The FAA released findings on 18 December of its first extensive test of ethanol in an aviation engine, which confirmed the decreased power from this alternative fuel that other researchers have reported.
"The engine produced an average of 4.3 (2.3%) more peak horsepower [3.2kW] when operating on the aviation grade ethanol (AGE)-85 than it did when operating on iso-octane fuel. However, peak power required 39.7lb/h [18kg/h] (56%) more fuel mass flow with the AGE-85 than with iso-octane," say the report's authors David Atwood and Anatoliy Ivanov. "Using AGE-85 would increase fuel weight by 9% above that of 100LL [low-lead] for an equivalent volume of fuel, and would reduce operating range by 35% from 100LL."
Decreased power may be acceptable considering the benefits of cleaner emissions and domestic production, the report says, pointing out that general aviation is exempt from the 1990 Clean Air Act Amendment in the USA and is a leading source of airborne lead.
The spark ignition aircraft engine endurance test did not study emissions, but other studies have found lower levels of carbon monoxide and volatile organic compounds than with avgas. Ethanol releases similar levels of carbon dioxide and slightly higher levels of nitrous oxide.
Of particular concern is the uncertain effect of ethanol on fuel systems. The FAA team tested a Textron Lycoming IO360-C, with adjusted ignition timing and increased fuel mass flow using AGE 85. The engine underwent over 150h of testing at maximum temperatures to test wear, performance, materials compatibility, range, efficiency, oil dilution and deposit formation.
The report says: "The engine experienced normal wear except for the exhaust valve face and stems, which showed a hammered effect. There were minimal combustion and fuel system deposits and a moderate level of intake valve deposits."
Future tests will compare the detonation performance of AGE-85 at standard engine ignition timing to 100LL in a 100/100LL-certificated IO360-A engine, says the report.
Source: Flight International