Zsak, Thomas William (1993) An investigation of the reacting vortex structures associated with pulse combustion. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-11212007-105308
An investigation of the reacting vortex structures associated with pulsating combustion is performed using a laboratory dump combustor in order to gain an understanding of the controlling physical and chemical processes present during the burning of the vortex structures. Stabilized on the lip of a rearward-facing step flame holder, the vortices are shed at acoustic longitudinal modes of the apparatus. In all cases examined, a fuel-rich mixture of methane and air is used, 30% greater than stoichiometric, and the velocity at the dump plane is 21 m/sec. Results are presented for the expansion ratios of 4.0 and 12.0.
A linearized one-dimensional acoustic model is developed to predict the resonant acoustic modes and mode shapes of the system for the two configurations. Heat addition is modeled as a sinusoidally varying volumetric mass source which can be placed at any location within the combustion chamber. Good agreement is found between the natural frequencies predicted by the model and those obtained experimentally under both hot- and cold-flow conditions. The effects of different combustion chamber temperatures on the pressure and velocity responses are revealed as are the effects of placing the heat addition at different axial locations downstream of the dump plane. It is shown that the pressure amplitude spectra for each expansion ratio can be successfully predicted given the relationship between heat release in the chamber and frequency.
The ignition mechanisms of the vortex structures are found to be different for the two chamber configurations, and the bulk of the heat release is shown to occur much closer to the dump plane for the chamber with the smaller expansion ratio. The influence of the lower wall of the combustor on the burning of the structures is shown to be weaker for the chamber with the larger expansion ratio. The additions of ionization probes and an intensified, charge-injection-device (CID) camera to the experimental program have allowed the burning histories of the shed vortex structures to be recorded. Capturing an image of the chemiluminescence from the burning of the vortices at nearly the same instant as a shadowgraph image of the density gradients within the chamber completely describes the reacting flow field. Temperature measurements made with fine-wire thermocouples complete the experimental investigation and complement the results obtained above.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Engineering and Applied Science|
|Major Option:||Mechanical Engineering|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||13 April 1993|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||06 Dec 2007|
|Last Modified:||26 Dec 2012 03:10|
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