In the current work, the combustion of NH₃/H₂/air blends is experimentally investigated in a constant-volume combustion chamber in terms of two different ignition modes: spark ignition (SI) mode and turbulent jet ignition (TJI) mode with ammonia and hydrogen fueled in the pre-chamber. The results show that for the SI mode, the burning rate and propagation of premixed NH₃/air flames are significantly accelerated by a hydrogen addition of only 3% (v/v). A cellular structure is observed and becomes more intense with the increasing hydrogen volume fraction. For the TJI mode, the hot jet generation and turbulent flame development of ammonia inside the main chamber are captured optically for the first time. The combustion process inside the main chamber can be categorized into three phases for both the TJI-ammonia and TJI-hydrogen modes. The cold jet that mainly contains the unburned fuel and air is observed under the TJI-hydrogen mode. The hot jet produced by the pre-chamber can effectively promote the ignition initiation and hence flame propagation in the main chamber. An accelerated burn rate of ammonia is obtained, and the TJI-hydrogen mode makes a stronger promoting impact on the combustion of the main chamber. Significantly, compared with SI-hydrogen mode, the TJI-hydrogen mode can bring a considerable promoting effect to ammonia combustion with significantly lower hydrogen consumption.