Study on ignition mode transition of methanol pre-chamber jet ignition system controlled by boundary condition parameters

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Optimizing boundary condition parameters is an effective means to substantially improve the combustion performance of methanol pre-chamber turbulent jet ignition systems. In this study, an optically accessible constant-volume combustion chamber was employed to delve deeply into the impacts of critical boundary condition parameters on the combustion performance of the pre-chamber jet ignition system. The findings suggest that adjusting the pre-chamber boundary condition parameters can lead to various jet ignition modes, including jet flame ignition, jet direct ignition, jet delayed ignition, jet wake ignition, and dual jet ignition. Different jet ignition modes result in variations in ignition timing, ignition location, combustion rate, and lean burn limits. Under identical initial temperature and pressure conditions, compared to jet flame ignition with the lowest combustion velocity and jet wake ignition with almost no lean burn capability, dual jet ignition can reduce the combustion duration by about 50% and elevate the lean burn limit by more than double. Unlike the patterns observed in traditional spark ignition systems, within the range of experimental tests, lowering the temperature and increasing the pressure significantly improved the lean combustion limit of the pre-chamber system and reduced the probability of jet wake ignition. This performance enhancement is attributed to the increase in the density of the mixture in the main combustion chamber.