An Experimental Study of Flame Response Mechanisms in a Lean-premixed Gas Turbine Combustor
Open Access
- Author:
- Peluso, Stephen
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 19, 2012
- Committee Members:
- Domenic Adam Santavicca, Dissertation Advisor/Co-Advisor
Domenic Adam Santavicca, Committee Chair/Co-Chair
Robert John Santoro, Committee Member
Stephen R Turns, Committee Member
Adrianus C Van Duin, Committee Member
Randy Lee Vander Wal, Committee Member - Keywords:
- combustion instability
flame response
flame dynamics
flame transfer function
flame response mechanisms
gas turbine - Abstract:
- The heat release rate response of a swirl-stabilized, turbulent, lean-premixed natural gas-air flame to velocity oscillations was investigated in an atmospheric variable length research combustor with a single industrial gas turbine injector. Operating conditions were similar to realistic gas turbine conditions with the exception of mean combustor pressure. Flame response was characterized across a range of frequencies and velocity oscillation magnitudes during self-excited and forced flame investigations. The variable-length combustor was used to determine the range of preferred instability frequencies for a given operating condition. Flame stability was classified based on combustor pressure oscillation measurements. Velocity oscillations in the injector barrel were calculated from additional pressure measurements using the two-microphone method. CH* chemiluminescence emission was used to quantify heat release rate. A filtered photomultiplier tube measured global emission and flame structure was characterized using an intensified CCD camera. Self-excited and forced global flame responses were compared in the linear and transition into the nonlinear regimes. For cases in this study, the gain and phase between velocity and heat release rate oscillations agreed across a range of velocity oscillation magnitudes, validating the use of forcing measurements to measure flame response to velocity oscillations. Analysis of the self-excited flame response indicated the saturation mechanism responsible for limit-cycle behavior can result from nonlinear driving or damping processes in the combustor. Global flame response to forced velocity oscillations between 100 and 440 Hz was measured over a wide range of operating conditions. Nearly all measurements showed similar qualitative behavior; gain decreased with increasing frequency until reaching a minimum value at a frequency fmin. After reaching a local minimum, gain increased with frequency. The frequency of minimum response fmin varied with operating condition and was found to be related to the mean velocity in the injector and a characteristic flame length determined from stable flame imaging. In addition, the phase between velocity oscillations and heat release rate oscillations scaled with mean velocity and flame length. The global response of the flame was separated into acoustic and convective components by modeling the response of the flame to a purely acoustic wavelength velocity oscillation. The phase of the reconstructed convective response was characteristic of a response to a flow disturbance originating from the end of the injector centerbody, the anchoring point of the flame. Phase-synchronized imaging of select flames over a range of frequencies showed global flame response was controlled by the interaction between axial velocity oscillations and vortical disturbances shed from the injector centerbody throughout the flame brush.