Study On NO_x Generation Characteristics Of Flameless Combustion Based On Dynamic Adaptive Chemistry

Mild combustion can reduce NO_x emissions and is a new generation of combustion technology that has received widespread attention in recent years.Due to the limitation of reaction mechanism and computing resources,the current numerical simulation research on NO_x generation in flameless combustion basically focuses on gas phase fuel,and there is less research on flameless combustion of pulverized coal.In this paper,in-situ adaptive tabulation and dynamic adaptive mechanism simplification methods are combined,and the self-developed detailed reaction mechanism including fuel nitrogen generation is used to study the characteristics of the NO generation process of pulverized coal flameless combustion.First,according to the simulation results of gas phase flameless combustion,the dynamic adaptive chemistry（DAC）,the in-situ adaptive tabulation method（ISAT）and the coupling of the two methods（ISAT-DAC）are evaluated in terms of calculation accuracy and calculation efficiency.The performance when simulating flameless combustion.From the perspective of calculation accuracy,the dynamic adaptive simplification method can accurately simulate flameless combustion.It shows that the ISAT-DAC coupling method can give full play to the advantages of the two simplified methods.The threshold of DAC is changed,and the best simplified threshold for simulating flameless combustion is comprehensively determined according to the relative error and calculation efficiency obtained by simulation.The influence of the main NO_x generation path of gas-phase flameless combustion and the simplified method on the analysis of NO_x conversion path is further analyzed.Then,based on the in-situ adaptive tabulation method and the dynamic adaptive mechanism simplification method,the detailed reaction mechanism including the fuel nitrogen conversion path was used to numerically simulate the NO_x generation characteristics of the International Flame Research Foundation（IFRF）pulverized coal flameless combustion test,study the fuel nitrogen migration characteristics of pulverized coal flameless combustion under different working conditions,and obtain important intermediate components in the NO generation process of pulverized coal flameless combustion.Studies have shown that NO in flameless combustion of pulverized coal is mainly formed by intermediates of NH₃,HCN and N₂O.HCN mainly generates NO through HNCO/CN and NCO,and NH₃ mainly generates NO through HNO.CH₃CN generates NO through NCO,so it is also an important intermediate component of NO.The N₂O pathway is mainly involved in the reduction reaction.In the IFRF mild combustion of pulverized coal and oxygen conditions,the more important components that generate NO are CH₃CN,NCO and HNO.Under oxygen conditions,the reaction path of N₂ to NO is suppressed,and the reaction rate related to the reduction of N₂O to N₂ is increased.