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A fuel tank is safe container for flammable liquids and typically part of an engine system in which the fuel is stored and propelled (fuel pump) or released (pressurized gas) into an engine. Fuel tanks range in size and complexity from the small plastic tank of a butane lighter to the multi-chambered cryogenic Space Shuttle external tank.

The fuel tanks for B-25 bombers

left: filler neck of a BMW for hydrogen, right filler neck for gasoline, Museum Autovision, Altlußheim, Germany

Typically, a fuel tank must allow or provide the following:

• Safe (UL Approved) fuel storage, there is some concern that UL (Underwriters Laboratories) is not the final arbitor of safety.
• Filling (the fuel tank must be filled in a secure way) No Sparks.
• Storage of fuel (the system must contain a given quantity of fuel and must avoid leakage and limit evaporative emissions)
• Provide a method for determining level of fuel in tank, Gauging (the remaining quantity of fuel in the tank must be measured or evaluated)
• Venting (if over-pressure is not allowed, the fuel vapors must be managed through valves)
• Feeding of the engine (through a pump)
• Anticipate potentials for damage and provide safe survival potential.

Plastic (HDPE) as a fuel tank material of construction, while functionally viable in the short term there is a long term potential for the container to become staturated as fuels such as diesel and gasoline are able to permeate the HDPE material.

Considering the inertia and kinetic energy of transported fuel in a plastic tank being transported by a vehicle, stress cracking is a definite potential. Add stress cracking to the flammable nature of a fuel being transported and you have what should be an important safety consideration of a potential catostrophic failure nature. Emergencies aside HDPE plastic is suitable for short term storage of diesel and gasoline. Underwriters Laboratories approved (UL 142) tanks would be a minimum design consideration.

[edit] Automotive

For each new vehicle a specific fuel system has to be developed, as they must optimize the empty space left by the car architecture.

Moreover, for one car model, different versions of fuel system architectures have to be developed with more or less components, depending on the type of the car, the type of fuel (gasoline or diesel), nozzle models and the region where the car will be circulating.

Two technologies are used to make fuel tanks for automobiles:

• Plastic High density polyethylene (HDPE) fuel tanks produced through blow moulding. This technology is increasingly used as it now shows its capacity to obtain very low emissions of fuel (see Partial zero-emissions vehicle). HDPE can also allow for complex shapes to be formed, this means the tank to be mounted directly over the rear axle, saving space and improving crash safety. Initially there were concerns over the low fracture toughness of HDPE, when compared to steel or aluminium. Concern for safety and long term ability to function should be considered and monitored.

• Metal (steel or aluminium) fuel tanks obtained by welding of stamped sheets. Although this technology is very good in limiting fuel emissions, it tends to be less competitive and thus less on the market.

[edit] Remote opening

Modern cars often feature remote opening of the fuel tank fuel filler flap using an electric motor or cable release. More and more cars can now be seen with fuel tanks that cannot be opened by hand or by any way from the outside of the car. This is done for both convenience as well as security.

[edit] Reserve tank

Sometimes called the reserve tank is a secondary fuel tank (in many cars/bikes it contains ~15% of the capacity of the primary tank)these are more commonly found on bikes, older cars (some without fuel gadgets) and vehicles designed for long distance or special use. A light on the instrument panel of autos typically illuminates when the fuel level dips below a certain point in the tank. There is no current standard, although some efforts are made to collect this data for all automobiles.

In vehicles modified for endurance the primary tank (the one that comes with the car) is made into a Reserve tank and a larger one installed. Some 4x4 vehicles can be fitted with a secondary (or sub-tank) by the dealership.

[edit] Racing fuel cells

A racing fuel cell is a fuel container that differs from an ordinary fuel tank in the following ways: It has a flexible inner liner to minimize the potential for punctures in the event of a collision or other mishap resulting in serious damage to the vehicle. It is filled with an open-cell foam core to prevent explosion of vapor in the empty portion of the tank and to minimize sloshing of fuel during competition that may unbalance the vehicle or cause inadequate fuel (fuel starvation) delivery to the motor.

[edit] Placement and Safety

Gas tank in an unsafe position behind the rear axle. Mercedes-Benz 300SL

For safety considerations, in modern cars the fuel tank is usually located ahead of the rear axle, out of the Crumple zones of the car. This location has been used by Volvo since 1974 ^[1].

Cars like the Ford Pinto or the Ford Crown Victoria are notorious for having the gas tank behind the rear axle. Since 1980 new Ford models corrected this problem and had the fuel tank in front of the rear axle ^[2].

General Motors 1973-1987 Pick Up trucks have the fuel tank located outside the frame. According to the Center for Auto Safety this creates a fire hazard ^[3].

[edit] Aircraft

Aircraft typically use three types of fuel tanks: integral, rigid removable, and bladder.

• Integral tanks are areas inside the aircraft structure that have been sealed to allow fuel storage. An example of this type is the "wet wing" commonly used in larger aircraft. Since these tanks are part of the aircraft structure, they cannot be removed for service or inspection. Inspection panels must be provided to allow internal inspection, repair, and overall servicing of the tank. Most large transport aircraft use this system, storing fuel in the wings and/or tail of the airplane.

• Rigid removable tanks are installed in a compartment designed to accommodate the tank. They are typically of metal construction, and may be removed for inspection, replacement, or repair. The aircraft does not rely on the tank for structural integrity. These tanks are commonly found in smaller general aviation aircraft, such as the Cessna 172.

• Bladder tanks are reinforced rubberized bags installed in a section of aircraft structure designed to accommodate the weight of the fuel. The bladder is rolled up and installed into the compartment through the fuel filler neck or access panel, and is secured by means of metal buttons or snaps inside the compartment. Many high-performance light aircraft and some smaller turboprops use bladder tanks.

Fuel tanks have also been implicated in aviation disasters, being the cause of the accident or worsening it (fuel tank explosion) ^[4]. For example:

• The official explanation for the explosion and subsequent crash of TWA Flight 800 is that an explosive fuel/air mixture was created in one of the aircraft's fuel tanks. Faulty wiring then provided an ignition source within the tank, destroying the airliner. While the accuracy of the official findings is still questioned in this case, similar explosions have occurred in other aircraft. It is possible to reduce the chance of fuel tank explosions by a fuel tank inerting system or foam in the tanks ^[5].

• Burning fuel can set fire or explode the same airplane or adjacent objects and people. On 17 December 1960 in Munich,Germany, a Twin Engine Convair 346 crashed into a major street. Burning fuel set fire to a tramcar. All 20 people aboard the plane and 32 passengers of the tram died. ^[6].

[edit] Water supply

Water supply systems can have primary or backup power supplied by diesel-fueled generators fed by a small "day tank" and a much larger bulk storage fuel tank. ^{[7] [8]}

[edit] Safety

The proper design and construction of a fuel tank plays a major role in the safety of the system of which the tank is a part.

In most cases intact fuel tanks are very safe, as the tank is full of fuel vapour/air mixture which is well above the flammability limits, and thus cannot burn even if an ignition source were to be present (which is rare).

In automotive applications, improper placement of the fuel tank has led to increased probability of fire in collisions. Circa 1990, General Motors faced over a hundred lawsuits related to fires allegedly caused by GM's decision to place the fuel tanks in its pickup trucks outside the protection of the vehicle's frame [2]. Ford's Pinto also sparked controversy for putting the gas tank in a poorly reinforced area which can cause deadly fires and explosions if the car got into a rear end collision, costing Ford $125 million. In 1993, as one of these lawsuits resulted in a US$101 million judgement against GM (later overturned), the television show Dateline NBC created its own controversy by staging an example of the failures. When it was discovered that Dateline's consultants had rigged the truck with incendiary devices in order to guarantee a fire, GM filed a defamation suit, and several NBC employees were fired.^{[citation needed]}

[edit] See also

• Fast fuel system
• Fuel line
• Fuel pump
• Electrification
• Explosion
• Fuel leak
• Jettison

[edit] References

[edit] External links

• Tank Sealing
• Reduction of Fuel Tank Flammability in Transport Category Airplanes (U.S. Environmental Protection Agency‎).
• Fuel tank harmonization (Aviation Rulemaking Advisory Committee)
• U.S. Unveils New Rule On Airplane Fuel Tanks, by Department of Transportation.