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

초록

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 similar to 40 %) expanded the flame stability range at equivalence ratio phi >= 0.76, preventing flashbacks and ensuring stable combustion, particularly at low flow rates. For phi < 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.

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