Pre-chamber combustion (PCC) enables leaner air-fuel ratio operation by improving its ignitability and extending flammability limit, and consequently, offers better thermal efficiency than conventional spark ignition operation. The geometry and fuel concentration of the pre-chamber (PC) is one of the major parameters that affect overall performance. To understand the dynamics of the PCC in practical engine conditions, this study focused on (i) correlation of the events in the main chamber (MC) with the measured in-cylinder pressure traces and, (ii) the effect of fuel concentration on the MC combustion characteristics using laser diagnostics. We performed simultaneous acetone planar laser-induced fluorescence (PLIF) from the side, and OH* chemiluminescence imaging from the bottom in a heavy-duty optical engine. Two different PC Fueling Ratios (PCFR, the ratio of PC fuel to the total fuel), 7%, and 13%, were investigated. The “negative” regions of the PLIF fields were used to visualize PC jets and the MC combustion. The absence of acetone seeding in the PC, and its consumption during the MC combustion contributed to the loss of PLIF signal (negative regions). The instantaneous PLIF/OH* fields showed the appearance of PC jets near its pressure maximum. The PC jet interacting with the piston surface was accompanied by an increase in OH* chemiluminescence intensity and its area. Increasing PCFR resulted in a lag of ~0.6° crank angle in the PC and MC pressure and the pressure difference (ΔPPC-MC) between the two, for the two PCFR cases. This led to a phase lag in the PC flame jet penetration distance, which in turn delayed the increase in the total OH* chemiluminescence intensity for the higher PCFR case. For similar ΔPPC-MC, we observed wider OH* regions with increased PCFR. This result distinguished the radical concentration effect on the MC combustion from the fluid mechanical effects controlled by ΔPPC-MC.
