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User function approach in modelling of nitrogen oxides in commercial CFD code FIRE

Dramatic improvements in computer hardware performance and advance in a science of NOx chemical reaction mechanisms have made modelling of NOx formation a valuable tool that can be used to investigate and improve understanding of the NOx formation in practical combustion systems. This paper presents a review of modelling work performed at Power Engineering Department (PED) regarding the NOx formation in combustion systems. The NOx prediction model has been implemented through the user functions in commercial CFD code FIRETM. This model is based on three different formation mechanisms: thermal, prompt and fuel NO, which are outlined. The effects of the turbulent fluctuations on the reaction rates when predicting NO concentrations are modelled by using the presumed Probability Density Function (PDF) approach. The model has been applied to the turbulent non-premixed jet diffusion flame (Sandia flame D) and the predicted NO mass fractions are compared to results obtained by a Steady Laminar Flamelet Model (SLFM) and to experimental data.

NOx; Sandia flame D; user functions; AVL FIRE

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