Influence of Passive Pre-Chamber Nozzle Diameter on Jet Ignition in a Constant-Volume Optical Engine under Varying Load and Dilution Conditions

Despite the growing prominence of electrified vehicles, internal combustion engines remain essential in future transportation. This study delves into passive pre-chamber jet ignition, a leading-edge combustion technology, offering a comprehensive visualization of its operation under varying load and dilution conditions in light-duty GDI engines. Our primary objectives are to gain fundamental insights into passive pre-chamber jet ignition and subsequent main combustion processes and evaluate their response to different load and dilution conditions. We conducted experimental investigations using a light-duty, optical, single-cylinder engine equipped with three passive pre-chamber designs featuring varying nozzle diameters. Optical diagnostic imaging and heat release analysis provided critical insights. Findings reveal that as load decreases, fuel availability and flow conditions deteriorate, leading to delayed and suboptimal jet characteristics impacting main chamber ignition and combustion. Notably, at high and medium loads without dilution, the 1.2 mm-PC (smallest nozzle diameter) excels, exhibiting superior jet ignition and main combustion. This is attributed to earlier jet ejection, improved penetration, and intensified jets, all enabled by the smaller nozzle diameter. Conversely, under low load conditions, the 1.6 mm-PC (largest nozzle diameter) performs better due to enhanced scavenging and reduced pre-chamber residuals, resulting in more balanced pre-chamber combustion and jet characteristics. Furthermore, nozzle diameter significantly influences cycle-to-cycle variations, with smaller diameters enhancing jet ignition but intensifying variability. The impact of external residuals (dilution) on jet ignition performance varies with nozzle diameter, with the 1.6 mm-PC displaying less degradation and demonstrating earlier jet ejection and CA50 timing under higher dilution conditions. In summary, this research underscores the importance of scavenging and residual levels in pre-chamber design, influencing dilution tolerance, and extending possibilities for high-efficiency engines. It contributes essential insights into the behavior of passive pre-chamber jet ignition systems, facilitating their optimization for future internal combustion engines.