JP-7
Encyclopedia
JP-7 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 air compression of 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 (although this is common in any low-volatility fuel including kerosene
and diesel).
The Boeing X-51
Waverider uses JP-7 fuel to run the Pratt & Whitney
SJY61 scramjet
engine, with fuel capacity of some 270 lbs. As with the SR-71, the X-51A design also uses fuel to absorb heat from the engine.
JP-7 is a mixture composed primarily of hydrocarbon
s, including alkane
s, cycloalkane
s, alkylbenzenes
, indane
s/tetralin
s, and naphthalene
s, with addition of fluorocarbon
s to increase its lubricant
properties, an oxidizing agent to make it burn better, and a cesium containing compound known as A-50, which aided in disguising the radar signature of the exhaust plume. The Blackbirds used approximately 36,000 - 44,000 pounds of fuel per hour of flight. It's estimated that over 20,000,000,000 (20 billion) pounds of fuel were burned during the life of the program.
JP-7 is unusual in that it is not a distillate
fuel but is created from special blending stocks in order to have very low (<3%) concentration of highly volatile components like benzene
or toluene
, and almost no sulfur, oxygen, and nitrogen impurities. It has low vapor pressure and high thermal oxidation stability. It must operate across a wide range of temperatures, from near freezing at high altitude, to high temperature of airframe and engine parts being cooled. Its volatility must be low to make it flash-resistant in these high temperatures.
The very low volatility and relative unwillingness of JP-7 to be ignited required triethylborane
(TEB) to be injected into the engine in order to initiate combustion and allow afterburner
operation in flight.
for the various aircraft and engine accessories which would otherwise overheat at the high temperatures encountered. This requires a fuel having high thermal stability so that it will not break down and deposit coke
and varnishes in the fuel system passages. A high luminometer number (brightness of flame index) is required to minimize transfer of heat to the burner parts. Other items are also significant, such as the amount of sulfur
impurities tolerated. Advanced fuels, JP-7 (PWA 535) and PWA 523E, were developed to meet the above requirements."
tankers were required to refuel the SR-71. The "Q-model" tanker had a modified "high-speed boom," which would allow refueling of the Blackbird at nearly the tanker's maximum airspeed, with minimum flutter. The Q-model also had a separate fuel system, which kept the tanker's fuel (either JP-4 or later JP-8) isolated from the JP-7 needed by the SR-71. During its operational life, the SR-71 had dedicated KC-135Qs and aircrews sitting on alert, ready to launch within minutes to tank up a Blackbird. Some of these alert birds were located on the east coast (Pease AFB, Loring AFB, Plattsburgh AFB etc.); on the west coast; at Hickham AFB, Hawaii; Mildenhall, England; and Guam. Several of the original KC-135Q aircraft are still serving on active-duty in the U. S. Air Force inventory as the KC-135T; a new designation given after the aircraft have been upgraded/reengined to the KC-135R standard.
Jet fuel
Jet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...
developed by the U.S. Air Force for use in supersonic
Supersonic
Supersonic speed is a rate of travel of an object that exceeds the speed of sound . For objects traveling in dry air of a temperature of 20 °C this speed is approximately 343 m/s, 1,125 ft/s, 768 mph or 1,235 km/h. Speeds greater than five times the speed of sound are often...
aircraft because of its high flash point
Flash point
The flash point of a volatile material is the lowest temperature at which it can vaporize to form an ignitable mixture in air. Measuring a flash point requires an ignition source...
and thermal stability. It is the fuel used in the Pratt & Whitney J58
Pratt & Whitney J58
The Pratt & Whitney J58 was a jet engine used on the Lockheed A-12, and subsequently on the YF-12 and SR-71 Blackbird aircraft. The J58 was a variable cycle engine which functioned as both a turbojet and a fan-assisted ramjet. The J58 was a single-spool turbojet engine with an afterburner...
engines, used in the Lockheed
Lockheed Corporation
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1912 and later merged with Martin Marietta to form Lockheed Martin in 1995.-Origins:...
SR-71 Blackbird
SR-71 Blackbird
The Lockheed SR-71 "Blackbird" was an advanced, long-range, Mach 3+ strategic reconnaissance aircraft. It was developed as a black project from the Lockheed A-12 reconnaissance aircraft in the 1960s by the Lockheed Skunk Works. Clarence "Kelly" Johnson was responsible for many of the...
. The air compression of Mach
Mach number
Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...
3+ cruising flight generates very high skin temperatures; therefore this special fuel was needed. The story told by Ben Rich
Ben Rich
Benjamin Robert Rich was the second director of Lockheed's Skunk Works from 1975 to 1991, succeeding its founder, Kelly Johnson. Regarded as the "father of stealth," Ben Rich was responsible for leading the development of the F-117, the first production stealth aircraft...
in his book Skunk Works
Skunk works
Skunk Works is an official alias for Lockheed Martin’s Advanced Development Programs , formerly called Lockheed Advanced Development Projects. Skunk Works is responsible for a number of famous aircraft designs, including the U-2, the SR-71 Blackbird, the F-117 Nighthawk, and the F-22 Raptor...
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 (although this is common in any low-volatility fuel including kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
and diesel).
The Boeing X-51
Boeing X-51
The Boeing X-51 is an unmanned scramjet demonstration aircraft for hypersonic flight testing. It successfully completed its first free-flight on 26 May 2010 and also achieved the longest duration flight at speeds over Mach 5.The X-51 Waverider program is run as a cooperative effort of the United...
Waverider uses JP-7 fuel to run the Pratt & Whitney
Pratt & Whitney
Pratt & Whitney is a U.S.-based aerospace manufacturer with global service operations. It is a subsidiary of United Technologies Corporation . Pratt & Whitney's aircraft engines are widely used in both civil aviation and military aviation. Its headquarters are in East Hartford, Connecticut, USA...
SJY61 scramjet
Scramjet
A scramjet is a variant of a ramjet airbreathing jet engine in which combustion takes place in supersonic airflow...
engine, with fuel capacity of some 270 lbs. As with the SR-71, the X-51A design also uses fuel to absorb heat from the engine.
JP-7 is a mixture composed primarily of hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
s, including alkane
Alkane
Alkanes are chemical compounds that consist only of hydrogen and carbon atoms and are bonded exclusively by single bonds without any cycles...
s, cycloalkane
Cycloalkane
Cycloalkanes are types of alkanes that have one or more rings of carbon atoms in the chemical structure of their molecules. Alkanes are types of organic hydrocarbon compounds that have only single chemical bonds in their chemical structure...
s, alkylbenzenes
Aromatic hydrocarbon
An aromatic hydrocarbon or arene is a hydrocarbon with alternating double and single bonds between carbon atoms. The term 'aromatic' was assigned before the physical mechanism determining aromaticity was discovered, and was derived from the fact that many of the compounds have a sweet scent...
, indane
Indane
Indane or indan is a hydrocarbon petrochemical compound.-Derivatives:Derivatives include compounds such as 1-methyl-indane and 2-methyl-indane , 4-methyl-indane and 5-methyl-indane , various dimethyl-indanes, and various pharmaceutical derivatives...
s/tetralin
Tetralin
Tetralin is a hydrocarbon having the chemical formula C10H12. This molecule is similar to the naphthalene chemical structure except that one ring is saturated.The compound can be synthesized in a Bergman cyclization...
s, and naphthalene
Naphthalene
Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...
s, with addition of fluorocarbon
Fluorocarbon
Fluorocarbons, sometimes referred to as perfluorocarbons or PFCs, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbon–fluorine bonds. Fluoroalkanes that contain only single bonds are more chemically and thermally stable than alkanes...
s to increase its lubricant
Lubricant
A lubricant is a substance introduced to reduce friction between moving surfaces. It may also have the function of transporting foreign particles and of distributing heat...
properties, an oxidizing agent to make it burn better, and a cesium containing compound known as A-50, which aided in disguising the radar signature of the exhaust plume. The Blackbirds used approximately 36,000 - 44,000 pounds of fuel per hour of flight. It's estimated that over 20,000,000,000 (20 billion) pounds of fuel were burned during the life of the program.
JP-7 is unusual in that it is not a distillate
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
fuel but is created from special blending stocks in order to have very low (<3%) concentration of highly volatile components like benzene
Benzene
Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
or toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
, and almost no sulfur, oxygen, and nitrogen impurities. It has low vapor pressure and high thermal oxidation stability. It must operate across a wide range of temperatures, from near freezing at high altitude, to high temperature of airframe and engine parts being cooled. Its volatility must be low to make it flash-resistant in these high temperatures.
The very low volatility and relative unwillingness of JP-7 to be ignited required triethylborane
Triethylborane
Triethylborane , also called triethylborine and triethylboron, is an organoborane , a near-colorless to yellowish transparent liquid with pungent ether-like odor. Its chemical formula can be written as C6H15B, or 3B, or 3B, or Et3B.Triethylborane is strongly pyrophoric, igniting spontaneously in...
(TEB) to be injected into the engine in order to initiate combustion and allow afterburner
AfterBurner
The AfterBurner is a lighting solution for the Game Boy Advance system that was created by Triton-Labs.Originally, portablemonopoly.net was a website created to petition Nintendo to put some kind of light in their Game Boy Advance system...
operation in flight.
Properties
- Melting Point −30 °C
- Boiling Point (1 atm) 282–288 °C
- Density (at 15 °C) 779–806 kg/m³
- Vapor Pressure (at 300 °F (149 °C)) 155 mmHg (20.7 kPa)
- Flashpoint 60 °C
- Net heat of combustion min. 43.5 MJ/kg
From the SR-71 Flight Manual
"The operating envelope of the JT11D-20 engine requires special fuel. The fuel is not only the source of energy but is also used in the engine hydraulic system. During high Mach flight, the fuel is also a heat sinkHeat sink
A heat sink is a term for a component or assembly that transfers heat generated within a solid material to a fluid medium, such as air or a liquid. Examples of heat sinks are the heat exchangers used in refrigeration and air conditioning systems and the radiator in a car...
for the various aircraft and engine accessories which would otherwise overheat at the high temperatures encountered. This requires a fuel having high thermal stability so that it will not break down and deposit coke
Petroleum coke
Petroleum coke is a carbonaceous solid derived from oil refinery coker units or other cracking processes. Other coke has traditionally been derived from coal....
and varnishes in the fuel system passages. A high luminometer number (brightness of flame index) is required to minimize transfer of heat to the burner parts. Other items are also significant, such as the amount of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
impurities tolerated. Advanced fuels, JP-7 (PWA 535) and PWA 523E, were developed to meet the above requirements."
JP-7 Aerial Refueling Requirements
The SR-71 required in-flight refueling to replenish the fuel expended on take-off and during long duration missions. To accomplish this, specialized KC-135QKC-135 Stratotanker
The Boeing KC-135 Stratotanker is an aerial refueling military aircraft. It and the Boeing 707 airliner were developed from the Boeing 367-80 prototype. The KC-135 was the US Air Force's first jet-powered refueling tanker and replaced the KC-97 Stratotanker...
tankers were required to refuel the SR-71. The "Q-model" tanker had a modified "high-speed boom," which would allow refueling of the Blackbird at nearly the tanker's maximum airspeed, with minimum flutter. The Q-model also had a separate fuel system, which kept the tanker's fuel (either JP-4 or later JP-8) isolated from the JP-7 needed by the SR-71. During its operational life, the SR-71 had dedicated KC-135Qs and aircrews sitting on alert, ready to launch within minutes to tank up a Blackbird. Some of these alert birds were located on the east coast (Pease AFB, Loring AFB, Plattsburgh AFB etc.); on the west coast; at Hickham AFB, Hawaii; Mildenhall, England; and Guam. Several of the original KC-135Q aircraft are still serving on active-duty in the U. S. Air Force inventory as the KC-135T; a new designation given after the aircraft have been upgraded/reengined to the KC-135R standard.
See also
- JP-1JP-1JP-1 was an early jet fuel, specified in 1944 by the U.S. government . It was a pure kerosene fuel with high flash point and a freezing point of −60 °C...
- JP-4JP-4JP-4, or JP4 was a jet fuel, specified in 1951 by the U.S. government . It was a 50-50 kerosene-gasoline blend. It has lower flash point than JP-1, but was preferred because of its greater availability. It was the primary U.S. Air Force jet fuel between 1951 and 1995. Its NATO code is F-40...
- JP-5JP-5JP-5 or JP5 is a yellow, kerosene-based jet fuel developed in 1952 for use in aircraft stationed aboard aircraft carriers, where the risk from fire is particularly great. JP-5 is a complex mixture of hydrocarbons, containing alkanes, naphthenes, and aromatic hydrocarbons that weighs and has a...
- JP-6JP-6Jet Propellant 6 is a type of jet fuel developed for General Electric YJ93 jet engine of the XB-70 Valkyrie supersonic aircraft. JP-6 was similar to JP-5 but with a lower freezing point and improved thermal oxidative stability...
- JP-8JP-8JP-8, or JP8 is a jet fuel, specified and used widely by the US military. It is specified by MIL-DTL-83133 and British Defence Standard 91-87, and similar to commercial aviation's Jet-A....
- JPTSJPTSJPTS stands for Jet Propellant Thermally Stable , and was created specifically for the Lockheed U-2 reconnaissance aircraft....
- Jet fuelJet fuelJet fuel is a type of aviation fuel designed for use in aircraft powered by gas-turbine engines. It is clear to straw-colored in appearance. The most commonly used fuels for commercial aviation are Jet A and Jet A-1 which are produced to a standardized international specification...
- Aviation fuelAviation fuelAviation fuel is a specialized type of petroleum-based fuel used to power aircraft. It is generally of a higher quality than fuels used in less critical applications, such as heating or road transport, and often contains additives to reduce the risk of icing or explosion due to high temperatures,...
- KC-135QKC-135 StratotankerThe Boeing KC-135 Stratotanker is an aerial refueling military aircraft. It and the Boeing 707 airliner were developed from the Boeing 367-80 prototype. The KC-135 was the US Air Force's first jet-powered refueling tanker and replaced the KC-97 Stratotanker...