Avgas is a high-octane fuel used in precision engines like airplanes and elite racing cars. It has a rating of 100 and lower volatility, making it suitable for high-altitude use. The fuel is identified by two numbers, denoting the octane rating in different fuel-air mixtures. Avgas is available in various grades, with unique dyes used to identify them. The largest users of avgas are North America, Australia, Brazil, and Africa. The aviation industry is investigating the use of regular diesel fuel as an alternative due to rising avgas prices.
Aviation gasoline is a high-octane fuel used to power precision engines like those found in airplanes, elite racing cars, and some boats. With an octane rating of 100, compared to a rating of between 95 and 98 for everyday automotive vehicles, it is commonly called avgas. This fuel also has lower volatility, which means it can withstand higher temperatures before igniting, and can run more smoothly than automotive gasoline, which is important for high-altitude use. In aviation circles, avgas is used to describe aviation gasoline, and mogas is used for motor or automobile gasoline.
Developed in the 1940s, aviation gasoline was used for commercial and military purposes. During World War II, it was used in Spitfire and Hurricane fighters, Mosquitoes, and Lancaster bombers. Interestingly, the mixes used today are very similar to those developed for the war effort.
Avgas is now available in various grades depending on the lead concentration of the fuel. The addition of lead, in the form of tetra-ethyl-lead (TEL), has been used to promote higher octane ratings. Now known to be toxic, TEL has been phased out for automotive use and is used sparingly to improve octane readings for aircraft.
The different grades of avgas are usually identified by two numbers. These two numbers make up the Engine Octane Number (MON) for the fuel. The first number denotes the octane rating of the fuel when it was tested using the aviation tilt setting, or when not enough fuel is added to the fuel-air mixture. The second number gives the octane reading for the rich aviation configuration, or when there is too much fuel in the fuel-air mixture. These settings attempt to simulate conditions that may occur during flight.
Unique dyes are used to identify the different grades of aviation gasoline. Popular in the late 20th century, 80/87 was dyed red. Due to its high lead content, it has been phased out and is available on a very limited basis. The green dye is used for 100/130 aviation gasoline, which has a much higher octane reading. The most commonly used aviation gasoline is known as hundred low lead levels (100LL), which is dyed blue and meets strict guidelines for lead additives.
The largest users of aviation gasoline are North America, Australia, Brazil and Africa. The steady rise in aviation gasoline prices has spurred an investigation into the aviation industry’s conversion to the use of regular diesel fuel. Its relatively inexpensive distillation process, lower cost, and similarity to avgas make it a desirable alternative.
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