Turbulent Reacting Jet Ignition of Methane/Air Using an Optical Pre-chamber in an Optical Rapid Compression Machine

The lean-burn strategy is one of the most promising solutions for emission reductions due to the increased specific heat ratio of the charge and reduced heat losses through walls. However, conventional internal combustion engines suffer from poor combustion stability and high cycle-to-cycle variations in lean operation. Thus, pre-chamber combustion is an advanced combustion strategy that enhances ignition energy and provides distributed ignition sites by igniting a small volume of fuel/air mixture in a pre-chamber. Although PCC looks promising to mitigate the drawbacks of lean-burn strategies, an in-depth understanding of pre-chamber generated reacting jets, transient ignition phenomena, turbulence-chemistry interactions, and extinction inside the pre-chamber is still missing. To address this, for the first time, a novel optical pre-chamber facility integrated inside a highly optical rapid compression machine at the University of Minnesota has been demonstrated in this study. It comprises a fused-silica optical pre-chamber housed inside an optically accessible rapid compression machine. The entire hemispherical volume of the pre-chamber, along with the nozzles, is optically visible. This study focuses on understanding the ignition mechanisms of premixed methane/air mixtures in the optical pre-chamber and main chamber via high-speed intensified chemiluminescence imaging. In addition to the pre-chamber geometry, the effects of varying spark energies and equivalence ratios are also investigated. The study delves into the fundamental dynamics of the reacting jet and investigates its impact on reaction chemistry.