Prechamber NOx formation in low BMEP 2-stroke cycle natural gas engines

Precombustion chambers (PCCs) are an ignition technology for large bore, natural gas engines enabling increased combustion stability while extending the lean limit of operation. A PCC is a small chamber, typically 1–2% of the clearance volume, in which a near-stoichiometric mixture of fuel and air is ignited by a standard spark plug. After the mixture in the PCC is ignited, its pressure rises and expels a flame jet of hot gas mixture into the main chamber. The amount of energy a typical PCC produces is roughly one million times that of a conventional spark plug. In this work the role that the PCC plays in the formation of oxides of nitrogen (NOx) is investigated. Previous research indicates that the PCC is responsible for a significant part of engine-out NOx, especially near the lean limit of engine operation. Experimental results are presented from a large bore lean-burn 2-stroke cycle engine. The data shows that the PCC is responsible for a significant part of engine-out NOx emissions. However, the PCC NOx does not form in the PCC. Rather it forms within the gas jet after it penetrates into the main chamber combustion gases.