A 3-step global reaction mechanism for a methane-air mixture is optimized against a detailed reference mechanism for perfectly stirred reactor (PSR) calculations. The global mechanism consists of three reactions corresponding to the fuel oxidation into CO and H_2O, and the CO - CO_2 equilibrium reaction. To ensure good agreement for rich conditions, correction functions that are dependent on the local equivalence ratio are introduced into the global mechanism. In a comparison of the optimized 3-step global reaction mechanism with the reference detailed reaction mechanism, GRI Mech 3.0, the results show that the gas temperature and emissions are reasonably well predicted for lean and rich conditions. The optimized 3-step global reaction scheme is adapted in the Computational Fluid Dynamics (CFD) analysis of a swirl-stabilized syngas burner, designed by Siemens Industrial Turbomachinery (SIT syngas burner) for gas turbines. The burner consists of a main premixed flame, a partially premixed pilot flame and a confined rich premixed lean flame which produces radicals that support both the pilot and the main flame. The CFD results are compared with experimental results obtained in an atmospheric version of the burner test rig at Lund University. Both steady-state Reynolds Averaged Navier Stokes (RANS) and hybrid Unsteady RANS/Large Eddy Simulation (URANS/LES) results were computed. The CFD results with the 3-step global reaction mechanism show good agreement with the experimental data on gas analysis and flame visualization, while the Westbrook Dryer 2-step (WD2) [2] and Meredith et al. [3] 3-step global reaction mechanisms failed in their predictions of the CO emissions downstream in the burner.
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