Numerical Investigation on NH3/H2/Air Combustion Flow in a Multiple Direct-Injection Combustor

To investigate the turbulence combustion characteristics of NH3/H2/Air in a multiple direct-injection combustor, the effects of equivalence ratio and hydrogen mixing ratio on the mixing characteristics of fuel–air in the mixing-nozzles as well as the flame and emission characteristics in the combustor are analyzed numerically. The results show that the spatial mixing deficiency of fuel–air mixture at the mixing-nozzle outlet is below 1% under all circumstances, which indicates that the mixing-nozzle exhibits satisfactory mixing performance and is capable of achieving the premixed combustion. Furthermore, the intensity of gas turbulence at the mixing-nozzle outlet (inlet of the combustor) is primarily affected by the gas flow within the fuel collision zone. Regarding the flame characteristics, the larger equivalence ratio increases the NH3 concentration (reducing combustion rate), and the larger hydrogen mixing ratio increases the gas turbulence intensity at the mixing-nozzle outlet (increasing gas flow velocity), which disrupts the stabilized combustion. Moreover, the reaction R18, NH3 + M ⇔ NH2 + H + M, inhibits NH3 consumption and the reactions R20, NH3 + O ⇔ NH2 + OH, and R21, NH3 + OH ⇔ NH2 + H2O, promote NH3 consumption, while R19, NH3 + H ⇔ NH2 + H2, initially inhibits and later promotes NH3 consumption, but primarily plays an inhibitory role. Furthermore, reactions R4, NH + H ⇔ N + H2, R11, NH2 + H ⇔ NH + H2, and R28, HNO + H ⇔ NO + H2, promote the H2 formation, and R19, NH3 + H ⇔ NH2 + H2, inhibits the H2 formation. As for the emission characteristics, R16, NH2 + NO ⇔ N2 + H2O, and R28, HNO + H ⇔ NO + H2, inhibit and promote NO generation in the upstream region of the combustor, respectively, while R36, NO2 + H ⇔ NO + OH, promotes NO generation in the whole area.