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Experimental and Numerical Study of Spray Combustion under Hot-diluted Conditions

Azimi, Amir Hossein | 2019

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 51874 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Mardani, Amir
  7. Abstract:
  8. In this thesis, combustion of liquid fuel spray under the condition of hot and diluted oxidizer, has been investigated. To this end, a novel type laboratory-scale test rig was designed to study the physics governing the MILD-Spray combustion conditions with an applied approach. The underlined test rig eliminates the operational problems of its predecessor test stands and is used for a heavier fuel with much more complex chemical composition (kerosene). The test section is axially symmetrical, in which the fuel is injected by a pressure-swirl atomizer in the direction of hot and diluted co-flowing air. With the use of the aforesaid test rig, the effect of variables such as oxygen concentration, temperature and velocity of the co-flowing air, fuel flow rate, and eventually the type of spray nozzle on the functional parameters such as the flame stability range, flame structure, flame brightness luminosity, temperature distribution and some species concentration in the reaction region, has been studied. Empirical results obtained from this study could be used as a database, allowing the development or evaluation of numerical models used in simulating the above-mentioned combustion conditions. In addition to the experimental study, in the current research, numerical simulation has also been used for extraction of some information such as velocity field and flow structure. Based on the results of the experimental research measurements, increase of the injection pressure, or the temperature of the air as well as the temperature of the fuel, resulted an improved combustion stability of the fuel spray, while the reduction of the oxygen concentration of the co-flowing air has reduced the flame stability. The pre-heating of the air (without dilution) leads to a change in flame structure from double to a single-fronted flame with very low lift-off. Under this condition, the reaction rate has increased sharply and the local concentration of chemical species has also increased significantly. Under the pre-heated and diluted conditions, the structure of the flame has changed as well and its integrated structure has been damaged. The internal flame front has also been severely weakened or lost. In addition, the rate of reaction is reduced and the concentration of chemical species in the reaction zone is accompanied by a significant reduction. In this condition, the temperature fluctuations have increased, although the temperature field has become more uniform. In overall, based on the results of this research, the possibility of reaching MILD condition for liquid fuels is corroborated
  9. Keywords:
  10. Spray Combustion ; Preheating ; Oxidizer Dilution ; Moderate or Intense Low Axygen Dilution (MILD) ; Test Rig

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