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 H2 mass fraction (ranging from 10 % to 100 %) on the structure of the combustion zone and the emission rules of NOx 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 H2 ratio increases. Increasing H2 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 YO2 = 6 % is only 69 % compared to that at YO2 = 3 %. Higher YO2 has a more significant impact on the relative increment of NO emissions. The NNH route consistently predominates, and increasing H2 ratio amplifies the production of thermal NOx and weakens the NO-reburning mechanism.