Abstract
An active prechamber turbulent ignition system is a forced ignition method for internal combustion engines fueled with low reactivity fuels, i.e., natural gas and gasoline, which could expand the lean-burn limit, promote flame propagation, and ensure cyclic stability. In the present study, the effects of charge concentration stratifications inside the prechamber on the jet characteristics and combustion process were numerically investigated using CONVERGE software coupled with a reduced methane mechanism by the coupling control of spark timing and prechamber global equivalence ratio. The results show that the jet characteristics and ignition mechanisms can be regulated by controlling the prechamber global equivalence ratio and spark timing. On the one hand, as the prechamber global equivalence ratio increases, the velocity of the jet increases firstly and then decreases, the temperature drops, and OH and CH2O radicals are reduced, but the stable combustion intermediates, CO and H2, are increased. Thus, the ignition mechanism changes from flame ignition (ignition by flame and reactive radicals) to jet ignition (ignition by hot combustion intermediates), and the ignition delay is shortened, but the combustion duration is extended, mainly due to more of the combustion intermediates, CO and H2, downstream of the jet. On the other hand, as spark timing is advanced, the jet velocity and the mass of the OH and CH2O radicals increase, which is conducive to flame ignition, and the ignition delay and combustion duration are reduced.