Account for variations in the H2O to CO2 molar ratio when modelling gaseous radiatve heat transfer with the weighted-sum-of-grey-gases model

This work focuses on models suitable for taking into account the spectral properties of combustion gasesin computationally demanding applications, such as computational fluid dynamics. One such model,which is often applied in combustion modelling, is the weighted-sum-of-grey-gases (WSGG) model.The standard formulation of this model uses parameters fitted to a wide range of temperatures, but onlyfor specific ratios of H2O to CO2. Then, the model is limited to gases from fuels with a given compositionof hydrogen and carbon, unless several sets of fitted parameters are used. Here, the WSGG model is modifiedto account for various ratios of H2O to CO2 concentrations. The range of molar ratios covers both oxyfuelcombustion of coal, with dry- or wet flue gas recycling, as well as combustion of natural gas. The nongreyformulation of the modified WSGG model is tested by comparing predictions of the radiative sourceterm and wall fluxes in a gaseous domain between two infinite plates with predictions by a statisticalnarrow-band model. Two grey approximations are also included in the comparison, since such modelsare frequently used for calculation of gas radiation in comprehensive combustion computations. It isshown that the modified WSGG model significantly improves the estimation of the radiative source termcompared to the grey models, while the accuracy of wall fluxes is similar to that of the grey models orbetter