| Dr. Harsha K. Chelliah, 9 April 2007 |
| Flame-Acoustic
Interactions and their Influence on Combustion-Generated Pollution |
ABSTRACT: Gas turbines operating under lean premixed conditions are becoming the preferred choice for medium sized (~10-100 MW) power plants. The primary motivation for the selection of lean premixed condition is the lower emission of pollutants, in particular oxides of nitrogen. Unfortunately, lean premixed gas-turbine combustors are accompanied by combustion-driven noise, commonly known as "thermo-acoustic" instabilities. Considerable effort has been devoted to better understand the physico-chemical mechanism driving such instabilities and their control. In the study presented here, the interaction between acoustics waves established in a simple combustion geometry and a one-dimensional premixed flame is investigated by numerically integrating the full nonlinear conservation equations. In well-resolved simulations, the growth rate of the instability is analyzed using time scales associated with the flame. When the characteristic transport or chemical time scales of the flame overlaps with the acoustic time scale, the predicted pressure oscillations are amplified. Fundamental knowledge gained can be used in future efforts on controlling such instabilities and reducing pollutant formation. The presentation will also include a live demonstration of the thermo-acoustic phenomenon! |
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