International Society for Industrial Process Tomography

The extension of Rayleigh criterion used in thermoacoustic instability of one dimension flame front model

Qiang Niu, Gang Xu, Chaoqun Nie

Institute of Engineering thermophysics Chinese Academy of Sciences

Beijing, China

ABSTRACT

From 1878, Rayleigh criteria has been the standard way to estimate the instability of the combustion perturbation. And it more and more became a powerful tool to explain,forecast and control the combustion oscillation in combustor along with the development of this problem. Rayleigh criterion said that if heat addition and pressure oscillations are positively correlated in time the acoustic field energy will grow up, otherwise it will decrease. However from the midlle of 20th century, some people thought that the traditional criteria did not include all of the factor, and became studying the connection of the temperature and heat release, and the effect on combustion instability of this connection. Chu and later Nicoud developed the FE equation to improve the Rayleigh criteria. But it is still unclear that how the fluctuation of temperature, pressure and heat release affect the others. The object of this paper is to revisit the two kinds of criteria on the exergy viewpoint, and use the exergy method to build a model. The result of the model show that the coupling of heat release and meanflow heat value fluctuation is another factor on combustion oscillation which was not included in the old critetias. This term decide the size of the so­called “entropy wave”. And through the comparison we can see that the instable zone in phase graph coming from the new criteria is larger than the former one.

Keywords Rayleigh criteria , entropy wave ,exergy method