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) reported "abnormal exhaust valve recession" in Lycoming engines after switching their fleet to UL94 unleaded fuel, subsequently reverting to 100LL.
Lycoming Engines' study determined that high aromatic concentrations in UL94, which are not strictly controlled by current ASTM standards, may contribute to valve seat recession under specific flight conditions.
The issue led UND to replace 126 cylinders, and Lycoming is now collaborating with the FAA to further evaluate engine sensitivity to aromatics and potentially refine fuel standards and operator guidance for unleaded fuels.
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.
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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.
