Emission characteristics of confined non-premixed ammonia-oxygen-nitrogen turbulent jet flames under oxygen-enriched conditions

As a potential hydrogen energy carrier and a carbon free fuel, various applications of NH3 are currently being considered. One way to directly use ammonia is to introduce it into industrial furnaces. However, the combustion of ammonia yields a lower flame temperature compared to hydrocarbon fuels, presenting a drawback in applications such as glass melting furnaces that demand particularly high temperatures. Therefore, oxygenenriched combustion is considered to be used, while its NOx emission characteristics are unknow. Therefore, for the first time, this paper demonstrates the fundamental emission characteristics of confined non-premixed ammonia-oxygen-nitrogen turbulent jet flames under oxygen-enriched conditions. The emission characteristics of the flames were investigated using a Fourier Transform Infrared spectrometer in a combustor with insulated and uninsulated walls over a wide range of global equivalence ratios, cbGlobal, oxygen concentrations in the oxidizer, (1O2, and heat output conditions up to 10 kW. The results indicated that the emissions of nonpremixed ammonia-oxygen-nitrogen turbulent jet flames exhibited a premixed flame characteristic, revealing a trade-off relationship between NO and unburned NH3. Moreover, there is a specific global equivalence ratio, cboptimal, at which NO and unburned NH3 emissions are minimal. Increasing (1O2 and the heat output promotes NO emission in global lean cases and reduces NH3 emission in global rich cases, further shifting the cboptimal to the richer side. Besides, a heat loss by glass liner leads to a significant decrease of furnace temperature and a shift of cboptimal to stoichiometric condition. Furthermore, the fundamental non-premixed ammonia-oxygen-nitrogen turbulent jet flame structure was discussed based on counterflow diffusion flame. It was considered that, in applications where the entire ammonia turbulent jet diffusion flame is used, the rich-lean two-stage combustion concept can be applied for low NOx combustion in industrial furnaces even at oxygen-enriched conditions.