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 fuel and can run on normal diesel fuel too. In this section we delve deeper into aircraft JET fuels, AVtur.

JET - Diesel Fuel Types

Diesel fuel is a light oil with density of around 850 gr/L and releases 40,9 MJ of energy per liter fuel. It is obtained at 200°C to 350°C in a fractional distillation unit. JET fuel / kerosene is derived from the same source at 150°C to 275°C 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 fuel pump, running only on JET fuel can ruin this pump if precautions are not taken.

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 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°C instead of maximum minus 47°C) and is available only in North America. Its 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 de-icer 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 fuel properties are:

JET fuel density
JET fuel / kerosene weighs 6.76 Lbs/US gallon or put another way: 0.81 g/mL at standard temperatures.

Learn more by reading JET-A fuel specifications here, and the details on JP-8 specifications (both by ConocoPhilips).

Detailed information on aviation and diesel fuels in these documents from Chevron (opens in new window):

• Aviation Fuels (pdf)
• Diesel Fuels (pdf)

Diesel Fuels

Diesel fuel is denser, heavier, contains more energy than gasoline. It also is used to lubricate the fuel pump. But not in aircraft diesel engine designs as JET fuel does not have the lubrication properties as normal diesel fuel. Either engine oil is used to lube the pump or an additive (some use a good synthetic two stroke oil in 1 : 100 ratio, Stanadyne also has some very good additives for fuel) is added to the fuel. Diesel engines can use a wide range of fuel: peanut oil (like the original design by Rudolph Diesel), algea oil, coconut and those renewable types also known as biodiesel. By using these fuels (biomass) the engine is CO₂ neutral, meaning that you will not add to the CO₂ in the atmosphere. Biodiesel also reduces PM (particulate matter) in the exhaust gasses.

Compared to a gasoline engine, an aircraft with a diesel engine of the same power will have more range, endurance, uses less fuel for the same performance and burning less fuel means less pollution in the environment and this is even more so when biodiesel is used as fuel. Diesel engines are more reliable, simpler in design, have less components thus having more hours to TBO, in short: it is the ideal 'new' engine for the future of general aviation.

Biodiesel
Aircraft diesel engines should be able to run on biodiesel too. Confirm this with the engine manufacturer. Biodiesel can be obtained from palm trees, coconuts, algea, plants and even from waste cooking oil and it has good lubrication and fuel tank cleaning properties. It is biodegradable, nonhazardous and doesn't add to the CO₂ in the atmosphere.

Cold weather
Diesel fuels are prone to gelling and waxing in cold weather if the right measures are not taken. Usually, fuel sold by roadside fuel stations is changed when winter sets in. But when an aircraft flies at high altitude temperatures can drop below freezing easily, if that aircraft was using roadside summer diesel it would experience fuel gelling and probably an engine failure. Special additives are needed to keep diesel fuel from gelling at low temperatures, or the exclusive use of JET fuel is recommended in these operations.