Comparative study on homogeneous NO-reburning in flameless and swirl flame combustion.

NO-reburning technology can effectively decrease NO x emissions during combustion. Despite extensive studies have been conducted on NO reburning under traditional combustion, homogeneous NO-reburning characteristics have not been systematically examined in flameless combustion (FLC). This study performs a systematic comparative investigation of homogeneous NO-reburning for the first time via experiments and simulations in a 20-kW furnace. The influences of combustion mode, air-preheating temperature (T a), and equivalence ratio (Φ) are studied in detail. The experimental results show that FLC can improve NO-reduction efficiency by more than 35% compared to swirl flame combustion (SFC). Moreover, the results also show that reducing T a from 723 K to 573 K can enhance NO-reburning during FLC, while the NO-reburning is insensitive to Φ in the range of 0.65–0.89. Furthermore, a detailed numerical simulation that couples the eddy-dissipation concept model and a well-verified skeletal mechanism for NO-reburning is validated and performed, to further reveal the reduction pathways of NO. By combining flameless combustion with NO-reburning, this study confirms the preponderance of flameless combustion under low-temperature air conditions (T a ≤ 573 K) for considerable NO reduction by reburning. The results offer novel fundamental insights into the homogeneous NO-reburning characteristics. • Homogeneous NO-reburning in flameless combustion is studied for the first time. • Flameless combustion can improve the NO reduction efficiency by more than 35%. • Reducing the air preheat-temperature enhances NO-reburning of flameless combustion. • Reaction pathways of NO reduction for swirl and flameless combustion are revealed. [ABSTRACT FROM AUTHOR]