Effects of H2 addition on the characteristics of the reaction zone and NOx mechanisms in MILD combustion of H2-rich fuels.

Hydrogen fuel has significant potential for various applications under MILD combustion conditions. This study investigates the impact of H 2 mass fraction (ranging from 10 % to 100 %) on the structure of the combustion zone and the emission rules of NO x in the JHC burner utilizing the detailed mechanism GRI-Mech 2.11. A contraction of the reaction zone and a decrease in the ignition delay is observed when the H 2 ratio increases. Increasing H 2 concentration results in the gradual loss of MILD combustion characteristics in the reaction area, and the downstream region gradually transforms to High Temperature Combustion. The MILD reaction volume at Y O2 = 6 % is only 69 % compared to that at Y O2 = 3 %. Higher Y O2 has a more significant impact on the relative increment of NO emissions. The NNH route consistently predominates, and increasing H 2 ratio amplifies the production of thermal NO x and weakens the NO-reburning mechanism. • Transition of reaction area from MILD to HTC is observed in pure hydrogen cases. • The boundary of pure hydrogen fuel under MILD combustion conditions is depicted. • Contributions of different NO formation routes under MILD conditions are conducted. • Trend of NO generation pathways with changing hydrogen ratio is revealed. [ABSTRACT FROM AUTHOR]