Precombustion Chamber Design for Emissions Reduction From Large Bore NG Engines

Abstract

Precombustion chambers (PCCs) are an ignition technology for large bore, natural gas engines, which can extend the lean operating limit through improved combustion stability. Previous research indicates that the PCC is responsible for a significant portion of engine-out emissions, especially near the lean limit of engine operation. In this work, six concept PCC designs are developed with the objective of reducing engine-out emissions, focusing on oxides of nitrogen (NOx). The design variables include chamber geometry, chamber volume, fuel delivery, nozzle geometry, and material thermal conductivity. The concepts are tested on a single cylinder of a large bore, two-stroke cycle, lean burn, natural gas compressor engine, and the results are compared with stock PCC performance. The pollutants of interest include NOx, carbon monoxide, total hydrocarbons, and volatile organic compounds (VOCs). The results indicate that PCC volume has the largest effect on the overall NOx–CO tradeoff. Multiple nozzles and electronic PCC fuel control were found to enhance main chamber combustion stability, particularly at partial load conditions. The PCC influence on VOCs was insignificant; rather, VOCs were found to be heavily dependent on fuel composition.