A Distributed Transfer Function for Non-Premixed Combustion Oscillations

Abstract

The present study discusses a general distributed transfer function for non-premixed flames based on conservation equations. Also, a distributed transfer function for idealized, two-dimensional, flat, non-premixed flames is calculated using Green's function method. The unsteady heat release can be represented in terms of thermodynamic relationships based on energy conservation equations. By this method, the distributed flame response in physical domain for both combustion zone and its further downstream is intensively investigated. The lumped unsteady heat release can be obtained by the integration along the axial coordination. For distributed heat release transfer function in frequency domain, a dual-peak response of magnitudes is observed in the fuel-rich zone and the fuel-lean zone, respectively. The processes of the generation and the evolution of hot spots in non-premixed flames are also investigated. Analysis of multiple related parameters is conducted to evaluate the effects of the Strouhal number, the Peclet number, and convective velocity on hot spot propagation. The results show that a smaller Strouhal number, a larger Peclet number, or a faster convective velocity causes the hot spots to move farther downstream. These results are valuable for a better understanding of the mechanisms of non-premixed combustion instabilities, which is beneficial to the development of more accurate control techniques.

Keywords:

• Combustion instabilities
• Distributed transfer function
• Green's function method
• Non-premixed flame

ACKNOWLEDGMENTS

This work was funded by the National Basic Research Program of China through grant No. 2007CB210106 and National Natural Science Foundation of China through Grant No. 51076071, whose support is gratefully acknowledged. The authors wish to thank Professors A. P. Dowling and K. N. C. Bray for their comments and suggestions.