Research on the ignition mechanism and structural optimization of turbulent jet pre-chamber in GDI engines

Turbulent jet ignition has been widely studied, but it is mainly focused on gas engines, the igniting mechanisms of pre-chamber (PC) on GDI engines and the contributions of heat and radicals of the jet in inhomogeneous charge still remain to be clarified. Thus, 3-D simulations with comprehensive spray mixing process were performed under variable structural parameters. The decoupling results of thermal and chemical effects show that the influence of jet temperature on the heat release rate (HRR) inside main chamber (MC) is greater than that of free radicals. The mechanism of hot jet ignition containing free radicals in MC is flame propagation without ignition delay. However, compared to jet temperature, the free radicals in the jet have less effects on HRR in MC after the ignition. The nozzle diameter significantly affects fuel entry into the PC, influencing the pressure difference between PC and MC, and thus the jet velocity and duration. The optimal diameter in this study is 1.0 mm, and the jet duration is prolonged for too small or too large diameters. The nozzle angle is constrained by combustion chamber geometry, with the optimal angle being 140 degrees to avoid jet impingement on cylinder head or piston.