Computational study of the impacts of the nozzle configurations on passive pre-chamber engine combustion

Abstract

The pre-chamber (PC) nozzle configurations are vital in the narrow-throat pre-chamber design. However, their impacts on the jet and combustion characteristics are poorly understood. In the current study, various parameters of nozzle configurations, including the number of rows, nozzle position, and the jet included angle were evaluated on a well-calibrated numerical model of a passive PC engine fueled with methane. The unique buffering effect of the bottom cavity below the orifice in the PC nozzle was discovered and investigated for the first time. Results show that the PC with double-row orifices exhibits slower general combustion than the single-row for the significant flow bypass from the upper-row orifices that generate low jet velocity. A higher orifice position favors combustion due to less interaction between the flame and the piston. Pressure accumulation at the nozzle was discovered to be the key factor affecting jet velocity. Jet velocity increases with the enlarged pressure accumulation decreasing the effective flow area of the orifices. However, it starts to decrease when the pressure accumulation becomes excessive and the obstruction to the flow outweighs the enhancement to the velocity. For single-row PCs without the bottom cavity, the pressure accumulation is enhanced as the jet included angle increases (from 111° to 180°) and the angle of 157° achieves the highest jet velocity, although the pressure difference decreases as the included angle increases. For single-row-orifice PCs with a bottom cavity, the buffering effect of the cavity produces close pressure accumulation to maintain similar jet characteristics when the jet included angle varies. Comparative analysis shows that the included angle of 157° achieves the fastest main chamber combustion mainly because the proper relative position of the PC jet and piston favors turbulence and flame spread.