Fuel tank
A fuel tank is safe container for flammable liquids. Though any storage tank for fuel may be so called, the term is typically applied to 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.
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[edit] Uses
Typically, a fuel tank must allow or provide the following:
- Storage of fuel: the system must contain a given quantity of fuel and must avoid leakage and limit evaporative emissions
- Filling: the fuel tank must be filled in a secure way, without sparks
- 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 (high-density polyethylene HDPE) as a fuel tank material of construction, while functionally viable in the short term, has a long term potential to become saturated as fuels such as diesel and gasoline 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. With the flammable nature of a fuel being transported, stress cracking is an important safety consideration of a potential catastrophic failure nature. Emergencies aside HDPE plastic is suitable for short term storage of diesel and gasoline. In the U.S., Underwriters Laboratories approved (UL 142) tanks would be a minimum design consideration.
[edit] Road vehicles
For each new vehicle a specific fuel system is developed, to optimize the use of available space. Moreover, for one car model, different fuel system architectures are developed, depending on the type of the car, the type of fuel (gasoline or diesel), nozzle models, and region.
Two technologies are used to make fuel tanks for automobiles:
- Plastic high-density polyethylene (HDPE) fuel tanks made by blow molding. 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 take complex shapes, allowing 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 aluminum. Concern for safety and long term ability to function should be considered and monitored.
- Metal (steel or aluminum) fuel tanks welded from stamped sheets. Although this technology is very good in limiting fuel emissions, it tends to be less competitive and thus less on the market.
Modern cars often feature remote opening of the fuel tank fuel filler flap using an electric motor or cable release. For both convenience and security, many modern fuel tanks cannot be opened by hand or otherwise from the outside of the car.
[edit] Reserve tank
Sometimes called the reserve tank is a secondary fuel tank (in many cars/bikes it contains around 15% of the capacity of the primary tank) these are more commonly found on bikes, older cars (some without fuel gauge) and vehicles designed for long distance or special use. A light on the instrument panel indicates 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 cell
A racing fuel cell 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
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.
Automobiles such as the Ford Pinto or the models that still use the Ford Panther platform (Ford Crown Victoria, Lincoln Town Car, and Mercury Grand Marquis) 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 [1].
General Motors 1973-1987 C/K pickup trucks have the fuel tank located outside the frame. According to the Center for Auto Safety this creates a fire hazard [2]. 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 product liability 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 US$125 million. In 1993, reportage on this matter for NBC News created a scandal over vehicles rigged to catch fire for the television camera.
[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, belly, and sometimes 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. One major down-side to this type of tank is the tendency for materials to work harden through extensive use making them brittle causing cracks. One major plus side is the ability to utilise as much of the aircraft as possible to store fuel.
- Combat aircraft generally use self-sealing fuel tanks.
Fuel tanks have been implicated in aviation disasters, being the cause of the accident or worsening it (fuel tankexplosion) [3]. 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 fire-fighting foam in the tanks [4].
- Burning fuel can explode or set fire to the same airplane or adjacent objects and people. In the 1960 Munich Convair 340 crash, a transport 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.[5].
[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.[6][7]
[edit] Safety
Proper design and construction of a fuel tank play 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 that is well above the flammability limits, and thus cannot burn even if an ignition source were present (which is rare).
Bunded oil tanks are used for safely storing domestic heating oil and other hazardous materials. Bunding is often required by insurance companies, rather than single skinned oil storage tanks.
[edit] See also
[edit] References
- ^ "Detroit's Uphill Battle". Time. 8 September 1980. http://www.time.com/time/magazine/article/0,9171,924408-5,00.html. Retrieved 3 May 2010.
- ^ http://www.autosafety.org/tort-liability-dealers-selling-1973-1987-gm-pickups
- ^ http://www.trantololaw.com/airplane_accidents.html
- ^ http://www.fire.tc.faa.gov/pdf/EXECSUM.pdf pg 3
- ^ http://www.emergency-management.net/airpl_acc60-89.htm
- ^ Maciag, Mike, Backup Facility to Power Water Works During Outages, Erie Times-News, 7 June 2007, pg 5B, says that the Erie Water Works is due to have a 20,000-gallon bulk storage tank and a 5,000-gallon day tank installed to support two diesel-fueled generators serving as backups to the Sommerheim Water Treatment Plant in Erie, Pennsylvania.
- ^ Comprehensive Everglades Restoration Plan, Section 8, pp 8-3, 8-4, says that small- and medium-sized pumping stations are to be equipped with fuel storage tanks capable of storing seven days capacity, plus "floor-mounted packaged system day tanks"[1]
[edit] External links
- 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 United States Department of Transportation.
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