Increasing the Lubricity of JP-8 to Fuel Two-stroke Spark Ignition Engines for Midsized Unmanned Aerial Vehicles

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. Results showed that adding two percent of lubricating oil to JP-8 and S-8 provides sufficient lubricity to meet two-cycle engine lubrication requirements. Adding two percent B100 biodiesel to the heavy fuel also sufficiently increases lubricity to meet two-stroke lubrication requirements. Existing Military Specification engine oils do not increase the lubricity of heavy fuels sufficiently to meet two-stroke lubrication requirements.