Effects of radiation modeling on non-premixed sooting flames simulations under oxyfuel conditions

Abstract

Radiative heat modeling has a central role for the simulation of soot formation in flames. Radiation heat transfer, gas-phase chemistry and soot formation are strongly coupled and highly dependent on temperature. Thus, it is of primary importance that simplified radiative models are able to reproduce detailed simulations at conditions found in flames of interest. In this work, the capabilities of the superposition WSGG radiation model is compared to the LBL spectral integration for a set of laminar non-premixed counterflow flames of ethylene burning with oxygen-rich oxidizer. The numerical solutions for both thermal radiation approaches are fully coupled with detailed chemistry and a discrete sectional model for soot formation. The role of thermal radiation and the importance of radiation absorption on soot formation were explored through systematic replacement of N2 by CO2 on either the fuel or on the oxidizer. In addition, the validity of the simplified optically thin approximation for modeling such flames was also discussed. The spectral superposition WSGG model is able to accurately describe general flame structure and soot predictions respective to the LBL integration for both the reference flame and for the cases of CO2 addition in the fuel and in the oxidizer mixtures. For the CO2 addition flames, the WSGG model tends to overestimate the radiation emission on high temperature regions and to overestimate the radiation absorption on low temperatures towards the reactant with CO2 addition. However, these discrepancies were not sufficient to significantly influence the flame structure. Some non-negligible discrepancies are observed only at very small strain rates. Finally, the evaluation of the soot spectral radiation coefficient (Cκ,s) reveled an important influence on the soot volume volume fraction for low levels of CO2 addition.