Development of Pilot Fuel Injection System for CNG Engine

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. Finally, a minimum pilot fuel delivery of 1 mmˆ3 and injection duration of 0.6 ms were achieved during bench testing, with other satisfactory injection characteristics. Although most of the objectives of pilot FIS development were met, it was concluded that significant potentials for further improvement exist.