Prediction of Nitrogen Oxide Formation in Ammonia-Doped Turbulent Syngas Jet Flames

Nitrogen-oxide formation from fuel-bound nitrogen in turbulent non-premixed flames was investigated. Calculations were performed using the k-epsilon model and a Reynolds-stress-equation model for turbulence and the Eddy Dissipation Concept for turbulent combustion (EDC) by Magnussen in conjunction with detailed chemistry of the chemical reaction mechanisms GRI Mech 3.0, GRI Mech 2.11, and Kilpinen97. The calculated case was a turbulent non-premixed syngas jet flame with ammonia added to the fuel, which was compared to experimental results reported in the literature. The results obtained for mean velocity, temperature, and mixture fraction agreed with the experimental data. Integrated values for NO formed from fuel-bound nitrogen were generally in good agreement with experimental data. This holds for all the three reaction mechanisms used. The GRI Mech 3.0 gave the highest, and the Kilpinen mechanism the lowest levels of nitrogen oxides. Furthermore, details of the chemistry of the turbulent flame were studied, and the most important elementary reactions for this case were identified when using the Kilpinen mechanism. The main path for NO formation was degradation of ammonia through NH. This conversion took place in the main part of the flame, to approximately 30 jet-nozzle diameters downstream. Throughout a longer zone, the jet flow down to approximately 100 diameters downstream, some of the NO reacted to HONO and further to NO2 and both these species were emitted from the flame.