The fuel used in a jet or turboprop/turboshaft engine; usually a kerosene, or, sometimes, a kerosene-gasoline blend, although turbine engines can run on a very wide variety of fuels in a pinch. Worldwide, jet fuel is the most widely available type of aviation fuel.
Jet fuel (also known as avtur), at its most basic, is any fuel used to power a jet-engine, turboprop, or turboshaft. Unlike a piston-engine, which is very picky about what it'll burn without tearing itself apart (which is why most varieties of avgas are chock-full of lead), turbine engines will run on practically any combustible fluid; thus, the ingredients used, or not used, in jet fuels are chosen mainly for other considerations, such as freezing point - you don't want the fuel freezing in your tanks - and flashpoint (the lowest temperature at which the fuel can easily be ignited) - you also don't want it setting the ground-operations personnel on fire, or, even worse, exploding inside your fuel-tanks.
Most jet fuels fall into four main types:
- Kerosenes, or narrow-cut fuels, which have high flashpoints (generally well above typical room temperature), but usually have somewhat higher freezing points than most other jet fuels.
- Jet A-1 (known as JP-8 in military use, and No. 3 in china) is the predominant type of jet fuel outside the united-states, and the most-widely-available grade of aviation fuel in the world. It has a freezing point of -47 celsius (-53 fahrenheits), and a flashpoint of 38C (100F).
- Jet A is the U.S. equivalent to Jet A-1; the major difference between the two is Jet A's higher freezing point (-40C/-40F), although Jet A is also slightly denser and more energetic than Jet A-1. Jet A is reliably available only in the U.S. and a few major airports in canada.
- TS-1 was originally a Soviet fuel specification, and is still widely used in post-Soviet russia (although Jet A-1 has been making inroads into the market there since 1991); its flashpoint is somewhat lower than that of Jet A-1 or A (28C/82F), but its freezing point is much lower (-60C/-76F), making it a better choice for the parts of Russia that get really cold in the winter.
- T-1 is very similar to TS-1, but has a slightly higher freezing point (-58C/-72F).
- JP-1 was a very early jet fuel (the official specification was written in 1944, during World War II) which, unusually for a kerosene, had not only a very high flashpoint but also a very low freezing point (-60C/-76F). The primitive oil-refinery technology of the time made JP-1 hard to produce, limited in supply, and quite expensive, although it remained available through at least the beginning of the 1970s if you knew where to look.
- JP-5 is a kerosene with a very high flashpoint (60C/140F) and a low freezing point (-46C/-51F), developed for aircraft-carrier use (where there's nowhere to run and no offsite fire departments to call for help if there's a fire).
- JP-6 was developed in the late 1950s and early 1960s specifically for the xb-70-valkyrie high-altitude supersonic bomber; it was similar to JP-5, but with an even lower freezing point (-54C/-65F) - it gets cold at 21 kilometers AMSL - and improved high-temperature stability - it gets hot at mach 3. It, and the Valkyrie, were retired in 1969.
- Kerosene-gasoline blends and other wide-cut fuels are cheaply produced in large quantities by even a backwoods Kentucky refinery (making them attractive to militaries until refinery technology advanced enough to make narrow-cut kerosenes cheaply available in similar quantities), have very low freezing points (making them attractive for use in places such as Alaska, Nunavut, or Siberia, which get cold enough in the winter to freeze solid such things as Jet A-1), and burn enthusiastically, even at low temperatures, due to their low flashpoints (making them unattractive for basically everyone else).
- Jet B is a 70-30 mix of gasoline and kerosene, and (along with the similar T-2, used in Russia) the only wide-cut fuel still in significant use; it doesn't freeze until you get down to -60C (-76F), but its flashpoint is -18C (0F), and its flame-spread speed (how fast you have to go to outrun a fire spreading across the top of a puddle of the stuff) is an order of magnitude or so faster than that of Jet A-1 or A.
- JP-3 was an early, extremely-wide-cut military fuel consisting of essentially the refinery's entire output lighter than bunker oil that didn't immediately evaporate; the drawbacks were a very low flashpoint and a considerable loss of fuel at high altitude due to the lighter components boiling off from the tanks (and, as a side effect, raising the freezing point of what remained unevaporated), and it was replaced by...
- JP-4, a 50-50 gasoline-kerosene mix, which, despite its different mixture ratio, had the same freezing point and flashpoint as Jet B. It was the primary military jet fuel in NATO countries for a long time, but was slowly phased out from the 1970s through the 1990s in favour of Jet A-1 (under the name JP-8) for safety reasons.
- Special-purpose blends are produced in small quantities for applications requiring a fuel with a special property or combination thereof not found in the more common jet fuels.
- JPTS (Jet Propellant, Thermally Stable) is used in the lockheed-u2; as the U-2 uses its fuel as coolant for hot parts and surfaces, and also flies at very high altitudes where the air is very cold, its fuel is specially blended to both have a very low freezing point and viscosity (to help it work better at low temperatures) and high thermal stability (to help keep it from breaking down at high temperatures).
- JP-7 is a special fuel with an extremely high flashpoint and extreme thermal stability, used by the sr-71 until its retirement. Flying at well above mach 3 produced enormous amounts of aerodynamic heating, requiring a fuel that wouldn't be prone to exploding even at high temperatures; this was achieved by blending together a number of hand-picked hydrocarbons in specific proportions. (One side effect of this was that JP-7 is very difficult to ignite; this is good for ground personnel, since it decreases their chances of getting set on fire, but caused headaches for the engine folks, who had to think up a specially-designed ignition system to light off the engines.)
- Zip fuel, or high-energy fuel (HEF), was a family of experimental fuels spiked with boranes (boron-hydrogen compounds) to greatly increase their energy content; they were pursued with wild and reckless abandon throughout the 1950s, then abruptly dropped when a number of serious problems became apparent (the fuels were extremely toxic, far more so than ordinary aviation fuels; boron compounds burn to produce a highly-corrosive exhaust laden with turbine-blade-destroying boron oxide and carbide particulates; and the boronic additives, when not yet mixed with the hydrocarbon components of the fuel, had an unfortunate tendency to spontaneously ignite upon contact with air, a property known as being "pyrophoric").
- Synthetic jet fuels and jet biofuels, which would free jets from dependence on the rapidly-dwindling supply of fossil fuels, have been under development for some time, but still have yet to make significant headway into the market at large.
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