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Combustion Instability in a Silo Type Gas Turbine Combustor

Nosrati Shoar, Somayeh | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40705 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Farshchi, Mohammad; Hejranfar, Kazem
  7. Abstract:
  8. Nowadays, one of the most important desires of the human being is to reduce his living environmental pollution. Using the diluted combustion systems in new gas turbines in order to produce the minimum amount of has been done to satisfy this desire. It should be noted that reducing this amount and using the lower flame temperature will result in some consequences. The most important problem occurred in industrial and aerial gas turbines are the instability of the combustion due to dilution of the fuel to air mixture which it results in heat release fluctuations. If the heat release fluctuations and acoustic pressure are in the same phases, the amplitude of the fluctuations will increase which will result in the unpredicted behavior of the flame. Subsequently, it can cause decrease in the lifetime of the chamber or even failure of the whole structure.
    In this thesis the instability of combustion in a silo type combustion chamber is investigated. This type of chamber is used in industrial gas turbines. In such applications, the coupling between generated heat from the flame and acoustic pressure of the container will result to pressure fluctuations, called Humming. This phenomenon is a great barrier in developing gas turbines with pre-mixture combustion capability using natural gas. To investigate this issue the combustion chamber is divided to five principal subsystems including plenum, Burner, flame plate, combustion chamber and output nozzle. At first acoustic matrix of all the subsystems is evaluated by means of thermodynamic conditions, flow speed, input and output conditions. At the second step, flame behavior is evaluated; transformation functions represent combustion’s dynamic behavior. Transformation functions relate speed fluctuations due to burner to fluctuations of flame’s generated heat. At the next step, flame’s response to flow regime’s fluctuations is found by transformation matrix. By assembling acoustic matrices of all subsystems to the flame’s one, a model is generated which can predict instable frequency modes and obtain thermo-acoustics’ domain of stability of silo type combustion chamber. Finally, amplitude of limited cycle fluctuations of silo type combustion chamber is achieved. By investigating specific combustion chamber which is available in the state (Iran), stability boundary for optimum utilization can be obtained.
  9. Keywords:
  10. Combustion Instability ; Limit Cycles ; Combustion Chamber ; Stability Boundary

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