Experimental investigation on the combustion characteristics of partially dissociated ammonia ignited by passive turbulent jet ignition

Ammonia (NH₃) is a potential alternative fuel for internal combustion engines to achieve zero-carbon emissions. And partial fuel dissociating is a feasible strategy to improve the reactivity of NH₃, the hydrogen (H₂) generated by dissociation can effectively promote the combustion of NH₃. This study aims to experimentally investigate the ignition and combustion characteristics of partially dissociated NH₃ ignited by passive turbulent jet ignition. The effects of the dissociation ratio and equivalence ratio were analyzed. The results show that the dissociation of NH₃ improves the ignition and combustion performance of NH₃, reflected in lower ignition delay and combustion duration. In addition, as the dissociation ratio increases, the ignition mechanism in the main chamber changes from jet ignition to flame ignition, which can significantly reduce the ignition delay. Lean conditions are more conducive to achieving flame ignition, the jet ignition mechanism on the rich side leads to a higher ignition delay compared to lean conditions at low dissociation ratios. However, the lean mixture shows a higher combustion duration due to its low reactivity. The inhibiting effect of additional nitrogen (N₂) increases with the dissociation ratio, but the ignition mechanism and flame propagation in the main chamber are not significantly affected.