Formation of NO and NH in NH3-doped CH4 + N2 + O2 flame: Experiments and modelling

Co-combustion of 5200 ppm NH3 with a stoichiometric, atmospheric pressure, CH4 + N2 + O2 flame has been investigated with experiments and kinetic modelling. Profiles of the amidogen (NH) radical and nitric oxide (NO) have been measured using laser-induced fluorescence, the latter being quantitatively determined. Temperature profiles were measured using Rayleigh scattering and thermocouple, the nonintrusive measurements were considered more reliable and were used for evaluation of LIF data as well as input for flame modelling. Experimental results are compared with predictions of a chemical mechanism developed by Mendiara and Glarborg (2009), with simulations based on solution of energy equation as well as on experimental temperature profiles as input. Compared with a neat flame, the NH3-doped flame shows a shift in position ∼0.7 mm downstream, as established from the measurements of the NH profile. Modelling prediction of post-flame NO concentrations in the NH3-doped flame, around 1160 ppm, was within the evaluated uncertainty with experimental data (1460 ppm). Reaction path analysis indicated NH2 as a key species in the formation of NO and N2 from the nitrogen added to the flame by NH3. Altogether, the mechanism predicts concentration levels rather well but fails to predict the shift in flame position obtained with addition of NH3 to the rather slowly burning hydrocarbon flame.