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