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Experimental Modeling of Influence of Exhaust Gas Recirculation on Flameless Combustion

Hassani, Masoud | 2010

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40328 (45)
  4. University: Sharif University of Technology
  5. Department: Aerospace Engineering
  6. Advisor(s): Ghorbanian, Kaveh; Farshchi, Mohammad
  7. Abstract:
  8. The aim of this work is to design, build and test a laboratory scale flameless combustion chamber. Also, a theoretical model is developed to simulate flameless combustion with a simple model. Flameless combustion is a combustion type with transparent flame which consumes less fuel than typical premix and diffusion flames and emits very low level of NOx. In flameless combustion, recirculation ratio is higher than typical diffusion flames so the flow field is highly turbulent. High recirculation ratio causes low oxygen concentration in combustion zone; thus requiring inlet air to be preheated for flame stabilization at low equivalence ratio and oxygen concentration. We have designed a flameless combustion chamber with a built-in heat exchanger to preheat inlet air. The heat exchanger absorbs wasted heat of combustion from combustor’s wall and increases inlet air temperature. Experiments are performed for three different types of recirculation and three different positions of the fuel injector. In each experiment, equivalence ratio is changed from rich to very lean while the flame is observed through a quartz window. These tests were conducted at the Sharif University’s combustion laboratory. Theoretical model shows increasing recirculation ratio cause decreasing in oxygen concentration in combustion zone. Experimental results show that higher recirculation may cause instability and lowers the flameless combustion range. It is believed that proper recirculation decreases the oxygen concentration and increases the combusting air temperature. Therefore flameless combustion can form in lower equivalence ratio, but an intense recirculation pattern may also cause higher turbulent intensity leading to instability. Further, it is believed that increasing the distance between the fuel injector and air injectors decreases the flameless combustion range and increases upper and lower value of equivalence ratio for flameless combustion. As inlet air’s temperature increases, stable flameless combustion forms in lower equivalence ratio; also, in flameless combustion NOx is minimum
  9. Keywords:
  10. Pollutant ; Fuel Consumption ; Heat Exchangers ; Fuel Preheating ; Flamless Combustion ; Preheat Air

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