Multi-objective performance optimization of an active pre-chamber combustion engine

Abstract

The pre-chamber combustion concept has gained increasing attention in engine research for its ability to accelerate combustion, extend lean-burn limits, and enhance overall performance. This study presents a comprehensive multi-objective optimization of an active pre-chamber natural gas engine using a detailed design of experiments integrated with multi-dimensional computational fluid dynamics simulations. The optimization targeted reductions in fuel consumption and emissions, including nitrogen oxides, carbon monoxide, and unburned hydrocarbons. Six independent and three dependent geometric parameters of the pre-chamber were considered. Using the Sobol sampling method, 300 design cases were generated through CAESES. Compared to the baseline narrow-throat 12-nozzle design, a pre-chamber featuring a wider throat and 8 nozzles demonstrated the best overall performance. This improvement was primarily due to mitigated turbulent jet interactions and reductions in wall heat transfer, incomplete combustion, and exhaust losses. In contrast, the least effective configurations exhibited weak reacting jets, resulting in slower flame propagation and delayed combustion in the main chamber. Among the geometric parameters studied, the nozzle included angle, throat radius, and cone height were found to have the most significant impact on combustion behavior. Conversely, nozzle diameter, nozzle count, and offset distance showed comparatively fewer effects. A narrower jet angle slowed combustion in the squish region, delaying combustion phasing and increasing exhaust losses. Similarly, deviations from optimal throat radius and cone height diminished jet intensity and combustion completeness, deteriorating engine performance. The findings are anticipated to provide valuable guidance for the design and optimization of pre-chamber geometries in high-efficiency internal combustion engines.