In recent years, solving the problems of high efficiency and low emission of gas turbines has become the focus of academia and industry. NOx is most difficult to control and fuel/air premixing uniformity is one of main factors affecting NOx generation in gas turbine combustor.

Premixing non-uniformity results in lean and rich zones in the combustion chamber, with different equivalence ratio distribution. Unmixedness combustion will lead to temperature non-uniformity, resulting in local hot spots and deterioration of emission performance. Therefore, to achieve low emissions of pollutants, it is necessary to achieve a uniform distribution of fuel and air. Vortex structures, geometric parameters (nozzles quantity, nozzle diameter, injection hole diameter and angle), premixing length, summarized the relationship between the turbulence, the fuel-air ratio and other factors were investigated to predict the mixing non-uniformity of the burner. While significant progress has been made in this field previously, fuel injection position is rarely discussed. The present work aims to bridge this gap and investigates the effects of fuel injection on the windward and leeward sides on fuel concentration distribution and premixing non-uniformity.

The calculation model is a typical radial swirler structure. The simplified calculation domain mainly includes: an air inlet, a methane fuel inlet and an outlet of the vane channel.  Pure methane is injected through a small orifice of diameter D =2 mm at the bottom wall. The mainstream direction is X, whereas the vertical and transverse directions are denoted by Y=12D and Z=13.25D, respectively. The boundary conditions are imposed as follows: air mass flow rate is 0.325kg/s, the pressure is 6bar, the temperature is 673K.The mass flow rate of methane fuel is 0.0125kg/s at 298K. After refining the fuel outlet and the wall, the final grid number is 1.3 million, and the minimum grid size of the fuel-air premixing domain area is 0.2 mm. The large eddy simulation (LES) is used to simulate the premixing process when the momentum ratios are 2.5 and 10. The fuel injection locate on the windward side of 3D or 9D and the leeward side of 6D from the inlet of vane channel respectively. When the fuel is injected from the windward side, recirculation region forms between the main and the jet flow. From the leeward side, the momentum ratio J=10, the fuel jet penetrates the recirculation region and divides it into two parts. When J=2.5, the jet barely penetrates the strong shear layer in the recirculation. The influence of momentum ratio on fuel distribution mainly comes from the difference of turbulent kinetic energy in shear layer at the initial stage of jet development. The fuel injection position on the leeward side has a minimum premixing non-uniformity of 60.27%.


Investigation on Mixing Characteristics of Methane Fuel in Low Emission Combustor

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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