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This paper will review the development and results of an accelerated test established to study the engine wear observed in some engines fueled with Biodiesel Fuel (BDF). BDF is a clean burning alternative fuel that can be produced from domestic renewable resources. Its basic composition is of multiple Fatty Acid Methyl Esters (FAME) (1). These fatty acid methyl esters are an excellent source of energy but have different physical properties as compared to petroleum based diesel fuel. The differences in physical properties can lead to increased dilution of BDF in the engine oil. Petroleum based diesel fuel (PDF) has increased volatility when compared to BDF, which allows the fuel to evaporate from the engine oil through the crankcase ventilation system. The lower volatility of BDF results in a lower evaporation rate and thus comparatively higher levels of BDF dilution in the oil. This higher dilution level alters the oil's viscosity and interacts with the oil's additives.

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.