Jet aircraft can use any of a number of different fuels:1
- Jet A-1 is a straight kerosene, not that much different from what you used to buy for
committing arsonfuelling portable space heaters.
- JP-8 is Jet A-1 with the military’s stamp of approval.
- Jet A, used almost exclusively in the United States (because ‘MURICA) and only available at a few non-US airports (most of them in Canada), is Jet A-1 with a slightly higher freezing point.2
- Jet B is a mixture of 30% Jet A-1 and 70% unleaded gasoline, used in climates where Jet A-1 would freeze into a solid wax, due to its (Jet B’s) extremely low freezing point, and not (nowadays) used elsewhere, due to its extremely low flashpoint and high flame-spread speed.
- JP-4 is Jet B with the military’s stamp of approval; it has now been retired from military service due to its excessive flammability and consequent handling difficulties, but is still included in the approved-fuels list for most jet engines, and, therefore, for the aircraft using said engines.
- JP-5 is a high-flashpoint kerosene developed specifically for naval-aviation use, as an aircraft carrier at sea, unlike an airport or airbase on land, can’t easily call for mutual-aid support if things get out of hand, making it even more important to keep a fire from starting in the first place.
- The Soviet Union had its own national jet fuels (both kerosenes, similar to Jet A-1, and cold-weather gasoline-kerosene blends [extra-important in places, like much of the former Soviet Union, that get really really cold in the winter], similar to Jet B), which can still be found in the former Soviet states, but are being gradually displaced by Jets A-1 and B. China, like the former Soviet Union, has its own national jet fuels; China, unlike the former Soviet Union, still uses its own fuels essentially exclusively, making it especially important that anyone planning on fuelling a jet in China have it certified to burn Chinese jet fuel.
Different fuels presumably have different energy contents (the main split would be expected to be between the straight kerosenes [Jet A-1/JP-8, Jet A, JP-5, etc.] and the gasoline-kerosene blends [Jet B/JP-4, etc.], but there could also be smaller differences between the energy contents of the different fuels within each of these categories), which would affect the maximum power an engine burning one of these fuels would be able to produce, which would make a difference in terms of things like takeoff distance, allowable takeoff weight, and service ceiling for a given weight; is the type of fuel being used taken into consideration when doing performance calculations, or do the calculations simply assume the use of the least-energy-dense fuel in common use, or is there some other solution at play?
1: For that matter, a jet engine will happily run (for a while, at least) on essentially any combustible fluid that doesn’t produce refractory particles when burned (engines without moving turbine blades, such as ramjets, scramjets, and motorjets, don’t even have the refractory-particle limitation; neither do the afterburners of jet engines so equipped [same reason], if the afterburner is capable of drawing fuel from a different source than the engine core does), but most engine manufacturers never bother to get their engines certified to run on any of these exotic fuels, and many of them (the fuels, not the engine manufacturers) have other drawbacks that make them less suitable for aircraft-jet-engine use (for instance, bunker oil is excessively viscous and its freezing point is much too high, RP-1 is far too expensive for anyone not an Arabian oil sheikh, ethanol has a tendency to dissolve various important fuel-system components, diesel is OK in hot climates, but prone to freezing in the winter, avgas not only usually contains lead, which deposits on your sparkplugs3 and makes them less reliable, but is also far more of a fire hazard [due to its dangerously-low flashpoint and extremely high flame-spread speed] than jet fuel, and, on the other end of the flammability spectrum, JP-7 is so reluctant to ignite that the sparkplugs on most jet engines can’t reliably start it burning, with most jet engines designed to burn JP-7 instead using hypergolic ignition); ground-based gas-turbine engines, on the other hand, are immune to many of these drawbacks, as anyone with an M1 Abrams tank in their back garage can tell you.
2: There is technically a second difference; Jet A, unlike Jet A-1, is not required to include an antistatic additive, but most Jet A distros put it in anyways, as people tend to dislike having their plane blow up from a static discharge.
3: It does that to piston-engine sparkplugs, too, but this is tolerated for piston-engine use because the antiknock (or antidetonation, as many aircraft engine manufacturers insist you call it) qualities of avgas’s lead content let piston engines operate at much higher compression ratios - and, thus, much higher power settings - without the engine destroying itself; in contrast, jet engines, which are immune to knocking/detonation, derive no benefit from the lead, but still suffer from fouled sparkplugs due to it.