Measurements and modelling of nitrogen species in CH4/O2/N2 flames doped with NO, NH3, or NH3+NO

Species profiles measurements were performed by using Molecular Beam Mass Spectrometry in low pressure CH4/O2/N2 flames doped with NO, NH3 or NH3+NO. The present paper aims to study NO/NH3 conversion in hydrocarbon flames. It is based on the analysis of CH2/CH3 radicals and NO, NH3 and HCN species profiles. In NO doped flame, NO-reburning prevails, but in NH3 and NH3+NO doped flames, NH3 conversion in NO was measured with a yield close to 90–100%. HCN peak mole fractions were found in similar amount in the NH3 and NH3+NO doped flames, twice higher than in the NO doped flame. Experimental results are compared to simulated species profiles by using three detailed mechanisms. A general good agreement between experimental and simulated NO and NH3 profiles is observed. However, simulated HCN peak mole fractions overpredict the experimental ones. Reaction pathways analysis performed by using detailed mechanisms reveals that the HCN formation is due to NO-reburning reactions and to reactions from the NH3 subset (via H2CN and HNCN). According to the mechanism from Tian et al. (2009), the importance of NH3 subset prevails in NH3 and NO+NH3 doped flames.