Multi-objective performance optimization of diesel engine lip jet combustion chamber based on RSM-NSGA-Ⅱ

A lip jet combustion chamber (LJCC) was designed to enhance fuel-air mixing and engine performance for diesel engines. Key parameters, including spray angle (SA), injector diameter (ID), injection pressure (IP), and injection timing (IT), were optimized using the coupled RSM-NSGA-II algorithm. The characteristics of fuel-air mixing, combustion, and pollutant formation in the LJCC were analyzed through computational fluid dynamics simulations. A Box-Behnken design was employed to guide experimental schemes, and the results were used to establish an RSM-based prediction model. The NSGA-Ⅱ optimization provided a Pareto solution set, with the optimal solution identified via the TOPSIS method. The LJCC directed part of the fuel jet toward the central and recirculation zones of the combustion chamber, forming distinct inner (bowl region), middle (central region), and outer (recirculation zone) mixing regions. This design improved fuel distribution and mixing quality. IT significantly affected thermal efficiency and NOx formation, while increasing SA and reducing ID enhanced the fuel atomization and suppressed the soot emissions. Compared to a baseline chamber, the LJCC achieved a 47.2 % reduction in soot emissions with negligible changes in thermal efficiency and NOx production. This study provides theoretical guidance for efficient and clean diesel engine combustion.