NO emission characteristics of air coflowed non-premixed ammonia jet flame at elevated ambient temperatures and with N2 dilution

Abstract

Ammonia is promising carbon-free alternative fuel, while the poor combustion performance and severe NO emission hinder its application. In this work, a strategy combined with preheating and dilution was discussed, and NO emission characteristics of air coflowed non-premixed ammonia jet flame were experimentally investigated over 550–700 °C and with N2 dilution, using a novel preheating facility. Results show that the general excess air coefficient is significant for NO emission, but not the unique factor. NO emission monotonically increases with the general excess air coefficient, while the slope decreases. Ambient temperature is also of a remarkable effect, that NO emission decreases by about 100 ppm (15% O2, dry) when the ambient temperature rises from 550 °C to 700 °C. Besides, effects of dilution were considered with three specific strategies. Air coflow dilution is of a negative influence on NO emission, while, NH3 jet dilution promotes NO emission in contrast. The interaction between the two single-dilution strategies is limited, and the effect of double dilution seems to be a simple sum of that of the other two single-dilution strategies. In addition, flame liftoff was observed in experiments and a considerable decline of NO emission was detected with the flame regime transition. According to the experimental results, the combination of elevated ambient temperature and air dilution is evaluated to be a promising low NO emission combustion method of ammonia.