Influence of Pre-Chamber Volume, Orifice Diameter and Orifice Number on Performance of Pre-Chamber SI Engine—An Experimental and Numerical Study

Abstract

This paper presented an experimental and numerical study of pre-chamber volume, number of orifices and orifice diameter influence on engine performance and emissions. All the measurements were performed on a single cylinder test engine at fixed engine speed of 1600 rpm, while engine load was varied by a change of the excess air ratio in the main chamber from a stochiometric mixture to a lean limit. The total of nine pre-chamber variants comprised three different pre-chamber volumes, two orifice number combinations (six and four orifices) and nine different orifice diameters. It was observed that the pre-chamber volume affects the indicated efficiency in a trend which is mostly independent of excess air ratio, with the efficiency gain between the best and worst results ranging from 1 to 4.4%. While keeping the same pre-chamber volume and the total cross-sectional area of the orifices, the larger number of orifices show better performance on two out of three investigated pre-chamber volumes, with the efficiency gains more pronounced at higher excess air ratios. Finally, on a fixed pre-chamber volume and number of orifices, the variation of orifice diameter leads to a trend in efficiency gains which favor larger orifice diameter. The comparison of the obtained efficiencies between all pre-chamber variants identified two pre-chambers, differing in each of the varied geometrical parameters, that show the best performance depending on excess air ratio range. On the other hand, a single variant which showed the worst performance on each excess ratio was identified. An additional investigation was performed by the application of the cycle-simulation model to quantify the share of emissions which are formed in the pre-chamber. The presented results showed that when PC volume is lowered, PC emission shares of NOX and CO grow larger. The influence of orifice number and size has a minor effect on the pre-chamber emissions shares. The maximum PC emission shares of 54.8% and 80.6% are achieved at lean limit (λ = 2.2) for NOX and CO, respectively. THC emission share, on the other hand, is not affected in a significant manner by either the pre-chamber geometry or operating conditions.