Investigation on NO emissions and thermal performance of an ammonia/methane-fuelled micro-combustor
He Zhao, Dan Zhao, Xu Dong
Abstract
To enhance ammonia's flammability, blending methane with ammonia is a viable strategy to improve the laminar burning velocity of ammonia combustion. We conducted three-dimensional numerical simulations to investigate the thermal performance, the 2nd thermodynamic law efficiency, and NO emissions of a micro-combustor fuelled by ammonia/methane. Three key parameters are identified and examined. They include: 1) the inlet volume flow rate, 2) the CH4 mole blended ratio, 3) the N2 dilution rate. It is found that increasing the inlet volume rate give rise to an increase of the combustor outer wall temperature, and so the thermodynamic second-law efficiency, but a reduction of NO emissions. For example, when the inlet volume flow rate is set to 14.4 mL/s, the wall temperature and 2nd law efficiency are increased by 36 % and 21 % respectively, but the NO emission is reduced by 15 %, in comparison with those in the presence of 7.2 mL/s inlet flow. While an increase of the CH4 blended ratio (molar fraction) is shown to have limited impact on the thermal performances. This variation of such blended ratio is found to be associated with a notable 22 % reduction of NO emissions. Additionally, injecting N2 as a dilution gas is shown to be not beneficial to the thermal performance. However, NO emissions are reduced. When the N2 dilution rate is set to 0.6, the wall temperature is found to be reduced by 173 K. However, 47 % more NO reduction is observed in comparison with those in the presence of the N_2 dilution rate being set to 0.3.