An Experimental Study on Combustion Dynamics and NOx Emission of a Swirl Stabilized Combustor with Secondary Fuel Injection

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  • RIAZI Rouzbeh
    Department of Aerospace Engineering, Sharif University of Technology
  • FARSHCHI Mohammad
    Department of Aerospace Engineering, Sharif University of Technology
  • SHIMURA Masayasu
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology
  • TANAHASHI Mamoru
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology
  • MIYAUCHI Toshio
    Department of Mechanical and Aerospace Engineering, Tokyo Institute of Technology

Abstract

To investigate the effects of flow rate, diameter and offset of secondary fuel injection on combustor noise level, pressure fluctuation and NOx emission, four types of injectors were examined in a swirl-stabilized combustor for overall equivalence ratio (φ) of 0.7 ∼ 0.9 and flow rate of secondary fuel (Qsec) from 0.6 to 4.2 L/min. As for the reference injector used in previous related studies, secondary fuel injection of 3.0 L/min is the best condition for the reduction of pressure fluctuation and combustion noise with tolerable NOx emission. For lower secondary fuel rate of 1.8 L/min, reduction of the injection diameter of reference injector results in a better performance in terms of combustion noise and pressure fluctuation reduction. By the secondary fuel injection with offset, NOx emission shows lower values than those of the injections without offset for the whole range of equivalence ratios. Spectral analysis of pressure fluctuations revealed that larger amount of secondary fuel (Qsec ≥ 3.0 L/min) by the injectors with injection offset induce a lot of new modes in the wide range of frequency. For near stoichiometric operating condition (φ ≥ 0.85) by higher amount of secondary fuel injection with offset (Qsec = 4.2 L/min), the flame lifts over the swirl injector, NOx emission decreases and instability modes appear in a frequency range lower than those of the injection without offset. The results also suggest that the emission index is deeply related to flame lift-off and the dominant mode of instability.

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