internal network structure.
14. The pressure vessel according to any one of claims 2 to 13, wherein the inner liner comprises an assembly of at least one inner liner section and at least two cap sections.
15. The pressure vessel according to any preceding claim, wherein each of the two or more skin layers comprises a resin-infused fibre cloth, an aluminium or titanium alloy, or fibre reinforced composite.
16. The pressure vessel according to any preceding claim, wherein each of the one or more filler layers is comprised from an aerogel, an aramid material, phenolic resin, an aluminium or titanium alloy, polyurethane, polyetherimide, polymethyacrylamide or wood.
17. Use of the pressure vessel according to any preceding claim, in a vehicle to store fuel.
18. Use of the pressure vessel according to claim 17, wherein the fuel is any one or more of: gaseous ammonia, methane, hydrogen, biogas, natural gas, oxygen, or, liquid ammonia, methane, hydrogen, biogas, natural gas, oxygen, or derivatives thereof.
19 A method for manufacturing the pressure vessel of any one of claims 1 to 16, comprising: applying a first skin around a surface based on the external shape of the surface; applying a filler layer onto the first skin; applying a second skin around the filler layer based on the external shape of the filler layer.
20. The method according to claim 19, wherein: the first and second skin are applied using filament winding if the external shape of the surface and the external shape of the filler layer are respectively tubular, toroidal, ellipsoidal, oblate spheroid or spherical; otherwise, the first and second skin are applied using at least one of the following: braiding or knitting of a fabric, infusing of the braiding or knitting with resin and curing of the resin infused braiding or knitting; compression moulding of a woven resin pre-impregnated fabric and curing of the resin pre-impregnated fabric; and/or hot pressing of a woven resin pre-impregnated fabric onto the surface and curing.
21. The method according to claim 19 or 20, wherein the surface forms an inner liner of the pressure vessel.
22. A method of manufacturing a pressure vessel according to any one of claims 1 to 13, comprising: arranging a metallic filler layer between a metallic first skin and a metallic second skin, wherein one or more spacers are arranged between each opposing side of the filler layer to separate the metallic filler in those regions from said skins; supplying a gas between the first and second skin at a pressure and temperature at which: the filler layer superplastically deforms, and diffusion bonds to the first and second skins in regions of contact with said skins.
23. The method according to any of claims 19 to 21, wherein the pressure vessel is fabricated by assembling and sealingly joining two halves of the pressure vessel together.
24. The method according to claim 23, wherein said halves of the pressure vessel are sealingly joined together by: welding of the first and second skins; or diffusion bonding of the first and second skins.