Non-premixed ammonia combustion in porous media to promote thermal cracking of NH3: A low-emission burner concept

This study investigates spatially-distributed, non-premixed ammonia/air combustion in porous media burners (PMBs) as a strategy to mitigate NO x emissions and improve flame stability, two key challenges for ammonia as a carbon-free fuel. To the best of our knowledge, this is the first experimental demonstration of this approach. Experiments are conducted over global equivalence ratios ( 0 . 7 ≤ Φ g ≤ 1 . 3 ) and thermal loads ( 0 . 25 ≤ P ≤ 0 . 76 MW m −2 ). Temperatures inside the porous matrix and global emissions of NO x , NH 3 , N 2 O, and H 2 are measured and compared between non-premixed and premixed operation. Results show that NH 3 /air flames are stably anchored in high-porosity foams (15 PPI) without external preheating. N 2 O emissions remain below 40 ppmv (normalized to 15 % O 2 ), and non-premixed operation reduces NO x by one order of magnitude compared to premixed operation, while maintaining low NH 3 slip. Low NH 3 and NO x emissions occur only in non-premixed operation, with the most favorable regimes under globally fuel-lean conditions. In the lowest non-premixed case (31 ppmv NH 3 , 111 ppmv NO x , P = 0 . 25 MW m −2 , Φ g = 0 . 8 ), NO x is reduced by 90 % compared to premixed operation (2 ppmv NH 3 , 1148 ppmv NO x ) at identical conditions. Complementary volume-averaged simulations (VAS) reproduce these trends and indicate that H 2 formed in NH 3 -rich zones promotes NO x reduction. These findings demonstrate that spatially-distributed, non-premixed combustion in PMBs enables stable, low-emission ammonia combustion and may further reduce NH 3 slip through improved downstream mixing and residence time control.