UND switched to UL94 at the end of June and returned to 100LL in October 2023. [Credit: Shutterstock]
Key Takeaways:
The University of North Dakota (UND) experienced abnormal exhaust valve recession in Lycoming engines after converting its fleet to UL94 unleaded fuel, leading them to switch back to 100LL.
Lycoming Engines' study determined that elevated aromatic concentrations in UL94, which are not directly specified by current ASTM standards, may contribute to valve seat recession under certain flight profiles.
UND has replaced 126 cylinders, and Lycoming is now working with the FAA to further evaluate piston engine sensitivity to aromatics in fuels and potentially refine UL94 specifications and provide operational guidance.
The change from 100LL to UL94 unleaded fuel is not without some growing pains in the aviation fleet.
Lycoming Engines has released the results of a study undertaken after receiving reports from the University of North Dakota (UND) about abnormal valve seat recession in the company’s powerplants that were using UL94.
CREATE A FREE ACCOUNT
Sign up to keep reading
Create a free account to continue. Already a member? Sign in below.
Meg Godlewski has been an aviation journalist for more than 24 years and a CFI for more than 20 years. If she is not flying or teaching aviation, she is writing about it. Meg is a founding member of the Pilot Proficiency Center at EAA AirVenture and excels at the application of simulation technology to flatten the learning curve. Follow Meg on Twitter @2Lewski.
