Investigations on NOx emissions from a turbulent non-premixed bluff body stabilized flame

Abstract

In this thesis work, we strive to describe and apply the modelling methodology for simulating a turbulent jet diffusion flame stabilized behind a bluff body by applying flamelet generated manifold (FGM) model and steady diffusion flamelet model for predicting the pollutant emissions from the flame. The flame under consideration is a CH4/H2 (1:1) bluff-body stabilized flame known as HM1. The numerical calculations of the flow physics has been completed by using a commercial CFD code namely Ansys Fluent 19-R3, where the computational domain is assumed to be two dimensional and axis-symmetric in nature due to the cylindrical symmetry of the burner with an structured grid for meshing. The turbulence is modelled by using a two equation Reynolds averaged Navier Stokes model, namely the standard k – ϵ model with a modification in the Cϵ1 from 1.44 to 1.60. The chemical mechanism used in the project was the GRI 2.11 mechanism developed by the Gas Research Institute, USA. Next, postprocessing tools like the Reactor Network Model (RNM) and Ansys NOx post-processor were used as an alternative, possibly a better way to obtain the NO species
concentrations. The acquired results from the simulation are thoroughly analysed and were compared to earlier results on the HM1 flame in the literature and validated by using the experimental data documented by the University of Sydney in collaboration with the TNF Workshop. The results showed that the steady diffusion flamelet performed better than the FGM model and was in acceptable agreement with the experimental data, although some under-prediction and overpredictions were reported for NO and OH species. In regard with the post-processing tools the RNM model performed better than the Ansys NOx post processor.