Development of Pre-chamber with Less Combustion Variation with Use of LES 2019-01-2223
Pre-chamber type gas engines have some merits; one is high efficiency thanks to lean combustion and the other is lower emissions such as CO2 compared to diesel engines. On the other hand, in pre-chamber type gas engines, one factor which frustrates higher efficiency is cycle-to-cycle variation of combustion. One reason why combustion variation occurs is assumed to be variation of fluid in pre-chamber. Such variation of fluid causes variation of equivalence ratio around the spark plug. It leads to unstable ignitability, and as a result, the peaks of in-cylinder pressure vary in different cycles. In order to overcome such technical problem, designing the pre-chamber shape with less cycle-to-cycle variation of combustion is needed. When designing the pre-chamber, CFD (Computational Fluid Dynamics) is a strong tool because detailed fluid history can be captured easily with CFD compared to experiments. LES (Large-Eddy Simulation) is assumed to have potential to realize cycle-to-cycle variation because it can calculate eddies whose size are larger than mesh size without modeling. Therefore, LES was applied to investigate the cause of cycle-to-cycle variation. In this study, some LES of pre-chamber type gas engines were conducted. From the simulated results, the factor of cycle-to-cycle variation has been revealed. After that, the new pre-chamber shape with less combustion variation has been designed. The effect of the new pre-chamber shape for less combustion variation was confirmed with use of both CFD and experiments.