Turbulent NO Reaction Time Model Study

In recent years,due to the public concern for environmental issues,the control of pollutant emissions has become more and more stringent.Therefore,simulation of turbulent combustion nitrogen oxide emissions has always been a hot issue.Nitrogen oxides are one of the main pollutants in combustion,and have a great harm to the environment.It is particularly important to develop a turbulent NO reaction model that can accurately predict NO emissions.The paper developed the new turbulent NO reaction time model on the one hand,validated the calculation accuracy of the model with multiple sets of flames,and on the other hand,the innovations in the implementation method are carried out,using the method of NO reaction rate database substantially improves the calculation speed.The study found that the model parameter C value in the turbulent NO reaction time model is not a constant,changing with the fuel type.The theoretical analysis shows that the C value of the fuel with fast mixing and fast combustion is small;the paper explores the mixing characteristics of the model parameter C and fuel,ie,the mass diffusion coefficient D,the combustion characteristics of the fuel,ie,the flame speed S,and gives the C and D The relationship of S,thus closing the turbulent NO reaction time model.Non-premixed jet flames with different fuels,different nozzle speeds,and different nozzle diameters were used to verify the accuracy of the turbulent NO reaction time model.The simulated NO concentration field agrees well with the measured NO concentration field wich confirms the simulation accuracy of the model.In terms of model implementation,the use of a look-up table similar to the PPDF flamelet model can significantly improve computational efficiency.The paper gives a detailed study of the relationship among turbulent NO reaction rate,mixing fraction,mixed fractional variance,and flame temperature difference.On this basis,the method of establishing the look-up table and the influence of the mixture fraction and mixture fraction variance segmentation on the calculation accuracy are studied.In the CFD calculation process,the corresponding NO reaction rate can be quickly retrieved and output from the table according to the temperature,mixture fraction,and mixture fraction variance of the local cell.The simulation speed can be improved by two orders of magnitude compared to the conventional integration method.