Three-feed combustion systems in which fuel gas, oxygen, and diluent (CO 2) are issued into a combustor are key components to realize an oxy-fuel type gas turbine in a zero-emission plant. Yet, simulations of such systems using mixture fraction-based models are difficult, since multiple mixture fractions are required to describe the system. In this study, large-eddy simulations (LES) with different formulations of non-adiabatic quasi-two-dimensional flamelet (Q2DF) models were performed on a three-feed non-premixed swirl burner. The Q2DF models are derived based on the treatments regarding the third stream; the diluent stream is put in the oxidizer side and/or in the fuel side, giving rise to three models called Q2DF1, Q2DF2, and Q2DF3 models. Results show that the three Q2DF models can predict the results of the experiment well; however, the deviations could not be overlooked. The analysis shows that the differences between the three models become apparent as the mixture fraction of the inactive third stream (Z3) evolves very large, otherwise, the three models give almost the same results. It is confirmed that for a pure inactive diluent third stream when Z3 is quite large, its scalar dissipation rate (χ3) plays an important role and the mixing way (premix or non-premix) of the third stream with other streams should be taken into account, however, the influence of χ3 on the performance of the three models is quite limited in the condition of a smaller Z3, for instance, less than 0.8, and thus the mixing way of the third stream in the three models will not affect the system.
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