Aviation Gasoline Notes
Aviation gasoline continued to develop and obtain increasingly higher octane ratings through the end of World War II. Since that time about 6 grades have seen service. Table below shows various current and historic grades. The advent of jet engines and the subsequent removal of gasoline powered aircraft from airline and military service, has resulted in reduced grade availability. Only one grade is now generally available in the in the United States. Fuel grades are designated by their anti-knock characteristics. Engine knock, which describes explosive detonation of the fuel/air mixture or preignition, can cause severe engine damage and subsequent failure in a short period of time. Anti-knock ratings are expressed as Octane Numbers for those of 100 or less and as Performance Numbers for those ratings above 100. These numbers relate the fuels performance compared to a reference fuel of pure isooctane. Because the anti-knock characteristics are influenced by the air/fuel mixture ratio, ratings are developed for both rich mixture performance and lean mixture performance. Rich mixture settings yield higher octane or performance numbers since the added fuel acts as an internal coolant and suppresses knock. Prior to 1975, both numbers were reported as the grade designation but current specification utilize only the lean mixture rating. Currently, ASTM (American Society for Testing and Materials) specifies five grades - 80, 82UL, 91, 100, and 100LL (low lead). In practice only 100LL is widely available. Production of Grade 80 has generally ceased due to small demand. Grade 100 is not now seen in the continental US. Two grades have been added in recent years. The all new 82UL an unleaded aviation gasoline designed to meet the requirements of older and lower horsepower engines. This grade was designed to be made in most refineries capable of manufacturing motor gasolines. The 91/98 grade dropped in the late 1960's was revived in 2001 to provide a fuel for development and testing purposes by engine and engine control manufacturers. It meet the requirements of the majority of general aviation engines and is thought to be a precursor to a widely available general aviation unleaded gasoline.
Last revised 08 January 2002