Development of Combustion System Strategies for High BMEP Natural Gas Engines, 03-R9660

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Principal Investigators
Timothy J. Callahan
Wei Li

Inclusive Dates:  10/1/06 – Current

Background - While combustion in reciprocating engines has continued to evolve, many issues remain. Especially for natural gas engines, flame propagation, NOx formation, knock, and lean misfire continue to be challenges that persist in the pursuit of high-efficiency and low-emission engines. These challenges can be overcome with appropriate combustion system designs. Traditionally, combustion system development is done through engine testing of various combustion system concepts. Numerous piston designs were evaluated on a recent program, and distinct differences in engine performance were noted. It is believed that these differences can be attributed to in-cylinder turbulence. Computational fluid dynamic simulation can provide insight into in-cylinder turbulence levels, which can be used to correlate to global parameters such as cylinder pressure and heat release (burn) rate.

The objective of this work is to use CFD in combination with experimental data already collected to develop a better understanding of fluid dynamic effects on combustion such that clear and efficient combustion chamber design strategies can be developed for natural gas combustion systems.

Approach - The approach will consist of re-examining the prior engine results for different piston designs using CFD, correlate the CFD results with combustion analysis, and apply this knowledge to the design or development of future combustion systems for natural gas engines.

Accomplishments - Geometry models and initial and boundary conditions of six combustion chamber designs were prepared for CFD analysis. Experimental data was available for each design. Two designs were based on pre-combustion chamber technology in which the combustion chamber is divided into two chambers, with the smaller of the two serving as the igniter for the main combustion chamber. Four designs were open-chamber designs in which a spark plug in the main chamber ignites the mixture. The CFD results for the prechamber designs compared well to the experimental measurement of cylinder pressure and heat release rate. Simulation of the four open-chamber piston designs is continuing.

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