Jet fuel is defined by how it behaves, not by a chemical recipe
Ask a chemist for the formula of jet fuel and there is no answer. Its hydrocarbon mix shifts with every crude oil it comes from, so the fuel is defined by tests it must pass, such as freezing point and flash point. Small differences in those numbers decide which grade flies where.
Commercial airliners mostly burn Jet A or Jet A-1, both kerosene-type fuels built from molecules of roughly 8 to 16 carbon atoms. Turbine engines are forgiving eaters because fuel is sprayed into an already hot combustion chamber, so they can use cheaper fuels with high flash points, which are less flammable and safer to move around than the volatile avgas that piston aircraft need. Early German jets like the Messerschmitt Me 262 ran on synthetic fuel or diesel, with gasoline an option dismissed as too thirsty.
Geography splits the grades. Jet A has been the American standard since the 1950s and is rarely found outside the United States, apart from a few Canadian airports such as Toronto. Most of the world uses Jet A-1, which freezes at a lower temperature and must include an antistatic additive; Russia and its neighbours favour TS-1. Both Jet A varieties have a flash point above 38 degrees Celsius and ignite on their own at 210 degrees. Where winter is brutal, in northern Canada and Alaska, operators use Jet B, roughly 30 per cent kerosene and 70 per cent gasoline, which stays liquid down to minus 60 degrees but is riskier to handle.
Water is a quiet enemy. As tanks chill at altitude, dissolved water separates, sinks and can form supercooled droplets that freeze on contact and block fuel pipes, which caused the British Airways Flight 38 accident. Airliners therefore carry fuel heaters, and a standard test uses a filter pad that turns green when free water exceeds 30 parts per million. Additives handle the rest, from antioxidants against gumming to biocides against microbes; one biocide, Kathon, is now banned from aviation.
Military fuels carry JP numbers. JP-4, a half-and-half blend of kerosene and gasoline, was the main United States Air Force fuel from 1951 to 1995. The chemist John D. Clark mocked an earlier, loosely specified grade, JP-3, as something almost any refinery better than a moonshiner's still could produce.
Source: Jet fuel
