Ammonia-hydrogen combination engine with injecting jet ignition (IJI): the concepts and ignition mechanism

This study introduces a novel concept for an internal combustion engine utilizing the injecting jet ignition (IJI) method, specifically designed for an ammonia-hydrogen combination strategy. The concept was explored through three-dimensional numerical simulations, focusing on combustion performance and ignition mechanisms. Four distinct engine ignition modes—Head ignition (HI_e), Center ignition (CI_e), Tail ignition (TI_e), and After tail ignition (ATI_e)—are defined based on the timing of hydrogen injection and ignition. In the ATI_e mode, the initial flame kernel develops slowly and spherically, resembling premixed combustion, while in the HI_e, CI_e, and TI_e modes, the flame propagates rapidly along the hydrogen jet direction due to sustained jet-induced turbulent kinetic energy. Among these, the HIe mode demonstrated the fastest flame development, optimal power performance, and lowest pollutant emissions, achieving a peak indicated thermal efficiency of 37.2 % at an excess air ratio (λ) of 1.1. In contrast, the ATI_e mode exhibited slower combustion and higher levels of unburned ammonia. These findings offer a new approach to achieving efficient combustion in ammonia-hydrogen engines, providing a theoretical basis for their future development and application.