Patent Description:
<CIT> discloses a fuel reservoir for compressed hydrogen to be used on a car. The fuel reservoir has several spherical individual voluminal that are connected to each other via a connection duct.

<CIT> discloses a storage pack for storing pressurized gas on a vehicle. The gas storage pack includes a pressure vessel formed from a plurality of hollow chambers which have either an ellipsoidal or spherical shape. For storing oxygen on a medical car, a portable gas storage pack is provided. The pressure vessel of the gas storage pack is configured as a single continuous serial strand of interconnected spherical or ellipsoid chambers bent back-and-forth upon itself in a sinuous fashion with all the chambers lying in a single plane. This pressure vessel is encased in a protective housing that has a handle.

<CIT> and <CIT> disclose a safety device for a pressure vessel which consists of a plurality of hollow spherical sections welded together and interconnected by an inner tube with a throttle between the spherical sections.

<CIT> discloses a continuous flow thermodynamic pump that connects an aircraft tank for LH2 with a consumer and that supplies the consumer with gaseous hydrogen.

<CIT> discloses a gas storage system including a tank having a tank gas outlet and a multitude of spherical gas emitting entities encapsulated by the tank. The gas emitting entities are freely contained in the tank. The gas emitting entities have a respective gas emitting device which is operable as a response to a stimulation signal. A volume surrounding the gas emitting entities inside the tank is the sole fluid connection between an opening of the gas release device and the tank outlet.

<CIT> discloses an aircraft tank according to the preamble of claim <NUM>.

Especially, the invention relates to tanks for aircrafts which run with alternative fuels, especially gases such as hydrogen.

Lightweight energy storage is one key topic for next generation aircrafts. Hydrogen offers highest energy densities, whereas the storage method (cryo, compressed, solid state/absorbed,. ) becomes a challenge.

Compressed and cryogenic hydrogen are the methods of choice for today's vehicles such as cars or airplanes. Cryo-tanks achieve the lowest added weight with approximately <NUM>,<NUM> material added per <NUM> of H2. All tanks work with applied inner pressure.

A full spherical or cylindrical outer geometry of the whole tank would be ideal to compensate pressure loads, but are suboptimal for a high volume utilization ratio so that increased drag would arise.

It is an object of the invention to enhance devices, systems and methods for storing liquified gases, especially liquified hydrogen such that they can be adapted to individual spaces within a vehicle while pressure loads can be compensated more efficiently.

For addressing this object, the invention provides a modular aircraft tank having several tank modules according to claim <NUM>. A tank system and an aircraft equipped therewith and an operation method therefore are the subject-matters of the further independent claims.

Advantageous embodiments are the subject-matters of the dependent claims. The invention provides a modular aircraft tank for storing cryogenic liquified gas, having several tank modules each comprising a series of hollow spheres connected by a tube.

Preferably, the spheres are linearly arranged.

According to the invention, the spheres are mounted on the tube.

Preferably, the spheres have a skin made of a skin material chosen from the group comprising composite material, plastic material, fibre reinforced composite material, metal, aluminium, steel and combinations of the aforementioned materials.

Preferably, the spheres are packed in or surrounded by a thermally insulating material.

Preferably, the spheres are packed in an ultralight high performance material such as aerogels and hollow glass spheres. Different foams, especially foams adapted for cryogenics, can be used as well.

Preferably, the spheres comprise a thermoplastic liner system, preferably a toroidal thermoplastic liner system.

Preferably, adjacent spheres touch each other laminarly at pole regions. Preferably, the spheres are arranged centrally on the tube.

According to one possible embodiment, all spheres of one tank module have the same size. Alternatively, the spheres of one tank module could have different sizes.

Preferably, the tube mechanically fixes the spheres.

Preferably, the tube communicates with the interior of each hollow sphere.

Preferably, the tube is configured as a fuel pipe to fill and/or empty the hollow spheres.

Preferably, the tube is a straight tube extending linearly.

For individual tank modules, the tube can also be curved.

According to the invention, the tube is self-supporting.

According to the invention, the tube is configured to bear mechanical loads introduced by the spheres.

Preferably, the tube is made of a material chosen from the group comprising Kevlar, Kevlar composite material, composite material, metal, aluminium, steel, plastic, fibre reinforced plastic and combinations of the aforementioned materials.

Preferably, the tube is arranged centrally in the tank module.

Preferably, the tube passes through the spheres.

According to the invention, the tank module is configured as cryogenic tank module to store liquified gas, especially liquified hydrogen.

The invention provides a modular gas tank comprising several tank modules according to any of the preceding configurations, wherein the spheres of adjacent modules are stacked together in a sphere packing.

Preferably, several linear tank modules are arranged upright.

According to the invention, the tank modules are replaceable separately.

According to the invention, a space between the tank modules is filled with thermally insulating material.

Preferably, the tank modules are packed in or surrounded by a thermally insulating material.

Preferably, the tank modules are packed in an insulating material from the group comprising aerogels, foams and hollow glass spheres.

Preferably, a surrounding insulation material is held in place by a thermoplastic vacuum bag.

Preferably, spheres of neighbouring tank modules touch each other laminarly at pole regions.

Preferably, spheres of at least a first and a second tank module differ in size.

According to the invention, the modular gas tank is configured as cryogenic tank to store liquified gas, especially liquified hydrogen.

According to the invention, the modular gas tank is configured as vehicle tank, namely an aircraft tank.

According to another aspect, the invention provides a tank system for a vehicle, namely for an aircraft, comprising at least one modular gas tank according to any of the aforementioned embodiments.

Preferably, the tank system comprises a 3d piping and valve network connecting the tubes of the tank modules.

Preferably, the tank system comprises a control configured to control filling and/or emptying tank modules or a several groups of tank modules seperately.

Preferably, the tank system comprises a control configured to control emptying the tank modules such that outer spheres are emptied first, before inner spheres are emptied.

Preferably, the tank system comprises a connection wherein the connection comprises at least one further tank module according to any of the aforementioned embodiments, wherein the at least one further tank module is configured such that gas to be delivered through the connection is passed through the tube thereof.

The connection can be a gas inlet connection between a filler and at least one modular gas tank, a tank connection for supplying gas from one of the modular tanks to another of the modular tanks, or an gas outlet connection between the at least one modular gas tank and a device to be supplied with the gas from the modular gas tank.

According to another aspect, the invention provides an aircraft preferably an airplane, comprising a modular aircraft tank according to any of the aforementioned embodiments and/or a tank system as mentioned above.

According to another aspect, the invention provides a method for operating the modular gas tank or the tank system according to any of the aforementioned embodiments, wherein the method comprises at least one of the steps:.

Some special advantages of preferred embodiments of the invention are explained below.

Preferred embodiments of the invention relate to a sphere array fuel tank system.

Especially, preferred embodiments relate to a fuel tank system for an aircraft, more preferred an airplane. The fuel tank system is especially adapted to store cryogenic gases, especially liquified hydrogen. Preferred embodiments relate to a fuel tank system and components thereof adapted to store liquified hydrogen at very low temperatures. More especially, preferred embodiments relate to pressurized cryogenic H2 tank systems.

In theory spheres are the optimal geometry for pressurized cryogenic H2 tank systems. This is because of the best (and constant) fuel to tank weight ratio and smallest possible surface to fuel volume ratio. The latter reduces the effort for thermal insulation to a minimum. In airplane systems however space restrictions lead to cylindrical tank systems in order to fit in an aerodynamic fuselage.

Preferred embodiments of the invention do not need thick and thus heavy fuel tanks walls in order to withstand bending and buckling due to tank and fuel weight.

Preferred embodiments of the invention do not need discrete stiffeners in order to withstand bending and buckling due to tank and fuel weight.

Preferred embodiments of the invention do not need load introduction rods in order to withstand bending and buckling due to tank and fuel weight.

In preferred embodiments of the invention, there are no or only a very reduced number of elements which bypass the insulation.

Preferred embodiments of the invention do not need load carrying insulation materials, which are usually heavier and less performant in terms of insulation.

With preferred embodiments of the invention, there is no sloshing. Further, the overall airplane weight can be balanced better during flight.

For achieving some or all of the above-mentioned advantages, preferred embodiments of the invention propose to use comparably small spherical tanks, that are linearly and centrically mounted on a tube. This tube serves as a mechanical fixation of the spheres and as a fuel pipe (boss). This preferred basic principle enables geometrical freedom by arranging this linear sub-element into a 2nd or 3rd dimension.

Besides multiple technical advantages, this tank-sub-elements may help to go for a 'one system fits all', thereby reducing cost of manufacturing and certification.

Therefore, these tanks may fit not only in the fuselage but also in other structures, e.g. a wing. This will also help to adapt the overall airplane balance during flight.

According to some embodiments, variations in sphere sizes is also possible to further increase dense-packaging and adapt to space restrictions. The weight of the spheres is directly proportional to the sphere diameter. At constant tank volume, small single tank-spheres achieve similar weight compared to large tanks.

Curved and closed loop arrangements are possible to further adapt to space restrictions.

If the spheres are small enough anti-sloshing elements are not necessary.

Linear elements may be positioned upright, thereby avoiding bending of the tubes and clearly separating liquid H2 from gaseous H2 and avoiding dead volume.

Smaller tank modules may be replaced completely instead of refilling the tank.

In case of leaking submodules, individual submodules can be emptied instead of losing the total propulsion fuel. After landing the individual element can be replaced instead removing or repairing the complete tank.

The surrounding insulation material may be held in place by a thermoplastic vacuum bag.

Spheres may also comprise a thermoplastic liner system (toroidal).

Load free insulation material can be made from ultralight high performance material such as Aerogels and hollow glass spheres.

Because of thermal conductivity, the tubes are preferably made out of Kevlar composites.

The system is preferably made out of composites, but could also comprise metals such as aluminium or steel.

Tubes may be used for structural loads. They can be straight but also curved (adapted to the outer geometry).

Elements could replace the tube system between tanks or to the energy/propulsion system.

Spheres may touch laminar at the pole region to reach tightness.

A smart thermal management system - preferably embodied by software anr/or hardware in a control of the tank system - can take advantage of the fact that the outer, less well insulated spheres, can be emptied first.

Spheres could be connected with a 3d orthogonal piping/valve network to connect/disconnect single tanks (leakage/failure scenario).

Embodiments of the invention are explained in more detail with reference to the accompanying drawings, in which:.

<FIG> shows schematically a tank module <NUM> for a modular cryogenic gas tank. The tank module <NUM> comprises a series of hollow spheres <NUM> connected by a tube <NUM>. While three speres <NUM> are shown, it should be noted that this is only an example, and the tank module <NUM> can have a number n of spheres <NUM> with n being a natural number with n ≥ <NUM>. Preferably the tank module <NUM> has <NUM> to <NUM> spheres.

The tube <NUM> serves as discrete mounting - mechanical fixation for the spheres <NUM> - and as fuel pipe. The tube <NUM> has at least one opening <NUM> for each sphere <NUM> communicating with the inner space thereof. The tube <NUM> passes through each sphere <NUM> of the tank module <NUM>. According to some embodiments (not shown), the tube <NUM> may end within the last sphere in the series of spheres <NUM>. In the embodiment shown in <FIG>, the tube <NUM> is straight, but as this is indicated in <FIG> at 10a, the tube <NUM> may be curved to adapt an individual tank module 10a to an inner space <NUM> of a vehicle <NUM>, namely an aircraft, especially an airplane <NUM>.

Preferably, the tube <NUM> is made from fibre reinforced Kevlar composite material. Hence, the tube <NUM> is self-supporting and configured to support the load of the spheres <NUM>. Although not shown in <FIG>, the tube <NUM> may have a valve between each neighbouring sphere <NUM> in order to connect/disconnect the spheres <NUM>.

The spheres <NUM> are configured as single liquid hydrogen (LH2) tanks and store liquid hydrogen LH2 in their inner space. In the embodiment shown in <FIG>, the spheres <NUM> are equal and are mounted linearly and centrally on the tube <NUM>. However, depending from the inner space <NUM> to be filled with tank modules <NUM>, several of the spheres <NUM> could vary in size. The spheres <NUM> have a wall or skin <NUM> made from a material suitable for cryogenic tanks. Preferably, the material of the skin <NUM> is made of composite material which can contain plastic, fibres, and metal such as aluminium and steel. Preferably, the neighbouring spheres <NUM> touch each other at their pole positions.

Several of the tank modules <NUM> as shown in <FIG> can be packed in a close sphere packing (see for example [<NUM>]) as this is shown in <FIG> by a stacking pattern <NUM> where spheres 12a of a further tank module <NUM> are indicated by simple circles.

The spheres <NUM>, 12a are packed in an insulating material <NUM>. Since the loads of the spheres <NUM> are supported by the tube <NUM>, the insulating material <NUM> is load free and can be made from ultralight high-performance material such as aerogel or hollow glass spheres.

<FIG> shows the airplane <NUM> as example for the vehicle <NUM> equipped with a tank system <NUM> in an inner space <NUM> thereof. The tank system <NUM> comprises one or several modular tanks <NUM> made by stacking several of the tank modules <NUM> and connections <NUM> for the at least one modular tank <NUM>.

<FIG> is a sectional view along plane A of <FIG> and shows a conventional tank system <NUM>. The conventional tank system <NUM> has several single tanks <NUM> formed as cylinders. While the inner space <NUM> of the airplane <NUM> could be theoretically filled up to <NUM> % by a close packing of cylinders, the actual use of the space is restricted in the third dimension. Hence, individual long cylinders would be needed, and an enforcement would be necessary to bear the loads thereof.

<FIG> shows the section through the airplane <NUM> along plane A of <FIG>, wherein the inner space <NUM> is filled by stacking several of the tank modules <NUM> using a close packing of the spheres <NUM>. The individually formed inner space <NUM> may be filled to a high degree (theoretically up to <NUM>%).

In <FIG>, one of the tubes <NUM> is indicated as a broken line. As visible therefrom, the linear tank modules <NUM> are arranged upright, i.e., the tube <NUM> and the series of spheres <NUM> are arranged vertically.

As further shown in <FIG>, the insulating material <NUM> is held in place by a vacuum bag, especially a thermoplastic vacuum bag <NUM>. The spheres <NUM> may also comprise a thermoplastic liner system (not shown).

As connections <NUM>, the tank system <NUM> comprises a gas inlet connection between a filler (not shown) and the at least one modular tank <NUM>, a gas outlet connection between the at least one modular tank <NUM> and a gas consuming device, such as a propulsion system <NUM>, and a communication connection between modular tanks <NUM>. Only one of these connections <NUM> is schematically indicated in <FIG>. As visible therefrom, the connection <NUM> may comprise one or several of further tank modules 10a, wherein the gas to be transported through the connection is passed through the tube <NUM> thereof.

Referring to <FIG>, the tank system <NUM> may comprise a 3d orthogonal piping valve network <NUM> to connect/disconnect single spheres <NUM> and/or tank modules <NUM>. A control <NUM> is connected to control elements of the network such as valves <NUM>. The control <NUM> embodies a smart thermal management system <NUM> and is configured to empty less insulated outer spheres 12b first and to empty spheres <NUM> located more in the interior of the modular tank <NUM> at a later time. Further, the control <NUM> is configured to empty and/or disconnect individual spheres <NUM> and/or tank modules <NUM> in case that a leakage or a failure thereof is detected.

Claim 1:
Aircraft tank configured as cryogenic tank to store liquified gas, especially liquified hydrogen, comprising hollow spheres (<NUM>, 12a, 12b) stacked together in a sphere packing,
characterized in that
the aircraft tank is a modular aircraft tank (<NUM>) comprising several tank modules (<NUM>) configured as cryogenic tank modules (<NUM>) to store the liquified gas and replaceable separately, wherein each of the tank modules (<NUM>) comprises a series of the hollow spheres (<NUM>, 12a, 12b) connected by and mounted on a tube (<NUM>) which is self-supporting and configured to bear mechanical loads introduced by the spheres (<NUM>), and wherein a space between the tank modules (<NUM>) is filled with thermally insulating material (<NUM>).