Mercedes Mullins
Aviation fuel, also known as avgas, has been an essential component of the aviation industry since the 1930s. The octane rating of aviation fuel is a critical factor in engine performance, with grades ranging from 80/87 to 115/145. 100 octane aviation fuel, specifically 100LL, has been widely used in general aviation, but its phase-out has raised concerns due to the limited alternatives for compatible aircraft. The cost of aviation fuel varies, with G100UL estimated to be $0.70 to $1.05 more per gallon than 100LL. This paragraph introduces the topic of 100 octane aviation fuel, highlighting its significance, historical context, alternatives, and pricing considerations.
| Characteristics | Values |
|---|---|
| Octane Rating | 100 at lean settings, 130 at rich settings |
| Engine Compatibility | Engines designed for 100-150 horsepower, e.g. Rotax 912 |
| Engine Maintenance | Spark plugs require regular rotation and servicing |
| Fuel Cost | Estimated to be 70 cents to $1.05 more per gallon than 100LL |
| Additives | Contains Tetraethyl Lead (TEL) |
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What You'll Learn
History of 100 octane aviation fuel
The history of 100-octane aviation fuel dates back to the early 20th century, specifically the 1920s and 1930s. During this period, a system for rating fuel based on its anti-knock characteristics was developed, with n-pentane having the lowest rating of zero and iso-octane the highest rating of 100. This scale became the standard for measuring the quality of aviation fuel.
In the 1930s, James H. "Jimmy" Doolittle, a renowned aviator and aeronautical engineer, joined Shell Oil's aviation department. Doolittle recognised the advantages of high-octane aviation gasoline (avgas) and urged Shell to increase its production capacity for 100-octane fuel. At the time, high-octane fuel was expensive and only available in small quantities, but Doolittle's advocacy, combined with his fame from air racing, helped persuade legislators and government officials about the importance of fuel development.
By 1934, Shell had made significant progress, producing small quantities of 100-octane fuel using hydrogenation and additives like tetraethyl lead (TEL). This reduced the price drastically from $30 per gallon to around $2 per gallon. Doolittle himself set aviation world speed records and won several air races using Shell's avgas.
During World War II, the development and use of 100-octane aviation fuel became even more crucial. The Allies, in particular, benefited from the work of French engineer Eugene J. Houdry, who immigrated to the United States in 1931. Houdry developed the "Houdry Process," a method for converting vaporised petroleum into high-octane gasoline. This process was key in producing 100/130 avgas at a much lower cost. The first large-scale plant using this process came online in 1940, just in time for the Battle of Britain, where the British were able to modify their Spitfire engines to use this new fuel. This gave them a significant performance advantage over German aircraft.
In the late 1990s, some lower-powered aviation engines were designed to run on unleaded fuel and on 100LL (low lead) aviation fuel. However, the phase-out of 100LL fuel has presented challenges, as many aircraft in the general aviation fleet are dependent on it and cannot easily switch to alternative fuels without significant modifications.
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Cost of 100 octane aviation fuel
The cost of 100 octane aviation fuel, also known as Avgas, is a concern for many in the aviation industry. While a specific price is difficult to pinpoint due to various factors influencing the cost, historical and comparative data can provide some insight.
In the 1930s, Shell Oil company recognised the benefits of high-octane aviation fuel and developed 100/130 octane fuel. However, due to the production process at the time, this fuel was over a hundred times more expensive than normal automotive gasoline. The higher cost was a barrier, but the performance advantages were significant, allowing higher compression ratios and greater horsepower without enlarging the engine.
During World War II, the development of high-octane Avgas became crucial for the Allies. French engineer Eugene J. Houdry developed a more affordable refinement process known as the Houdry Process, which played a pivotal role in enhancing aircraft performance during the war.
Today, the cost of 100 octane aviation fuel remains a pressing issue. The phase-out of 100LL (low lead) aviation fuel has left a significant portion of the aviation fleet without a suitable alternative. As a result, the aviation industry is facing the challenge of transitioning to alternative fuel types, such as automotive or jet fuel.
GAMI's G100UL unleaded Avgas has emerged as a functional replacement for 100LL. However, it is estimated to cost 70 cents to $1.05 more per gallon than 100LL. While this may seem like a significant increase, it's important to consider the potential offset by reduced maintenance costs associated with the use of unleaded fuel.
In summary, the cost of 100 octane aviation fuel has been a historical challenge, with prices previously reaching a hundred times that of automotive gasoline. Today, the transition away from 100LL fuel is driving the search for alternatives, with G100UL unleaded Avgas offering a promising solution, despite its higher price per gallon.
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Compatibility with aircraft engines
The compatibility of 100 octane aviation fuel, also known as 100/130 avgas, with aircraft engines is a complex topic with a long history.
The first number, 100, indicates the octane rating of the fuel when tested to "aviation lean" standards, simulating lean settings used for cruising. The second number, 130, indicates the octane rating when tested to "aviation rich" standards, simulating supercharged conditions with a rich mixture, elevated temperatures, and high manifold pressure during take-off and other full-power conditions.
Many high-performance and turbocharged aircraft engines have been designed to use 100 octane fuel. Modifications are typically necessary to use lower-octane fuel in these engines. Originally, many general aviation aircraft engines were designed to run on lower octane fuel, such as 80/87 octane, which is similar to the standard for unleaded automotive gasoline in North America.
Direct conversions to run on automotive fuel are possible through supplemental type certificates (STCs). However, the alloys used in aviation engine construction are chosen for their compatibility with lead, and engine wear in the valves can be an issue when converting to unleaded automotive gasoline.
In recent years, the phase-out of 100LL fuel has been a significant challenge for the aviation industry. This fuel contains lead and is used by 30% of the aircraft in the general aviation fleet, and suitable alternatives are limited. Teledyne Continental Motors (TCM), for example, has expressed concern about the future availability of 100LL and has turned to developing diesel engines.
Some lower-powered aviation engines developed in the late 1990s are designed to run on unleaded fuel or 100LL, such as the Rotax 912. Additionally, some aircraft with Supplemental Type Certificates (STCs) can use automotive gasoline (mogas or autogas) that does not contain ethanol. However, ethanol-treated gasoline is susceptible to phase separation due to altitude and temperature changes during flight, which can lead to engine failure and octane requirement issues.
In Europe, unleaded Avgas grades have been introduced, such as UL91 and UL94, which are transitional steps towards more sustainable aviation fuel. These fuels can be used in certified engines and aircraft in Europe and the UK.
To ensure compatibility, it is crucial to refer to aircraft and engine manuals, as well as regulatory guidelines, when selecting the appropriate fuel for a specific aircraft engine.
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Alternatives to 100 octane aviation fuel
100 octane aviation fuel, also known as 100/130 avgas, has been used since the 1930s. It has an octane rating of 100 when tested to "aviation lean" standards and 130 when tested to "aviation rich" standards. The higher octane rating allows for higher compression ratios, resulting in greater horsepower without increasing engine size. While 100LL (low lead) is a more common variant of 100 octane aviation fuel, it has been phased out due to concerns over the future availability of tetraethyl lead (TEL), a lead additive used in the fuel. This has left the aviation industry with automotive fuel and jet fuel as the only alternatives.
Automotive gasoline, also known as mogas or autogas, can be used as an alternative fuel in some aircraft with lower-powered engines, typically those developed in the late 1990s. However, it is not a fully viable replacement for all aircraft as many high-performance and turbocharged engines have been designed to use 100 octane fuel and would require modifications to use lower-octane automotive gasoline. Additionally, the alloys used in aviation engine construction may not be compatible with automotive gasoline, potentially leading to engine wear.
Jet fuel is another alternative to 100 octane aviation fuel. It has a higher flashpoint and a lower freezing point than automotive gasoline, making it more similar to diesel fuel. However, jet fuel is not rated for cetane, a measurement of ignition quality, as it is not an issue for turbine engines. The aviation industry is also developing biofuels, such as biokerosene made from algae or plant oils, as sustainable alternatives to jet fuel.
Swift Enterprises has developed Swift Fuel, a non-alcohol-based fuel derived from biomass fermentation. This fuel has been found to have a motor octane number of 104.4 and meets most of the ASTM D910 standard for leaded aviation fuel. It is claimed to be a cheaper alternative to 100LL, although this has been debated in the aviation press.
Another alternative to 100 octane aviation fuel is unleaded Avgas, which was first introduced in Europe by Hjelmco Oil in 2003. This fuel meets the ASTM D7547 standard and is certified for use in many common Lycoming engines and a large number of Cessna piston fleet aircraft. It can also be used in any aircraft in Europe or the United Kingdom where the engine is certified to use it, regardless of airframe certification.
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Maintenance of engines using 100 octane aviation fuel
The use of 100 octane aviation fuel, also known as avgas or Grade 100LL, has been a significant aspect of aviation history, especially during World War II. This fuel, with its higher compression ratios, enabled increased horsepower without enlarging engine sizes. While it offers advantages, the maintenance of engines that utilise 100 octane aviation fuel requires careful attention to specific aspects. Here are some detailed guidelines for maintaining engines that operate on this high-octane fuel:
Understanding the Fuel and its Variations:
100 octane aviation fuel is identified by two numbers associated with its Motor Octane Number (MON). For instance, 100/130 avgas has an octane rating of 100 when the engine is leaned for cruising and 130 when set at rich for take-off and other high-power conditions. The fuel contains tetraethyl lead (TEL) as an anti-knock agent to prevent premature detonation. Grade 100LL, which stands for "one hundred low lead," contains half the amount of TEL compared to its predecessor, reducing lead content from 4 ml to 2 ml per gallon.
Engine Compatibility and Conversion:
Some aviation engines, particularly those developed in the late 1990s with lower power outputs (100-150 horsepower), are designed to operate on unleaded fuel or 100LL. Examples include the Rotax 912. However, for engines originally certified for Grade 80 aviation gasoline, the use of higher leaded 100-octane fuel may raise concerns. Engine conversions to automotive gasoline (known as mogas or autogas) are possible through Supplemental Type Certificates (STCs), but caution is advised due to potential issues with valve wear.
Spark Plug Maintenance:
The use of 100-octane fuel in engines certified for lower octane fuel can result in increased engine deposits, particularly on spark plugs. To address this, regular spark plug maintenance is crucial. Spark plugs should be rotated on a 50-hour basis and serviced on a 100-hour basis. If excessive spark plug lead fouling occurs, a hotter or colder plug from the approved list in Service Instruction No. 1042 may be selected depending on the lead deposit type and engine operation.
Oil Changes and Engine Deposits:
The higher lead content in 100-octane fuel can contribute to increased engine deposits and may require more frequent oil changes. Lycoming provides specific techniques to manage these deposits, ensuring that engine operating temperatures remain unaffected.
Exhaust Valve Erosion:
During the mid-1970s, when Grade 80 aviation gasoline was phased out, exhaust valve erosion was a concern for low-compression engine operators. However, this issue has been addressed with Grade 100LL, which does not cause exhaust valve erosion. Additionally, the materials used in modern exhaust valves, such as those in Lycoming engines, are highly resistant to erosion.
Transition to Unleaded Fuels:
The aviation industry is transitioning towards unleaded fuels, such as UL91 and UL94, as a long-term strategy for sustainability. While this shift aims to benefit the entire general aviation fleet, pilots and aircraft owners must ensure their specific aircraft engines and fuel systems are compatible with the new fuels. Referring to flight manuals, pilot operating handbooks, and placards near fuel caps is essential for making informed decisions.
In summary, maintaining engines that use 100 octane aviation fuel involves understanding the fuel's properties, ensuring engine compatibility, performing regular spark plug maintenance, managing engine deposits and oil changes, and staying informed about industry transitions to unleaded fuels. By following these guidelines, operators can ensure the optimal performance and longevity of their aviation engines.
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Frequently asked questions
100 octane aviation fuel, also known as avgas, is a type of fuel used in aircraft engines. It has a high octane rating, which allows for higher compression ratios and greater horsepower without increasing engine size.
The cost of 100 octane aviation fuel can vary depending on various factors such as location and supply. In the 1930s, Shell's 100/130 octane fuel was over a hundred times more expensive than normal automotive gasoline. Today, the premium components in G100UL avgas, a type of unleaded 100 octane aviation fuel, are estimated to cost 70 cents to $1.05 more per gallon than 100LL fuel.
100 octane aviation fuel can be purchased from aviation fuel suppliers and distributors. Specific brands and types of 100 octane aviation fuel, such as G100UL avgas, may have their own dedicated websites and distribution channels. It is important to ensure that the fuel is compatible with your aircraft's engine and that you follow the recommended maintenance procedures for your aircraft when using high-octane fuels.
