DE102009029245A1 - Tank for aircraft - Google Patents

Abstract

The invention relates to a mobile tank for a cryogenic, d. H. cryogenic fuel, especially for LNG, i.e. liquid natural gas or liquid methane. The invention further relates to an aircraft with this tank and a method for retrofitting an aircraft with such tanks. According to the invention, a tank for a cryogenic fuel is provided with an outer structure and a flexible, pressure-resistant, cold-resistant inner shell (4). In order to retrofit an aircraft with a tank for a cryogenic fuel, a tank for kerosene is lined with a film (2), plastic tiles (3) are glued to the film and a pressure-resistant inner shell (4 ) applied, preferably glued on.

Description

The invention relates to a mobile tank for a cryogenic, d. H. cryogenic fuel or fuel, in particular for LNG, ie liquid natural gas or liquid methane. The invention further relates to an aircraft with this tank and a method for retrofitting an aircraft with such tanks.

In contrast to a conventional fuel such as kerosene, low-temperature fuels such as LNG in the tank evaporate due to temperature increases due to the usually prevailing outside temperatures. Such vaporized fuel is called "boil-off" gas. Boil-off gas increases the pressure in the tank.

From the publication DE 19543163 An aircraft with tanks for a cryogenic fuel forth, which are provided in the fuselage or as external tanks on the wings.

From the publication DE 198 16651 C2 goes out a vacuum insulation for a tank of the type mentioned.

The publication US 2006278761 A discloses the placement of tanks in wings of an aircraft.

The publication DE 3309768 A1 discloses an aircraft trapezoidal wing, wherein the wing is used as a fuel tank

The present invention has for its object to provide a mobile tank for cryogenic fuel, with which in particular an aircraft is driven.

To achieve the object, a tank is provided, which comprises an outer structure and a pressure-resistant, cold-resistant, flexible inner shell, which is able to absorb an overpressure arising in the tank. For example, the sheath is an aramid-reinforced or aramid sheath, such as an aramid fiber-reinforced sheath, hereinafter called an aramid sheath. Aramid fibers are commercially sold by DuPont under the trademark Kevlar ^®. By such a pressure-resistant inner shell pressure can be compensated, which is caused by Boil-off gas. An internal pressure in the tank of 2 to 3 bar absolute can be compared to the outer structure by an aramid shell caught. Due to the flexibility of the inner shell can be easily adapted to predetermined geometries, which facilitates retrofitting an aircraft or ship with a tank according to the invention.

An envelope is particularly pressure-resistant in the sense of the present invention, if it is able to withstand a pressure of 2 bar absolute at least. This information refers to the storage temperature of the fuel. A casing is resistant to cold in the sense of the present invention, when it has grown the storage temperature of the cryogenic fuel stored in the tank.

To provide a pressure-resistant tank, this is regularly made of steel or aluminum. A pressure-resistant inner shell is relatively light in comparison, so that so a relatively light tank can be provided. The provision of a light tank is important for mobile use in order to minimize the fuel needed for the drive.

Although there are steel tanks, which are provided with an inner flexible shell, so as to reliably secure the tank against leakage. This is required by law, for example, in underground tanks where fuel oil is stored. However, a material which is used in these cases is not cold-resistant in the sense of the present invention. Such shells of underground tanks are instead designed to withstand the prevailing ambient temperatures.

LNG is usually cooled to -161 ° C to -164 ° C. The material of the envelope is then to be selected so that it is at least equal to the temperatures at which LNG stored in the tank has been cooled. There are aramid sheaths that can withstand temperatures of -197 ° C. Such a casing is particularly well suited for the storage of LNG.

The aramid sheath is preferably 100% aramid. In one embodiment, this comprises hollow fibers.

In another embodiment, the envelope is impregnated with a gas-tight rubber material such as rubber, or coated with a thin 1 to 1.5 mm layer of flexible thermal insulation and sealants, such as sprayable polyurethanes.

The sheath is preferably 1 to 10 mm, more preferably 3 to 7 mm, for example about 5 mm thick.

If this aramid is used as the material of the inner shell, the security is particularly increased, which is especially important for aircraft, since such casings are particularly flexible and more stable than steel and aluminum.

In one embodiment of the invention, the pressure-resistant inner shell is applied to a compressible plastic material, which is the thermal insulation serves. If a pressure increase occurs in the tank due to boil-off gas, the compressible plastic material makes no significant contribution to catch the pressure and not forwarded to the surrounding structure of the aircraft or ship in which it is embedded, and charged. What remains is mainly the mass forces, caused by the acceleration of the traffic systems, which have to be intercepted in the form of surface pressure by the structure of the aircraft. The internal gas pressure in the tank is instead absorbed by the pressure-resistant inner shell energetically in deformation work, the elongation of the material Kevlar, for example. In this embodiment, a wide range of heat-insulating, lightweight materials is available. Thus, for example, for the thermal insulation of a polyurethane existing material used and in particular in the form of a foam, for example in the form of a soft foam. However, polyurethane can also be present as a mounting foam so as to provide a thermal insulation with low weight.

Kevlar is an elastic material that can stretch up to 4%. Polyurethane is a resilient material. If an overpressure occurs in the tank according to the invention, an inner sheath reinforced by kevlar will stretch and absorb the overpressure, but not a layer consisting of polyurethane, which adjoins the inner sheath.

In one embodiment of the invention, the tank comprises a film as an outer shell, which preferably also has good heat-insulating properties. The outer foil protects an adjacent inner layer of the tank. A suitable, about 10 mm thick film is available under the trade name "Mija". In order to equip an aircraft with a tank according to the invention, in one embodiment of the invention, the above-mentioned outer film is first applied to walls of a room in the aircraft. In particular, a space in a wing of the aircraft is lined with a foil.

An aircraft wing or a wing of an aircraft of today's design consists of two milled parts, namely an upper side and a lower side. Internal stringer (longitudinal reinforcements) of such a wing are milled out. Stringer such a wing protrude regularly depending on the size of the wing to 120 mm into the interior of the wing. In order to retrofit an aircraft with a tank according to the invention, in one embodiment u. a. Applied to such stringers a first outer film and in particular glued. The film can be easily adapted to the given geometries.

In a next step, heat-insulating, preferably made of plastic tiles are applied to the film. For example, the tiles may be made of polyurethanes. The tiles are preferably between 6 and 10 cm thick. With tiles, the heat insulating layer thus provided can be easily adapted to predetermined geometries. The tiles are preferably adhered to the film, for example, with a silicone adhesive so as to attach the tiles quickly.

Subsequently, a pressure-resistant shell is applied to the inside of the tile. Preferably, the inside is previously provided with an adhesive. Thereafter, the pressure-resistant shell is brought into the interior and inflated. The cover then attaches itself to the tiles and is thus glued to them.

On wing tanks with deep-frozen gas, particularly high demands are to be made with regard to thermal insulation, so that there is no additional risk of vane icing, especially during landings. Therefore, in one embodiment, a heating foil is applied to the wings of an aircraft in order to be able to counteract icing by heating with electrical energy. A very thin two-dimensional sheet of carbon is particularly suitable as a heating foil. The material used is very particularly preferably "graphene", which was developed by Prof. Andre Greim from the Netherlands, which, moreover, can advantageously also be made gas-tight.

Preferably, one or more existing kerosene tanks of an aircraft are retrofitted in the manner described, and in particular tanks of a wing, which adjoin the aircraft fuselage, ie wing root tanks. Other tanks of an aircraft, which are located further out in the wings, however, are not converted. According to the invention, the kerosene stored therein serves as safety, for example in order to be able to operate an aircraft even if it consumes more than the fuel originally intended for a flight.

If a tank is retrofitted in the manner described, two gas-tight casings are available, namely, on the one hand, an outer shell of the kerosene tank and, on the other hand, the inner pressure-resistant shell, which is particularly stable if it comprises aramid. In turn, graphene is particularly preferred as the outer gastight shell, since this material is particularly gas-tight. Graphene is extremely thin and therefore light that such a film is also referred to as a two-dimensional film. Graphene is only one atomic layer thick. As a result, a low-temperature fuel is then stored very safe. Especially problematic is the boil-off gas, which can ignite, even though the flame temperature is 400 ° C higher than kerosene. The safety requirements that must be met by a corresponding tank are correspondingly high.

In an Airbus A 380, 15 to 20 tons of weight can be saved by the invention if the aircraft is refueled with LNG and kerosene-filled tanks are only available for reserve reasons as described correspondingly limited. The specified weight saving already takes into account the additional weight that occurs when refitting tanks and additional fuel lines. The fuel weight saving is therefore higher.

An aircraft which is to be retrofitted with tanks according to the invention is preferably retrofitted with further tanks, which are installed, for example, to the left and right of a central tank of an aircraft. Sufficient space is available for passenger aircraft in the long-haul area. This provides extra tank volume needed because the volume of LNG is greater than that of kerosene for the same energy content.

In one embodiment of the invention, tubes and coupling systems connected to a tank according to the invention are also provided with a shell of graphene, for example wrapped in such a way that the graphene foil further improves gas-tightness.

A graph of graphene can be easily unwound and applied with the aid of another film. Due to adhesion, graphene adheres very easily and reliably to other surfaces.

In one embodiment of the invention, a space provided for the tank comprises scandium. But it can also be an existing scandium, outer film that limits the tank space. It succeeds in such a weight reduction, for example, compared to tanks that have an outer shell made of aluminum. For the same stability, scandium is lighter compared to aluminum.

In one embodiment, the inner shell of the tank includes webs or apertured walls that extend from an inner wall of the shell to an opposite inner wall and are secured to both inner walls. These webs or walls contribute to improved that a pressure prevailing in the tank overpressure is absorbed by the inner shell. The holes provided with walls are preferably arranged honeycomb to each other.

1 shows a tank in section, an outer metallic, preferably made of aluminum shell 1 has, a film adjacent thereto 2 adjacent, polyurethane-made tiles 3 and an adjacent aramid shell 4 , In addition, the tank is with one or more inlets or outlets 5 provided, which for safety reasons preferably lead out of the tank as shown above.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19543163 [0003]
• DE 19816651 C2 [0004]
• US 2006278761 A [0005]
• DE 3309768 A1 [0006]

Claims (20)

Tank for a cryogenic fuel with an outer structure and a flexible, pressure-resistant, cold-resistant inner shell ( 4 ). Tank according to claim 1, wherein the inner shell ( 4 ) can withstand a pressure of 2 bar absolute, preferably of 3 bar absolute. Tank according to one of the preceding claims, in which the inner shell ( 4 ) is cold-resistant at -170 ° C. Tank according to one of the preceding claims, in which the inner shell ( 4 ) consists of aramid or is reinforced by aramid. Tank according to one of the preceding claims, in which the inner shell ( 4 ) is an aramid shell. Tank according to one of the preceding claims, in which the inner shell ( 4 ) on a compressible layer ( 3 ) is present. Tank according to the preceding claim, in which the compressible layer ( 3 ) is at least 8 cm thick and / or made of plastic. Tank according to the preceding claim, in which the compressible layer ( 3 ) consists of polyurethanes. Tank according to one of the two preceding claims, in which the compressible layer ( 3 ) is formed by tiles. Tank according to one of the preceding claims with a foil ( 2 ) from the outside on a compressible, heat-insulating layer ( 3 ) is present. Tank, in particular according to one of the preceding walls with an outer shell consisting of graphene. Tank according to one of the preceding claims with associated pipes and / or coupling elements which are shielded with graphene gas-tight to the outside. Tank in particular according to one of the preceding claims with a container formed from scandium. Aircraft with a tank according to one of the preceding claims. Aircraft, in particular according to the preceding claim, with an electrically heatable film on aircraft wings. Aircraft according to the preceding claim, wherein the heatable film is formed from graphene. A method of retrofitting an aircraft with a cryogenic fuel tank by forming a kerosene tank with a foil ( 2 ), on the film of plastic existing tiles ( 3 ) and on the tiles ( 3 ) a pressure-resistant inner shell ( 4 ) is applied, preferably glued. Method according to the preceding claim, in which the inner shell ( 4 ) is an aramid shell. Method according to one of the two preceding claims, in which the tiles ( 3 ) consist of polyurethanes. Method according to one of the three preceding claims, in which tanks located inside are retrofitted by wings which adjoin the aircraft fuselage, but not tanks which lie outside relative to it.

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