Avgas (also known as aviation spirit in the United Kingdom) is an aviation fuel that is used in aircraft with spark-ignited internal combustion engines. Avgas differs from regular gasoline (petrol) used in automobiles, which is referred to as mogas (motor gasoline) in aviation. Unlike motor gasoline, which has been manufactured since the 1970s to allow the installation of platinum-content catalytic converters for pollution reduction, avgas still contains tetraethyllead (TEL), a hazardous chemical used to reduce engine knocking (premature detonation). Experiments are under underway to reduce or eliminate the usage of TEL in aviation gasoline.
Kerosene-based jet fuel is designed to meet the needs of turbine engines, which have no octane need and can fly over a far larger range of altitudes than piston engines. Most diesel piston engines developed for aviation usage, such as those made by SMA Engines, Austro Engine, and Thielert, use kerosene as well.
What makes aviation gasoline different from conventional gasoline?
Tetra-ethyl lead additives are still used in aviation gas to lubricate the engine. In 1986, lead was removed from automobile gasoline. Despite years of testing, Avgas still includes lead since a suitable substitute has yet to be discovered. In a modern car, using leaded avgas will destroy components like the catalytic converter.
Jet-A, on the other hand, would not work in a gas engine. It’d be like putting diesel fuel in a gasoline-powered automobile, right? It simply will not start. Jet-A, on the other hand, could be used in diesel engines, but it lacks some of the lubricants found in regular diesel fuel.
What exactly does the term “aviation gasoline” imply?
Aviation fuels are petroleum-based or petroleum-and-synthetic fuel mixtures that are used to propel planes. They must meet more stricter standards than fuels used on the ground, such as heating and road transportation, and incorporate additives to improve or preserve critical fuel performance or handling features. For gas turbine-powered aircraft, they are kerosene-based (JP-8 and Jet A-1). Aircraft with piston engines utilize gasoline, whereas those with diesel engines may use jet fuel (kerosene). To keep fuel costs stable, all aircraft operated by the United States Air Force were certified to use a 50-50 blend of kerosene and synthetic fuel generated from coal or natural gas by 2012.
When choosing fuel for an airplane, specific energy is a crucial factor to consider. Hydrocarbon fuels have a far higher energy storage capacity than batteries, which has precluded electric aircraft employing batteries as the primary propulsion energy store from being practical for even tiny personal aircraft.
Hydrogen-powered aircraft may become more frequent as aviation goes towards the renewables era. These are zero-emission in terms of CO2, but not in terms of. mw-parser-output.template-chem2-su.mw-parser-output.template-chem2-su>span.mw-parser-output sub.template-chem2-sub.mw-parser-output sub.template-chem2-sub.mw-parser-output sub.template-chem2-sub.mw-parser-output sub.template-chem2-sub sup.template-chem2-sup.mw-parser-output
What is the octane rating of aviation gasoline?
Avgas 100LL and Jet A-1 are the two most used types of aviation fuel; Jet A-1 is used in turbine engines and Avgas is used in spark ignition piston engines. If you’re a general aviation pilot, you’re probably more familiar with Avgas, which is what we’ll be talking about here.
As you may know, Avgas contains Tetra Ethyl Lead (TEL), an additive that has lately been banned in European Union automobile forecourt fuels due to environmental concerns. Despite the fact that aviation uses less than 0.5 percent of the total gasoline used in Europe’s automobile industry, environmental lobbyists are putting pressure on Avgas producers to remove or replace TEL and develop an unleaded grade.
To comprehend what is involved, we must first consider the advantages of TEL. Lead compounds from TEL form a protective layer on the valve seat, preventing the soft valve seats from degrading, as you may know from the problems with Automotive fuels. Small sections of a soft metal valve seat will fuse to the valve and be “plucked” from the face of the seat if TEL is not used.
They generate an abrasive surface once bonded to the valve, severely damaging the valve seat. Because the valve seat wears away and recedes into the cylinder head, this sequence of events is known as Valve Seat Recession (VSR). Use a VSR additive or install reinforced valve seats that are resistant to this action as a solution to this problem.
VSR additives are currently widely utilized in Lead Replacement Petrol on car forecourts, however they have not yet been certified for use in aircraft engines for a variety of reasons. This means that reinforced valve seats are now the only way to prevent Valve Seat Recession in aviation engines that run on unleaded fuel. This is typical in new Avco Lycoming and Teledyne Continental engines, but older engines may require modifications.
The issue of Octane rating is another more serious issue with unleaded gasoline.
The higher the Octane rating, the more the fuel/air combination can be compressed without detonating; the lower the Octane rating, the more the fuel/air mixture can be compressed without detonating. To be clear, the octane rating is a measure of the fuel’s resistance to explosion rather than its energy content.
Greater octane fuels provide the advantage of allowing a higher compression ratio or supercharging ratio to be employed, resulting in higher engine cycle efficiency and, as a result, more power output for a given fuel burn. To add to the confusion, there are four different ways to calculate the Octane rating: RON, MON, Lean Mixture, and Rich Mixture.
Unleaded fuels tend to be 95-98 RON but only 85-87 MON on the RON scale for road fuels. Avgas has a Rich Mixture Octane rating as well as a Lean Mixture Octane rating (equivalent to MON).
The Lean Mixture rating is 100 octane (15 octane higher than unleaded Mogas’ equivalent 85 MON), but Avgas also has a Rich Mixture rating of 130, which allows for higher supercharger boost pressures without detonation. This is especially problematic when high power settings are used at low altitude, as as during takeoff.
As you can see, TEL in avgas affects the octane rating significantly, and without it, octane ratings would be reduced to 80 – 85 Lean Mixture – the level for road fuels – rather than 100 / 130. This isn’t an issue for most modern normally aspirated engines because their compression ratios are low, and detonation isn’t an issue with 80-85 Lean Mixture Octane gasoline.
Low octane unleaded fuels, on the other hand, would not be suited for planes with supercharged or turbocharged engines. The only way to run these turbo engines on current unleaded technology fuels would be to cut the supercharger’s boost pressure and de-rate the engines drastically. Many of the engines would no longer be powerful enough for the plane in question as a result of this de-rating.
Unleaded aircraft fuels, such as 82UL in the United States, are actively being developed. This fuel has an 82 octane rating and is allowed for use in non-turbo Avco Lycoming engines, among other things. It is not yet available in Europe, and it is also not available to everyone; your aircraft manufacturer must submit an Aircraft Modification paperwork to authorise its usage.
Although certain new Cessnas have been permitted to use 82UL, most aircraft types do not have manufacturer permission at this time. The number of Avgas piston-engined aircraft that may utilize this grade is expected to be over 60% worldwide, however some would likely require fuel system upgrades before being approved.
There are currently no additions available to replace TEL that raise the Octane rating of the fuel; the additives used in automobile Lead Replacement Fuels primarily address valve seat recession and have no influence on the fuel’s Octane rating. As a result, if Avgas 100LL is discontinued, the only other option for owners of turbocharged or supercharged engines is for the aircraft manufacturer to issue a retrofit to replace their engine with a turboprop or diesel engine.
This takes us to another recent advancement in General Aviation engines: the development of diesel engine technology by numerous engine manufacturers. Shell is working closely with all of the major potential aviation diesel engine manufacturers on these projects. Compared to Avgas engines, these engines may have a number of important advantages.
They have the potential to be retrofitted to many light aircraft, replacing their current Avgas type engines, and return up to 30% higher fuel economy. They utilise Jet A-1 instead of Avgas. The expense of engine replacement and aircraft modification will be a disadvantage, and while some applications may be able to benefit from this technology, it will not be a viable option for everyone.
In conclusion, aviation engines provide numerous unique obstacles in the production of avgas, and while no clear timeframe for replacing Avgas 100LL has been set, there is little question that Leaded Avgas will be phased out soon. However, this does not appear to be a plausible scenario until adequate fully developed alternatives are available, which is likely to be some years away.
Is there a distinction between aviation and jet fuel?
AVGAS and Jet Fuel are the two most common forms of airplane fuel in general aviation. Choosing the correct aviation fuel for your aircraft is mostly determined by the type of engine it has. For piston-engine airplanes, AVGAS (aviation gasoline) is utilized. The push generated by the propellers allows these aircraft to fly. Aircraft with turbine-engine jets use Jet Fuel. The push of exhaled air propels them.
Is avgas available for purchase?
In the general aviation sector, there are two main avgas grades (100 and 100LL low lead). The octane rating is represented by the numbers in each of these categories. Other types of aviation fuel are either infrequently used or no longer manufactured.
Avgas 100
For aviation piston engines, this is the conventional high-octane gasoline. It is coloured green and contains a lot of lead. The ASTM D910 and the UK DEF STAN 91-090 are the two main specifications for Avgas 100. The antioxidant content, oxidation stability criteria, and maximum lead content are all different.
Avgas 100LL
Avgas 100 Low-Lead is a low-lead variant of Avgas 100. This grade is specified in the same ASTM D910 and UK DEF STAN 91-090 specifications as Avgas 100. Avgas 100LL is blue in color.
Avgas 80
This type of aviation fuel is no longer manufactured. If the aircraft’s type certificate operating limitations allow it, Avgas 100LL is the best fuel to use in its place. For more information, consult the aircraft’s operating manual.
Avgas 115
This was a high-octane avgas that was primarily employed in military combat aircraft in the late 1940s when great power output was required. The majority of military aircraft now have turbine engines. As a result, there is no longer any need for Avgas 115, and it is therefore unavailable.
Avgas UL91 and Avgas UL94
These are avgas grades that are free of lead. Both are similar in composition to Avgas 100LL, but the reduced lead content produces in a lower octane rating. Neither grade is presently available from Shell.
Future unleaded avgas
Shell is working on developing an unleaded Avgas that has an octane rating that is equivalent to or better than Avgas 100LL at the time of writing.
The goal is for this grade to be a complete unleaded replacement for the leaded grades Avgas 100LL and Avgas 100, although testing and development work is still on to prove the fuel’s appropriateness for fleet-wide use.
This fuel is not commercially available at the time of writing, however it is governed by ASTM D7960.
Is avgas the same as diesel?
Avgas and Jet-A are the two most common aviation fuels. They are comparable to automobile fuel (unleaded gasoline) and diesel in nature, but their qualities and capabilities to be employed in aviation applications differ significantly.
What is the most common composition of aviation fuel?
Crude oil, the common name for liquid petroleum, is the primary source of jet fuel. Petroleum-derived jet fuels are the name given to these jet fuels. Jet fuels can also come from kerogen or petroleum solids, an organic substance found in shale that can be transformed to shale oil with heat.
Is it possible to run a motorcycle on avgas?
It appears that there is a lot of disagreement over its benefits and risks to one’s health. However, I haven’t seen anything about it causing major engine damage, only lead deposits on valves and spark plugs. However, a beta dealer from my local group chipped in with the following statement: “Toy does a dreadful thing. For a motorcycle, avgas is a no-no “..