Large-Eddy Simulation and analysis of a sooting lifted turbulent jet flame

Abstract

A Large-Eddy Simulation (LES) is performed for a sooting, lifted, well characterized, non-premixed, turbulent jet flame. In order to accurately predict the lifted flame, a finite-rate chemistry model is used, which requires no assumptions concerning the combustion regime. Furthermore, feedback effects between all gaseous species and soot are captured inherently, by simultaneously solving the thermo-chemical state equations in a fully coupled way. Soot evolution is described by a sectional model, coupled to the gas phase by another sectional model for polycyclic aromatic hydrocarbons. The entire approach has already been comprehensively validated in premixed and non-premixed flames. The first aim of the present work is to extend the validation for LES. It is found that the simulated lift-off height and flame structure agree well with the measurements. A good prediction of soot evolution is achieved, which enables detailed investigations of soot formation and oxidation. Consequently, the second aim of the paper is to analyze the soot evolution by means of correlated statistics. It will be shown that the statistics depend on axial distance over the entire flame and on radial distance close to the base of the flame. These trends in temperature - soot volume fraction space can be attributed to the changing dominance of growth and oxidation of soot. Soot evolution is strongly affected by an oxygen leakage into the core of the flame caused by the flame lift-off. A combustion regime analysis reveals that the leakage leads to soot growth under premixed conditions, which causes the dependency of the correlated statistics on radial distance.