JP-4

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JP-4, or JP4 (for "Jet Propellant") was a jet fuel, specified in 1951 by the U.S. government (MIL-J-5624E). It was a 50-50 kerosene-gasoline blend. It has lower flash point than JP-1, but was preferred because of its better availability. It was the primary U.S. Air Force jet fuel between 1951 and 1995. Its NATO code is F-40. It is also known as avtag. The maximum burning temperature of this type of fuel is 3688 °C.

JP-4 is a mixture of aliphatic and aromatic hydrocarbons. It is a flammable transparent liquid with clear or straw color, with a kerosene-like smell. It evaporates easily. Its freeze point is at -77 °F (-60 °C) and its flash point temperature is 0 °F (-18 °C).

Commercial aviation uses a similar mixture under the name Jet-B. JP-4 in addition contains corrosion inhibitors and icing inhibitors. Since the mid 1980s, antistatic agent was added to the fuel to decrease the risk of fires caused by static electricity discharges.

JP-4 is a nonconductive liquid, prone to build up static electricity charge when being moved through pipes and tanks. As it is volatile and with low flash point, the static discharge may cause a fire. An antistatic agent is used as a fuel additive to lower the charge buildup, the flow rates have to be controlled, and all the equipment used has to be electrically interconnected and well grounded.

JP-4 was phased out by the U.S. Air Force, and was replaced with JP-8. The transition was finished by the fall of 1996, and was motivated by the desire to use less flammable, less hazardous fuel.

JP-4 floats on water and when a lit match is dropped into it, ignition does not occur.