The 21st century aviation landscape is changing and aviation gasoline (Avgas) is preparing to return full circle to an unleaded format in response to environmental pressure, following the example of the motor industry. Grade UL91 mid-octane unleaded avgas is available today for compatible aircraft and high-octane test fuels are being evaluated.
Avgas specifications were first introduced in 1917 to improve the reliability of engine operation and flight safety. Studies had revealed that aircraft engines, which need to operate over a wide range of temperatures and atmospheric pressures, required a different fuel than motor gasoline. With the discovery of Tetraethyl Lead (TEL) in 1921, performance Avgas grades gradually changed from unleaded to leaded.
The dominance of the turbine engine in modern aviation has left Avgas more or less unchanged for over 60 years with Grade 100LL dominating the market today. This long period of stability has allowed many thousands of light aircraft to be developed around the world, performing important commercial, training and recreational roles where turbines are too costly to operate.
For Avgas the transition to a high octane unleaded fuel is technically challenging because performance piston engine development has relied on TEL to give an octane quality beyond the capability of traditional hydrocarbons and far in excess of motor gasoline.
Over the last 20 years the FAA has been a key player in examining options for an unleaded Avgas with support from regulators, pilots associations, aircraft and engine manufacturers and Avgas producers, including Air BP, which has contributed fuels and expertise. A three-year Piston Aviation Fuels Initiative (PAFI) is underway, focussed on developing a high-octane unleaded Avgas Grade.
In the meantime, the aviation industry has developed Grade UL91, an unleaded mid-octane fuel manufactured to ASTM D7547 and soon to be incorporated in Defence Standard 91-90. It is available for use today in compatible aircraft, which account for approximately 55% of the piston engine fleet covering numerous types, from Cessnas to Technams, and flex-winged micro-lights to autogyros.
For pilots and owners of compatible aircraft, UL91 reduces deposits in the engine combustion chamber and helps improve engine oil cleanliness, which helps increase the time before overhaul. It benefits the environment by eliminating lead emissions from exhaust gases. Like traditional Avgas, UL91 is designed for flight therefore it contains no ethanol, which reduces aircraft range and can damage fuel system components. It offers good volatility for operation over a wide range of ambient conditions and altitudes and the right characteristics to separate water for draining from wing tanks. For airport operators it has good storage stability.
Airport operators are beginning to take the initiative toward introducing UL91 and Air BP has experienced an increase in requests in Europe for fuel suppliers to offer UL91. For airport operators, important factors include security of supply and managing the safe introduction of a new fuel grade. Air BP has converted tankage at its terminal in Cardiff to hold UL91 so it can supply the product to UK airfields together with 100LL and Jet A1 and Jet+AL48, with further supply options in Europe. Air BP also has the technical capability to provide advice, industry approved equipment and training for product quality and misfuel prevention.
Another concern for airport operators is creating awareness and demand for UL91 among pilots and air operators and this is another area where a fuel partner can support airports by promoting UL91 with bespoke marketing campaigns.
The future for Avgas is unleaded and Air BP is part of this movement toward a greener footprint, seeking to meet customer requirements for quality aviation fuels and helping them to make the transition.
About the author
Mark Atherton has 25 years of experience within the fuels and lubricants industry. In the last five years he has specialized in the general aviation sector working as the sales and marketing manager for Western Europe for Air BP. Within this role he has focused on delivering valued added solutions to both airports and end users.
September 1, 2015