Educational /Awareness article

Jet fuel, the most common type in commercial aviation being “Jet-A”, is essentially kerosene, with some additives. It is water-clear in color and smells just like lantern fuel. It is NOT Diesel fuel, it is NOT “like” Diesel fuel, and it does not have Diesel fuel mixed into it because at -60F, the temperature that airliners routinely encounter at 35,000 feet, Diesel fuel would be frozen solid. Jet-A is formulated to stay liquid in subzero temperatures. Aviation gasoline is any of a number of highly refined grades of gasoline, similar to automotive fuel. It is refined to remove most of the light volatile compounds which could boil in the low atmospheric pressures at the high altitudes that airplanes operate and cause vapor lock, thus causing fuel starvation and loss of power. It is also refined to remove the heaviest compounds that would tend to gum up carburetors and fuel injectors. (Unlike automotive gasoline, spilled avgas won’t leave a smelly residue on hands and clothing that persists for days. It evaporates quickly and leaves little perceptible odor.) The most common grade in use today is 100LL, i.e., 100 octane Low Lead. It is dyed blue. Some very old engines, chiefly those built prior to 1950, can use 80 octane avgas. It is dyed red. A few high performance engines require 130 octane leaded avgas. It is dyed green. Most airports have 100LL for sale, but not all have 80 or 130 octane. Jet fuel is a clear to strawcolored fuel, based on either an unleaded kerosene (Jet A-1), or a naphtha-kerosene blend (Jet B). It is similar to diesel fuel, and can be used in either compression ignition engines or turbine engines Aviation 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 temperature, among other properties. Most aviation fuels available for aircraft are kinds of petroleum spirit used in engines with spark plugs (i.e. piston and Wankel rotary engines), or fuel for jet turbine engines, which is also used in diesel aircraft engines. Aviation fuel is often dispensed from a tanker or bowser, which is driven up to parked aircraft and helicopters. Some airports have pumps similar to filling stations to which aircraft must taxi. Some airports have permanent piping to parking areas for large aircraft. Aviation fuel is transferred to an aircraft via one of two methods: over wing or under wing. Over wing fueling is used on smaller planes, helicopters, and all piston-engine aircraft. Over wing fueling is similar to car fueling — one or more fuel ports are opened and fuel is pumped in with a conventional pump. Underwing fueling also called single-point refueling or pressure refueling where not dependent on gravity, is used on larger aircraft and for jet fuel exclusively. (Most wide body aircraft use a double single-point) For pressure refueling, a high-pressure hose is attached and fuel is pumped in at 275 kilopascals (40 psi) and a maximum of 310 kilopascals (45 psi) for most commercial aircraft. Pressure for military aircraft, especially fighters, ranges up to 415 kilopascals (60 psi). Air being displaced in the tanks is usually vented overboard through a single vent on the aircraft. Because there is only one attachment point, fuel distribution between tanks is either automated or it is controlled from a control panel at the fueling point or in the cockpit. An early use of pressure refueling was on the de Havilland Comet and Sud Aviation Caravelle.[6] Larger aircraft allow for two or more attachment points, however this is still referred to as single-point refueling, as either attachment point can refuel all of the tanks. Multiple attachments allow for faster fuel flows. Mis fueling - because of the danger of confusing the fuel types, precautions are taken to distinguish between avgas and jet fuel beyond clearly marking all containers, vehicles, and piping. The aperture on fuel tanks of aircraft requiring avgas cannot be greater than 60 millimeters in diameter. Avgas is often dyed and is dispensed from nozzles with a diameter of 40 mm (49 mm in the USA). Jet fuel is clear to straw-colored, and is dispensed from a special nozzle called a J spout that has a rectangular opening larger than 60 mm diagonally, so as not to fit into avgas ports. However, some jet and turbine aircraft, such as some models of the Astar helicopter, have a fueling port too small for the J spout, and thus require a smaller nozzle.


Types

Jet A

Jet A specification fuel has been used in the United States since the 1950s and is usually not available outside the United States and a few Canadian airports such as Toronto and Vancouver, whereas Jet A-1 is the standard specification fuel used in the rest of the world other than the former Soviet states where TS-1 is the most common standard. Both Jet A and Jet A-1 have a flash point higher than 38 °C (100 °F), with an auto ignition temperature of 210 °C (410 °F).[7]

Differences between Jet A and Jet A-1

The primary difference is the lower freezing point of A-1
Jet A’s is −40 °C (−40 °F)
Jet A-1’s is −47 °C (−53 °F)
The other difference is the mandatory addition of an anti-static additive to Jet A-1. As with Jet A-1, Jet A can be identified in trucks and storage facilities by the UN number 1863 Hazardous Material placards. Jet A trucks, storage tanks, and plumbing that carry Jet A are marked with a black sticker with “Jet A” in white printed on it, adjacent to another black stripe.

Typical physical properties for Jet A and Jet A-1

Jet A-1 fuel must meet:
DEF STAN 91-91 (Jet A-1),
ASTM specification D1655 (Jet A-1), and
IATA Guidance Material (Kerosene Type), NATO Code F-35.
Jet A fuel must reach ASTM specification D1655 (Jet A)


Typical physical properties for Jet A / Jet A-1

The less Sulphur, the better, 0.05% is the super quality for vehicles, etc., while other qualities are for generators, power plants, etc.


Jet B

Jet B is a fuel in the naphtha-kerosene region that is used for its enhanced cold-weather performance. However, Jet B’s lighter composition makes it more dangerous to handle. For this reason it is rarely used, except in very cold climates. A blend of approximately 30% kerosene and 70% gasoline, it is known as wide-cut fuel. It has a very low freezing point of −60 °C (−76 °F) and a low flash point as well. It is primarily used in some military aircraft. It is also used in Canada, Alaska and sometimes Russia because of its freezing point.

The DEF STAN 91-91 (UK) and ASTM D1655 (international) specifications allow for certain additives to be added to jet fuel, including:
• Antioxidants to prevent gumming, usually based on alkylated phenols, e.g., AO-30, AO-31, or AO-37;
• Antistatic agents, to dissipate static electricity and prevent sparking; Stadis 450, with dinonylnaphthylsulfonic acid (DINNSA) as a component, is an example
• Corrosion inhibitors, e.g., DCI-4A used for civilian and military fuels, and DCI-6A used for military fuels;
• Fuel system icing inhibitor (FSII) agents, e.g., Di-EGME; FSII is often mixed at the point-of-sale so that users with heated fuel lines do not have to pay the extra expense.
• Biocides are to remediate microbial (i.e., bacterial and fungal) growth present in aircraft fuel systems. Currently, two biocides are approved for use by most aircraft and turbine engine original equipment manufacturers (OEMs); Kathon FP1.5 Micro biocide and Biobor JF.
• Metal deactivator can be added to remediate the deleterious effects of trace metals on the thermal stability of the fuel. The one allowable additive is N,N’-disalicylidene 1,2-propanediamine.
As the aviation industry’s jet kerosene demands have increased to more than 5% of all refined products derived from crude, it has been necessary for the refiner to optimize the yield of jet kerosene, a high value product, by varying process techniques. New processes have allowed flexibility in the choice of crudes, the use of coal tar sands as a source of molecules and the manufacture of synthetic blend stocks. Due to the number and severity of the processes used, it is often necessary and sometimes mandatory to use additives. These additives may, for example, prevent the formation of harmful chemical species or improve a property of a fuel to prevent further engine wear.
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. Since the water is no longer in solution, it can form droplets which can supercool to below 0 °C. If these super cooled droplets collide with a surface they can freeze and may result in blocked fuel inlet pipes. This was the cause of the British Airways Flight 38 accident. 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 30 ppm (parts per million) free water.
Worldwide demand of jet fuel has been steadily increasing since 1980. Consumption more than tripled in 30 years from 1,837,000 barrels/day in 1980, to 5,220,000 in 2010.



Top uses of Jet Fuel

• Turbine Engines
• Heaters and Cookers
• Lighting

Top uses of Aviation Gasoline / Avgas

• Piston engine powered private planes
• Most commercial aircrafts
• Combat – type planes during military training procedures

Specifications / Grades of Aviation Gasoline or Avgas

Avgas 100 - The standard high octane fuel for aviation piston engines. It has a high lead content and is dyed green. There are two major specifications for Avgas 100. The ASTM D 910 and UK DEF STAN 91-90. These two specifications are essentially the same but differ over antioxidant content, oxidation stability requirements and max lead content.
Avgas 100LL - This grade is the low lead version of Avgas 100. Low lead is a relative term. There is still up to 0.56 g/litre of lead in Avgas 100LL. This grade is listed in the same specifications as Avgas 100, namely ASTM D 910 and UK DEF STAN 91-90. Avgas 100LL is dyed blue.
Avgas 82UL - This is a relatively new grade aimed at the low compression ratio engines which don’t need the high octane of Avgas 100 and could be designed to run on unleaded fuel. Avgas 82UL is dyed purple and specified in ASTM D 6227.

Specification / Worldwide Jet Fuel Civil jet Fuel Grades

• Jet A-1
• Jet A
• Jet B
• TS-1
• American Civil Jet Fuels
• UK Jet Fuels
• Former Soviet Union and East European Jet Fuels
• Chinese Jet Fuels
• International Specifications - AFQRJOS Checklist
• Other National Civil Jet Fuel Specifications
Today’s kerosene jet fuels have been developed from the illuminating kerosene used in the early gas turbine engines. These engines needed a fuel with good combustion characteristics and a high energy content. The kerosene type fuels used in civil aviation nowadays are mainly JET A-1 and Jet A. The latter has a higher freezing point (maximum minus 40 degrees C instead of maximum minus 47 degrees C) and is available only in North America.