Occurrence of NO-reburning in MILD combustion evidenced via chemical kinetic modeling

A numerical study of the diluted oxidation of CH4 was performed to investigate the potential importance of the NO-reburning mechanism in conditions relevant to MILD combustion. It turns out that the NO–HCN conversion reactions are particularly active before auto-ignition. During this period, the nitrogen contained initially in NO is stored in HCN and NH3. The extent of this phenomenon depends on the equivalence ratio and on the unmixedness. Subsequently, nitrogen is restored in its original NO form. In the post-ignition period, thermal and N2O pathway to NO grow in importance. Therefore, this study revealed a sequential character of the nitrogen chemistry. Although these effects have both chemical and thermal origin, a transient NO-reburning mechanism was also evidenced via modeling at constant temperature demonstrating it is mainly related to the fuel-ignition chemistry.