Simultaneous emission reduction and energy conversion enhancement of ammonia/hydrogen combustion by partially inserting porous media

This work numerically evaluates the feasibility of porous media in taming pollutant formation and enhancing energy conversion performance in ammonia/hydrogen combustion systems. Effects of porosity, length, and materials on micro-combustor with a partial insertion of porous media are extensively examined with detailed chemistry. It is confirmed that partially inserting porous media significantly reduces NO emissions but can also result in an increase in N2O emissions. The resulting lowest NOx mole fraction in the presence of porous media is 0.002770, accounting for a 72.5% percentage drop compared to the traditional combustor. Such emission mitigation is mainly due to the reduced OH radical formation as the free flame exists in the presence of porous media. This is also accompanied by a 140.3 K increase in the averaged wall temperature, more uniform temperature distributions, and higher radiation efficiencies. Further, a smaller porosity contributes to low NOx emissions and temperature standard deviation due to enhanced heat recirculation but plays a negligible role in the averaged temperature. Meanwhile, extending porous media length is effective in promoting thermal performance and removal efficiency. Finally, applying SiC as the porous media material contributes to the lowest pollutant formation and highest temperature uniformity, but reduces the averaged temperature by 20.7 K, mostly attributed to the intensified heat and mass transfer arising from high thermal conductivity. Generally, developing porous media-assisted combustion is an effective means to reduce NOx emissions and enhance combustion performance.