Abstract
To understand key physical aspects of volume in narrow-throat pre-chambers, computational fluid dynamics simulations were performed using CONVERGE™. A major advantage of a narrow-throat feature is to allow for drop-in replacement of a diesel injector, hence facilitating technology deployment. Despite broad literature on conventional pre-chambers, the narrow-throat has been shown to induce a different behavior, hence a thorough computational characterization is needed. The considered simulations were at lean conditions with methane, except the pre-chamber, which was additionally fueled thus providing an active mode of operation. The modeling work was validated with experiments and provided additional insights into key remaining questions on the small and large pre-chambers effects. The G-Equation combustion model was adopted; Peters’ turbulent flame speed correlation was used, while a skeletal methane mechanism was used for tabulating the laminar flame speed. The simulation data reveals that reducing the volume leads to significant stratification and low turbulence inside the pre-chamber. This combined with lower surface area led to lower heat transfer losses when compared to larger pre-chambers. Furthermore, the shorter jet issuing duration of small pre-chambers caters to longer combustion duration, as the turbulence and convection from the jets quickly dissipate. The Borghi-Peters diagram was further utilized to correlate the results with fundamental quantities and expected turbulent regimes encountered for the different pre-chambers.
