Experimental and numerical study of rich inverse diffusion flame structure

An experimental and numerical investigation of a laminar confined and inverse diffusion flame (IDF) with pure oxygen as oxidizer considering global stoichiometry of partial oxidation processes is presented. The present burner setup allows studying the structure of the high temperature oxidation zone and the subsequent reforming region in a simplified geometry considering typical operating conditions as found in large scale gasifiers for the production of synthesis gas out of different hydrocarbon feedstocks. The use of pure O-2 as oxidizer leads to extremely high temperatures and higher concentrations of radiating species, i.e. H2O and CO2, compared to a partial oxidation process with air as oxidizer. Hence the flame structure is strongly influenced by radiation and diffusion effects. The scope of this paper is to determine how the Soret effect and the radiative heat transfer at high temperatures in combination with low strain rates in the downstream region influences the flame structure. In this respect the radiation model and potential self-absorption of radiating species become of major importance for the numerical predictions. In the experimental part the flame structure was studied with a planar OH-laser-induced fluorescence (LIF) setup, while the temperature was determined by a two-line LIF approach using the rotational temperature of the OH radical. The correlation between OH concentration and temperature was used as an indicator for comparison purposes. In the numerical part two-dimensional laminar CFD calculations with detailed chemistry and transport were performed and the numerical results show the importance of the Soret effect. The optically thin radiation model yields good agreement with the experiments at high strain rates close to the nozzle, but the radiation model underpredicts the temperature further downstream at low strain rates with potentially significant self-absorption of the radiating species. (C) 2012 The Combustion Institute. Published by Elsevier Inc. All rights reserved.