University of Twente Student Theses
Comparison of methods for thermoacoustic stability analysis of a hydrogen-fuelled condensing boiler
Shair Ali, M.R. (2024) Comparison of methods for thermoacoustic stability analysis of a hydrogen-fuelled condensing boiler.
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| Abstract: | Thermoacoustic instability is a combustor pressure oscillation due to feedback of unsteady heat release of a flame and acoustic perturbations. This feedback can cause premature failure of systems. Due to fast chemical kinetics in hydrogen combustion as compared to natural gas, a hydrogen-fuelled system is likely to be more sensitive to thermoacoustic instability. Conventionally this instability is analyzed with transient CFD simulation of the combustion process. In this work, a residential hydrogen-fuelled condensing boiler is analyzed. This study compares methods to determine the Flame Transfer Function (FTF), a function describing the effect of the flame on the heat release due to a flow perturbation (equivalence ratio perturbations in this work). This thesis work is performed as part of the ‘combustion DYNamics and Acoustics oscillations in large industrial Furnaces and boilers’ (DYNAF) project. For large scale boilers, transient simulations can be more expensive due to the large time and length scales involved. The development of a steady state based method to replace these simulations is interesting to determine with modest effort thermoacoustic stability in the design process of the burners. Two transient methods, impulse excitation and white noise excitation, are compared to a steady state method, the Linear Coefficient Method (LCM), to evaluate computational expense and accuracy. The FTF is determined for the hydrogen-fuelled condensing boiler. The Finite Rate/Eddy Dissipation Model (FR/EDM) is compared to the UT-Flamelet Generated Manifold (UT-FGM) combustion model. The FTF is determined using the different methods and implemented in an Acoustic Network Model (ANM) of the condensing boiler to determine thermoacoustic stability. Speed improvements have been made to the LCM such that the computation time is low compared to the transient methods for the case study. The used implementation of the LCM did not give accurate results. The transient methods showed good agreement in the FTF. A peak in the gain at St ≈ 1 is observed which is a direct result of the excitations applied to the transient simulations. The eigenfrequencies of the system as found using the ANM are similar. The analyzed condensing boiler is stable. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 52 mechanical engineering |
| Programme: | Mechanical Engineering MSc (60439) |
| Link to this item: | https://purl.utwente.nl/essays/104636 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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