Forced Flame Response of a Lean Premixed Multi-Nozzle Can Combustor

Abstract

An experimental investigation was conducted to determine the air-forced flame response of a five-nozzle, 250 kW, lean premixed gas turbine can combustor. Operating conditions were varied over a range of inlet temperatures, inlet velocities, and equivalence ratios, while the forcing frequency was varied from 100 to 450 Hz with constant normalized velocity fluctuations of approximately 5%. The response of the flame’s rate of heat release to inlet velocity fluctuations is expressed in terms of the phase and gain of a flame transfer function. In addition, chemiluminescence imaging is used to characterize the time-averaged and phase-averaged spatial distribution of the flame’s heat release. The resulting flame transfer functions and chemiluminescence flame images are compared to each other to determine the effects of varying the operating conditions. In addition, they are compared to data obtained from a single-nozzle combustor with the same injector. The forced response of the multi-nozzle flame demonstrates a similar pattern to those obtained in a single-nozzle combustor with the same injector. An exception occurs at high frequency where the multi-nozzle flame responds to a greater degree than the single-nozzle flame. At low frequency the multi-nozzle flame dampens the perturbations while the single-nozzle flame amplifies them. A number of minima and maxima occur at certain frequencies which correspond to the interference of two mechanisms. The frequency of these minima is nearly the same for the single- and multi-nozzle cases. When plotted with respect to Strouhal number instead of frequency there is a degree of collapse that occurs around the first observed minima.

Structure of Flames in Flame Interaction Zones

“…The differences in total flame area and the resultant flame area fluctuations in the experiments by Reuter and coworkers is congruent with other two-V-flame experiments from Francois et al [5] and Dunstan et al [6,7]. More recent studies have focused on flame interaction in annular and can-annular gas turbine combustors [8][9][10][11][12][13]. In these configurations, three-dimensional effects are important and the flames are typically swirl-stabilized, introducing a very complex flow interaction mechanism that is beyond the scope of this work.…”

“…Studies from Worth and Dawson [10][11][12] and Samarasinghe and coworkers [8,9,14] have both noted that flame interaction in gas turbine configurations enhances the turbulent flame brush and the chemiluminescence signal in the flame interaction region. OH-planar laser-induced fluorescence (OH-PLIF) and tomographic chemiluminescence imaging were used to investigate the interaction.…”

The Effect of Fuel Staging on the Structure and Instability Characteristics of Swirl-Stabilized Flames in a Lean Premixed Multinozzle Can Combustor

“…Experiments are conducted in a fivenozzle can combustor. Details on this combustor have been presented in previous publications [13,18], which can be referred to for in-depth information about the test rig. The industrial scale, swirl, and bluff body stabilized nozzles are arranged in a "fouraround-one" configuration with nozzle spacing relative to the diameter of the combustor can being typical of industrial combustors.…”

Statistics of Local Flame-Flame Interactions in Flame Interaction Zones of Two V-Flames

“…Results from some of these studies have shown that flame area fluctuations from interactions between two adjacent flames can change the feedback mechanism and flame response [27][28][29][30]. Other studies have investigated the impact of interacting flames on global flame characteristics in gas turbine configurations; their results have shown that closer flame spacing results in a wide flame brush [31][32][33][34][35]. Worth and Dawson have also shown that greater levels of flame interactions result in increased negative curvatures; this increase in negative curvatures is due to enhanced flame cusping events in the interaction regions.…”