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.
