A combustor model for control oriented simulation of combustion instabilities

Abstract

This paper describes the development and application of a theoretical model of an actively controlled combustor. The main objective of the study was to develop a model that could be used as a platform for studying closed loop control of unstable combustors. The model uses a heuristic approach and global kinetics to describe mixing and combustion processes in a one dimensional gaseous combustor. Initially, the model is used to investigate a combustor's response to open loop excitation by periodic fuel injection. The predicted amplitude of the excited combustor pressure oscillation decreases with increase in the frequency of fuel pulsation and is in good agreement with experimental data. Next, closed loop control is studied. The investigated controller determines the characteristics of the most unstable mode in real time and damps the instability by modulating the injection rate of a fraction of the injected fuel to excite a secondary combustion process within the combustor out of phase with respect to the most unstable mode of pressure oscillations. Results showing the dependence of the controller's performance upon the secondary fuel flow rate and the time delay involved in implementing the control signal are presented.