lunduniversity.lu.se

Division of Fluid Mechanics

Faculty of Engineering, LTH

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Optimum fuel flexibility – CFD modelling

Michael Bertsch, Senbin Yu, Robert Szász, Xue-Song Bai

Background

It is desired that industrial gas turbines can operate on a wide range of fuels. However, increasing the fuel-flexibility of a gas turbine affects the stability of the combustion process. It is therefore of essential importance to study the limits of stable operation for different fuel blends and to understand the phenomena governing combustion stability.

A swirl burner was designed and manufactured as part of the fuel flexibility project in the framework of the Centre for Combustion Science and Technology (CECOST) research project [1]. The setup consists of an upstream section with an axial swirler, a rectangular combustion chamber, and a cylindrical mixing section in between. These components constitute the swirl burner and are referred to as the Cecost burner. A schematic representation of the setup is shown in Figure 1. The Cecost burner was developed in collaboration with the Division of Combustion Physics, Lund University. Experimental investigations were performed to characterise the CECOST burner when operated with hydrogen-enriched methane and syngas as fuel. Imaging of OH chemiluminescence, OH/CH2O planar laser-induced fluorescence, and particle image velocimetry (PIV) were used to study the flame-flow interaction. The boundaries of the flashback and the blow-off regimes were determined experimentally.

Objectives

The objective of the CFD modelling project is to extend the existing model from the combustion of natural gas to more complex fuel mixtures. However, before aiming at increasing the fuel flexibility, the current model will be further validated against experimental data. Furthermore, a sensitivity analysis will be performed with respect to burner geometry, flow speed and equivalence ratio.

Recent Results

Development of flamelet generated manifold (FGM) model was made to consider the local flow strain effect. Figure 2 shows a comparison of experimental and combustion simulation results for the instantaneous OH distribution at the mid-plane of the combustor for Re=15000 and equivalence ratio φ=0.56. The OH distribution predicted by the FGM model shows two possible structures of the flames, a M-shaped structure and a V-shaped structure. The FGM model without strain rate effect predicts an M-shaped flame front, where an OH layer is clearly attached to the outer recirculation zone around the corner of the combustion chamber. In the OH-PLIF image, this reaction front is absent due to the high strain rate in the shear layer of the outer RZ. With strain rate effect taken into account in the FGM model, the model can replicate the V-shaped reaction flame structure observed in the experiments.

Recent Publications

  1. E. Hodzic: Analysis of flow dynamics and flame stabilization in gas turbine combustors. PhD thesis, Lund University, 2016.
  2. E. Hodzic, S. Yu, A. Subash, Xin Liu, Xiao Liu, R.-Z. Szász, X.-S. Bai., Z. Li, and M. Aldén: Numerical and Experimental Investigation of the CeCOST Swirl Burner. ASME Turbo Expo, Volume 4A: Combustion, Fuels, and Emissions, GT2018-75760, 2018.
  3. E. Hodzic, A. Subash, S. Yu, R.-Z. Szász, X.-S. Bai, and M. Aldén: A new swirl burner – preliminary experiments and simulation. Presentation delivered at the 16th International Workshop on Premixed Turbulent Flames, July 27-28, Dublin, Ireland, 2018.
  4. M. Bertsch, S. Yu, R.-Z. Szász, X.-S. Bai, A. A. Subash, and M. Aldén: Numeric incestigation of the flame stability for lean premixed combustion of hydrogen-enriched methane and syngas in a lab-scale atmospheric swirl burner. Nordic Flame Days 2019, Aug. 28-29, Turku, Finland.
  5. X. Liu, M. Bertsch, A. A. Subash, S. Yu, R.-Z. Szász, Z. Li, P. Petersson, X.-S. Bai., M. Aldén, and D. Lörstad: Investigation of turbulent premixed methane/air and hyrogen-enriched methane/air flames in a laboratory-scale gas turbine model combustor. Manuscript submitted to the 38th International Symposium on Combustion.

Funding agency: STEM/CECOST

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