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The paper discusses objectives, approaches and results of the development of a pilot fuel injection system (FIS) for a dedicated, compression ignition, high-speed, heavy duty natural gas/diesel engine. The performance of the pilot FIS is crucial for the success of a dual fuel concept. The Servojet electro-hydraulic, accumulator type fuel system was chosen for the pilot fuel injection. An alternative pilot FIS based on the “water hammer” (WH) effect was also considered. The modifications to a stock 17 min injector is described. Three different types of pilot injector nozzle were investigated: standard Valve Covered Orifice (VCO), modified minisac and new designed, unthrottled pintle. Preliminary results from engine tests proved that the optimum pilot fuel quantity is the minimum quantity. Based on that finding, the pilot FIS design was further optimized.

Impending emissions regulations for diesel engines, specifically exhaust particulate emissions have caused engine manufacturers to once again examine the potential of alternative fuels. Much interest has centered around compressed natural gas (CNG) due to its potential for low particulate and NOx emissions. Natural gas engine development projects have tended toward the use of current gasoline engine technology (stoichiometric mixtures, closed-loop fuel control, exhaust catalysts) or have applied the results of previous research in lean-burn gasoline engines (high-turbulence combustion chambers). These technologies may be inappropriate for foreseeable emissions targets in heavy-duty natural gas engines.

The potential for existing small natural gas-fueled engines to meet the demands of commercial cogeneration applications was demonstrated. Six small engines, ranging in size from 6 to 35 kW electrical output, modified for operation on natural gas were evaluated for performance, durability, serviceability, and reliability through extended engine operation. Initially performance of both engines and generators was measured, followed by extended durability runs. Maintenance was performed as needed, and engine and component wear were monitored. The major barriers which limit engine durability and reliability were identified. Engine improvements were made, where possible, and evaluated for their effectiveness. Results indicate that some small gas-fueled engines can achieve 4,000-hour service intervals and 20,000-hour engine life. Engine reliability and life are largely dependent on the detailed design of the engine.