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

Abstract

To investigate the turbulence combustion characteristics of NH 3 /H 2 /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 NH 3 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, NH 3 + M ⇔ NH 2 + H + M, inhibits NH 3 consumption and the reactions R20, NH 3 + O ⇔ NH 2 + OH, and R21, NH 3 + OH ⇔ NH 2 + H 2 O, promote NH 3 consumption, while R19, NH 3 + H ⇔ NH 2 + H 2 , initially inhibits and later promotes NH 3 consumption, but primarily plays an inhibitory role. Furthermore, reactions R4, NH + H ⇔ N + H 2 , R11, NH 2 + H ⇔ NH + H 2 , and R28, HNO + H ⇔ NO + H 2 , promote the H 2 formation, and R19, NH 3 + H ⇔ NH 2 + H 2 , inhibits the H 2 formation. As for the emission characteristics, R16, NH 2 + NO ⇔ N 2 + H 2 O, and R28, HNO + H ⇔ NO + H 2 , inhibit and promote NO generation in the upstream region of the combustor, respectively, while R36, NO 2 + H ⇔ NO + OH, promotes NO generation in the whole area.