Pre-chamber jet ignition technologies have been garnering significant interest in
the internal combustion engine field, given their potential to deliver shorter
burn durations, increased combustion stability, and improved dilution tolerance.
However, a clear understanding of the relationship between pre-chamber geometry,
operating condition, jet formation, and engine performance in light-duty
gasoline injection engines remains under-explored. Moreover, research
specifically focusing on high dilution levels and passive pre-chambers with
optical accessibility is notably scarce. This study serves to bridge these
knowledge gaps by examining the influence of passive pre-chamber nozzle diameter
and dilution level on jet formation and engine performance. Utilizing a modified
constant-volume gasoline direct injection engine with an optically accessible
piston, we tested three passive pre-chambers with nozzle diameters of 1.2, 1.4,
and 1.6 mm, while nitrogen dilution varied from 0 to 20%. With the help of
high-speed imaging, we captured pre-chamber jet formations and subsequent flame
propagation within the main chamber. Our novel findings reveal that asymmetric
temporal and spatial jet formation patterns arising from pre-chambers
significantly impact engine performance. The larger-nozzle-diameter pre-chambers
exhibited the least variation in jet formation due to their improved scavenging
and main mixture filling processes, but had the slowest jet velocity and lowest
jet penetration depth. At no dilution condition, the 1.2 mm-PC demonstrated
superior performance attributed to higher pressure build-up in the pre-chamber,
resulting in accelerated jet velocity and increased jet penetration depth.
However, at high dilution condition, the 1.6 mm-PC performed better,
highlighting the importance of scavenging and symmetry jet formation. This study
emphasizes the importance of carefully selecting the pre-chamber nozzle
diameter, based on the engine’s operating conditions, to achieve an optimal and
balanced configuration that can improve both jet formation and jet
characteristics, as well as scavenging.
