Common Aviation Fuels, JET
Experimental aircraft commonly use engines which consume AVgas (Lycoming / Continental / Franklin and equivalent types) or engines running Mogas (Rotax, Subaru, Jabiru etc). Some engines are capable of running either fuel, although with restrictions. Purpose built diesel aircraft engines are designed to use JET and can run on normal diesel too. In this section we delve deeper into aircraft JET fuels also called AVtur.
Diesel is a light oil with density of around 850 gr/l and releases 40,9 MJ of energy per liter. It is obtained at 200 °C to 350 °C in a fractional distillation unit. JET / kerosene is derived from the same source at 150 °C to 275 °C but has 5% less energy.
The basic properties compare so much that either fuel can be used in a diesel engine. Main difference is that the lubrication properties of diesel are much better and as the fuel is sometimes used as lubricant for the high pressure pump, running only on JET can ruin this pump if precautions are not taken.
Mixing JET with about 2 to 5 % biodiesel will aid in increasing lubricity for the high pressure fuel pump thereby prolonging engine life.
JET - Diesel Types
Todays kerosene 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 high energy content. The kerosene type fuels used in civil aviation nowadays are mainly A-1 and A. The latter has a higher freezing point (maximum minus 40 °C instead of maximum minus 47 °C) and is available only in North America. The color is straw like clear.
Typical JET - Diesel fuel types suitable for aircraft diesel engines are:
- Automotive high grade diesel, low sulfur - Fuel stations sell this fuel nowadays with a lower sulfur content, if not flying from a large airport with JET-A(1) this is the fuel you should use.
- Red 'off the road' diesel - Red diesel is much cheaper than automotive diesel due to the fact that there is less tax on it; it is used mainly by farmers. Check with your local authorities if there is a problem using it in an aircraft (there should not be any).
- JET A is a kerosene grade fuel, normally only available in the U.S.A. It has the same flash point as JET A1 but a higher freeze point maximum (-40 °C). It is supplied against the ASTM D1655 (JET A) specification.
- JET A1 is a kerosene grade of fuel suitable for most turbine engined aircraft. It has a flash point minimum of 38 °C (100 F) and a freeze point maximum of -47 °C. It is widely available outside the U.S.A. The main specifications for JET A1 grade are the UK specification DEF STAN 91-91 (JET A1) NATO code F-35, (formerly DERD 2494) and the ASTM specification D1655 (JET A1).
- JET-B, JP-4 (MIL-T-5624, NATO F-40) - JET B is a distillate covering the naphtha and kerosene fractions. It can be used as an alternative to Jet A-1 but because it is more difficult to handle (higher flammability), there is only significant demand in very cold climates where its better cold weather performance is important. ASTM have a specification for Jet B but in Canada it is supplied against the Canadian Specification CAN/CGSB 3.23.
- JP-5 (MIL-T-5624, NATO F-44) and JP-8 (MIL-T-83133, NATO F-34) - These fuels should be hard to come by and only available on military fields, in case of emergency they can be used. JP-8 is JET-A1 with deicer and corrosion inhibitor, JP-5 is jet fuel kerosene based.
- DL-1, DI-2 (W-F-800 CONUS, NATO F-54) - Specified Military use inside the Continental USA.
- DF-2 (W-F-800 OCONUS, NATO F-54) - Specified Military use outside the Continental USA.
Some typical JET - Diesel properties are:
|Property||JET A/A-1||JP-5||JP-8||Diesel #1||Diesel #2|
|API Gravity @ 60°F||44.3||41.1||45.6||43||39|
|Flash point in °C||38||62||45||38||52|
|Viscosity cSt @ 40°C||-||1.5||1.2||1.2-2.4||1.9-4.1|
|Sulfur, %mass||0.3 max||0.4 max||0.4||0.05||0.05|
|Heat content Btu/Gallon, Net.||123608||125270||123069||130000 (typical)||129500|
JET / kerosene weighs 6.76 lbs/US gallon or put another way: 0.81 g/ml at standard temperature (15°C).