Effects of CO2 dilution on partially premixed CH4-air flames in swirl and bluff body stabilized combustor

2020 ◽  
Author(s):  
S. Aravind ◽  
R.K. Gohiya ◽  
R.S. Prakash ◽  
R. Sadanandan
Keyword(s):  
Bluff Body ◽  
Partially Premixed

Non-Linear Effects in a Lean Partially Premixed Combustor During Limit Cycle Operation

2012 ◽  
Author(s):  
J. C. Roman Casado ◽  
J. B. W. Kok
Keyword(s):  
Structural Damage ◽  
Bluff Body ◽  
Frequency Doubling ◽  
Broadband Noise ◽  
Operating Conditions ◽  
Main Peak ◽  
Combustion Dynamics ◽  
Non Linear ◽  
Linear Effects ◽  
Partially Premixed

In a gas turbine combustor limit cycles of pressure oscillations may occur due to a coupling of combustion dynamics to the acoustic field inside the system. In this case, the engine is subjected to high vibrations and the possibility of structural damage. Experimental research in this subject was carried out in a laboratory combustor operating in a lean, partially premixed methane/air flame, where the flame stabilizes on a triangular bluff body inside a rectangular combustor duct. Depending on the operating point, the flame shows a stable or unstable behavior. In this last case, amplitudes up to 155 dB (ref 20 μPa) have been recorded. The variation of behavior of the instability with operating conditions is well known. The stable combustion presents a low amplitude broadband noise. The unstable regime is more interesting. It has a main peak with high amplitude and fixed frequency and several secondary peaks at multiple times the frequency of the fundamental one. This peaks can be seen in the pressure and heat release spectrum. The secondary peaks of the pressure spectrum are due to non-linear effects. Odd numbered peaks came from a change in the acoustic boundary conditions in the burner. The even peaks are the result of frequency doubling of the odd frequencies. The frequency doubling comes from a second order source term of the Ligthill’s analogy.

Modelling Flame-Generated Noise in a Partially Premixed, Bluff Body Stabilized Model Combustor

2012 ◽  
Author(s):  
Saverio Tufano ◽  
Phil Stopford ◽  
J. C. Roman Casado ◽  
J. B. W. Kok
Keyword(s):  
Gas Turbine ◽  
Bluff Body ◽  
Cfd Simulation ◽  
Experimental Results ◽  
Combustion Model ◽  
Acoustic Oscillations ◽  
Gas Turbine Combustors ◽  
Resonance Frequencies ◽  
Partially Premixed ◽  
Good Agreement

Numerical simulation using Computational Fluid Dynamics (CFD) has become increasingly important as a tool to predict the potential occurrence of combustion instabilities in gas turbine combustors operating in lean premixed mode. Within the EU-funded Marie Curie project, LIMOUSINE (Limit cycles of thermo-acoustic oscillations in gas turbine combustors), a model test burner has been built in order to have reproducible experimental results for model validation. The burner consists of a Rijke tube of rectangular section having a flame-stabilizing wedge at about 1/4 of its length. Fuel and air supplies were carefully designed to give closed end acoustic inlet boundary conditions while the atmospheric outlet representing an acoustically open end. A transient CFD simulation of the turbulent, partially premixed, bluff body stabilized combusting flow has been carried out for the LIMOUSINE burner using ANSYS CFX commercial software. A 2-D section has been modelled by means of the scale resolving turbulence model, Scale-Adaptive Simulation (SAS), and a two-step Eddy Dissipation combustion model. Experiments were performed on the LIMOUSINE model burner to measure the dynamic variation of pressure and temperature. Results were obtained for several cases with power input ranging from 40 to 60 kW and air factors between 1.2 and 1.8. The CFD results are found to be in good agreement with experiments: the flame is predicted to stabilise on the bluff body in the fluid recirculation zone; resonance frequencies are found to change depending on power and air excess ratio and have a good agreement with experimental results and analytical values; pressure oscillations are consistent with pipe acoustic modes.

Development of a Multilayer Mesoscale Burner Array for Gas Turbine Reheat

2004 ◽  
Author(s):  
S. Lee ◽  
C. F. Edwards ◽  
C. T. Bowman
Keyword(s):  
Bluff Body ◽  
Flame Stabilization ◽  
Liquid Fuels ◽  
Nox Emissions ◽  
Fluid Inertia ◽  
Fuel Distribution ◽  
Design Changes ◽  
Partially Premixed ◽  
Swirl Flame ◽  
Diffusive Processes

Mesoscale burner arrays allow combustion to be conducted in a distributed fashion at the millimeter (meso) scale. At this scale, diffusive processes are fast, but not yet dominant, such that a number of advantages over conventional burners can be achieved without giving up the possibility to use fluid inertia to advantage. Since the scale of the reaction zone follows from the scale at which the reactants are mixed, very compact flames result. We expect that this compact, distributed form of combustion can provide not only the opportunity of inter-turbine reheat, but also the potential for lean premixed or highly vitiated combustion to suppress NOX emissions. In previous work, a 4×4 array, with burner elements on 5-mm centers, was fabricated in silicon nitride using shape deposition manufacturing. Results from both fully premixed (mixing prior to the array) and partially premixed (mixing in the array) configurations demonstrated the degree to which premixed performance can be achieved with this design and pointed to ways in which the array design could be improved. In the present work, a next-generation 6×6 array has been developed and tested. Major design changes in this array include use of a combination of bluff-body and swirl flame stabilization and a multilayer architecture with a separate fuel manifold for more uniform fuel distribution. In this multilayer design, the array is fabricated in three separate pieces, one of which is a vaporization layer designed for use with liquid fuels. Results using gaseous fuel (methane) in a fully premixed operating condition, including pressure drop, flame stability, temperature distribution in the burned gas, and NOx emissions, are reported for both bluff-body and no-bluff-body configurations. Tests for a partially premixed configuration are being carried out to evaluate the potential of the design modifications.

Dynamics of Flame Stabilized by Triangular Bluff Body in Partially Premixed Methane-Air Combustion

2011 ◽  
Author(s):  
T. V. Santosh Kumar ◽  
P. R. Alemela ◽  
J. B. W. Kok
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Reaction Rates ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Partially Premixed Combustion ◽  
Computational Fluid Dynamics Analysis ◽  
Partially Premixed

In the design and operational tuning of gas turbine combustors it is important to be able to predict the interaction of the flame stabilization recirculation area with the burner aerodynamics. In the present paper transient computational fluid dynamics analysis is used to study these effects. Vortex interactions with the flame play a key role in many practical combustion systems. The interactions drive a large class of combustion instabilities and are responsible for changing the reaction rates, shape of the flame and the global heat release rate. The evolution of vortex shedding in reactive flows and its effects on the dynamics of the flame are important to be predicted. The present study describes dynamics of bluff body stabilized flames in a partially premixed combustion system. The bluff body is an equilateral wedge that induces the flame recirculation zone. The wedge is positioned at one-third length of the duct, which, is acoustically closed at the bottom end and open at the top. Transient computational modeling of partially premixed combustion is carried out using the commercial ANSYS CFX code and the results show that the vortex shedding has a destabilizing effect on the combustion process. Scale Adaptive Simulation turbulence model is used to compare between non-reacting cases and combustion flows to show the effects of aerodynamics-combustion coupling. The transient data reveals that frequency peaks of pressure and temperature spectra and is consistent with the longitudinal natural frequencies and Kelvin-Helmholtz instability frequency for reactive flow simulations. The same phenomenon is observed at different operating conditions of varying power. It has also been shown that the pressure and heat release are in phase, satisfying the Rayleigh criterion and therefore indicating the presence of aerodynamic-combustion instability. The data are compared to the scarce data on experiments and simulations available in literature.

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