Effects of fuel composition and wall thermal conductivity on thermal and NOx emission performances of an ammonia/hydrogen-oxygen micro-power system

As a renewable fuel, ammonia NH3 is identified as one of the most potential candidates to tackle greenhouse gas challenge. For this, ammonia-hydrogen-oxygen combustion in micro-power systems is numerically investigated in this work. The computational model is first validated with experimental data available in the literature. Then, emphasis is placed on the effects of (1) the fuel composition ratio epsilon (defined as the hydrogen molar fraction relative to the mixed fuel of ammonia and hydrogen) and (2) the wall thermal conductivity (WTC) on the system's working performance. Results indicate that increasing epsilon can not only lead to the outer wall temperature (OWT) and radiation efficiency (RE) being decreased, but also enable the flame propagate towards the combustor inlet. An optimized epsilon is found to minimize the NOx emission by approximately 54.9% compared to 100% NH3 combustion. Further analyses show that a high WTC has a potential to increase OWT at low fuel flow rates, while RE varies non-monotonically with the NH3 volumetric flow rate. It is also shown that WTC has a slight effect on NOx emission and the flame shape. This work sheds light on a simple but effective way to improve thermal and emission behaviors.