Study of Knocking Mitigation and Thermal Efficiency Enhancement of Pre-chamber Jet Combustion in Stoichiometric Gasoline Engine

Pre-chamber jet combustion is known to be effective in knocking mitigation as it can increase the combustion speed in spark ignition engines. Therefore, a study was made of the effect of knocking mitigation and thermal efficiency improvement when passive type pre-chamber jet combustion is applied to a gasoline stoichiometric spark ignition combustion engine. Compared to conventional spark ignition combustion engines, pre-chamber jet combustion has enhanced penetration of flame propagation depending on flow rate and flow velocity at the pre-chamber jet hole, and the flame propagation combustion rate inside the pre-chamber. Due to the jet ejected from the pre-chamber, the flame could quickly reach the end of the bore. Moreover, the combustion period was shortened, and the unburned portion of the end gas in the latter half of the combustion was reduced, resulting in knocking mitigation. Furthermore, increasing the number of jets by increasing the number of pre-chamber holes caused the unburned region to be divided and become smaller, which mitigated auto-ignition and knocking. Optimized specifications to achieve the maximum knocking mitigation effect and thermal efficiency, made it possible to raise the compression ratio by 1.8 and therefore made it possible to improve thermal efficiency by 1.1 percentage points.