Numerical analysis of combustion stability and efficiency improvement in ammonia engines utilizing Passive Turbulent Jet Ignition (PTJI)

Ammonia, recognized as a carbon-neutral fuel, is considered a promising candidate for next-generation engine applications. Nevertheless, its combustion performance is constrained by its low flame speed and prolonged ignition delay, leading to limitations in combustion stability and efficiency across high-speed/high-load and low-speed/low-load operating conditions. Notably, incomplete combustion resulting from limited residence time is a critical issue at high speeds, while ignition instability and low combustion temperatures pose significant challenges at low speeds. To overcome these limitations, Passive Turbulent Jet Ignition (PTJI) system has been proposed. By promoting turbulent mixing within the combustion chamber and employing multiple ignition strategies, PTJI demonstrates potential for mitigating the inherent drawbacks associated with ammonia combustion. This research investigates the optimization of a PTJI system for ammonia-fueled engines through a three-phased methodology. Initially, an 800cc two-cylinder gasoline engine was adapted for ammonia operation, facilitating a comparative analysis of combustion behavior. Subsequently, a preliminary investigation focusing on turbulence intensity analysis within the PTJI system was performed to determine a stable configuration that promotes improved combustion. The influence of the PTJI system compared to conventional ammonia engine configurations was then evaluated under both high-speed and low-speed operating conditions. The primary findings are summarized as follows: At low-speed conditions, the implementation of the PTJI system resulted in an increase in combustion temperature and a reduction in ignition delay, thereby significantly enhancing combustion stability. At high-speed conditions, the PTJI system enhanced flame propagation velocity and facilitated complete combustion of the fuel-air mixture, leading to improvements in both combustion efficiency and emission performance. In conclusion, this study demonstrates that PTJI is an effective technology for enhancing the combustion performance of ammonia engines, presenting the potential to optimize ammonia's inherent combustion characteristics through turbulence control.