JP-7

JP-7 (Jet Propellant 7, MIL-DTL-38219) is a jet fuel developed by the U.S. Air Force for use in supersonic aircraft because of its high flash point and thermal stability. It is the fuel used in the Pratt & Whitney J58 engines, used in the Lockheed SR-71 Blackbird. The skin friction of the aircraft's surface with the atmosphere at Mach 3+ cruising flight generates very high skin temperatures; therefore this special fuel was needed. The story told by Ben Rich in his book Skunk Works is that a lit match can be dropped in a bucket of JP-7 and the fuel will not ignite, and the match will be extinguished.

The Boeing X-51 Waverider uses JP-7 fuel to run the Pratt & Whitney SJY61 scramjet engine, with fuel capacity of some 270 lb (120 kg). As with the SR-71, the X-51A design super-cools this fuel (cooled by extended subsonic flight in the stratosphere; prior to acceleration to supersonic speeds); then, when in supersonic flight, the fuel is heated by its circulation through heat exchangers which transfer to it the heat load of the interior spaces of the airframe. The fuel is then pumped through rotating mechanical parts of the engines and auxiliary mechanical equipment, providing both lubrication and cooling. Finally at a temperature of nearly 550 degrees, it is pumped into the fuel nozzles of the engines.