Ammonia-rich vs. Hydrogen-rich blending: A review of dual-route research progress on ammonia-hydrogen mixed combustion

Against the backdrop of the “dual carbon” goals, hydrogen and ammonia have attracted widespread attention as typical carbon‑free fuels. Unlike previous reviews that largely focused on a single route or a single application scenario, this paper takes the dual‑route utilization of ammonia‑hydrogen blended fuels as its main thread, categorizing them into two complementary pathways—“ammonia‑rich with hydrogen addition” and “hydrogen‑rich with ammonia addition”—and systematically reviews the research progress in fuel properties, reaction kinetics, fundamental combustion behavior, nitrogen‑containing emission mechanisms, and engineering applications for both routes. The review shows that the ammonia‑rich with hydrogen addition route can significantly improve the ignition and flame propagation performance of ammonia fuel, but its application remains constrained by NOx, N 2 O, and unburned ammonia emissions. The hydrogen‑rich with ammonia addition route, on the other hand, can modulate the reactivity of hydrogen fuel to a certain extent, reducing the risks of auto‑ignition, flashback, and explosion propagation, thus offering a new perspective for the safe utilization of hydrogen. Further comparison reveals that the two routes have distinct technical objectives and engineering constraints in terms of fuel ratio, combustion organization, emission control, and safety boundaries. Overall, ammonia‑hydrogen blended fuels show potential application value in internal combustion engines, gas turbines, and marine propulsion, but their large‑scale development still relies on validation under high‑pressure real‑world conditions, synergistic design of power systems, and comprehensive life‑cycle assessment.