Pre-chamber ignition systems for high-speed large-bore gas engine: technology investigation through 3D-CFD analysis

• High-speed large bore gas engines equipped with pre-chamber ignition systems. • 3D-CFD comparison of passive and active pre-chamber ignition systems. • Comparative analysis through energy, jet penetration and Borghi diagrams. • High efficiency and low NOx reached by calibration and geometry optimization. • Active pre-chamber extends the lean limit compared to passive design. Nowadays large bore gas engines are gaining popularity in the market for power generation and marine applications. Methane is preferred over conventional diesel because of its favourable H/C ratio and lower soot emissions. Furthermore, the global transition to renewable energy sees eMethane as one of the most promising options for clean energy storage. Consequently, the enhancement of the efficiency of large bore gas engines through innovative combustion strategies, such as pre-chamber ignition, is of growing importance. This technology increases ignition energy, shortens combustion duration, and achieves higher thermal efficiency compared with conventional ignition systems due to extended lean operation. However, it remains unclear which factors fundamentally limit the achievable lean operation of passive and active pre-chamber ignition systems, thereby influencing their combustion behaviour and pollutant emission. In this context, this paper presents a 3D-CFD numerical investigation of a large bore gas engine (∼4 L/cyl.) equipped with both passive and active pre-chamber systems, operating under lean air/methane mixtures at high load. The study aims to evaluate the influence of calibration and geometric parameters, define and optimize the lean limit of each system, and assess the resulting impact on engine thermal efficiency and pollutant emissions. A comprehensive comparison between the two systems is provided. Finally, the results of the optimization process demonstrate that both passive and active pre-chamber systems can be effectively tailored through geometry and calibration to address the dual challenge of high efficiency and low NO x emissions in large bore methane engines.