Abstract:

Low NOx, lean premixed combustion systems are more prone to combustion instability, which can significantly constrain system operability and increase maintenance expenses. Combustion instability occurs due to a feedback loop between the heat release rate and system acoustics and / or hydrodynamic instabilities. Because typical high power combustion systems also operate in a turbulent regime, prediction of combustion instability requires understanding the interaction of coherent and turbulent flame disturbances. Therefore, this thesis concentrates on understanding and modeling these interactions. Two primary avenues of research are pursued: development and validation of a flame position and heat release model and experimental investigations of the ensemble-averaged flame.

The turbulent modeling method is based on the G-equation approach used in laminar flame position and heat release studies. The dependence of the ensemble-averaged turbulent flame speed on the ensemble-averaged flame curvature is incorporated using a flame speed closure proposed by Shin and Lieuwen (2013). This reduced order turbulent modeling approach is validated by comparison with three-dimensional simulations of premixed flames. Second, the development of and results from a novel experimental facility are described. This facility has the capability to subject premixed flames to simultaneous broadband turbulent fluctuations and narrowband coherent fluctuations, which are introduced on the flame using an oscillating flame holder. Mie scattering images are used to identify the instantaneous flame edge position, while simultaneous high speed PIV measurements provide flow field information.

Results from this experimental investigation include analysis of the ensemble-averaged flame dynamics, the ensemble-averaged turbulent displacement and consumption speeds, and the dependence of both the displacement speed and consumption speed on the ensemble-averaged flame curvature. Together, the results indicate potential in using this approach for modeling the ensemble-averaged flame position and heat release.

Committee:

Dr. Tim Lieuwen (Adviser)

Dr. Jerry Seitzman

Dr. Devesh Ranjan

Dr. Lakshmi Sankar

Dr. Wenting Sun

Location and Data

Location: MK 317

Data and Time: March 29, 12:00 noon