Evaluation of NOx emissions characteristics in a CO2-Free micro-power system by implementing a perforated plate

Abstract

Ammonia (NH3), as a carbon-free fuel with a high hydrogen content, has been considered as a promising candidate to be applied for transportation, propulsion, and power generation sectors. However, due to the presence of nitrogen atoms, direct combustion of NH3 features a high NOx emission, which could hinder its wide application. Thus it is important to mitigate or minimize these emissions. For this, a three-dimensional (3D) computational model is developed by considering a detailed chemical-kinetic mechanism. The effects of 1) the perforated plate porosity σ, 2) the perforated plate thickness t1, 3) the perforated orifice off-z axis distance d, and 4) inlet thermodynamic pressure Pin are evaluated. Numerical results indicate that σ plays an important role in determining the NO formation. This is the combined effect of the strong species preferential diffusion and low flame temperature within the recirculation zone. Furthermore, varying t1 is shown to affect the NO generation rate due to the varied recirculation zone. Although the flow field is affected by d to some degree, it has a negligible effect on the NO generation. Finally, the emission behavior is found to have a strong dependence on Pin. Approximately 50% reduction of NO emission is achieved as the inlet pressure is varied from 1 to 3 atm. The present work opens up an applicable way to enable low-NOx ammonia-fueled power systems, and some of the findings could be applied for hydrocarbon systems design.