Prediction of Pollutant Emissions from Bluff-Body Stabilised Nonpremixed Flames

Nelu Munteanu,Shokri M Amzaini

doi:10.1155/2018/8924370

Abstract

Construction of a stable flame is one of the critical design requirements in developing practical combustion systems. Flames stabilised by a bluff-body are extensively used in certain types of combustors. The design promotes mixing of cold reactants and hot products on the flame surface to improve the flame stability. In this study, bluff-body stabilised methane-hydrogen flames are computed using the steady laminar flamelet combustion method in conjunction with the Reynolds-averaged Navier-Stokes (RANS) approach. These flames are known as Sandia jet flames and have different jet mean velocities. The turbulence is modelled using the standard k-ϵ model and the chemical kinetics are modelled using the GRI-mechanism with 325 chemical reactions and 53 species. The computed mean reactive scalars of interest are compared with the experimental measurements at different axial locations in the flame. The computed values are in reasonably good agreement with the experimental data. Although some underpredictions are observed mainly for NO and CO at downstream locations in the flame, these results are consistent with earlier reported studies using more complex combustion models. The reason for these discrepancies is that the flamelet model is not adequate to capture the finite-rate chemistry effects and shear turbulence specifically, for species with a slow time scale such as nitrogen oxides.

Highlights

Combustion of fossil fuels has a severe impact on the environment and humankind
R/D r/D for turbulent combustion modelling. These results are consistent with earlier reported studies using more complex combustion models. The reason for these discrepancies is that the flamelet model is not adequate to capture the finiterate chemistry effects and shear turbulence for species with a slow time scale such as nitrogen oxides
The overall aim of this study is to predict pollutants using the flamelet method from nonpremixed flames stabilised by a bluff-body and to compare the results with the experimental measurements, precisely, to predict pollutants with slow time scale such as carbon monoxide (CO) and NO

Summary

Introduction

Combustion of fossil fuels has a severe impact on the environment and humankind. Environmental and healthrelated issues such as global warming, acid rain, and ocean acidification will continue to be at the forefront for years to come [1, 2]. The primary products generated from combustion are carbon dioxide (CO2) and water (H2O) among other primary pollutants such as nitrogen oxides (NOx), sulphur oxides (SOx), carbon monoxide (CO), unburned hydrocarbons (UHC), and particle matter (PM). Nitrogen oxides and sulphur oxides react with water in the atmosphere and fall as acid rains causing a severe health and economic losses [2]. Replacing fossil fuels with another source of renewable energy especially for high energy density application such as the aviation sector is unlikely to be soon. Engineers and scientists are required to develop cleaner combustion systems that meet the environmental legislation demands and at the same time maintain high efficiency

Objectives

Results

Conclusion