Detailed radiation modeling of a partial-oxidation flame

Abstract

A numerical study of a laminar methane partial oxidation flame (POX-flame) is presented to investigate different radiation modeling approaches. A laminar reference flame for large-scale gasification, which was previously investigated both experimentally and numerically by Stelzner et al. [1], is particularly suitable for such a study because of the distinct temperatures and radiating species concentrations. A second study of a well-known methane–air flame [2] is also included. The fully resolved and coupled solution of the reactive flows was achieved with an OpenFOAM® based solver using detailed approaches for diffusion and chemistry. Different combinations for solving the radiative transfer equation (RTE) and the evaluation of the radiative properties were implemented and investigated. The discrete ordinate method (DOM), the modified differential approximation (MDA), the P1 model and the optically thin model (OTM) were used for the solution of the RTE, whereas the spectral line-based weighted sum of gray gases model (SLW), the weighted sum of gray gases model (WSGG) and gray absorption (RADCAL) was used for the evaluation of the radiative properties.In both flame setups gaseous radiation was found to be important and needs to be considered. In the POX-flame radiative absorption has a significant impact on the radiative source terms and significant non-gray gas effects were found. Simple radiation modeling approaches, typical for combustion regimes, namely the OTM with RADCAL, were not able to capture these effects. More sophisticated radiation models were required. The MDA with both the SLW and the WSGG provided reasonable results at still acceptable computational costs. In contrast, in the methane–air flame, the simple radiation models achieved a reasonable agreement with the temperature measurements.Finally, particular combinations of RTE solution methods and property models are recommended for the different flame setups based on the differences in the temperature and the radiating species concentrations in the different flame regions.