Combustion Dynamics of Annular Systems

Abstract

New results on the dynamics of annular combustors during ignition and combustion instabilities will be reviewed. Ignition dynamics is considered first by examining experiments carried out in a system comprising a plenum feeding premixed gaseous reactants through multiple swirling injectors and an annular combustor formed by two concentric transparent quartz walls allowing full optical access to the flame. The analysis focuses on the "light-round" process during which the flame spreads from one injector to the next eventually leading to established flames on each injector. The transparent lateral walls allow a full view of the flame propagation from a spark igniter located in the neighborhood of one injector. High speed imaging is used to examine flame displacement and deduce the ignition delay yielding a full light around of the annular combustor. Changes associated to operation with spray flames are then discussed. The second part of this article is concerned with combustion instabilities of annular systems coupled by azimuthal modes. This type of oscillation has received considerable attention in recent years because the underlying coupling is often observed in the advanced premixed combustion architectures used in modern gas turbines. Recent studies have allowed a detailed examination of the dynamics of annular devices comprising multiple swirling injectors. Experiments on annular systems and single sector configurations provide new insight on the coupling process between acoustics and unsteady combustion. Results for self-sustained combustion oscillations coupled by azimuthal modes are presented for operation with gaseous premixed reactants and with spray flames.

Swirler effects on combustion instabilities analyzed with measured FDFs, injector impedances and damping rates

“…The experimental observations were supported by analytical representation based on a network model using acoustic transfer matrices leading to an instability criterion. Indications on the notable influence of the injection parameters are also derived from recent experiments on annular combustors, which are reviewed in [18]. The potential of using low-order models in representing complicated swirler geometries was explored, for instance, by Fischer et al [19] using transfer matrices that were experimentally validated under cold flow conditions in a combustor with a variable swirl number.…”

“…Comparison of the model predictions with experimental data underlines the importance of including injector dynamics in the theoretical model for instability analysis. Experiments are carried out in a single injector setup (SICCA-Spray) representing one segment of the laboratory-scale annular combustor, MICCA-Spray [18]. The exploded view of the swirling injector is shown in Fig.…”