Future zero carbon ammonia engine: Fundamental study on the effect of jet ignition system characterized by gasoline ignition chamber

Ammonia is a carbon-free fuel with tremendous potential for clean internal engine applications in the future. However, the combustion and emissions limitations of ammonia fuel have impeded the development of ammonia engine. As a combustion enhancement technology, the ignition chamber (pre-chamber) jet ignition system has emerged as an effective solution to address the challenges associated with ammonia combustion. This study utilized a high-speed camera to capture the evolution of jet and the combustion processes of ammonia. The combustion method entailed the injection of gasoline into the ignition chamber, while ammonia was injected into the main chamber. The experimental results demonstrated that ignition chamber jet ignition system significantly enhanced ammonia combustion and shortened the combustion duration as compared to spark plug ignition system. The study involved evaluating the ammonia combustion performance under different equivalence ratios (1.0 and 0.8) while comparing it to various gasoline energy percentages (2.5%, 2.0%, 1.5%, and 1.0%). The results revealed that the combustion performance at 1.5% was superior to other gasoline energy percentages. Additionally, in comparison to ignition chamber outlet diameter of 4.5 mm and 6.0 mm, it was found that the 3.0 mm diameter exhibited weak ignition capability, resulting in a 107.1% and 40.3% increase in ignition delay at the equivalence ratio of 0.8, and ignition failure at the equivalence ratio of 0.6. However, its high jet velocity induced a more homogeneous mixing of radicals with ammonia/air, leading to a 30.6% reduction in rapid combustion and a 43.1% decrease in combustion duration at the equivalence ratio of 0.8. Additionally, the investigation of equivalence ratios (0.8, 1.0, and 1.1) demonstrated that the fastest initial combustion of ammonia occurred at the equivalence ratio of 0.8, with an ignition delay of only 4.7ms. Therefore, an appropriate reduction in the equivalence ratio could enhance the ammonia combustion efficiency to some extent. The findings of this study provide a fundamental ignition technique for future applications of zero carbon ammonia engines.