By using molecular beam sampling mass spectrometry, the structure of a NH3/H-2/O-2/Ar flat premixed flame burning at 50 mbar and with an equivalence ratio equals to one has been determined. Simulated mole fraction profiles have been obtained by using the kinetic mechanisms of Konnov (2000), Bian et al. (1990), Lindstedt et al. (1994), and Smith (1999), but only the first two give results in agreement with the experimental ones. Furthermore, an initial study on a spark ignition engine has been performed to define which parameters must be applied to reach the best possible efficiency and reduce the formation of pollutants when ammonia is used as fuel in engines.