Numerical study on effects of mixture stratification and fuel-rich region distribution on turbulence jet energy and ignition efficacy in a methanol active pre-chamber

The mixture stratification within methanol active pre-chamber (APC) significantly governs combustion characteristics and ignition effectiveness under ultra-lean combustion conditions. This study investigates the coupled effects of internal methanol mixture stratification on flame propagation, jet characteristics, and ignition performance in the main chamber (MC) by employing Large Eddy Simulation (LES). Distinct stratification configurations were designed to systematically examine the relationships between staged heat release, species evolution, and jet energy composition. Results demonstrate that mixture stratification fundamentally alters internal flame propagation pathways and combustion modes. When the fuel-rich region is positioned at the APC top, APC inner combustion is more complete with thermal energy dominant jets with proportion of 46.21%. As the fuel-rich region moves downward, chemical energy from unburned fuel and intermediate species increases in the jet. Further analysis reveals thermal energy and chemical energy dominate the total energy budget of more than 80%, governing jet temperature maintenance and reactivity. Kinetic energy that accounts for less than 10% primarily promotes radial flame expansion. The optimal case with fuel-rich region in the mid-lower APC section achieved sustained high jet temperature and maximum ignited mixture due to balanced active species, chemical energy and thermal energy, the ignition heat release has increased by 17.4% compared to the worst case (from 1598.8J to 1877.4J). This study clarifies how APC internal mixture stratification and distribution influences ignition effectiveness by regulating jet energy components, providing crucial theoretical guidance for optimizing APC design toward highly efficient lean combustion.