Prechamber Combustion Behaviour in an Optical Constant Volume Vessel for Large Natural Gas Engines.

Prechamber-assisted turbulent jet ignition has the potential to extend the lean limit of fuel-air mixtures and improve the combustion stability in internal combustion engines. The high-temperature radical-rich turbulent jet exiting from the prechamber nozzle provides multiple ignition spots inside the control volume, allowing sustained combustion at lean conditions. Turbulent jet ignition is especially relevant for large-bore natural gas compressor station engines which accumulate and release unburnt fuel/air mixture as greenhouse gases. In the present work, prechamber-assisted combustion of premixed methane/air mixtures has been studied in a custom-built optical 8000 cc constant volume vessel (CVV). A spark plug-assisted single nozzle cylindrical prechamber (PC) with an internal volume of 121 cc is attached to the top of the combustion vessel. The CVV is rated for a maximum combustion pressure of 100 bar and comprises seven sapphire windows: four 4-inch sapphire windows to view the main flame chamber combustion, one 3-inch sapphire window at the bottom of the chamber to provide an axisymmetric view of the turbulent jet and two 3-inch sapphire windows at the prechamber level. High-speed imaging techniques have been used to capture the turbulent flame propagation. Equivalence ratios of 0.6 and 0.8 have been studied and compared using the captured image and pressure data, and the evolution of prechamber-to-main chamber combustion has been investigated.