Aviation Gasoline
Aircraft piston engines operate using the same basic principles as spark ignition engines of cars, but they have a much higher performance requirement. Aircraft engines normally run at 55% power or more, where as car engines run at 30% or lower. The design of the engine is different in terms of strength: think of bearings, crankshaft etc, etc.
Avgas is gasoline fuel developed for reciprocating piston engined aircraft. Common additives to Avgas include alkyl-lead anti-knock additives, metal deactivators, color dyes, oxidation inhibitors, corrosion inhibitors, icing inhibitors, and static dissipaters. It is very volatile and extremely flammable at normal operating temperatures. Proper and safe handling of this product is therefore of the highest importance. Avgas grades are defined by their octane rating. Two ratings are applied to aviation gasolines (the lean- and the rich mixture rating) resulting in a multiple numbers e.g. Avgas 100/130 (lean mixture is 100 and the rich mixture is 130).
Avgas types
Avgas 100, high lead - colored green
The standard high lead (1 gr/liter) high octane fuel for aviation piston engines. There are two specifications for Avgas 100. The ASTM D 910 and UK DEF STAN 91-90. These are almost the same but have some differences in antioxidant content, oxidation stability requirements and lead content.
Avgas 100LL, low lead - colored blue
Low lead version of Avgas 100. Still containing about 0.5 gr lead per litre of fuel, low lead is a relative term. This grade is listed in the same specifications as Avgas 100, ASTM D 910 and UK DEF STAN 91-90.
Avgas 82 UL, unleaded - colored purple
A relatively new grade targeted at the low compression ratio engines not needing high octane Avgas 100(LL) and designed to run on unleaded fuel (0,1 gr/liter).
The octane rating can be increased beyond the simple proportion of octane to heptane by adding anti-knock agents, which delay the onset of detonation. Until recently, the most important such additive, for both automotive and aviation use, was tetra-ethyl lead (TEL). It's found in aviation fuels in the following proportions:
Fuel grade Color Lead / Gallon
80/87 Red 0.5 mL
100LL Blue 1.2 - 2.0 mL
100/130 Green 3.0 - 4.0 mL
115/145 Purple 4.6 mL
