A Novel Method for the Computation of the Linear Stability of Combustors

TLDR: Sattelmayer and Polifke as discussed by the authors showed that the commonly employed open-loop Bode plot stability analysis can lead to erroneous results for a Nyquist diagram, if the interpretation of the openloop gain curve follows the standard rules of traditional control theory.

Abstract: A negative characteristic of low-emission flames is their weak dynamic flame stability, which leads in many cases to periodic pulsations of heat release and combustor pressure. Due to the extremely complex nature of the forcing and feedback mechanisms in flows with heat release, reliable prediction of the stability limits of combustors has not been achieved yet with satisfactory accuracy. The dynamics of complicated thermoacoustic systems, which are modeled on the basis of linear acoustics and a representation of the system as a network of acoustic elements, can be analyzed using methods derived from control theory. It was shown in a companion article (Sattelmayer and Polifke, Combustion Science and Technology , vol. 175, pp. 453-476, 2003) that the commonly employed open-loop Bode plot stability analysis can lead to erroneous results. Similar problems may occur also for a Nyquist diagram, if the interpretation of the open-loop gain curve follows the standard rules of traditional control theory. A lack of...