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The performance and exhaust emissions of a commercially available, propane fueled, air cooled engine with Electronic Fuel Injection (EFI) were investigated by varying relative Air to Fuel Ratio (λ), ignition timing, and Compression Ratio (CR). Varying λ and ignition timing was accomplished by modifying the EFI system using TechniCAL Industries’ engine development software. The CR was varied through using pistons with different bowl sizes. Strong relationships were recorded between λ and ignition timing and the resulting effect these parameters have on engine performance and emissions. Lean operation (λ > 1) has the potential to significantly reduce NOx production (110 g/kW-hr down to 5 g/kW-hr). Unfortunately, it also reduces engine torque by up to an order of magnitude (31 Nm down to 3 Nm).

Natural gas is a viable alternative to gasoline and diesel fuel because it is a clean burning fuel that is available from a large domestic reserve through a mature infrastructure. The heavy dependence of the small engine sector on oil, much of which is imported from foreign countries and the small engine sector's negative impact on the air quality in urban areas are two pervasive problems that can be helped by using Compressed Natural Gas (CNG) as a small engine fuel. In addition, CNG is typically over 80% methane, which is produced by the decay of organic material, so while natural gas is not renewable its use enables much of the infrastructure required for a methane-based renewable energy system. In order to determine the emissions benefit of using CNG as compared to gasoline in a small engine, a 750 cc 90 degree V Twin port-fuel-injected production engine rated at 29 horsepower (HP), designed and built by Kohler Inc.

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.