A fuel tank system must allow for the storage of a given quantity of fuel, avoiding leakage and limiting evaporative emissions. It must also facilitate secure filling without sparks. A method for determining the level of fuel in the tank, or gauging, is required to measure or evaluate the remaining quantity. If over-pressure is not allowed, fuel vapors must be managed through valves, a process known as venting. Finally, the tank must provide for the feeding of the engine, typically through a pump.
While most fuel tanks are manufactured, some are still fabricated by metal craftsmen or hand-made, particularly bladder-style tanks for custom and restoration projects in automotive, aircraft, motorcycles, boats, and tractors. The construction process generally begins with a mockup to determine the accurate size and shape, often using foam board. Design issues such as the placement of the outlet, drain, fluid level indicator, seams, and baffles are then addressed. Craftsmen determine the thickness, temper, and alloy of the sheet metal to be used. After cutting the sheet to shape, pieces are bent to create the basic shell, ends, and baffles. Many fuel tanks, especially in aircraft and racecars, incorporate baffles with lightening holes, which reduce weight while adding strength. Openings for the filler neck, fuel pickup, drain, and fuel-level sending unit are added. Baffles and ends can be riveted, with rivet heads frequently brazed or soldered to prevent leaks. Ends can be hemmed and soldered, or flanged and brazed (and/or sealed with an epoxy-type sealant), or flanged and welded. Once soldering, brazing, or welding is complete, the fuel tank is leak-tested.
In the aerospace industry, fuel tank sealants are commonly used for high-temperature integral fuel tanks, providing resistance to fluids like water, alcohols, synthetic oils, and petroleum-based hydraulic fluids.
Plastic, specifically high-density polyethylene (HDPE), is a functionally viable material for fuel tanks in the short term. However, it has a long-term potential to become saturated as fuels like diesel and gasoline permeate the HDPE material. Given the inertia and kinetic energy of fuel in a plastic tank transported by a vehicle, environmental stress cracking is a definite potential, and the flammability of fuel makes stress cracking a possible cause of catastrophic failure. For short-term storage of diesel and gasoline, HDPE plastic is suitable. In the U.S., Underwriters Laboratories approved (UL 142) tanks are considered a minimum design consideration.
A larger fuel tank provides a greater range for a car between refills, but the increased weight and space requirements are often undesirable, especially in smaller cars. The average fuel tank capacity for cars is 50–60 L (12–16 US gal). The most common materials for automotive fuel tanks are metal (steel or aluminium), typically built by welding stamped sheetmetal parts, or plastic, usually constructed using blow molding, which allows for more complex shapes. Some vehicles include a smaller reserve tank for use when the main tank is empty. Other vehicles, particularly 4WD vehicles, may have a large secondary tank, or "sub-tank," to increase their range. Automotive gas tanks are attached to a carbon canister that captures fuel vapor. This canister is connected to the tank via a rollover valve, which prevents fuel flow in the event of a car accident where the vehicle rolls over.
A racing fuel cell features a rigid outer shell and a flexible inner lining to minimize the potential for punctures during a collision or other mishap causing serious vehicle damage. It is filled with an open-cell foam core to prevent vapor explosions in the empty portion of the tank and to minimize fuel sloshing during competition, which could unbalance the vehicle or lead to inadequate fuel delivery to the motor, known as fuel starvation.
The "ship in a bottle" fuel tank is a manufacturing design developed by TI Automotive in Rastatt, Germany. In this design, all fuel delivery components, including the pump, control electronics, and most hosing, are encased within a blow-molded plastic fuel tank. This technique was developed to reduce fuel vapor emissions in response to Partial Zero-Emission Vehicle (PZEV) requirements.
Aircraft typically utilize three types of fuel tanks: integral, rigid removable, and bladder.
Integral tanks are areas within the aircraft structure that have been sealed for fuel storage, such as the "wet wing" common in larger aircraft. These tanks are part of the aircraft structure and cannot be removed for service or inspection, requiring inspection panels for internal access. Most large transport aircraft use this system, storing fuel in the wings, belly, and sometimes the tail.
Rigid removable tanks are installed in a compartment designed to accommodate them. They are typically of metal construction and can be removed for inspection, replacement, or repair. The aircraft's structural integrity does not rely on these tanks. They are commonly found in smaller general aviation aircraft, such as the Cessna 172.
Bladder tanks, also known as fuel cells, are reinforced rubberized bags installed in a section of the aircraft structure designed to accommodate the fuel's weight. The bladder is rolled up and installed through the fuel filler neck or access panel, secured by metal buttons or snaps. Many high-performance light aircraft, helicopters, and some smaller turboprops use bladder tanks. A major drawback is the tendency for materials to work harden with extensive use, becoming brittle and causing cracks. A significant advantage is the ability to utilize as much of the aircraft as possible for fuel storage.
Combat aircraft and helicopters generally employ self-sealing fuel tanks.
Fuel tanks have been implicated in aviation disasters, either as the cause or by worsening the accident through a fuel tank explosion. For example, the official probable cause for the explosion and crash of TWA Flight 800 was an explosive fuel/air mixture in one of the aircraft's fuel tanks, ignited by faulty wiring. Similar explosions have occurred in other aircraft, and the chance of such explosions can be reduced by a fuel tank inerting system or fire-fighting foam in the tanks. Burning fuel can also explode or ignite the same airplane or adjacent objects and people, as seen in the 1960 Munich Convair 340 crash, where burning fuel ignited a tramcar, resulting in fatalities for all aboard the plane and 32 tram passengers. In some areas, an aircraft's fuel tank is also referred to as an aircraft fuel cell.
Proper design and construction of a fuel tank are crucial for the safety of the system it is part of. Intact fuel tanks are generally very safe because they are full of a fuel vapor/air mixture that is well above flammability limits, preventing combustion even if an ignition source were present. Bunded oil tanks are used for safely storing domestic heating oil and other hazardous materials, often required by insurance companies over single-skinned oil storage tanks. Systems like BattleJacket and rubber bladders have been developed to protect military vehicle fuel tanks from explosions caused by enemy fire in conflict zones. For stationary fuel tanks, burying them is an economical way to protect them from hazards like temperature extremes and vehicle crashes, though buried tanks are difficult to monitor for leaks, leading to concerns about environmental hazards of underground storage tanks. Electrostatic discharges near a fuel tank during filling can cause a fire or explosion. This risk can be mitigated by a vapor recovery system that reduces flammable vapor concentration during refueling, or by reducing the risk of electrostatic discharge at a refueling station.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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