MILITARY JET FUELS

CHEMICAL COMPOSITION OF AVIATION FUEL:

Aviation fuels consist of blends of over a thousand chemicals, primarily Hydrocarbons (paraffins,olefins, naphthenes, and aromatics) as well as additives such asantioxidants and metal deactivators, and impurities. 

The main components include n-octane and isooctane. Like other fuels, blends of aviation fuel used in piston engined aircraft are often described by their Octane rating.

 CIVIL AVIATION FUEL

They are classified as   A, B, TS-1, A1

MILITARY AVIATION FUEL

They are classified as jet propellant-1   (JP-1),  (JP-4),  (JP-5),  (JP-8), (JP-8)+100  and  100LL  (low lead)

JP-8

JP-8, (Jet Propellant-8) is a kerosene based jet fuel, converted by the U.S. government  from JP-4 fuel. It is a less flammable, less hazardous fuel for better safety. Its NATO code is F-35, with FSII is F-34. JP-8 has a flash point of 46 °C (100 °F) compared to -18 °C (0 °F) for JP-4. 

Commercial aviation uses a similar mixture under the name Jet-A. 

JP-8 is formulated with icing inhibitor, corrosion inhibitors, lubricants, and antistatic agents, and less benzene (a carcinogen) and less n-hexane (a neurotoxin) than JP-4. However, it also smells stronger than JP-4. JP-8 has an oily feel to the touch, while JP-4 feels more like a solvent.  As JP-8 is less volatile, it remains on the contaminated surfaces for longer time, increasing the risk of exposure.

JP-8+100

It is a version of JP-8 with an additive that increases its thermal stability by 56°C (a difference of 100°F). The additive is a combination of a surfactant, metal deactivator, and an antioxidant, and was introduced in 1994 to reduce cocking and fouling in engine fuel systems. 

FSII

Fuel system icing inhibitor (FSII) is an additive to aviation fuels that prevents the formation of ice crystals and microbiological growth in fuel tanks and lines.

When the aircraft goes to higher altitude, the temperature drops and Jet fuel's capacity to hold water is diminished. Particulate water can separate out and could become a serious problem if it freezes in fuel lines or filters, blocking the flow of fuel and shutting 

down an engine.

FSII is an agent that is mixed with jet fuel as it is pumped into the aircraft. The mixture of FSII must be between 0.10% and 0.15% by volume for the additive to work correctly, and the FSII must be distributed evenly throughout the fuel. Simply adding FSII after the fuel has been pumped is therefore not sufficient.

Large aircraft do not require FSII as they are usually equipped with electric fuel line heaters that keep the fuel at an appropriate temperature to prevent icing. However, if the fuel heaters are inoperable, the aircraft may be still be declared fit to fly, if FSII is added to the fuel.

WATER IN THE FUEL

It is very important that jet fuel be free from water contamination. During flight,the temperature of the fuel in the tanks decreases, due to the low temperatures in the upper atmosphere. 

This causes precipitation of the dissolved water from the fuel. The separated water then drops to the bottom of the tank, because it is denser than the fuel. From this time on, as the water is no longer in solution, it can freeze, blocking fuel inlet pipes. Removing all water from fuel is impractical, therefore fuel heaters are usually used on commercial aircraft to prevent water in fuel from freezing.

There are several methods for detecting water in jet fuel. A visual check may detect high concentrations of suspended water, as this will cause the fuel to become hazy in appearance. An industry standard chemical test for the detection of free water in jet fuel uses a water-sensitive filter pad that turns green if the fuel exceeds the specification limit of 30ppm (parts per million) free water.