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Measurements of Combustion Dynamics with Laser-Based Diagnostic Techniques


Kang, Dal Mo (2006) Measurements of Combustion Dynamics with Laser-Based Diagnostic Techniques. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6F5N-9G88.


Since the early days of gas turbine engines, combustion/flow instability inside the combustor has been an issue in many engines, but little has been understood as to how the dynamics of the system involved contribute to the instability. The primary objective of this work is to provide general experimental procedures and to validate methods for examining the dynamic behaviors of combustion systems, and to provide accurate measurements of the combustion dynamics for use as a foundation for further theoretical and numerical research. Knowledge of the fundamental dynamics of combustion systems is crucial in understanding and modeling the flame behavior and enabling the use of insights in design process and for creating robust active control of combustors.

Since mixing plays significant roles in combustion processes, the dynamics of fuel/air mixing were studied. A non-premixed burner was examined with acoustic excitations at 22~55 Hz to assess the mixing and its relation to the thermo-acoustic coupling. Phase-resolved acetone-PLIF was used to image the mixing, and from this the unmixedness was calculated, which quantifies the degree of mixing. The results show that (1) the acoustic waves induce periodicity in the degree of mixing; (2) the way the unmixedness behaves coincides well with the behavior of the Rayleigh index, implying the degree of mixing is a major factor in determining the stability of the combustion system; (3) the two-dimensional measurements of temporal unmixedness effectively visualize the shear mixing zone.

A second low-swirl premixed burner was studied to examine the impact of acoustic waves on the combustion dynamics. Measurements were performed with OH-PLIF, with acoustic forcing up to 400 Hz. Swirl burners at higher pressure are industry standard, and this study examined the dynamics at elevated combustor pressure. The results show that (1) the thermo-acoustic coupling seems to be closely coupled to the vortices generated at the flame boundary; (2) high magnitude of flame response coincides with the high absolute value of Rayleigh index; (3) the way the thermo-acoustic coupling is distributed over the space is highly dependent on the excitation frequencies; (4) high pressure suppresses the sensitivity of combustions system to outside disturbances.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:combustion dynamics; combustion instabilities; forced acoustic excitation; laser induced fluorescence
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Mechanical Engineering
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Culick, Fred E. C.
Thesis Committee:
  • Culick, Fred E. C. (chair)
  • Ratner, Albert
  • Goodwin, David G.
  • Hornung, Hans G.
  • Hunt, Melany L.
Defense Date:2 December 2005
Non-Caltech Author Email:balmoa1 (AT)
Record Number:CaltechETD:etd-12182005-164746
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:5041
Deposited By: Imported from ETD-db
Deposited On:19 Dec 2005
Last Modified:10 Dec 2020 19:07

Thesis Files

PDF (ThesisDMKang.pdf) - Final Version
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