Combustion instability characteristics in a dump combustor using different hydrocarbon fuels

2019 ◽  
Vol 123 (1263) ◽  
pp. 586-599
Author(s):  
D. Hwang ◽  
Y. Song ◽  
K. Ahn
Keyword(s):  
Dynamic Pressure ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Hydrocarbon Fuels ◽  
Chamber Length ◽  
Dump Combustor ◽  
Geometric Conditions ◽  
Power Spectral ◽  
Dynamic Combustion

ABSTRACTThe combustion instability characteristics in a model dump combustor with an exhaust nozzle were experimentally investigated. The first objective was to understand the effects of operating conditions and geometric conditions on combustion instability. The second objective was to examine more generalised parameters that affect the onset of combustion instability. Three different premixed gases consisting of air and hydrocarbon fuels (C2H4, C2H6, C3H8) were burnt in the dump combustor at various inlet velocity, equivalence ratio and combustion chamber length. Dynamic pressure transducer and photomultiplier tube with a bandpass filter were used to measure pressure fluctuation and CH* chemiluminescence data. Peak frequencies and their maximum power spectral densities of pressure fluctuations at same equivalence ratios showed different trends for each fuel. However, the dynamic combustion characteristics of pressure fluctuations displayed consistent results under similar characteristics chemistry times regardless of the used hydrocarbon fuels. The results showed that characteristic chemistry time and characteristic convection time influenced combustion instabilities. It was found that the convective-acoustic combustion instability could be prevented by increasing the characteristic chemistry time and characteristic convection time.

scholarly journals Experimental Study on Dynamic Combustion Characteristics in Swirl-Stabilized Combustors

Energies ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1609
Author(s):  
Donghyun Hwang ◽  
Kyubok Ahn
Keyword(s):  
Experimental Study ◽  
Heat Release ◽  
Dynamic Pressure ◽  
Combustion Instability ◽  
Flame Structure ◽  
Pressure Sensors ◽  
Necessary Condition ◽  
Rayleigh Criterion ◽  
Pressure Oscillations ◽  
Geometric Conditions

An experimental study was performed to investigate the combustion instability characteristics of swirl-stabilized combustors. A premixed gas composed of ethylene and air was burned under various flow and geometric conditions. Experiments were conducted by changing the inlet mean velocity, equivalence ratio, swirler vane angle, and combustor length. Two dynamic pressure sensors, a hot-wire anemometer, and a photomultiplier tube were installed to detect the pressure oscillations, velocity perturbations, and heat release fluctuations in the inlet and combustion chambers, respectively. An ICCD camera was used to capture the time-averaged flame structure. The objective was to understand the relationship between combustion instability and the Rayleigh criterion/the flame structure. When combustion instability occurred, the pressure oscillations were in-phase with the heat release oscillations. Even if the Rayleigh criterion between the pressure and heat release oscillations was satisfied, stable combustion with low pressure fluctuations was possible. This was explained by analyzing the dynamic flow and combustion data. The root-mean-square value of the heat release fluctuations was observed to predict the combustion instability region better than that of the inlet velocity fluctuations. The bifurcation of the flame structure was a necessary condition for combustion instability in this combustor. The results shed new insight into combustion instability in swirl-stabilized combustors.

Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine

1998 ◽  
Vol 120 (4) ◽  
pp. 721-726 ◽  
Author(s):  
J. R. Seume ◽  
N. Vortmeyer ◽  
W. Krause ◽  
J. Hermann ◽  
C.-C. Hantschk ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Preventive Measure ◽  
Feedback System ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Instability Control ◽  
Heavy Duty Gas Turbine

During the prototype shop tests, the Model V84.3A ring combustor gas turbine unexpectedly exhibited a noticeable “humming” caused by self-excited flame vibrations in the combustion chamber for certain operating conditions. The amplitudes of the pressure fluctuations in the combustor were unusually high when compared to the previous experience with silo combustor machines. As part of the optimization program, the humming was investigated and analyzed. To date, combustion instabilities in real, complex combustors cannot be predicted analytically during the design phase. Therefore, and as a preventive measure against future surprises by “humming,” a feedback system was developed which counteracts combustion instabilities by modulation of the fuel flow rate with rapid valves (active instability control, AIC). The AIC achieved a reduction of combustion-induced pressure amplitudes by 86 percent. The Combustion instability in the Model V84.3A gas turbine was eliminated by changes of the combustor design. Therefore, the AIC is not required for the operation of customer gas turbines.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high cycle fatigue. In addition to the well-established high frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes, the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing high cycle fatigue during the design phase. The unsteady fluid-structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries, therefore they are not critical and confirm a robust and reliable design.

Experimental Determination of Mechanical Stress Induced by Rotating Stall in Unshrouded Impellers of Centrifugal Compressors

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Philipp Jenny ◽  
Yves Bidaut
Keyword(s):  
High Cycle Fatigue ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Rotating Stall ◽  
Operating Conditions ◽  
Design Phase ◽  
Cycle Fatigue ◽  
Centrifugal Compressors ◽  
Impeller Blade ◽  
Pressure Transducers

Unshrouded centrifugal compressor impellers typically operate at high rotational speeds and volume flow rates. The resulting high mean stress levels leave little margin for dynamic excitations that can cause high-cycle fatigue. In addition to the well-established high-frequency impeller blade excitations of centrifugal compressors caused by the stationary parts, such as vaned diffusers or inlet guide vanes (IGVs), the presented study addresses an unsteady rotating flow feature (rotating stall) which should be taken into account when addressing the high-cycle fatigue during the design phase. The unsteady fluid–structure interaction between rotating stall and unshrouded impellers was experimentally described and quantified during two different measurement campaigns with two full-size compression units operating under real conditions. In both campaigns, dynamic strain gauges and pressure transducers were mounted at various locations on the impeller of the first compression stage. The casing was also equipped with a set of dynamic pressure transducers to complement the study. Rotating pressure fluctuations were found to form an additional impeller excitation at a frequency that is not a multiple of the shaft speed. The measurements show that the excitation amplitude and frequency caused by the rotating pressure fluctuations depend on the operating conditions and are therefore challenging to predict and consider during the design phase. Furthermore, the excitation mechanism presented was found to cause resonant impeller blade response under specific operating conditions. For the experimentally investigated impeller geometries, a rotating pressure fluctuation caused approximately 1.5 MPa of additional dynamic stress in the structure per 1 mbar of dynamic pressure amplitude when exciting the first bending mode of the impeller. The induced dynamic mechanical stresses due to rotating stall are in the order of 10% of the endurance limit of the material for the tested impeller geometries; therefore, they are not critical and confirm a robust and reliable design.

Active Control of Combustion Instability in a Liquid-Fueled Low-NOx Combustor

1999 ◽  
Vol 121 (2) ◽  
pp. 281-284 ◽  
Author(s):  
J. M. Cohen ◽  
N. M. Rey ◽  
C. A. Jacobson ◽  
T. J. Anderson
Keyword(s):  
Control System ◽  
Active Control ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Full Scale ◽  
Operating Conditions ◽  
Engine Fuel ◽  
Fuel Flow ◽  
Fuel Nozzle ◽  
Active Control System

A practical active control system for the mitigation of combustion instability has been designed and demonstrated in a lean, premixed, single-nozzle combustor at realistic engine operating conditions. A full-scale engine fuel nozzle was modified to incorporate a simple fuel flow actuator. Results indicate that the system was capable of reducing pressure fluctuations by 82 percent (15 dB or 5.6×) while maintaining or reducing NOx and CO emissions levels.

scholarly journals Active Control of Combustion Instability in a Liquid–Fueled Low–NOx Combustor

1998 ◽  
Author(s):  
Jeffrey M. Cohen ◽  
Nancy M. Rey ◽  
Clas A. Jacobson ◽  
Torger J. Anderson
Keyword(s):  
Control System ◽  
Active Control ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Full Scale ◽  
Operating Conditions ◽  
Engine Fuel ◽  
Fuel Flow ◽  
Fuel Nozzle ◽  
Active Control System

A practical active control system for the mitigation of combustion instability has been designed and demonstrated in a lean, premixed, single -nozzle combustor at realistic engine operating conditions. A full -scale engine fuel nozzle was modified to incorporate a simple fuel flow actuator. Results indicate that the system was capable of reducing pressure fluctuations by 82% (15 dB or 5.6X) while maintaining or reducing NOx and CO emissions levels.

Experimental Study of Damper Position on Instabilities in an Annular Combustor

2018 ◽  
Author(s):  
Marek Mazur ◽  
Håkon T. Nygård ◽  
James Dawson ◽  
Nicholas Worth
Keyword(s):  
Bluff Body ◽  
Dynamic Pressure ◽  
Pressure Fluctuations ◽  
Operating Conditions ◽  
Mode Switching ◽  
Periodic Mode ◽  
Pressure Oscillations ◽  
Helmholtz Resonators ◽  
Flame Dynamics ◽  
Annular Combustor

The present study experimentally investigates the effects of different circumferential damper configurations on the instabilities in an annular combustor. The combustor consists of multiple bluff body swirl stabilized flames. It is operated with an ethylene-air premixture at a power of 66 kW. Combinations of Helmholtz resonators are used as dampers circumferentially arranged around the combustion chamber. The tests are performed at operating conditions where the combustor is self-excited and characterized by a strong standing mode and periodic mode switching. For each test, the dynamic pressure is measured at different locations and overhead imaging of OH* of the entire combustor is conducted simultaneously at a high sampling frequency. The measurements are then used to compare the pressure fluctuations of the different cases in order to find the best positioning of the dampers. The azimuthal modes in the chamber are determined and the phase shift between OH* and pressure is analysed. Based on the Rayleigh criterion, these investigations allow us to find out if the dampers only remove energy from the pressure oscillations, or if they also influence the instability margins of the combustor and the flame dynamics. Finally, the results are compared with the theoretical findings in literature and observed discrepancies are discussed.

scholarly journals Application of Active Combustion Instability Control to a Heavy Duty Gas Turbine

1997 ◽  
Author(s):  
J. R. Seume ◽  
N. Vortmeyer ◽  
W. Krause ◽  
J. Hermann ◽  
C.-C. Hantschk ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Combustion Instability ◽  
Pressure Fluctuations ◽  
Preventive Measure ◽  
Feedback System ◽  
Operating Conditions ◽  
Combustion Instabilities ◽  
Instability Control ◽  
Heavy Duty Gas Turbine

During the prototype shop tests, the Model V84.3A ring combustor gas turbine unexpectedly exhibited a noticeable “humming” caused by self-excited flame vibrations in the combustion chamber for certain operating conditions. The amplitudes of the pressure fluctuations in the combustor were unusually high when compared to the previous experience with silo combustor machines. As part of the optimization program, the humming was investigated and analyzed. To date, combustion instabilities in real, complex combustors cannot be predicted analytically during the design phase. Therefore, and as a preventive measure against future surprises by “humming”, a feedback system was developed which counteracts combustion instabilities by modulation of the fuel flow rate with rapid valves (Active Instability Control, AIC). The AIC achieved a reduction of combustion-induced pressure amplitudes by 86%. The combustion instability in the Model V84.3A gas turbine was eliminated by changes of the combustor design. Therefore, the AIC is not required for the operation of customer gas-turbines.

Scale Resolving CFD Investigations of Aerothermal Field and Emissions of a Lean Burn Aeroengine Combustor

2021 ◽  
Author(s):  
S. Paccati ◽  
L. Mazzei ◽  
A. Andreini ◽  
S. Patil ◽  
S. Shrivastava ◽  
...  
Keyword(s):  
Pressure Fluctuations ◽  
Computational Cost ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Tetrahedral Mesh ◽  
Main Stream ◽  
Nox Emissions ◽  
Lean Burn ◽  
Emission Data ◽  
Hexahedral Elements

Abstract Due to the increasingly stringent international limitations in terms of NOx emissions, the development of new combustor concepts has become extremely important in order for aircraft engines to comply with these regulations. In this framework, lean-burn technology represents a promising solution and several studies and emission data from production engines have proven that it is more promising in reducing NOx emissions than rich-burn technology. Considering the drawbacks of this combustion strategy (flame stabilization, flashback or blowout or the occurrence of large pressure fluctuations causing thermo-acoustics phenomena) as well as the difficulties and the high costs related to experimental campaigns at relevant operating conditions, Computational Fluid Dynamics (CFD) plays a key role in deepening understanding of the complex phenomena that are involved in such reactive conditions. During last years, large research efforts have been devoted to develop new advanced numerical strategies for high-fidelity predictions in simulating reactive flows that feature strong unsteadiness and high levels of turbulence intensity with affordable computational resources. In this sense, hybrid RANS-LES models represent a good compromise between accurate prediction of flame behaviour and computational cost with respect to fully-LES approaches. Stress-Blended Eddy Simulation (SBES) is a new global hybrid RANS-LES methodology which ensures an improved shielding of RANS boundary layers and a more rapid RANS-LES “transition” compared to other hybrid RANS-LES formulations. In the present work, a full annular aeronautical lean-burn combustor operated at real conditions is investigated from a numerical point of view employing the new SBES approach using poly-hexcore mesh topology, which allows to adopt an isotropic grid for more accurate scale-resolving calculations by means of fully regular hexahedral elements in the main stream. The results are compared to experimental data and to previous reference numerical results obtained with Scale Adaptive Simulation formulation on a tetrahedral mesh grid in order to underline the improvements achieved with the new advanced numerical setup.

scholarly journals Strong Azimuthal Combustion Instabilities in a Spray Annular Chamber With Intermittent Partial Blow-Off

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Kevin Prieur ◽  
Daniel Durox ◽  
Thierry Schuller ◽  
Sébastien Candel
Keyword(s):  
Light Intensity ◽  
High Speed ◽  
Transverse Velocity ◽  
Pressure Fluctuations ◽  
Pressure Sensors ◽  
Nodal Line ◽  
Operating Conditions ◽  
Acoustic Energy ◽  
Transverse Motion ◽  
Azimuthal Mode

This article reports experiments carried out in the MICCA-spray combustor developed at EM2C laboratory. This system comprises 16 swirl spray injectors. Liquid n-heptane is injected by simplex atomizers. The combustion chamber is formed by two cylindrical quartz tubes allowing full optical access to the flame region and it is equipped with 12 pressure sensors recording signals in the plenum and chamber. A high-speed camera provides images of the flames and photomultipliers record the light intensity from different flames. For certain operating conditions, the system exhibits well defined instabilities coupled by the first azimuthal mode of the chamber at a frequency of 750 Hz. These instabilities occur in the form of bursts. Examination of the pressure and the light intensity signals gives access to the acoustic energy source term. Analysis of the phase fluctuations between the two signals is carried out using cross-spectral analysis. At limit cycle, large pressure fluctuations of 5000 Pa are reached, and these levels persist over a finite period of time. Analysis of the signals using the spin ratio indicates that the standing mode is predominant. Flame dynamics at the pressure antinodal line reveals a strong longitudinal pulsation with heat release rate oscillations in phase and increasing linearly with the acoustic pressure for every oscillation levels. At the pressure nodal line, the flames are subjected to large transverse velocity fluctuations leading to a transverse motion of the flames and partial blow-off. Scenarios and modeling elements are developed to interpret these features.

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