NOx emission reduction in ammonia-powered micro-combustors by partially inserting porous medium under fuel-rich condition

Based on the fact that NOx generation will be inhibited under the condition of high equivalence ratio, the micro-combustors with double-rib structure partially inserted with porous medium (PM) are selected to examine the NOx emission performances in fuel-rich combustion of ammonia. The effects of: 1) the inlet velocity, 2) the porous material and 3) the porosity are evaluated on NOx emission reduction. Besides, the kinetic rate of key reactions contributing NOx production are analyzed. It is found that, the PM can effectively reduce NO generation and emission under a larger inlet velocity. With the increased thermal conductivity of porous material, the emission of NO is shown to be decreased by 99.98% from 2.70 × 104 ppm to 5.17 ppm, while N2O emission is increased by 10000% from 24.8 ppm to 2.52 × 103 ppm. In addition, the porous material with a higher thermal conductivity is beneficial to improving the uniformity of the combustor outer wall temperature. When the PM’s porosity is increased from 0.5 to 0.9, NO emission is increased by 4120% from 3.53 × 102 ppm to 1.49 × 104 ppm, while N2O emission is decreased by 71.5% from 3.29 × 103 ppm to 9.38 × 102 ppm. The present work reveals that the NOx emission can be effectively reduced, while increasing the thermal performance of micro-combustors by adopting appropriate porous medium.