Explosion-resistant fuel tank device

An explosion resistant fuel tank comprises an explosion resistant insert, which comprises a compressible resilient structure. The structure is placed within a conventional fuel tank, and has interconnecting capillary-sized cells for containing a liquid fuel. The cells have equivalent cross-sectional diameters of no more than about 0.005 inch. The fuel tank also comprises means for compressing the compressible structure to a reduced volume so that the liquid fuel contained therein passes out of the compressible structure. In one version, the compressible structure is a sponge. In another version, the compressible structure comprises an elongated honeycomb structure having elongated tubular cells lined up side by side. The honeycomb is substantially incompressible along the length of the tubular cells.

CROSS-REFERENCE TO RELATED APPLICATION 
This application is related to U.S. Ser. No. 792,743, filed on Oct. 30, 
1985, which disclosure is incorporated by reference herein. 
BACKGROUND OF THE INVENTION 
This invention relates to an explosion resistant fuel tank. 
It is common knowledge that conventional fuel tanks on vehicles such as 
cars, boats and aircrafts can explode on severe impact. The liquid fuels 
generally used in these vehicles, such as gasoline or aviation fuel, are 
relatively volatile. When the fuel tank becomes ruptured on impact, the 
force of the impact can cause the fuel to be ejected violently from the 
tank, often splashing over a large area. The resulting increase in 
evaporation surface area leads to rapid volatilization. The mixture of the 
fuel vapors and the oxygen in the air can be dangerous. The mixture can be 
set off by the smallest of sparks or open fires to cause a serious 
explosion. Many travelers have died a fiery death from exploding fuel 
tanks. What is needed is a fuel tank which is less prone to explode on 
impact. 
SUMMARY 
The present invention satisfies this need by incorporating an explosion 
resistant insert within a conventional fuel tank container. The insert 
comprises a compressible, resilient structure comprising a plurality of 
cells for containing a liquid fuel. The compressible structure decreases 
in volume from a first volume to a reduced second volume when subjected to 
a compressive force, the reduced second volume being no more than about 
75% of the first volume. Compression of the structure forces the liquid 
fuel to flow out of the structure. The compressible structure is 
sufficiently resilient that when the compressive force is released the 
structure returns to have the first volume for soaking up additional 
liquid fuel. 
Preferably the compressible structure is formed of a non-wicking, 
non-combustible material which is compatible with the liquid fuel. 
Preferably the cells in the compressible structure are capillary sized 
with equivalent cross-sectional diameters of no more than about 0.005 
inch. Preferably the compressible structure is formed of a heat-shrinkable 
material such that its surface deforms when exposed to temperatures higher 
than about 150.degree. C. to become impervious to the liquid fuel. 
In one preferred version, the compressible structure is an open pore 
sponge. In another preferred version, the compressible structure is an 
elongated honeycomb structure comprising elongated tubular cells, the 
honeycomb structure being substantially incompressible along at least one 
of its dimensions. The cross-section of the cells need not be hexagonal. 
Both the size of the pores of the sponge and the cross-sectional dimension 
of the tubular cells are preferably less than about 0.005 inch, measured 
as equivalent cross-sectional diameter. In the honeycomb version, the fuel 
tank fuel tank is oriented so that the substantially incompressible 
dimension of the honeycomb is in line with the usual direction of travel 
of the vehicle fitted with the fuel tank fuel tank. 
The compression means can comprise an inflatable bag placed inside the 
container and proximate to the compressible structure, and means for 
inflating the bag so as to apply compressive forces on the compressible 
structure. There can also be more than one inflatable bag and more than 
one compressible structure, with each compressible structure being placed 
between two bags, or between a bag and the wall of the container. In the 
case of the honeycomb, preferably the compressive forces are substantially 
transverse to the incompressible dimension of the honeycomb. 
In another version, the insert further comprises a flexible bladder inside 
the container. The bladder has an inlet and an outlet. The compressible 
structure is inside the bladder. Preferably the compressible structure 
substantially fills the bladder and is capable of swelling to a volume 
larger than that of the bladder, for soaking up additional liquid fuel. 
Preferably the bladder is formed of a rupture resistant, non-combustible 
material compatible with the liquid fuel. 
In the version equipped with the flexible bladder, the compressive means 
preferably comprise means biasing the pressures at the outlet and the 
outside of the bladder, such that both the bladder and the resilient 
structure therein are compressed to have reduced volumes.

DESCRIPTION 
The present invention incorporates an explosion resistant insert within a 
conventional fuel tank container. The container usually comprises a metal 
shell in the shape of a tank, but can also be made of suitable plastics or 
other materials. The insert comprises a compressible structure comprising 
a plurality of cells for containing a liquid fuel. The compressible 
structure decreases in volume from a first volume to a reduced second 
volume when subject to a compressive force, the reduced second volume 
being no more than about 75% of the first volume. The compressible 
structure has inherent memory and resiliency, and is capable of regaining 
its first volume when the compressive forces are removed for soaking up 
additional liquid fuel. Preferably the compressible structure has 
capillary sized cells so that the liquid fuel is usually held within the 
compressible struction by capillary action. By "capillary sized cells" it 
is meant that the cells each have an equivalent cross-sectional diameter 
of no more than about 0.005 inch. Equivalent cross-sectional diameter, D, 
is defined as: 
##EQU1## 
where A is the cross sectiona- area of the cell. There are also means for 
compressing the compressible structure to the reduced second volume such 
that the liquid fuel passes out of the compressible structure. 
Examples of the fuels for which the invention is useful are gasoline, 
diesel fuel, kerosene, aviation fuels, etc. Examples of vehicles for which 
this invention is useful include automobiles, motorcycles, aircrafts, 
boats, etc. 
With reference to FIG. 1, the explosion resistant insert 10 is placed 
within a conventional fuel tank container 15. The container 15 preferably 
comprises an inlet 20 and an outlet 21 which are preferably fitted with 
one-way flow valves 25 and 26, respectively. Preferably the inlet and 
outlet are on the bottom of the container 15. The inlet and outlet can be 
one and the same. 
The insert 10 comprises a compressible resilient structure 30, which can be 
a sponge 35. Preferably the sponge 35 comprises interconnecting open pores 
for containing a liquid fuel 40, the pore sizes are no more than about 
0.005 inch. The sponge 35 preferably is non-wicking and is formed of a 
non-combustible material compatible with the liquid fuel. The sponge can 
be formed of a heat-shrinkable material, wherein the surface of the 
sponge, when heated to a temperature above about 150.degree. C. shrinks to 
become impervious to the liquid fuel contained within the sponge. 
The sponge 35 rests on a porous support that keeps the sponge from getting 
into the inlet 20 and outlet 21, and also serves as a distribution header. 
Support 45 can be a thin layer of wire mesh. The support 45 can be a 
continuous layer covering the bottom of the container 15. It can also 
comprise discrete pieces covering the inlet and outlet openings only. 
In a preferred version, the means for compressing sponge 35 comprises an 
inflatable bag 50 inside the container 15, inflatable through a gas inlet 
55. The bag 50 can be inflated with air or other gases, preferably a gas 
that helps prevent explosions and does not support combustion, such as 
nitrogen and/or carbon dioxide. The bag 50 is placed proximate to the 
sponge 35 within the container 15. FIG. 1 shows the bag 50 deflated, when 
the space within the container 15 is substantially filled by the sponge 
35. When bag 50 is inflated, it exerts a compressive force on the sponge 
35. As shown in FIG. 2, the sponge 35 is thus compressed from its first 
volume to a reduced second volume, and the fuel 40 contained therein 
passes out of container 15 through the outlet 21. There is substantially 
no air within the container 15, except inside the bag 50. 
For larger fuel tanks, more than one compressible structure and more than 
one inflatable bag can be used. Each compressible structure is preferably 
sandwiched between two inflatable bags, or between an inflatable bag and 
the wall of tne container 15. This configuration allows more efficient 
compression of each compressible structure. 
In another version of the present invention, as shown in FIGS. 3 and 4, a 
compressible structure 30 further comprises a flexible bladder 60 inside 
the container 15. Bladder 60 has an inlet 20' and an outlet 21' extending 
outside the container 15. The sponge 35' is inside tne bladder 60. The 
sponge 35' is capable of swelling to a volume larger than that of the 
bladder, such that when it is released from the bladder, it is capable of 
soaking up more fuel than when the sponge is inside the bladder. There is 
no air within the bladder 60 when it is filled with the liquid fuel. The 
side of bladder 50 in contact with the fuel is formed of a non-combustible 
material compatible with the liquid fuel. Preferably the bladder 60 
comprises at least one layer of rupture resistant material. Suitable 
rupture resistant materials include Kevlar.TM. (aromatic polyamide) 
fabrics, which are generally used in bullet-proof vests, etc. 
In this version of the invention, the means for compressing the 
compressible structure can be a pressure biasing means, such as a pump, 
for creating a pressure differential between the outlet 21' and the space 
80 (FIG. 4) outside of the bladder 60. As shown by the schematic of FIG. 
3, the pressure biasing means can be a pump 65 which draws a suction on 
the outlet 21'. The pressure differential compresses the bladder 60 and 
the sponge 35 to occupy reduced volumes, as shown in FIG. 4, and the 
liquid fuel passes out of the container 15. As shown in FIG. 3, the liquid 
fuel 40 can be pumped by the pump 65 into a reservoir 70, which is 
equipped with a level sensor 75 which in turn controls the pump 65. The 
fuel 40 can then be passed to the engine of the vehicle, and can be partly 
recirculated to the container 15 through inlet 20'. 
Alternatively, the pressure differential can be created by pressurizing the 
space 80 (FIG. 4) between the bladder 60 and the container 15. Yet another 
alternative is to use the inflatable bag 50 as described above. 
In another version of the present invention, the compressible structure 30 
is substantially incompressible along at least one of its dimensions. When 
installed in the vehicle, the structure 30 is oriented so that its 
incompressible dimension is substantially in line with the usual direction 
of travel of the vehicle. Referring to FIG. 5, the compressible structure 
30 comprises an elongated honeycomb structure 85 having elongated tubular 
cells 90 arranged side by side. 
Preferably the mean cross-sectional diameter of each cell is no more than 
about 0.005 inch. The cross-section of the cells need not be hexagonal, 
although they can be. In fact, the cross-section of the cells can be any 
convenient shape that allows compression in at least one direction, and 
provides resiliency and memory such that the honeycomb structure 85 
regains its non-compressed volume when the compressive force is released. 
For example, as shown in FIGS. 7 and 8, the cells each have cross-sections 
formed from arcs 95. When the compressive forces are applied as shown in 
FIG. 7 and 8, the arcs flatten. Dimension B decreases and dimension A 
increases, and the volume of the honeycomb 85 also diminishes. When the 
compressive forces are released, the arcs regain their original shapes and 
the honeycomb 40 regains its normal non-compressed first volume. 
As shown in FIGS. 7 and 8, the honeycomb 85 is less compressible along 
dimension A than along dimension B. In aircraft applications, dimension A 
is preferably oriented substantially vertically, so that sudden changes in 
altitude due to air turbulences, etc., does not deform the honeycomb 
structure 85. For this reason, a honeycomb having a cross-section as shown 
in FIG. 7 and 8 is favored over one having a hexagonal cross-section. A 
hexagonal cross-section gives substantially uniform compressibility along 
directions transverse to the axes of the tubular cells, and is undesirable 
for aircraft applications. 
To facilitate fuel flow into and out of the capillary sized cells, there 
can be headers 100 and 101 on the two ends of the honeycomb 85 as shown in 
FIG. 5. Each header comprises a porous material, which is preferably 
compressible. The headers can be formed of the sponge described above. 
Preferably the inlet 20' and the outlet 21' lead into the headers 100 and 
101, respectively. 
Honeycomb structures are usually prepared by one of two processes: 
expansion or corrugation. To impart resiliency and memory, the corrugation 
method is preferred. Sheets of the material for forming the walls of the 
elongated cells 90 are preformed, usually between corrugating rollers, to 
give the correct corrugation (the aves 95). The sheets are then formed 
into the honeycomb by the application of appropriate adhesives. 
Alternatively, the honeycomb 85 can be extruded. 
Optionally the elongated cells 90 can have perforated walls so that they 
are in liquid communication with adjacent cells through their walls. The 
perforations can be formed in the honeycomb 85 after the honeycomb is 
formed. Alternatively the perforations can be formed in the sheets of 
material for forming the walls of the elongated cells, before the sheets 
are corrugated. The perforations allow rapid fluid flow across cells so 
that the honeycomb structure can quickly regain its non-compressed first 
volume on removal of the compressive force. 
The honeycomb 85 and the headers 100 and 101 can be used in conjunction 
with either an inflatable bag 50 or a flexible bladder 60, or both, as 
described above, or with other compression means suitable for use with the 
sponge 35. One limitation is that the compression means should be disposed 
such that the compressive forces are substantially transverse to tne 
incompressible dimension of the honeycomb 85. Preferably the compressive 
forces are substantially perpendicular to the plane of the honeycomb 85 
that offers the least resistance to compression. FIG. 6 shows the 
honeycomb 85 in use with an inflatable bag 50, which is partly inflated. 
If the honeycomb is placed inside a bladder, it is preferable that the 
honeycomb 85 be capable of swelling to a volume larger than that of the 
bladder so that the honeycomb 85, or any part of it, can soak up 
additional fuel when released from the bladder. 
FIG. 9 shows an example of how the fuel tank of the present invention can 
be used in an airplane wing tank. Multiple compressible structures are 
placed within the wing tank. Each compressible structure 30, comprising a 
honeycomb 85 and the appropriate headers 100 and 101, is sandwiched 
between two inflatable bags 50. When the bags are pressurized, fuel 40 
passes out of the compressible structures through outlet 21, and through 
fuel line 105 to the engines. 
Preferably the honeycomb 85 is formed of a material which is incombustible 
or fire retardant, and which is compatible with the liquid fuel. 
Preferably the material is also heat shrinkable, such that the open ends 
of the tubular cells 90, when heated to a temperature above about 
105.degree. C., shrink to become substantially impervious to the liquid 
fuel, thereby retaining the liquid fuel within the honeycomb 85. 
The heat-shrinkable material suitable for forming the sponge 35 or 
honeycomb 85 can be many of the polymers known is the art to be useful 
production of heat-recoverable articles. Generally the material is of 
constant composition throughout; however laminates of different polymers 
bonded or fused together may be used in certain instances. Suitable 
polymers include, for example, polyolefins, especially polyethylene, 
copolymers of ethylene and vinyl acetate, copolymers of ethylene and ethyl 
acrylate; chlorinated and fluorinated polymers, especially polyvinyl 
chloride, polyvinylidene fluoride and polymers incorporating units from 
vinylidene fluoride, and hexafluorethylene; and rubbers such as 
ethylene/propylene rubber, chlorinated rubbers, e.g. Neoprene.TM., and 
silicone rubbers which may be used in a blend with a crystalline or glassy 
polymer such as an olefin polymer. All of the above materials can, if 
desired, be cross-linked for example by irradiation and/or chemical means. 
For both the sponge and honeycomb versions, liquid fuel 40 is normally 
retained within the capillary-sized cells (equivalent cross-sectional 
diameters less than about 0.005 inch) until the compressible structure 30 
is compressed. Surface tension and capillary action keeps the bulk of the 
fuel within the compressible structure 30, even when it, or any part 
thereof, is being released from the container 15. When the container 15 is 
ruptured on impact, the bulk of the fuel remain inside the compressible 
structure 30. Less fuel is spilled, and therefore the risk of explosion is 
diminished. 
The risk of explosion is even smaller when a flexible bladder is put around 
the sponge 35 or the honeycomb 85. When the container 15 is ruptured on 
impact, the fuel generally remains inside the bladder 60. In general the 
wall of a flexible bladder more difficult to rupture than the rigid walls 
of a conventional fuel tank, if all the walls have about the same tensile 
strength. On impact, the flexible bladder wall "gives" and the impact 
force is evenly distributed by the fuel inside the bladder to the inside 
surface of the bladder. Thus the impact force is distributed over a large 
area, and does less damage. 
Even in the event that the bladder itself becomes torn, the resilient 
structure 30 retains the bulk of the fuel therein. Therefore the liquid 
fuel is prevented from being spilled over a large area to create an 
explosive situation. Even if the fuel near the outside of the structure 30 
catches fire, the fire will not be sustained, because the structure 30 is 
non-wicking. Moreover, the surface of the structure 30 can shrink when 
exposed to heat (such as an open fire on the surface of the structure), so 
as to become impervious to the liquid fuel, and to retain the liquid fuel 
within the structure. Again the fire cannot be sustained without fuel. 
Overall, the particular combination described above is highly effective in 
preventing fuel tank explosions in vehicle collisions. 
In the honeycomb versions, the high structural strength of a honeycomb 
structure is used to great advantage. 
In use, the honeycomb 85 is oriented so that the elongated tubular cells 
are in line with the usual direction of travel of the vehicle. When the 
fuel tank is hit, it is more likely than not that the honeycomb 85 is hit 
with its incompressible dimension (along the length of the tubular cells) 
being normal to the surface of the object that hits it. Honeycomb 
structures are well known for their capability in dissipating and 
absorbing impact energy by permanent deformation along their substantially 
impressible axes. As compared to a conventional fuel tank, or even as 
compared to a fuel tank having a sponge 35 as the compressible structure, 
a fuel tank having the honeycomb-version of the compressible structure 30 
suffers the least amount of permanent deformation on impact. The honeycomb 
structure acts as a reinforcing element within the tank. If a bladder 35 
is also used, there is smaller chance of the bladder being ruptured on 
impact, as compared to the sponge version with the bladder. A large 
portion of the impact energy is absorbed by permanent deformation of the 
honeycomb structure, and the impact force is not fully brought to bear on 
the walls of the bladder 60. 
Although the present invention has been described in considerable detail 
with reference to certain versions thereof, other versions are possible. 
Therefore, the spirit and scope of the appended claims should not 
necessarily be limited to the description of the preferred versions 
contained herein.