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Study of Dilution and Preheating Effects on the Flame Structure of a Double-Swirl Gas Turbine Model Combustor with Fuel Flexibility

AghaBeige Aminabadi, Amir | 2024

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 58247 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Mardani, Amir
  7. Abstract:
  8. Large eddy simulations of a gas turbine model combustor are performed in normal and diluted/preheated conditions to have a better understanding of MILD combustion in gas turbine combustors. The corresponding flame structures are studied using the graphical and statistical tools and the reaction rates, strain rates, and flow structures are compared. In addition, the accuracy of the simulations is assessed by comparing the time-averaged results to the available experimental data. To simulate the MILD combustion conditions, about 36% reduction in fuel flow rate and 32% dilution of the oxidizer (by EGR) in addition to an air preheat to 730 K are used in the investigated case of oxidizer dilution. Furthermore, landfill gas was used instead of methane to study fuel dilution effects. Dilution and preheating of the incoming air are shown to cause stronger vortices (due to higher inlet velocities), faster mixings, and lower rates of H-atom abstraction in the upstream parts of the reactant jet, which helped expanding the heat release region of the diluted/preheated case. Moreover, it is observed that preheating inhibits HO2 formation in upstream parts of the reactant jet, which also caused lower activities of the H2O2 oxidation route in the diluted/preheated mode. The concentration of some radicals (e.g., CH3), and the rate of both chain branching and recombination reactions are also observed to be higher in the diluted/preheated case. Next, a generalized autoignition index is proposed and used to compare the flame propagation and autoigntion regions for the investigated flames, which shows the spatial expansion of both flame and autoignition spots in the diluted/preheated combustion mode. It is shown that while the rate of kinetically slower elementary reactions drops sharply in high strain regions of the normal combustion case, the rate of these reactions are less affected in the diluted/preheated mode. Consequently, some of the OH producing reactions are inhibited in high strain regions of the conventional combustion case, which helps the flame of this case to be stabilized outside of the high strain zones, in contrary with the distributed flame of the diluted/preheated case. It is also shown that fuel dilution can also lead to MILD combustion and consequently more distributed reaction zones compared to thin flames of the normal combustion case for the studied burner
  9. Keywords:
  10. Gas Turbine Model Combuster (GTMC) ; Moderate or Intense Low Axygen Dilution (MILD) ; Dilution ; Preheating ; Chemical Kinetic Simulation ; Large Eddy Simulation (LES) ; Nitrogen Oxide Emission ; Combustion Stability ; Flamless Combustion

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