A Compact WSGG Formulation to Account for Inhomogeneity of H₂O–CO₂ Mixtures in Combustion Systems

An alternative weighted-sum-of-gray-gases (WSGG) model is proposed with a single set of constant pressure-based absorption coefficients that accounts for different mole fraction ratios (MRs) of H₂O–CO₂. The method requires no further interpolation, which in turn brings not only less uncertainty into the model but also simplifies its use. The hitemp2010 spectral database along with the line-by-line (LBL) integration is employed to generate a set of accurate total emissivities from which the WSGG coefficients are fitted. The fitting procedure employs a novel formulation to account for the MR dependence, leading to a more compact set of WSGG correlations when compared to the alternatives available in the literature. The new formulation takes advantage of the weak interdependence of temperature and molar fraction ratio in the weight factors and therefore separates their effects by two independent correlations. As oxy-fired combustion usually occurs in two distinct scenarios, dry- and wet-flue gas recirculation (FGR), the paper also proposes two other sets of coefficients intended to support the MR ranges corresponding to these specific conditions. Comparisons made against the benchmark LBL integration and other WSGG models, for one- and three-dimensional calculations, show the satisfactory level of accuracy of the proposed sets of correlations. In particular, the three-dimensional test case illustrates that the new model is also applicable to conditions observed in air–fuel combustion.