Study on Unsteady NOx Formation Characteristics in Diffusion Flame and Verification of Combination Method Predicting NOx Emission of Turbulent Flame (Extension to Diluted Fuel and Preheated Oxidizer Conditions)

Abstract

In order to predict accurately the NOx emission of turbulent diffusion flame, we proposed the combination method based on the laminar flamelet model. In this method, the detailed kinetics calculation is separated from the turbulent flow calculation, and then they are recombined in terms of recombination parameters. We examined whether this method could be extended to diluted fuel and preheated oxidizer conditions. With the aim to find out the recombination parameters and to prove the validity of them for these conditions, we carried out the numerical calculation for the unsteady combustion characteristics of counterflow diffusion flame, in which the spout velocities of counterflow varied in a cyclic. The obtained results are as follows : It is necessary for extending this method to change the definition of the mixture fraction Z in consideration of fuel dilution. The production/consumption rates of major stable species are mostly determined by the scalar dissipation rate at flame surface SDRq, and the production rates of intermediate products and nitric oxides are mostly determined by SDRq and the maximum flame temperature Tmax. Consequently, it is verified that SDRq and Tmax are appropriate as the recombination parameters for diluted fuel and preheated oxidizer conditions.