Military Aviation Fuel
Jet fuels, or turbine fuels, are one of the primary fuels for internal combustion engines worldwide and are the most widely available aviation fuel. "JP" stands for "jet propulsion." The classification jet fuel is applied to fuels meeting the required properties for use in jet engines and aircraft turbine engines. Because of its availability compared to gasoline during wartime, commercial illuminating kerosene was the fuel chosen for early jet engines. Consequently, the development of commercial jet aircraft following World War II centered primarily on the use of kerosene-type fuels. Thus, many commercial jet fuels have basically the same composition as kerosene, but they are under more stringent specifications than those for kerosene.
The early development of jet fuels differed in Europe and the USA. The outset of the Korean War coincided with a program to convert jet aircraft from use of JP-1 grade fuel to JP-3 grade jet fuel. Most of the Air Force jet aircraft in Korea required jet fuel known as JP-1. Navy and Marine jet aircraft used in Korea were designed to use JP-3 fuel, but can, and did, utilize avgas 100/130 or avgas 115/145. The wide-range distillate-type turbine fuel originated in the USA and evolved to the current jet propulsion JP-4 military fuel where readily available gasoline fractions were used to supplement the basic kerosene type of fuel. In Europe, gasoline was less available, so kerosene-based jet fuels prevailed. In the postwar years, due to the North Atlantic Treaty Organization (NATO) desire to standardize, the British AVTAG wide-cut fuel has been brought closely in line with JP-4. A recent development with NATO forces in Europe has been the decision to convert miliary aircraft fuel completely from JP-4 to JP-8 kerosene fuel. The schedule was completed by 1990.
Of the most common causes for engine stoppage, number one is poor/irregular maintenance, number two is fuel exhaustion, and number three is misfueling. Misfueling is simply fueling with the wrong grade of fuel. Aviation Gasoline (AVGAS) has been better known for its flammability than for its significant toxicity. Exposure may occur during handling, storage, or engine maintenance. JP4 and JP5 are jet engine fuels. JP4 is 65 percent kerosene and 35 percent gasoline, while JP5 is kerosene. AVGAS is used to power piston engines, while jet fuel is used to to power jet engines.
Aircraft fuels may be classified under 4 general types:
- Aviation Gasoline [AVGAS] is a petroleum distillate with an approximate boiling range of 35°-165°C (95°-330°F). Gasoline type fuels are not used to any large extent in aircraft turbojet and turboprop engines because of poor lubricating properties as compared to kerosene type fuels and because of lead additives which have an adverse effect on aircraft turbine engines.
- Wide Cut Type (JP 4 and Jet B) fuels are mixtures of gasoline and kerosene distillate fractions with an approximate boiling range of 35°-315°C (95°-600°F). These jet fuels are called wide-cut because the kerosene is cut with gasoline. They are also called wide-range, because of the wide range of boiling temperatures. These distillate-type turbine fuels originated in the USA where readily available gasoline fractions were used to supplement the basic kerosene type of fuel.
- Kerosene Type (JP 8, Jet A 1, and Jet A) fuels are petroleum distillates with an approximate boiling range of 165°-290°C (330°-550°F). In Europe, gasoline was less available after World War II, so these kerosene-based jet fuels prevailed.
- High Flash Point Kerosene (JP 5) fuel has essentially the same characteristics as the kerosene type fuels, but with a minimum flash point of 60°C (140°F). This higher flash point fuel is used to some extent in Presidential Fleet aircraft and is required by the Navy for fire safety purposes aboard aircraft carriers.
All 4 types may be utilized in turbojet and turboprop engines with certain restrictions. Only aviation gasoline, because of its high volatility and minimum octane requirements, is suitable for use in reciprocating engines.
A Primary Fuel is the fuel or fuels used during aircraft tests to demonstrate system performance (contract compliance) through the complete operating range for any steady state and transient operating condition. An Alternate Fuel is a fuel authorized for continuous use. The operating limits, thrust outputs and thrust transients, shall not be adversely affected. The applicable aircraft flight manual shall define limitations, if any, of a significant nature on aircraft performance parameters such as range, altitude, loiter time, or rate of climb, and engine performance parameters, such as specific fuel consumption or starting and stopping time. The use of an alternate fuel may result in a change of maintenance or overhaul cost. External engine trim adjustments may be necessary or desirable for use of an alternate fuel. An Emergency Fuel is a fuel which may cause significant damage to the engine or other systems; therefore, its use shall be limited to 1 flight. The applicable aircraft flight manual or system manager should be consulted regarding operating restrictions and post flight maintenance actions necessary when using an emergency fuel. Examples of conditions that might warrant use of emergency fuels are: Accomplishing an Important Military Mission; Countering Enemy Actions; Emergency Evacuation Flights; or Emergency Aerial Refueling.
Aircraft using a lower than specified grade of AVGAS must be operated In Accordance With (IAW) the power schedule or operating limits as indicated in applicable flight manuals. Engines using a higher than specified grade of fuel may develop spark plug fouling and require increased maintenance. Refer to flight manuals for spark plug anti fouling procedures. Mixing different grades of AVGAS in aircraft tanks is permitted when necessary. The aircraft must be operated TAW limits established for the lower grade. Commercial Grade 100 (dyed green) or 100LL (low lead, dyed blue) may be used as an alternate when Grade 100/130 (dyed blue) is authorized .
General use of any fuel is limited to operations where the temperature of the fuel remains above the freezing point. Slush (particles of frozen fuel) is formed at the freezing point and as the temperature is lowered, the liquid fuel will be converted to a solid state. Slush formations can cause blockage of fuel filters, pumps, and lines, resulting in engine flame out. Engine restarts under such conditions become practically impossible.
Use of an alternate fuel may necessitate the observance of special precautions. The appropriate aircraft flight manual must be consulted for unique precautions. In general, the freezing point of some fuels limits use at flight conditions where the stagnation temperature approaches the freeze point of the fuel. Aircraft not equipped with fuel temperature gauges will not operate for an appreciable period at altitudes where the stagnation temperature is within 3°C (6°F) above the fuel freezing temperature. Further, special maintenance procedures may be required for ground starting at temperatures approaching the freezing point of the fuel. Consult the appropriate aircraft technical manual for these procedures.
Fuel temperatures are determined directly on aircraft having fuel temperature gauges. On aircraft temperature gauges but having an Outside Air Temperature (OAT) gauge, the indicated OAT is equivalent to the stagnation temperature and these aircraft should not be operated for an appreciable period at flight conditions where the indicated OAT is within 3°C (6°F) above the fuel freezing temperature. For aircraft not equipped with either type of temperature gauge, the same operational restriction as above applies using the stagnation temperaturefor the actual flight conditions being experienced based on a temperature for cold or standard atmosphere as considered most appropriate. Flight manuals should be consulted for specific operating instructions for flights scheduled in areas of extremely low air temperature.
When military fuels are not available, commercial fuels may be used as suitable replacement fuels. Commercial fuels have higher freeze points than JP 4 and the specifications do not require FSII or corrosion inhibitor. A conductivity additive is generally included in fuels procured outside of the United States. Precautionary procedures will be accomplished when using commercial fuel. Commercial turbine fuels conform to Specification D 1655 established by the American Society for Testing and Materials (ASTM).
Military fuel specifications require the addition of corrosion inhibitors. The corrosion inhibitors provide added lubricity. Commercial jet fuel specifications do not require the addition of lubricity additives (corrosion inhibitors). Refer to the applicable aircraft technical order for restrictions involving use of commercial jet fuels that do not contain fuel system corrosion inhibitor. When aviation gasoline is used in jet engine aircraft, 3% lubricating oil, Specification MIL L 22851, Type II, will be added to improve its lubricity characteristic. Oil, Specification MIL L 22851, can normally be mixed with AVGAS for this use by adding the required quantity of oil into the fuel tank prior to fueling the aircraft with AVGAS. Where fuel or oil temperatures are colder than 4°C (40°F), the oil will be mixed with 25% aviation gasoline prior to adding it to the aircraft fuel tank. This may be done in a bucket, drum, or other suitable container.
For turbojet and turboprop engines, it is permissible to mix different grades (JP 4, JP 5, or JP 8) of military fuels in aircraft fuel tanks. The aircraft flight manual should be consulted for operating instructions when fuels are mixed. Generally, the aircraft operating parameters for the most restrictive fuel in the mixture will be followed.
Jet A is a kerosene type fuel similar to JP 8, but having a maximum freezing point of 40°C ( 40°F). The specification for Jet A does not require corrosion or icing inhibitors. Jet A 1 is a kerosene type fuel similar to JP 8, but the specification for Jet A 1 does not require corrosion or icing inhibitors. Jet Fuel A-1 is a petroleum distillate blended from kerosene fractions and used in civil aviation. Jet A-1 is similar to Jet A except for a lower freezing point. Jet A-1 is an operational fuel for all turboprop and turbojet aircraft requiring a low freezing point product).
Jet B is a fuel similar to JP 4 but has a maximum freeze point of 50°C ( 58°F). The specification for Jet B does not require corrosion or icing inhibitors.
Jet fuel 4 (JP-4) is a form of no. 1 fuel oil, and was one of the most commonly used petroleum products in the US Military. Jet fuel no. 4 is a middle distillate refined petroleum product that was primarily used in military planes. JP-4 was the standard fuel of the US Air Force and Army Aviation, and at one time constituted 85% of the turbine fuels used by the Department of Defense.
JP-4 is essentially a 50:50 mixture of heavy naphtha fraction (like gasoline) and kerosene. This fuel is not considered to be an acceptable substitute/alternate for diesel fuel. JP-4 is interchanged within NATO under NATO Code Number F-40. JP-4 is mainly procured as ASTM D 975 Jet B (or perhaps as CAN/CGSB 3.22). The chief difference between JP-4 and Jet B is that JP-4 contains the three mandatory additives while Jet B does not unless requested during procurement.
In terms of refining crude oil, JP-4 is a middle distillate. The middle distillates include kerosene, aviation fuels, diesel fuels, and fuel oil #1 and 2. These fuels contain paraffins (alkenes), cycloparaffins (cycloalkanes), aromatics, and olefins, from approximately C9 to C20. Aromatic compounds of concern included alkylbenzenes, toluene, naphthalenes, and polycyclic aromatic hydrocarbons (PAHs). Compositions range from avgas and JP-4, which are similar to gasoline, to Jet A and JP-8, which are kerosene-based fuels. JP-4 is a volatile, complex mixture of aliphatic and aromatic hydrocarbons that was principally used in military aircraft. The volatility meant that inhalation exposure is a potential problem near fueling facilities, either from spills or leaks. Once the soil has become saturated, remedial activities create both fire and inhalation hazards.
The conversion of Air Force bases from JP-4 to JP-8 has been completed. The need for and availability of JP-4 for new air vehicles remains unclear. Reference Technical Order (T.O.) 42B-1-14 for a more detailed definition of primary, alternate, and emergency fuel. Consult Air Standardization Coordinating Committee (ASCC) AIR STD 15/1Y for allied country fuel designations. When using a fuel other than JP 4, it may be necessary to manually adjust fuel controls of turbine engines to avoid exceeding engine operating limits, particularly RPM and EGT. Applicable flight manuals and engine technical orders should be consulted for specific operation and adjustment instructions when using alternate fuels.
Jet fuel 5 (JP-5) is a form of no. 1 fuel oil. Many commercial jet fuels have basically the same composition as kerosene, but they are under more stringent specifications than those for kerosene. JP-5 is a military aircraft turbine fuel. JP-5 is considered to be the naval equivalent of JP-4, the former standard fuel of the US Air Force and Army Aviation. Naval aircraft have somewhat different requirements from those for land-based planes, such as less volatility and higher flash points, in order to minimize vapor exposure of personnel as well as reduce fire risk in enclosed areas below decks. This led to the development of JP-5, a 60 degree C minimum flashpoint kerosene-type fuel for use in shipboard service. The flash point is the temperature the fuel ignite. JP5's flash point is 140 degrees Fahrenheit.
If there's too much water in JP5, it may freeze in aircraft that fly at high altitudes, such as the SH-60. Sediment, or small foreign particles, presents another problem. Too much sediment will clog up certain intakes on an aircraft, putting an aircraft out of service for labor-intensive maintenance for weeks. To check for these JP5-spoiling elements, the QA Lab uses a combined contaminated fuel detector, or CCFD.
In terms of refining crude oil, JP-5 is a middle distillate. The middle distillates include kerosene, aviation fuels, diesel fuels, and fuel oil #1 and 2. These fuels contain paraffins (alkanes), cycloparaffins (cycloalkanes), aromatics, and olefins from approximately C9 to C20. Aromatic compounds of concern included alkylbenzenes, toluene, naphthalenes, and PAHs. Compositions range from avgas and JP-4, which are similar to gasoline, to Jet A and JP-8, which are kerosene-based fuels. JP-4 and JP-5 are volatile, complex mixtures of aliphatic and aromatic hydrocarbons and are principally used in military aircraft. The volatility means that inhalation exposure is a potential problem near fueling facilities, either from spills or leaks. Once the soil has become saturated, remedial activities create both fire and inhalation hazards. Toxic effects are similar to those described for gasoline. Chronic effects associated with middle distillates are mainly due to exposure to aromatic compounds, which are found primarily in JP-4 and JP-5.
A Department of Defense (DoD) Directive Number 4140.43 dated 5 December 1975 stated that all new turbine powered air vehicles should be designed to operate on middle distillate turbine fuel, JP-8, as well as JP-5 and JP-4. JP-8 has since been identified as the Single Fuel for the Battlefield. Shipboard based air vehicles continue to require JP-5 fuel because of safety considerations in storing and handling fuel aboard ships. These fuels can be routinely encountered in world wide deployment and should be considered in the design of the air vehicle systems. All other fuels should be designated alternate, restricted or emergency fuels.
JP-8 is a 100% kerosene blend and is an acceptable substitute/alternate for diesel fuel. JP-8 is interchanged within NATO under NATO Code Number F-34. In terms of refining crude oil, jet fuel 8 is a middle distillates. The middle distillates include kerosene, aviation fuels, diesel fuels, and fuel oil #1 and 2. These fuels contain paraffins (alkenes), cycloparaffins (cycloalkanes), aromatics, and olefins from approximately C9 to C20. Aromatic compounds of concern included alkylbenzenes, toluene, naphthalenes, and polycyclic aromatic hydrocarbons (PAHs). Compositions range from avgas and JP-4, which are similar to gasoline, to Jet A and JP-8, which are kerosene-based fuels . Kerosene normally has a boiling range well above the boiling-point of benzene; accordingly, the benzene content of the kerosene fraction (and therefore jet fuel 8) is usually below 0.02%. However, since wide-cut jet fuels (such as jet fuel 4) are made by blending with gasoline, they may contain more benzene (normally < 0.5%).
The JP-8 +100 fuel thermal stability additive for JP-8 was developed by the Air Force Research Lab (AFRL/PRSP) to increase the thermal stability of jet fuel by 100?F and increase the fuel's heat sink capacity by 50%. The +100 additive is a fuel injector cleaner additive package consisting of detergent, dispersant, metal deactivators and antioxidant. The additive was developed to facilitate fielding of future advanced fighter air vehicles requiring enhanced thermal margins for fuel. During field evaluation of the additive in F-16 air vehicles, benefits of reduced engine coking were reported. The Air Force has been evaluating the benefits of this additive in fighter and trainer air vehicles. However, the additive disarms the current generation of filter coalescer elements making them ineffective for removing water, and dirt.
The Air Force developed an implementation method to inject the +100 additive downstream after the fuel has been filtered through current filters, for application on truck refueled air vehicles. A new generation of filter coalescer element is required to remove dirt and water from fuel with +100 additive so that fuel can be dispensed in a hydrant system. The Navy has expressed concerns on unique problem with filters for their ships and requires that a drop-in filter and coalescer element be developed before they use the +100 additive. The Army has voiced similar concerns on the additive implementation prior to filter development.
The three services are currently working on a new generation filter coalescer development. Initial prototypes have been tested, but would require significant modification to be used in existing Air Force, Army and Navy filter coalescer vessels.
During the B-2 development phase, the primary fuel for the air vehicle was changed from JP-4 to JP-8. This was desired due to the requirement to refuel the air vehicle within a hangar and due to limited air flow for ventilating air vehicle compartments adjacent to the fuel tanks. The low volatility of JP-8 greatly reduced the probability of a fuel explosion. JP-4 was re-designated as an emergency fuel. With the routine exposure to JP-4 removed, other fuel subsystem changes could be made. The fuel tank pressurization system, which was mandatory for the fuel subsystem for hot JP-4, was deleted providing a reduction in system complexity and air vehicle weight along with an improvement in system maintainability. Also, fuel tank lightning protection was reduced due to the reduction in risk of fuel tank explosion.
The Air Launched Cruise Missile (ALCM) changed to a high density fuel to improve the range capability of the missile. The missile was volume limited and therefore, the increased pounds of fuel could be loaded in the existing tank volume. The fuel designated for ALCM has been defined by MIL-P-87107B.
JP-9 is a mixture of three specific hydrocarbon compounds blended to obtain a freezing point below -65°F, high volatility to enable ignition of a cold soaked missile, a maximum viscosity of 80 centistokes at -65°F, very high stability and cleanliness, and no aromatic components to minimize material compatibility problems. A report on the long term evaluation of the effects of JP-9 on various fuel subsystem elastomers was issued by the Air Force Material Laboratory (AFML) reference AFML-MX-79-14, dated 8 March 1979. It was concluded that most of the fuel subsystem elastomers were compatible with JP-9. Two exceptions were identified. Chromate cured polysulfide exhibited shrinkage during long term storage and Nitrile o-rings exhibited excessive swell. A report on the compatibility of JP-9 fuel with metals was issued as AFML-MX-79-22. The report indicated that 2219-T87 aluminum alloy in contact with A286, 304 CRES, or cadmium plated steel fasteners is not compatible with water contaminated JP-9. JP-9 will be serviced in a clean, dry condition and the ALCM fuel tank will be sealed to prevent absorption of water into the fuel. A data accumulation plan was formulated by the prime contractor under the Effectiveness Verification Improvement Program to provide a data base to show that the fuel subsystem will operate correctly without oxidation, gum formation, or microbacteriological growth for a period of five years or longer.
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