Effect of NH3/H2/O2 premixed combustion on energy conversion enhancement and NOx emission reduction of the segmented nozzle micro-combustor in thermophotovoltaic system

Abstract

In the context of international carbon neutrality, ammonia as a carbon-free energy has attracted extensive attention and research, and its renewability is the most prominent advantage. However, ammonia combustion is unstable, and harmful nitrogen oxides will be generated at the same time. In order to enhance the combustion stability of ammonia and control the emission of nitrogen oxides, the premixed combustion of NH3/H2/O2 in a segmented nozzle micro-combustor is studied in this paper. The mean wall temperature of segmented micro-combustor is 11.5 K higher than that of non-segmented micro combustor, and NO emission is reduced by 7.91 % at most. When mass fraction of hydrogen in the gas mixture XH2 increases from 10 % to 30 %, radiation efficiency increases by 13.5 %, but NO emission also increases. Considering that fuel-rich combustion can reduce NO emission, when hydrogen equivalence ratio ΦH2 = 1.0 and ammonia equivalence ratio ΦNH3 = 1.2, NO emission is reduced by 13.3 %, while radiation efficiency remains above 60 %. In addition, the radiation efficiency of the combustor increases by up to 4.15 % when the dimensionless length of segmented channel L6 is 7.5 mm and the dimensionless width of segmented channel D4 is 2.5 mm, and NO emission is reduced by 5.14 %.