Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification. The only other jet fuel commonly used in civilian turbine-engine powered aviation is Jet B which is used for its enhanced cold-weather performance.
Jet fuel is a mixture of a large number of different hydrocarbons. The range of their sizes (molecular weights or carbon numbers) is restricted by the requirements for the product, for example, the freezing point or smoke point. Kerosene-type jet fuel (including Jet A and Jet A-1) has a carbon number distribution between about 8 and 16 carbon numbers; wide-cut or naphtha-type jet fuel (including Jet B), between about 5 and 15 carbon numbers.[1]
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Fuel for piston-engine powered aircraft (usually a high-octane gasoline known as avgas) has a low flash point to improve its ignition characteristics. Turbine engines can operate with a wide range of fuels, and jet-aircraft engines typically use fuels with higher flash points, which are less flammable and therefore safer to transport and handle. The first jet fuels were based on kerosene or a gasoline-kerosene mix, and most jet fuels are still kerosene-based. Both British and American standards for jet fuels were first established at the end of World War II. British standards derived from standards for kerosine use for lamps, whereas American standards derived from aviation gasoline practices. Over the subsequent years, details of specifications were adjusted, such as minimum freezing point, to balance performance requirements and availability of fuels. Very low temperature freezing points reduce the availability of fuel. Higher flash point products required for use on aircraft carriers are more expensive to produce.[2] In the United States, ASTM produces standards for civilian fuel types, and the U.S. Department of Defense produces standards for military use. The British Minstry of Defence establishes standard for both civil and military jet fuels.[2] For reasons of interoperability, British and American military standards are to a degree harmonized.
Jet A specification fuel has been used in the United States since the 1950s and is only available in the United States, whereas Jet A-1 is the standard specification fuel used in the rest of the world. Both Jet A and Jet A-1 have a flash point higher than 38 °C (100 °F), with an autoignition temperature of 210 °C (410 °F). This means that the fuel is safer to handle than traditional avgas.
The primary differences between Jet A and Jet A-1 are the higher freezing point of Jet A (−40 °C vs −47 °C for Jet A-1), and the mandatory requirement for the addition of an anti-static additive to Jet A-1.
Like Jet A-1, Jet A can be identified in trucks and storage facilities by the UN number 1863 Hazardous Material placards.[3] Jet A trucks, storage tanks, and pipes that carry Jet A are marked with a black sticker with a white "Jet A" written over it, next to another black stripe.
The annual U.S. usage of jet fuel was 20.2 billion US gallons (7.6×1010 L) in 2009.[4]
Jet A-1 Fuel must meet the specification for DEF STAN 91-91 (Jet A-1), ASTM specification D1655 (Jet A-1) and IATA Guidance Material (Kerosine Type), NATO Code F-35.
Jet A Fuel must reach ASTM specification D1655 (Jet A) [5]
Typical physical properties for Jet A / Jet A-1 fuel:[6]
| Jet A-1 | Jet A | |
| Flash point | 42 °C | 51.1 °C |
| Autoignition temperature | 210 °C (410 °F)[7] | |
| Freezing point | −47 °C (−52.6 °F) | −40 °C (−40 °F) |
| Open air burning temperatures | 260-315 °C (500-599 °F)[7] | |
| Density at 15 °C (59 °F) | .804 kg/L | .820 kg/L |
| Specific energy | 43.15 MJ/kg | 43.02 MJ/kg |
| Energy density | 34.7 MJ/L | 35.3 MJ/L |
Jet B is a fuel in the naphtha-kerosene region that is used for its enhanced cold-weather performance. However, Jet B's lighter composition makes it more dangerous to handle.[5] For this reason it is rarely used, except in very cold climates.
The DEF STAN 91-91 (UK) and ASTM D1655 (international) specifications allow for certain additives to be added to jet fuel, including:[8][9]
It is very important that jet fuel be free from water contamination. During flight, the temperature of the fuel in the tanks decreases, due to the low temperatures in the upper atmosphere. This causes precipitation of the dissolved water from the fuel. The separated water then drops to the bottom of the tank, because it is denser than the fuel. From this time on, as the water is no longer in solution, it can freeze, blocking fuel inlet pipes. Removing all water from fuel is impractical, therefore fuel heaters are usually used on commercial aircraft to prevent water in fuel from freezing.
There are several methods for detecting water in jet fuel. A visual check may detect high concentrations of suspended water, as this will cause the fuel to become hazy in appearance. An industry standard chemical test for the detection of free water in jet fuel uses a water-sensitive filter pad that turns green if the fuel exceeds the specification limit of 30ppm (parts per million) free water.[11]
Military organizations around the world use a different classification system of JP numbers. Some are almost identical to their civilian counterparts and differ only by the amounts of a few additives; Jet A-1 is similar to JP-8, Jet B is similar to JP-4. Other military fuels are highly specialized products and are developed for very specific applications. JP-5 fuel is fairly common, and was introduced to reduce the risk of fire on aircraft carriers (JP-5 has a higher flash point—a minimum of 60 °C). Other fuels were specific to one type of aircraft. JP-6 was developed specifically for the XB-70 Valkyrie and JP-7 for the SR-71 Blackbird. Both these fuels were engineered to have a high flash point to better cope with the heat and stresses of high speed supersonic flight. One aircraft-specific jet fuel still in use by the United States Air Force is JPTS, which was developed in 1956 for the Lockheed U-2 spy plane.
Jet fuels are sometimes classified as kerosene or naphtha-type.[2] Kerosene-type fuels include Jet A, Jet A-1, JP-5 and JP-8. Naphtha-type jet fuels, sometimes referred to as "wide-cut" jet fuel, include Jet B and JP-4.[2]
Syntroleum has been working with the U. S. Air Force to develop a synthetic jet fuel blend that will help the Air Force to reduce its dependence on imported petroleum. The Air Force, which is the U.S. military's largest user of fuel, began exploring alternative fuel sources in 1999. On December 15, 2006, a B-52 took off from Edwards AFB for the first time powered solely by a 50-50 blend of JP-8 and Syntroleum's FT fuel. The seven-hour flight test was considered a success. The goal of the flight test program was to qualify the fuel blend for fleet use on the service's B-52s, and then flight test and qualification on other aircraft. On August 8, 2007, Air Force Secretary Michael Wynne certified the B-52H as fully approved to use the FT blend, marking the formal conclusion of the test program. This program is part of the Department of Defense Assured Fuel Initiative, an effort to develop secure domestic sources for the military energy needs. The Pentagon hopes to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016. With the B-52 now approved to use the FT blend, the USAF will use the test protocols developed during the program to certify the C-17 Globemaster III and then the B-1B to use the fuel. To test these two aircraft, the Air Force has ordered 281,000 US gallons (1,060,000 L) of FT fuel. The Air Force intends to test and certify every airframe in its inventory to use the fuel by 2011. They will also supply over 9,000 US gallons (34,000 L) to NASA for testing in various aircraft and engines.
Jet fuel is very similar to diesel fuel, and in some cases, may be burned in diesel engines. The possibility of environmental legislation banning the use of leaded avgas, and the lack of a replacement fuel with similar performance, has left aircraft designers and pilot's organizations searching for alternative engines for use in small aircraft.[12] As a result, a few aircraft engine manufacturers, most notably Thielert, have begun offering diesel aircraft engines which run on jet fuel. This technology has potential to simplify airport logistics by reducing the number of fuel types required. Jet fuel is available in most places in the world, whereas avgas is only widely available in a few countries which have a large number of general aviation aircraft. A diesel engine may also potentially be more environmentally friendly and fuel-efficient than an avgas engine. However, very few diesel aircraft engines have been certified by aviation authorities, and widespread use of diesel aircraft engines is still years in the future.
Jet fuel is often used in ground support vehicles at airports, instead of diesel. The United States military makes heavy use of JP-8, for instance. However, jet fuel tends to have poor lubricating ability in comparison to diesel, thereby increasing wear on fuel pumps and other related engine parts. Civilian vehicles tend to disallow its use, or require that an additive be mixed with the jet fuel to restore its lubricity. Since jet fuel is also significantly more expensive than diesel, some critics consider using jet fuel in ground vehicles as wasteful.
A significant effort is under way to certify Fischer–Tropsch (FT) synthetic fuels for use in U.S. and international aviation fleets. In this effort is being led by an industry coalition known as the Commercial Aviation Alternative Fuels Initiative (CAAFI),[13] also supported by a parallel initiative under way in the U.S. Air Force,[14] to certify FT fuel for use in all aviation platforms. The U.S. Air Force has a stated goal of certifying its entire fleet for use with FT synthetic fuel blends by 2011.[15] The CAAFI initiative aims to certify the civilian aviation fleet for FT synthetic fuels blends by 2010, and has programs under way to certify HRJ hydrogenated biofuels as early as 2013.[16]
Synthetic jet fuels show a reduction in pollutants such as SOx, NOx, particulate matter, and hydrocarbon emissions.[17] It is envisaged that usage of synthetic jet fuels will increase air quality around airports which will be particularly advantageous at inner city airports.[18]
The air transport industry is responsible for 2 percent of man-made carbon dioxide emitted .[21] Boeing estimates that biofuels could reduce flight-related greenhouse-gas emissions by 60 to 80 percent. One possible solution which has received more media coverage than others would be blending synthetic fuel derived from algae with existing jet fuel:[22]
Green Flight International became the first airline to fly jet aircraft on 100% biofuel. The flight from Stead airport in Stead, Nevada was in an Aero L-29 Delfín piloted by Carol Sugars and Douglas Rodante.[23]
Oil prices increased about fivefold from 2003 to 2008, raising fears that world petroleum production is becoming unable to keep up with demand. The fact that there are few alternatives to petroleum for aviation fuel adds urgency to the search for alternatives. Twenty-five airlines were bankrupted or stopped operations in the first six months of 2008, largely due to fuel costs.[27]