Have you ever wondered what the different types of aviation fuel are? Just like vehicles, aircraft can use a variety of different fuels. Two, though, are the most common. Avgas is used for piston-engine aircraft, and Jet A1 (as you may see on tankers at airports) for jet engines. This article explores the difference.
Avgas – powering piston engines and smaller aircraft
Avgas, short for aviation gas, is used to power traditional propeller aircraft. Typically, today these are smaller aircraft, such as those at flight school, clubs or sports, and aerobatic aircraft. This does not include turbojet aircraft, whose propellers are powered by a turbine engine using Jet A1 fuel.
Stay informed: Sign up for our daily aviation news digest.
Propeller aircraft use piston engines that operate in a similar way to the combustion engine in a motor vehicle. This is the same spark ignition based system, so the fuel will have a much lower flashpoint than Jet A1. Aircraft engines, though, are much higher performance than road vehicles, and Avgas, therefore, has a higher octane content than standard automotive gasoline.
Jet A1 – the most common fuel for jet aircraft
Jet A1 belongs to the wider family of jet fuels used to power all jet aircraft. It is by far the most common, although Jet A is also common in the US (the two differ mostly in their freezing point, and can be used interchangeably).
Jet fuel is a highly refined Kerosene fuel that is ignited by a combination of pressure and heat. A simple spark ignition system would not be sufficient to burn jet fuel, and it instead requires a highly compressed fuel-air mixture to ignite.
It is actually a ‘simpler’ fuel than Avgas. They both, of course, come from the refining of crude oil. Through the refining process, various fuels are produced at different distillation points. Kerosene and diesel fuels (to which jet fuel belongs) come off first and are, therefore, easier to obtain. Avgas (and motor gasoline) are later to be distilled, and also have to go through additional reforming and alkylation processes (which combines different products to upgrade the result) to produce the final fuels.
For some insight into the fueling process for aircraft with Jet A1, look at this Simple Flying article.
Advantages of Jet A1
Jet fuel has certain key advantages for jet aircraft:
- It has a lower freezing point, essential for high altitude flying. Jet A1 has a freezing point of -47 degrees Celsius and Jet A slightly higher at -40 degrees.
- It has a higher flashpoint and is, therefore, safer to transport. It is much less likely to be ignited unsafely. But it is still extremely flammable, especially when vaporized.
- It is cheaper than Avgas. This may seem strange as it powers such great engines, but it is a much simpler fuel to produce. It is also produced in much higher quantities, reducing costs.
What about switching fuels?
As Jet A1 is cheaper and more available, it would be great if the fuels were interchangeable. There are not, though! Fuelling a piston engine aircraft with Jet A1 would likely flood the engine and not be ignited. The fuel requires the higher temperatures and pressurization that a jet engine is designed to produce.
Fuelling a jet engine with Avgas would be much more dangerous. It would ignite at a lower temperature, with potentially devastating results.
There have been some attempts to convert piston aircraft to take jet fuel, such as the Diesel Cessna 172 Turbo Skyhawk and the Diesel Piper Archer aircraft. It is an expensive conversion, but allows the use of lower-priced fuel and increases range.
Best of the rest – other jet fuels
Jet A and Jet A1 are not the only jet fuels in use. There are several other in different regions or for different aircraft, with specific modifications. Some of the main ones include:
- Jet B. This is probably the most common alternative in civil aviation. It is modified to offer a lower freezing point of -60 degrees Celsius and has a lower flashpoint. This makes it more dangerous to handle but is useful in colder climates such as Canada and Alaska.
- TS-1. This is a common fuel in Russia, again modified for a lower freezing point (-50 degrees Celsius).
- JP-8. This is military-grade jet fuel. It is designed for use in aircraft without fuel heaters, and also contains additional anti-corrosion additives.
And don’t forget biofuel. This sustainable fuel is seen as part of the way forward for the aviation industry to reduce its carbon footprint. Several airlines have started to make use of biofuel, but it is far from common.
Jet fuel and Avgas are not things we discuss that often on Simple Flying. Let us know in the comments if you would like to share any thoughts or facts.