WO2002081247A1

WO2002081247A1 - Impact-resistant fuel tank device

Info

Publication number: WO2002081247A1
Application number: PCT/GB2002/001638
Authority: WO
Inventors: James Edward Atkinson; David John Shepherd; Philip Vaughan
Original assignee: Darchem Engineering Limited
Priority date: 2001-04-06
Filing date: 2002-04-05
Publication date: 2002-10-17
Also published as: GB2374056B; GB0108653D0; GB2374056A

Abstract

An impact and/or explosion resistant insert for a fuel tank comprising a matrix of rigid cells with voids that allow storage of liquid fuel; where the matrix may prevent rupture of a fuel tank during an impact or may be progressively and irreversibly crushed when subjected to a sufficiently large impact; thereby absorbing energy and also reducing the risk of igniting fuel released from the cells to the air.

Description

Impact-resistant Fuel Tank Device

This invention relates to an impact and/or explosion resistant liquid storage tank device, particularly such a device suitable for use within a vehicle fuel tank.

The hazards associated with storage of hazardous and flammable liquids, particularly for transport applications are well known. Thus, collisions between vehicles such as lorries or trains and accidents in aircraft may all result in fuel tanks being subjected to destructive impact forces that can for an instant over pressurise the contents and then rupture the fuel tank allowing fuel to escape. Such circumstances frequently result in the formation of atomised liquid fuel and in this event the possibility of a catastrophic explosion through ignition of the intimate fuel air mixture is much greater.

The use of fuel additives that modify the atomisation characteristics of the liquid fuel with the aim of reducing the risk of fire and explosion following accidental impacts is known. However, in itself it only partially effective. It is also known to install baffles within fuel tanks in order to mitigate the effects of over pressurisation. Again such systems are only partially effective and are also generally difficult to install within fuel tanks.

An object of the present invention is to provide an improved means of storing hazardous liquids, particularly flammable liquids and fuels that can be used alone or in combination with other measures to reduce the risk of accidental ignition of fuel in the event of an accidental impact releasing fuel to the air. Another object of the invention is to provide a fuel tank that has greater resistance to impact forces. A further object of the invention is to provide a fuel tank that resists discharge of fuel to the air when ruptured by an impact.

According to one aspect of the invention there is provided an impact and/or explosion resistant fuel tank insert comprising a plurality of rigid cells, having walls that present a storage volume for fuel, wherein the cells may be progressively and irreversibly crushed when subjected to a sufficiently large impact; thereby absorbing energy and also reducing the risk of igniting fuel released from the cells to the air. Preferably, the cells are elongate and preferably at least some of the cells are substantially parallel. The plurality of cells will normally take the form of a matrix. The longitudinal axes of a first group of cells may be substantially parallel and lie in a first direction and the longitudinal axes of a second group of cells may also be substantially parallel but lie in a second direction. The first and second directions may be substantially orthogonal to one another. The cells may be polygonal, oval, elliptical or curved in a cross section orthogonal to the longitudinal axis of the cells. The cells are preferably hexagonal in a cross section. Preferably, the hexagon is regular and the distance between parallel sides is between 6 and 100 mm, more preferably about 25 mm. Preferably the wall thickness of the cell is between 0.2 and 1 mm, more preferably about 0.4 mm. Preferably, the volume of material forming the cell matrix is between 1 to 12% of the total volume of the matrix, and preferably about 6% of that volume.

An aperture or void in the matrix may be provided in order to assist ingress of fuel during filling of the tank. The aperture or void may have generally cylindrical boundaries within the matrix.

Preferably, the fuel tank insert is made of a plastically deformable material such as a metal, more preferably of steel.

The fuel tank insert will normally be enclosed within a fuel tank. Preferably, the longitudinal axis of cells lie in the same direction or directions as most likely direction(s) of impact. The fuel tank may have a header volume located at an end of the tank or at the end of a group of parallel cells in order to assist free movement of fuel during filling of the tank.

In a further embodiment the invention comprises an impact and/or explosion resistant fuel tank insert system wherein a plurality of fuel tank inserts as together form a composite insert used together to substantially fill a fuel tank.

In another embodiment the invention comprises a fuel tank having a plastically deformable non-planar insert that presents individual localised storage volumes for fuel, wherein the insert may be progressively and irreversibly crushed when subjected to a sufficiently large impact, thereby absorbing energy; wherein the localised storage volumes reduce fuel egress from the tank and hence risk of accidental ignition.

In a yet further embodiment the invention comprises an impact and/or explosion resistant fuel tank system comprising an insert having a plurality of rigid cells comprising walls that present a storage volume for fuel, wherein the cells substantially resist deformation when subjected to an impact; thereby preserving the integrity of the tank and thus preventing release of fuel into the air.

Embodiments of the invention will now be described, by way of example only, with reference to the following schematic drawings in which:

Figure 1 is a perspective view of an embodiment of the invention as seen from above,

Figure 2 shows the preferred direction of impact,

Figure 3 shows an insert with volumes cut out to accommodate various tank equipment,

Figure 4 shows a partial cross section corresponding to Figure 1 ,

Figure 5 shows a variety of cell configurations and joints,

Figure 6 shows a bi-directional matrix constructed using corrugated sheets,

Figure 7 shows cells prior to impact and after impact, and

Figure 8 shows a further embodiment of the invention where the device comprises a number of separate components that may be fitted within a conventional fuel tank.

A first embodiment of the invention will now be described by reference to Figures 1 to 7. Figure 1 shows a fuel tank insert 10 (without a surrounding fuel container) comprising a matrix of longitudinal cells 12 of equal length arranged side by side to form trapezoid end faces 14 and 16. The insert 10 is rectangular in plan view, end views and underside view. The matrix of cells may be formed by joining appropriately angularly corrugated sheets; a first sheet on top of a similar but inverted second sheet. The insert is dimensioned to fit within a similarly shaped fuel tank. However, the tank may provide free header space adjacent end face 14 and/or face 16 in order to facilitate filling of the tank and insert with fuel. Figure 2 shows the preferred orientation of the insert when mounted within the fuel tank of a vehicle relative to the normal direction of travel of the vehicle. Thus, in the event of a destructive impact the force of the impact will ideally be in a direction D. This arrangement has two advantages. Firstly, the insert matrix 10 has greatest strength in this direction and so a greater energy absorbing capacity. Secondly, on impact in direction D the ends of the cells progressively collapse such that they eventually substantially seal the damaged end of the cell, thus encouraging retention of at least part of the fuel inventory following a serious collision or impact.

Figure 3 shows the addition of apertures or voids 22, 24, 26 and 28 within the fuel tank insert 10. The upper face of the insert has an aperture 22 that is rectangular in plan view, extending downwardly through the matrix to the lower face 20 of the insert. This void is provided to assist the ingress of liquid fuel during filling and so is preferably located near the fuel inlet (not shown). The position of the void within the matrix may vary. However, it is preferably arranged so that it extends through the entire length, depth or height of the matrix in a direction generally perpendicular to the longitudinal axes of the cells. Figure 3 also shows a void 24 in the upper face of the insert that is generally rectangular in section and is provided in order to accommodate a protrusion in the inner surface of the fuel tank (not shown). The position and number of such voids on the outer surface of the insert may vary according to the requirements of the particular fuel tank being protected. A slot 26 is provided in end face 14 of the insert 10 in order to provide space for a fuel level gauge or other similar equipment and a slot 28 is provided in a side face 18 of the insert 10 in order to accommodate a fuel take off or overflow pipe.

Figure 4 shows a cross section of some of the cells of Figure 1. The cells walls are typically made of steel and are typically 0.4 mm thickness (T). The distance between opposite parallel sides of a cell (L) is typically 25 mm.

Figure 5 shows how a matrix of cells may be formed by joining adjacent corrugated sheets 30, 32 at points 34, for example, by welding a first sheet 30 to an inverted second sheet 32. Spot-welding is particularly suitable for joining metal sheets such as steel. Figures 5B and 5C show how various cell shapes can be constructed from suitably corrugated sheets. Other cell shapes are possible the choice in part being influenced by design factors such as crush resistance required in various planes. Thus, oval or elliptical cells or the like offer greater crush resistance along the major axis than along the minor axis and therefore may be preferred when it is desired to produce a matrix that has different crush resistance in each plane (x,y,z).

All of the inserts illustrated in Figures 1 to 5 use a one-directional matrix, that is all of the longitudinal axes of the cells are parallel and lie in a single direction. In contrast the fuel tank insert illustrated in Figure 6 uses a bi-directional matrix; that is the longitudinal axes of a first group of cells 40 lie in a first direction (X) while the longitudinal axes of the remaining cells 42 lie in a second direction (Y). In the example shown in Figure 6 the directions X and Y are mutually orthogonal. While this is a generally preferred arrangement other orientations are possible; for example directions X and Y may be at a mutually acute or obtuse angle. A bi-directional matrix such as that illustrated in Figure 6 will have high strength and good energy absoφtion properties in both the X and Y direction. It is thus particularly suitable for use in situations where impact damage to a tank is judged to be likely in more than one direction or plane. The fuel tank insert using a bi-directional matrix may be constructed by a similar to that described above for a one-directional matrix, except that the direction of the corrugations is changed in alternate layers.

The fuel tank insert will normally be made of a plastically deformable material; for example a metal. However, where it is important that the weight of the fuel tank be minimised, for example in aircraft, non-metallic plastically deformable materials are preferable; for example, polypropylene.

Figure 8 shows a second embodiment of the invention wherein several inserts 50-56 arranged side by side and end to end form a composite assembly that may piece by piece be inserted within a fuel tank Fl, F2. This arrangement is particularly attractive when it is desired to retrofit an existing tank by adding inserts. This would not be possible using a single insert as shown in Figure 1 without disassembly of the fuel tank Fl. The insert arrangement shown is only indicative and the number and the shape of inserts can take many forms.

The fuel tank inserts described in the above embodiments of the invention help prevent movement of fuel within a tank and so avoid the need to use baffles. Optionally, the inserts may be physically fixed within the tank; for example, by welding or riveting or other conventional fixing method. Such fixing may reduce expansion of the tank during an impact.

The fuel tank inserts of the invention may be used alone or in combination with other means to reduce the likelihood of ignition of fuel following impact damage to a fuel tank. Addition of an insert according to the invention has only a marginal impact on the fuel capacity of a tank (see Table 1) and a modest impact on the weight of a full tank, especially when replacing baffles. The fill rate of the fuel tank is not noticeably affected and the fuel can be withdrawn from the tank without the need for any special expulsion system.

Table 1 - Typical Fuel Tank Data

Weight, kg Volume occupied by Tank fuel capacity,

Tank & Insert by insert matrix % (litres) (litres)

245 6(26) 440

By placing an insert according to the invention within a tank containing a liquid, particularly a flammable / hazardous liquid, the extent of any fuel loss and atomisation during a destructive impact event is greatly reduced (thereby greatly reducing the risk of fire and explosions). The cell structure creates a channel arrangement in which the fuel is held, this modifies the bulk liquid properties of the fuel such that that the fuel does not behave as a single entity within the tank, and thus bulk fuel movement is largely prevented during any destructive impact event. The cell matrix performs in three different ways, depending on the type of impact it suffers.

The first possibility is that an impact that creates a force less than the crush strength of the matrix, that normally results in an undamaged tank.

The second possibility is that an impact force that is greater than the crush strength, which normally results in crushing of the honeycomb cells against the outer skin of the tank, thereby creating a sealing action across both ends of each cell (see Figure 7) to prevent or at least considerably reduce atomisation.

The third possibility is that the matrix suffers a point impact, resulting in crushing of the contacted cells and generally resulting in fuel only being expelled from those impacted cells.

Claims

1. An impact and/or explosion resistant fuel tank insert comprising a plurality of rigid cells, having walls that present a storage volume for fuel, wherein the cells may be progressively and irreversibly crushed when subjected to a sufficiently large impact; thereby absorbing energy and also reducing the risk of igniting fuel released from the cells to the air.

2. A fuel tank insert according to Claim 1 wherein the cells are elongate.

3. A fuel tank insert according to Claim 2 wherein the longitudinal axes of at least some of the cells are substantially parallel.

4. A fuel cell insert according to Claim 2 wherein the longitudinal axes of a first group of cells are substantially parallel and lie in a first direction and the longitudinal axes of a second group of cells are also substantially parallel but lie in a second direction.

5. A fuel tank insert according to Claim 4 wherein the first and second directions are substantially orthogonal one another.

6. A fuel tank insert according to any of Claims 2 to 5 wherein the cells are oval, elliptical or curved in a cross section orthogonal to the longitudinal axis of the cells.

7. A fuel tank insert according to any of Claims 2 to 5 wherein the cells are polygonal, preferably hexagonal in a cross section orthogonal to the longitudinal axis of the cells.

8. A fuel tank insert according to Claim 7 wherein the hexagon is regular and the distance between parallel sides (X) is between 6 and 100 mm, and preferably between 20 and 30 mm.

9. A fuel tank insert according to any preceding claim wherein the wall thickness of the cell (T) is between 0.2 and 1 mm, preferably about 0.4 mm.

10. A fuel tank insert according to any preceding claim wherein volume of material forming the cell matrix is between 1 and 12 % of the total volume of the matrix and, preferably about 6% of that volume.

11. A fuel tank insert according to any preceding claim wherein an aperture or void in the matrix is provided in order to assist ingress of fuel during filling of the tank.

12. A fuel tank insert according to Claim 11 wherein the void has generally cylindrical boundaries with the matrix.

13. A fuel tank insert according to any preceding claim wherein the cell walls are of metal, preferably steel.

14. A fuel tank insert according to any preceding claim enclosed within a fuel tank.

15. A fuel tank and insert according to any of Claims 2 to 14 wherein the longitudinal axis of cells lie in the same direction or directions as most likely direction(s) of impact.

16. A fuel tank and insert according to Claim 14 or 15 comprising a header volume located at an end of the tank or at the end of a group of parallel cells in order to assist free movement of fuel during filling of the tank.

17. An impact and/or explosion resistant fuel tank insert system wherein a plurality of fuel tank inserts according to any of Claims 1 to 16 form a composite insert used together to substantially fill a fuel tank.

18. An impact resistant liquid storage tank insert comprising a plurality of rigid cells, having walls that present a storage volume for fuel, wherein the cells may be progressively and irreversibly crushed when subjected to a sufficiently large impact; thereby absorbing energy and also reducing the risk of loss and/or atomisation of the liquid released from the cells.

19. A fuel tank having a plastically deformable non-planar insert that presents individual localised storage volumes for fuel, wherein the insert may be progressively and irreversibly crushed when subjected to a sufficiently large impact, thereby absorbing energy; wherein the localised storage volumes reduce fuel egress from the tank and hence risk of accidental ignition.

20. An impact and/or explosion resistant fuel tank system comprising an insert having a plurality of rigid cells comprising walls that present a storage volume for fuel, wherein the cells substantially resist deformation when subjected to an impact; thereby preserving the integrity of the tank and thus preventing release of fuel into the air.

21. A fuel tank insert substantially as described above by reference to any of Figures 1 to 8.