Properties of Jet Fuel

Jet Fuel

Jet fuel is a distillate fraction of crude oil having boiling points between 150~ and 250 °C. This fuel is lighter than diesel cut and heavier than naphtha and gasoline cut. Kerosene-type jet fuel (including Jet A and Jet A-1, JP-5, and JP-8) has a carbon number distribution between about 8 and 16 (carbon atoms per molecule); wide-cut or naphtha-type jet fuel (including Jet B and JP-4), between about 5 and 15.

Jet fuel is a mixture of a variety of hydrocarbons. Because the exact composition of jet fuel varies widely based on the petroleum source, it is impossible to define jet fuel as a ratio of specific hydrocarbons. Jet fuel is therefore defined as a performance specification rather than a chemical compound. Furthermore, the range of molecular mass between hydrocarbons (or different carbon numbers) is defined by the requirements for the product, such as the freezing point or smoke point.

Today’s kerosine jet fuels have been developed from the illuminating kerosine used in the early gas turbine engines. These engines needed a fuel with good combustion characteristics and high energy content. The kerosine-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.

Jet Fuel Properties

The specifications of Jet A and Jet A-1 Fuel properties are shown in the table below;

Property Jet A Jet A-1
Acidity, mg KOH/g 0.10 Max. 0.10 Max.
Aromatics, Vol. % 25 Max. 25.0 Max.
Sulphur, mercaptan, Wt. % 0.003 Max. 0.0030 Max.
Sulphur, total, Wt. % 0.30 Max. 0.30 Max.
10% Distillation, ºC 205 Max. 205.0 Max.
Final Boiling Point, ºC 300 Max. 300.0 Max.
Distillation Residue, % 1.5 Max. 1.5 Max.
Distillation Loss, % 1.5 Max. 1.5 Max.
Flash Point, ºC 38 Min. 38.0 Min.
Density @ 15ºC, kg/m3 775 to 840 775.0 to 840.0
Freeze Point, ºC -40 Max -47.0 Max
Viscosity @ -20ºC, mm/s 8.0 Max. 8.000 Max.
Net Heat of Combustion, MJ/kg 42.8 Min. 42.80 Min.
One of the following shall be met:
1) Smoke Point, mm, or 25.0 Min. 25.0 Min.
2) Smoke Point, mm, and 18.0 Min. 18.0 Min.
Naphthalenes, Vol. % 3.0 Max 3.00 Max.
Copper Strip Corrosion, 2 h % 100ºC No. 1 Max. No. 1 Max.
Thermal Stability @ 260ºC:
-Filter pressure drop, mm Hg 25 Max. 25 Max.
-Tube Deposits < 3 Max. No Peacock (P) or Abnormal (A) < 3 Max. No Peacock (P) or Abnormal (A)
Existent Gum, mg/100 mL. 7 Max. 7 Max.
MSEP Rating
-Without electrical conductivity additive 85 85
-With electrical conductivity additive 70 70
Electrical conductivity, pS/m 50 Min. 600 Max.*
*Use of conductivity improver additive and resulting limits are optional in ASTM D1655
Distillation Point

Jet A-1 fuel has a flash point of a minimum of 38 °C with typical boiling ranging from 150 ~ 250oC. The ideal kerosene freezing point determines where to stop the Kerosene cut. The freezing point of jet A-1 fuel is -52oC. The production of jet fuel from a particular crude oil may be increased by increasing the endpoint temperature of the cut, and vice versa, if the freezing point is raised.

Smoke Point (ASTM D 1322)

The ability of jet fuels to produce smoke in a diffusion flame is shown by the results of this test. Fuels’ smoke points are correlated with the percentage of hydrocarbons in their chemical makeup. Higher levels of aromatics in gasoline often result in a lower smoke point and increased smoke production. Low aromatic concentration and low smoke-producing are both indicators of a high smoke point. Because of the potential radiant heat transmission from the combustion products of fuel, it is associated with the smoke point and luminometer number. The smoke point is measured using a wick-style kerosene lamp.

 Aniline Gravity Product (ASTM D 1405/IP 193)

Calculating the net heat of combustion by experimentation is time-consuming. However, using the fuel’s aniline point and API gravity, one may get a rather precise approximation of the heat of combustion of jet fuels. The API gravity of different aviation fuel classes has been shown to correlate with their net heat of combustion and the product of aniline point. Sulfur-free samples are assumed in these connections.

Thermal Oxidation Stability (ASTM D 3241)

To prevent the engine components from overheating, subsonic jets employ fuel that may reach temperatures of up to 200 oF. Fuel is also utilized to cool the hydraulic system, the air conditioning system, and the engine lubricating system in supersonic aircraft prior to combustion, turbine fuel temperatures may rise by 300 to 500oF. Fuel oxidation and deposit in heat exchangers, filters, and fuel injectors may occur at low levels because of the fuel’s high temperature.

Heating Value

Target high-density fuels with a density of less than 37 API 0.84 gcc having net heating values that are larger than 130,000 Btu gal and might enhance the range of aeroplanes by up to 15.

Water Reaction (ASTM D 1094)

The goal of this analysis is to ascertain whether turbine fuels include any components that are miscible with water and, if so, what influence those components have on the fuel-water interface. An ethanol fuel sample is agitated with a phosphate buffer solution at room temperature. The water reaction of the fuel is measured by observing the volume of the aqueous layer, the appearance of the interface, and the degree of separation between the two phases. Aeronautical fuel undergoes a water extraction process that discloses pollutants like surfactants that are only partially soluble in the fuel. Free water and particles may be let through to the engine if the filter separator is swiftly disarmed by impurities that disrupt the interface or produce emulsions in the water or fuel layers.

Mercaptan Sulfur (ASTM D 3227)

The presence of mercaptan sulfur in aircraft turbine fuel is corrosive to fuel system components and elastomers and may give the fuel an unpleasant odour. Merox and other treatment techniques, as well as hydrodesulfurization processes, may effectively eliminate mercaptans. Analytical techniques can detect mercaptans in petrol.

Acidity (ASTM D 3242)

Natural organic acids or traces of acid left over from the refining process may be found in aviation turbine fuel. Even trace amounts of acids in aviation turbine fuels may be harmful since they can accelerate corrosion and reduce the efficiency with which water can be separated from the fuel.

Hydrogen Content (ASTM D 3343)

The generation of soot in gas turbines is significantly influenced by the nature of jet fuel. The smoke point and luminometer number are two examples of combustion parameters that are heavily influenced by the hydrogen concentration of aviation fuels. Fuels for aircraft that contain more hydrogen provide more energy and produce less carbon dioxide gas when burned.

Viscosity and Fuel Lubricity

Low temperatures boost jet fuel’s already impressive viscosity, and the fuel’s line pressure drop as well as pumping capabilities are further enhanced by these conditions. Given that jet fuel is expected to withstand extended cold soak periods at temperatures as low as -40 °C, understanding its viscosity at these extremes is becoming more critical. Because of their low viscosity, boundary layer lubricants are absorbed into the surface and prevent the formation of a hydrodynamic film. The viscosity at -52 oC is 11.11.940 mPas.

Low-Temperature Properties

There are three temperature thresholds for jet fuel: freeze Point (at which wax crystals dissolve), pour Point (1.5-inch cylinder test; 4oC to 20 oC below Freeze Point), and Cloud Point (at which haze occurs). When the temperature falls below the pour point, jet fuel will not flow. When the recovery temperature drops below the pour point, fuel begins to harden.

Operational Considerations

Low-temperature operations pose a threat to fuel transfer, boost pump inlets, and fuel lines, thus pilots must keep fuel temperature at least 3 oC above the fuel freeze point. Air temperature, aircraft geometry, fuel management schedule, and time all have a role in the pace at which the fuel temperature decreases. The fuel temperature will rise and eventually reach the recovery point.

Jet Fuel Color

The color of Jet fuel is bright clear and minimum +20 Saybolt color is accepted.

Electric Conductivity

50~600 (pS/m), the electric conductivity of jet fuel is maintained.

Top References

[1]  S. Parkash, Petroleum Fuels Manufacturing Handbook: Including Specialty Products and Sustainable Manufacturing Techniques

[2]  www.wikipedia.com

[3]  www.exxonmobil.com


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