Novel Prechamber Fueling Strategy Development, 03-9452

Principal Investigators
Timothy J. Callahan
Chad H. Stovell

Inclusive Dates:  01/01/04 – 07/01/05

Background - Stationary engines must meet increasingly more stringent emission standards while maintaining high efficiency. Natural gas engines serve an important role in both stationary power generation and gas pipeline markets. The majority of the installed and purchased power are large engines with bore diameters of more than 200 millimeters. These engines typically use a spark-ignited prechamber (SIPC) with a separate fuel supply for ignition of the main combustion chamber fuel-air mixture. Fuel is generally admitted into the prechamber at low pressure during the intake stroke. Proper fuel-air mixing in the prechamber is a critical factor affecting engine performance and emissions. This process is a complex one typically relying on turbulence generated when the main chamber fuel-air mixture is forced into the prechamber during the compression stroke. 

Approach - The objective of this project is to develop novel prechamber fueling methods using electronically control injection. A direct injection gas prechamber system for evaluation on a single-cylinder engine was designed and fabricated. The system was designed for an ALCO 251 single-cylinder research engine with a bore diameter of 229 millimeters. An electronically controlled, high-pressure gas injection system was designed and procured for this application. Parameters to be examined include the lean limit performance, the knock limit, and the NO_x-efficiency trade-off. 

Accomplishments - The direct injection of natural gas as a pilot fuel ignited by a spark event was successfully demonstrated. Stable engine operation was achieved at injection (pilot) quantities as low as 0.4 percent of the total fuel flow. This quantity is similar to diesel pilot quantities reported in the literature. The results indicated that NO_x could be reduced 25 percent by controlling the energy in the prechamber (injection quantity), which is a function of the injection pressure and injection duration. The NO_x reduction was accomplished without an efficiency penalty since the spark timing was used to phase the 50-percent burned location and maintain efficiency

The direct injection concept has shown interesting possibilities for reducing NO_x from spark-ignited prechamber engines. The prechamber filling, fuel injection, and mixing processes are complex, and CFD analysis would add to the understanding and further optimization of this concept. The benefit of the direct injection strategy should be compared to the micro-pilot strategy.

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