Originally Posted On: https://abovegroundfuelstoragetanks.com/2011/03/26/avgas/

AVGAS: Comprehensive Overview of Aviation Gasoline

Aviation gasoline, or avgas, fuels piston-engine and Wankel-engine aircraft. Unlike regular gasoline or jet fuel, avgas meets the unique needs of planes flying at high altitudes and in extreme conditions. Its special formula, grades, storage needs, and environmental impact set it apart in aviation. This article explores avgas in detail, covering its makeup, types, storage, environmental concerns, and future trends, while clarifying how it differs from jet fuel.

What is Avgas?

Avgas powers small aircraft, like general aviation planes, vintage aircraft, and some helicopters with piston engines. It contains tetraethyl lead (TEL), which boosts combustion and prevents engine knocking. According to Chemeurope.com, avgas’s low volatility ensures stable performance at high altitudes where air pressure and temperature vary. For example, it resists vapor lock, a problem where fuel turns to gas in fuel lines, disrupting engine function.

Unlike jet fuel, which uses kerosene for turbine engines in large planes, avgas suits smaller, piston-driven aircraft. Its unique properties support rapid throttle changes and high power output. Therefore, pilots and ground crews must use the correct fuel to avoid engine damage.

Avgas Composition and Properties

Avgas relies on tetraethyl lead to raise its octane rating and prevent knocking, which happens when fuel burns too early in the engine. This additive ensures smooth combustion in high-performance aircraft. However, lead raises health and environmental concerns, pushing the industry toward lead-free options.

Additionally, avgas has low vapor pressure to avoid vapor lock at high altitudes. This feature keeps fuel liquid in lines, ensuring reliable ignition from ground level to over 20,000 feet. Consequently, avgas supports consistent engine performance across diverse conditions.

Avgas Grades

Manufacturers identify avgas grades with two numbers: the “aviation lean” octane rating for normal conditions and the “aviation rich” rating for supercharged engines with rich fuel mixtures, high pressure, and hot temperatures. Here are the main grades:

• 100LL (Low Lead):
  • Color: Blue
  • Details: Most piston-engine planes use 100LL. It has less lead than 100/130 but faces phase-out due to lead’s toxicity.
  • Octane: 100 (lean) / 100 (rich)
  • Uses: Powers single-engine trainers and high-performance aircraft.
• 82UL (Unleaded):
  • Color: Purple
  • Details: Like car gasoline, 82UL works in low-compression engines with an octane of 82 or an anti-knock index of 87 or less. It contains no lead, making it eco-friendly.
  • Uses: Suits ultralight or vintage planes.
• 80/87:
  • Color: Red
  • Details: With the least lead among leaded avgas, 80/87 fits low-compression engines. It’s less common today due to 100LL’s dominance.
  • Octane: 80 (lean) / 87 (rich)
  • Uses: Found in older, less powerful aircraft.
• 100/130:
  • Color: Green
  • Details: This high-octane, high-lead fuel preceded 100LL. Its lead content led to 100LL as a replacement.
  • Octane: 100 (lean) / 130 (rich)
  • Uses: Powers high-performance or vintage planes.

Color Coding

To avoid fueling mistakes, avgas grades use distinct dyes. This system helps pilots and crews identify the right fuel quickly. The colors are:

• 100LL: Blue
• 82UL: Purple
• 80/87: Red
• 100/130: Green

For instance, a pilot seeing blue fuel knows it’s 100LL, preventing errors that could harm engines. Thus, color-coding enhances safety at busy airports.

Storing Avgas

Proper storage keeps avgas effective and safe. The Experimental Aircraft Association (EAA) notes that avgas lasts about one year if stored correctly. After that, oxidation and gum buildup can clog fuel lines or reduce engine power, risking failure.

Storage Tips

• Cool, Dry Location: Keep avgas away from sunlight and heat to slow oxidation.
• Nitrogen Blanket: Add a nitrogen layer above the fuel to limit oxygen and moisture exposure, extending shelf life.
• Safe Tanks: Use impact-, fire-, and ballistics-rated tanks, either above-ground (ASTs) or underground (USTs).
• Regular Checks: Inspect tanks for leaks, rust, or damage to ensure safety.
• Moisture Removal: Test for water regularly and remove it to prevent corrosion or microbial growth.

ASTs vs. USTs

Airports traditionally use underground tanks (USTs) for avgas. However, smaller airstrips now prefer above-ground fuel storage tanks (ASTs). ASTs cost less to install, simplify inspections, and allow faster leak detection. For example, a small airport can spot an AST leak sooner than a UST leak, reducing environmental harm.

Environmental and Health Issues

Tetraethyl lead in avgas pollutes air and soil, harming health and ecosystems. As a result, the U.S. Environmental Protection Agency (EPA) and others aim to eliminate leaded avgas. The push for unleaded fuels reflects growing environmental awareness.

Shift to Unleaded Avgas

The FAA’s EAGLE initiative seeks to replace leaded avgas by 2030. Promising alternatives include:

• G100UL: General Aviation Modifications, Inc. developed this lead-free fuel to match 100LL’s performance. It works in most piston engines.
• Swift Fuels UL94: This unleaded option suits lower-octane engines and is available at some airports.
• Biofuels and Synthetics: Researchers explore sustainable fuels to meet aviation needs with less environmental impact.

However, challenges remain. New fuels must work in existing engines, require a reliable supply chain, and gain regulatory approval. Despite hurdles, the industry’s commitment to sustainability drives progress.

Avgas vs. Jet Fuel

Many confuse avgas with jet fuel, but they differ greatly:

• Avgas: Gasoline-based, leaded, high-octane, for piston engines.
• Jet Fuel: Kerosene-based, for turbine engines like those in jets or turboprops. Common types include Jet A and Jet A-1.

Using jet fuel in a piston engine or avgas in a turbine can destroy the engine. Therefore, proper fuel selection is critical for safety.

The Future of Avgas

The aviation industry faces changes as leaded avgas phases out. Unleaded options like G100UL and UL94 gain traction, and new engine technologies may lower the need for high-octane fuels. Meanwhile, electric and hybrid-electric planes could reduce avgas use in the future. However, piston-engine aircraft will likely remain common in general aviation for years, ensuring avgas’s relevance.

Moreover, global regulations and consumer demand for greener solutions push innovation. For instance, sustainable aviation fuels (SAFs) may complement or replace avgas in some applications. As technology evolves, avgas will adapt to balance performance, safety, and environmental goals.

Conclusion

Aviation gasoline powers piston-engine aircraft with its high-octane, leaded formula. Its grades, colors, and storage needs meet aviation’s unique demands. However, lead’s environmental impact drives the shift to unleaded fuels like G100UL. As the industry innovates, avgas remains vital but faces a greener future. For more details, visit Wikipedia’s Avgas page or Chemeurope’s Avgas entry.