scholarly journals Multiphase Flow LES Study of the Fuel Split Effects on Combustion Instabilities in an Ultra Low-NOx Annular Combustor

2015 ◽  
Author(s):  
M. Bauerheim ◽  
T. Jaravel ◽  
L. Esclapez ◽  
E. Riber ◽  
L. Y. M. Gicquel ◽  
...  
Keyword(s):  
Multiphase Flow ◽  
Analytical Model ◽  
Vortex Shedding ◽  
Liquid Fuel ◽  
Gaseous Fuel ◽  
Combustion Instabilities ◽  
Thermoacoustic Instabilities ◽  
Flame Dynamics ◽  
Global Correlation ◽  
Annular Combustor

This paper describes the application of a coupled Acoustic model/LES approach to assess the effect of fuel split on combustion instabilities in an industrial ultra low-NOx annular combustor. Multiphase flow LES and an analytical model (ATACAMAC) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: 1) a gaseous type in the multi-point zone where acoustics generates vortex shedding, wrinkling the flame front and 2) a multiphase flow type in the pilot zone where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the pilot zone and mechanism 2) and therefore assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using the analytical model and validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations which strongly depend on the fuel split parameter. However, the global correlation between heat release fluctuations and acoustics highlights no dependency on the fuel split staging. It suggests that vortex shedding in the multi-point zone, almost not depending on the fuel split here, is the main feature controlling the flame dynamics for this LEMCOTEC engine.

scholarly journals Multiphase Flow Large-Eddy Simulation Study of the Fuel Split Effects on Combustion Instabilities in an Ultra-Low-NOx Annular Combustor

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
M. Bauerheim ◽  
T. Jaravel ◽  
L. Esclapez ◽  
E. Riber ◽  
L. Y. M. Gicquel ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Multiphase Flow ◽  
Analytical Model ◽  
Vortex Shedding ◽  
Gaseous Fuel ◽  
Combustion Instabilities ◽  
Eddy Simulation ◽  
Flame Dynamics ◽  
Large Eddy ◽  
Annular Combustor

This paper describes the application of a coupled acoustic model/large-eddy simulation approach to assess the effect of fuel split on combustion instabilities in an industrial ultra-low-NOx annular combustor. Multiphase flow LES and an analytical model (analytical tool to analyze and control azimuthal modes in annular chambers (ATACAMAC)) to predict thermoacoustic modes are combined to reveal and compare two mechanisms leading to thermoacoustic instabilities: (1) a gaseous type in the multipoint zone (MPZ) where acoustics generates vortex shedding, which then wrinkle the flame front, and (2) a multiphase flow type in the pilot zone (PZ) where acoustics can modify the liquid fuel transport and the evaporation process leading to gaseous fuel oscillations. The aim of this paper is to investigate these mechanisms by changing the fuel split (from 5% to 20%, mainly affecting the PZ and mechanism 2) to assess which mechanism controls the flame dynamics. First, the eigenmodes of the annular chamber are investigated using an analytical model validated by 3D Helmholtz simulations. Then, multiphase flow LES are forced at the eigenfrequencies of the chamber for three different fuel split values. Key features of the flow and flame dynamics are investigated. Results show that acoustic forcing generates gaseous fuel oscillations in the PZ, which strongly depend on the fuel split parameter. However, the correlation between acoustics and the global (pilot + multipoint) heat release fluctuations highlights no dependency on the fuel split staging. It suggests that vortex shedding in the MPZ, almost not depending on the fuel split, is the main feature controlling the flame dynamics for this engine.

scholarly journals Flame Edge Dynamics and Interaction in a Multi-Nozzle Can Combustor With Fuel Staging

2019 ◽  
Author(s):  
Daniel Doleiden ◽  
Wyatt Culler ◽  
Ankit Tyagi ◽  
Stephen Peluso ◽  
Jacqueline O’Connor
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Pollutant Emissions ◽  
Destructive Interference ◽  
Combustion Instabilities ◽  
Acoustic Oscillations ◽  
Oscillation Phase ◽  
Phase Cancellation ◽  
Flame Dynamics ◽  
Fuel Staging

Abstract The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines is necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multi-nozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancellation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 degrees (∼114 degrees), suggesting that the phase-cancellation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.

scholarly journals Flame Edge Dynamics and Interaction in a Multinozzle Can Combustor With Fuel Staging

2019 ◽  
Vol 141 (10) ◽  
Author(s):  
Daniel Doleiden ◽  
Wyatt Culler ◽  
Ankit Tyagi ◽  
Stephen Peluso ◽  
Jacqueline O'Connor
Keyword(s):  
Vortex Shedding ◽  
High Speed ◽  
Pollutant Emissions ◽  
Destructive Interference ◽  
Combustion Instabilities ◽  
Acoustic Oscillations ◽  
Previous Theory ◽  
Oscillation Phase ◽  
Flame Dynamics ◽  
Fuel Staging

The characterization and mitigation of thermoacoustic combustion instabilities in gas turbine engines are necessary to reduce pollutant emissions, premature wear, and component failure associated with unstable flames. Fuel staging, a technique in which the fuel flow to a multinozzle combustor is unevenly distributed between the nozzles, has been shown to mitigate the intensity of self-excited combustion instabilities in multiple nozzle combustors. In our previous work, we hypothesized that staging suppresses instability through a phase-cancelation effect in which the heat release rate from the staged nozzle oscillates out of phase with that of the other nozzles, leading to destructive interference that suppresses the instability. This previous theory, however, was based on chemiluminescence imaging, which is a line-of-sight integrated technique. In this work, we use high-speed laser-induced fluorescence to further investigate instability suppression in two staging configurations: center-nozzle and outer-nozzle staging. An edge-tracking algorithm is used to compute local flame edge displacement as a function of time, allowing instability-driven edge oscillation phase coherence and other instantaneous flame dynamics to be spectrally and spatially resolved. Analysis of flame edge oscillations shows the presence of convecting coherent fluctuations of the flame edge caused by periodic vortex shedding. When the system is unstable, these two flame edges oscillate together as a result of high-intensity longitudinal-mode acoustic oscillations in the combustor that drive periodic vortex shedding at each of the nozzle exits. In the stable cases, however, the phase between the oscillations of the center and outer flame edges is greater than 90 deg (∼114 deg), suggesting that the phase-cancelation hypothesis may be valid. This analysis allows a better understanding of the instantaneous flame dynamics behind flame edge oscillation phase offset and fuel staging-based instability suppression.

Experimental Investigation of Thermoacoustic Instabilities for a Model Combustor With Varying Fuel Components

2011 ◽  
Author(s):  
X. Y. Zhang ◽  
H. Zhang ◽  
M. Zhu
Keyword(s):  
Boundary Conditions ◽  
Acoustic Waves ◽  
Thermal Power ◽  
Supply System ◽  
Dynamic Processes ◽  
Combustion Instabilities ◽  
Thermoacoustic Instabilities ◽  
Instability Modes ◽  
Syngas Combustion ◽  
Fuel Components

In this study, a combustion facility was constructed that includes a flexible fuel supply system to produce synthesis gas using a maximum of three components. The rig with lean premixed burner is able to operate at up to 5 bars. The length of the inlet plenum and the outlet boundary conditions of the combustion chamber are adjustable. Experiments were carried out under a broad range of conditions, with variations in fuel components including hydrogen, methane and carbon monoxide, equivalence ratios, thermal power and boundary conditions. The dynamic processes of self-excited combustion instabilities with variable fuel components were measured. The mechanisms of coupling between the system acoustic waves and unsteady heat release were investigated. The results show that instability modes and flame characteristics were significantly different with variations in fuel components. In addition, the results are expected to provide useful information for the design and operation of stable syngas combustion systems.

A Strategy to Tune Acoustic Terminations of Single-Can Test-Rigs to Mimic Thermoacoustic Behavior of a Full Engine

2020 ◽  
Author(s):  
Matthias Haeringer ◽  
Guillaume J. J. Fournier ◽  
Max Meindl ◽  
Wolfgang Polifke
Keyword(s):  
Wave Theory ◽  
Bloch Wave ◽  
Reflection Coefficients ◽  
Test Rig ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor ◽  
Passive Acoustic ◽  
Thermoacoustic Properties ◽  
Dominant Frequencies

Abstract Thermoacoustic properties of can-annular combustors are commonly investigated by means of single-can test-rigs. To obtain representative results, it is crucial to mimic can-can coupling present in the full engine. However, current approaches either lack a solid theoretical foundation or are not practicable for high-pressure rigs. In the present study we employ Bloch-wave theory to derive reflection coefficients that correctly represent can-can coupling. We propose a strategy to impose such reflection coefficients at the acoustic terminations of a single-can test-rig by installing passive acoustic elements, namely straight ducts or Helmholtz resonators. In an iterative process, these elements are adapted to match the reflection coefficients for the dominant frequencies of the full engine. The strategy is demonstrated with a network model of a generic can-annular combustor and a 3D model of a realistic can-annular combustor configuration. For the latter we show that can-can coupling via the compressor exit plenum is negligible for frequencies sufficiently far away from plenum eigenfrequencies. Without utilizing previous knowledge of relevant frequencies or flame dynamics, the test-rig models are adapted within a few iterations and match the full engine with good accuracy. Using Helmholtz resonators for test-rig adaption turns out to be more viable than using straight ducts.

scholarly journals Effects of liquid fuel/wall interaction on thermoacoustic instabilities in swirling spray flames

2020 ◽  
Vol 219 ◽  
pp. 86-101 ◽  
Author(s):  
E. Lo Schiavo ◽  
D. Laera ◽  
E. Riber ◽  
L. Gicquel ◽  
T. Poinsot
Keyword(s):  
Liquid Fuel ◽  
Thermoacoustic Instabilities ◽  
Spray Flames ◽  
Wall Interaction

Low-Order Modeling to Investigate Clusters of ITA Modes in Annular Combustors

2020 ◽  
Author(s):  
Guillaume Jean Jacques Fournier ◽  
Matthias Haeringer ◽  
Camilo Silva ◽  
Wolfgang Polifke
Keyword(s):  
Reflection Coefficient ◽  
Analytical Model ◽  
Underlying Mechanism ◽  
Riemann Invariants ◽  
Azimuthal Mode ◽  
Annular Combustor ◽  
1D Model ◽  
Phasor Analysis ◽  
Peculiar Behavior ◽  
Mode Order

Abstract The intrinsic thermoacoustic (ITA) feedbackloop constitutes a coupling between flow, flame and acoustics that does not involve the natural acoustic modes of the system. One recent study showed that ITA modes in annular combustors come in significant number and with the peculiar behavior of clusters, i.e. several modes with close frequencies. In the present work an analytical model of a typical annular combustor is derived via Riemann invariants and Bloch theory. The resulting formulation describes the full annular system as a longitudinal combustor with an outlet reflection coefficient that depends on frequency and the azimuthal mode order. The model explains the underlying mechanism of the clustering phenomena and the structure of the clusters associated with ITA modes of different azimuthal orders. In addition, a phasor analysis is proposed, which enclose the conditions for which the 1D model remains valid when describing the thermoacoustic behavior of an annular combustor.

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