Combustion and emission characteristics of an ammonia-hydrogen engine using hydrogen-nitrogen jet ignition

Ammonia is a promising carbon-free fuel for internal combustion engines, but its low reactivity poses significant ignition challenges. Hydrogen jet ignition has emerged as a potential solution. While using ammonia decomposition as a hydrogen source is safer and more practical than hydrogen cylinders, the ignition performance of its decomposition gas (a hydrogen-nitrogen mixture with a molar ratio of 3:1) remains poorly studied. This study investigated the performance of an ammonia-hydrogen engine using a hydrogen-nitrogen mixture with a molar ratio of 3:1 as the ignition gas for active jet ignition under two categories of injection strategy: varying injection times and durations. The results showed that, compared to pure hydrogen, the hydrogen-nitrogen mixture increases the density inside the jet chamber, resulting in an increase in jet flame penetration length and flame ignition area. Moderately reducing the hydrogen energy ratio (αH2) could reduce heat loss and improve indicated thermal efficiency (ITE). Additionally, slightly lean combustion could achieve better thermal efficiency. The maximum ITE of 44.2 % was obtained with an excess air ratio (λ) at 1.18 and αH2 = 1.1 %. Slightly lean burn improved ITE but too lean mixture led to unstable combustion. As λ increased, NOx emissions first increased and then decreased at the maximum ITE operating condition under the same injection strategy and αH2. Under αH2 = 3.5 % and λ = 1.0, the minimum NOx was measured at 2796 ppm. This study validates the ignition capability of ammonia decomposition products and proposes optimized combustion strategies for improving efficiency and reducing emissions.