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In order to satisfy a single-fuel mandate, the U.S. Department of Defense has a need for engines in the 20 to 50 hp range to power midsized Unmanned Aerial Vehicles (UAVs) and the ability to operate on JP-8 also known as “heavy” fuel. It is possible to convert two-stroke aircraft engines designed to operate on a gasoline-oil mixture to run on JP-8/oil using the Sonex Combustion System (SCS) developed by Sonex Research, Inc. Conversion of the engine involves replacing the cylinder heads with new components designed to accept a steel combustion ring insert. Also required are glow-plugs to preheat the cylinder head prior to engine start. The converted engine produces the same power output as the stock engine operating on gasoline. Conversion of both a 20 hp and 40 hp engine was successfully achieved using the SCS.

In order to satisfy the single-fuel initiative, the U.S. Department of Defense (DoD) has the need for engines in the 20 to 50 hp range to power midsized Unmanned Aerial Vehicles (UAVs) able to operate on JP-8 “heavy” fuel. It may be possible to convert two-stroke engines designed to operate on a gasoline-oil mixture to run on JP-8; however, one concern is that using JP-8 in lieu of the original fuel mixture will have an impact on engine lubrication. The research described in this paper investigated the lubricity of JP-8 and S-8 (synthetic heavy fuel) and compared it to the lubricity of a gasoline and lubricating oil combination typically used in two-stroke engines. In addition, three lubricity agents, synthetic lubricating oil, B100 biodiesel, and Military Specification engine oil, were added to heavy fuel and the resulting lubricity measured.