Title page for ETD etd-04232003-153301


Type of Document Master's Thesis
Author DeCastro, Jonathan Anthony
Author's Email Address jdecastr@vt.edu
URN etd-04232003-153301
Title Design and Validation of a High-Bandwidth Fuel Injection System for Control of Combustion Instabilities
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Saunders, William R. Committee Chair
Leo, Donald Committee Member
Vandsburger, Uri Committee Member
Keywords
  • lean premixed
  • piezoceramic actuator
  • thermoacoustic instabilities
  • compressibility
  • atomization
  • fuel modulation
Date of Defense 2003-02-07
Availability unrestricted
Abstract
The predictive design of fuel injection hardware used for active combustion control is not well established in the gas turbine industry. The primary reason for this is that the underlying mechanisms governing the flow rate authority downstream of the nozzle are not well understood. A detailed investigation of two liquid fuel flow modulation configurations is performed in this thesis: a piston and a throttle-valve configuration. The two systems were successfully built with piezoelectric actuation to drive the prime movers proportionally up to 800 Hz.

Discussed in this thesis are the important constituents of the fuel injection systemthat affect heat release authority: the method of fuel modulation, uncoupled dynamics of several components, and the compressibility of air trapped in the fuel line. Additionally, a novel technique to model these systems by way of one-dimensional, linear transmission line acoustic models was developed to successfully characterize the principle of operation of the two systems. Through these models, insight was gained on the modes through which modulation authority was dissipated and on methods through which successful amplitude scaling would be possible. At high amplitudes, it was found that the models were able to successfully predict the actual performance reasonably well for the piston device.

A proportional phase shifting controller was used to test the authority on a 40-kW rig with natural longitudinal modes. Results show that, under limited operating conditions, the sound pressure level at the limit cycle frequency was reduced by about 26 dB and the broadband energy was reduced by 23 dB. Attenuation of the fuel pulse at several combustor settings was due to fluctuating vorticity and temporal droplet distribution effects.

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