Influence of wall heat loss on emission characteristics of NH₃/CH₄/air premixed flame in a model gas-turbine combustor

This study investigated the effect of wall heat loss on the flame stability and emission characteristics of NH₃/CH₄/air premixed flames in a model gas-turbine combustor. Increasing ammonia mole fraction (10 ∼ 40 %) expanded the flame stability range at equivalence ratio ϕ ≥ 0.76, preventing flashbacks and ensuring stable combustion, particularly at low flow rates. For ϕ < 0.76, the stable region was narrower, approaching the blow-off limit. These stable regions exhibited more significant fluctuations at swirl number S = 0.78 than at S = 0.45, and lift-off occurred earlier at the dump plane. Detailed analyses revealed the impact of heat loss on flame behavior and emissions. Notably, local extinction phenomena significantly influenced flame dynamics, resulting in a pronounced increase in the N₂O concentration while NO decreased. The chemical reactions responsible for NO and N₂O production are highly sensitive to heat loss, particularly under unsteady flame conditions. A chemical reactor network model (CRN) was developed to predict and analyze emission characteristics. Although the model qualitatively captured the measured emission trends of NO and N₂O, it exhibited significant discrepancies, particularly in predicting N₂O, and NO was overestimated. This is induced by the incompetence of the model, which does not account for local extinction phenomena, and the limitations of the chemical mechanism used in this study.