Combustor Model for Simulation of Combustion Instabilities and Their Active Control

Abstract

The development and application of a numerical model of an actively controlled combustor are described. The main objective 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-dimensionalgaseous combustor. Initially, themodel is used to investigate a combustor’s response to open-loopexcitation by periodic fuel injection. The numerical model’s prediction that 1) the pressure oscillation amplitude decreases and 2) the phase shift between the fuel injection rate and heat-release oscillations increases linearly, as the frequency of fuel injection rate increases, are in good agreement with experimental data from a gas rocket. Next, closed-loop control is studied. The investigated controller determines the characteristics of the most unstablemode 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. Active control examples include the study of the dependence of the controller’s performance on the amount of fuel pulsed.