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) fleet experienced abnormal exhaust valve recession in Lycoming engines after switching to UL94 unleaded fuel, leading them to revert to 100LL and replace many cylinders.
Lycoming Engines' study found that while engine components conformed to specifications, UL94 could contribute to valve seat recession under certain conditions.
Lycoming's analysis suggests that elevated aromatic concentrations in UL94, which are not directly specified by ASTM D7547, may be a factor due to impacts on flame speed and particulate abrasiveness.
Lycoming is collaborating with the FAA to further evaluate engine sensitivity to aromatics in fuels and may work to redefine UL94 standards and provide operator 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.
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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.
