Advanced combustion chamber design and ignition system strategies for homogeneous lean operation in a hybrid-dedicated gasoline engine

초록

This study focuses on enabling stable and efficient homogeneous lean combustion in a hybrid-dedicated gasoline engine through advanced combustion chamber design and high-energy ignition strategies. A production-based 2.5-liter engine was modified with optimized intake port and piston geometries, and an innovative dual-coil multi-stage ignition system. Large eddy simulation and engine dynamometer tests demonstrated that the new chamber design significantly increased tumble flow and turbulence, strengthening early flame development under lean conditions. The high-energy ignition system, employing sequential dual-coil discharges, sustained ignition channel current during strong in-cylinder flows and maintained robust flame growth. Engine testing at 2000 rpm and 8.5 bar BMEP confirmed a marked improvement in early combustion process, enabling reliable lean combustion up to λ = 2.2. These enhancements resulted in maximum brake thermal efficiency of 45% and reduced engine-out NOx emissions to 0.2 g/kWh. Compared to previous lean-burn engine studies, which often relied on single-cylinder research or focused on individual technologies—this work validates the synergistic integration of an advanced design of combustion chamber and a high-energy dual-coil ignition system in a production-level multi-cylinder engine. This system-level approach achieves substantial gains across all key performance metrics, representing a significant advancement over previous studies in lean-burn gasoline engine. Previous studies have typically been limited to lean limits below λ = 2.0 with correspondingly higher NOx emissions, whereas the present work demonstrates clear improvements beyond these performance. The synergistic optimization of in-cylinder flow and ignition strategy extends the practical lean limit while minimizing emissions and improving efficiency. This work highlights the potential of integrating advanced combustion chamber and ignition approaches to facilitate next-generation low-emission, high-efficiency hybrid powertrains and provides valuable guidance for powertrain development toward stricter carbon regulations. © 2026 Elsevier Ltd.

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