Apparatus, methods and systems reside in the decomposition of ammonia into a hydrogen-containing product mixture. An ammonia-rich gaseous mixture containing ammonia and oxygen enters a conduit, within which combustion and decomposition of the mixture is initiated, thereby liberating hydrogen. A mixture of products, resulting from the reactions, is expelled from the outlet of the conduit, the mixture including non-combusted hydrogen gas, which may then be used for other purposes. The incoming reactants, including ammonia and oxygen, are heat exchanged with the outgoing product mixture containing non-combusted hydrogen gas.