June 20, 2021

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Stabilization and Dynamic of Premixed Swirling Flames

Stabilization and Dynamic of Premixed Swirling Flames
Author : Paul Palies
Publisher : Academic Press
Release Date : 2020-07-03
Category : Technology & Engineering
Total pages :400
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Stabilization and Dynamic of Premixed Swirling Flames: Prevaporized, Stratified, Partially, and Fully Premixed Regimes focuses on swirling flames in various premixed modes (stratified, partially, fully, prevaporized) for the combustor, and development and design of current and future swirl-stabilized combustion systems. This includes predicting capabilities, modeling of turbulent combustion, liquid fuel modeling, and a complete overview of stabilization of these flames in aeroengines. The book also discusses the effects of the operating envelope on upstream fresh gases and the subsequent impact of flame speed, combustion, and mixing, the theoretical framework for flame stabilization, and fully lean premixed injector design. Specific attention is paid to ground gas turbine applications, and a comprehensive review of stabilization mechanisms for premixed, partially-premixed, and stratified premixed flames. The last chapter covers the design of a fully premixed injector for future jet engine applications. Features a complete view of the challenges at the intersection of swirling flame combustors, their requirements, and the physics of fluids at work Addresses the challenges of turbulent combustion modeling with numerical simulations Includes the presentation of the very latest numerical results and analyses of flashback, lean blowout, and combustion instabilities Covers the design of a fully premixed injector for future jet engine applications

Combustion Dynamics and Fluid Mechanics in Acoustically Perturbed Non-premixed Swirl-stabilized Flames

Combustion Dynamics and Fluid Mechanics in Acoustically Perturbed Non-premixed Swirl-stabilized Flames
Author : Uyi O. Idahosa
Publisher : Unknown
Release Date : 2010
Category : Acoustic impedance
Total pages :161
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The prevalence of gas turbines operating in primarily lean premixed modes is predicated on the need for lower emissions and increased efficiency. An enhancement in the mixing process through the introduction of swirl in the combustion reactants is also necessary for flame stabilization. The resulting lean swirling flames are often characterized by a susceptibility to feedback between velocity, pressure and heat release perturbations with a potential for unstable self-amplifying dynamics. The existing literature on combustion dynamics is predominantly dedicated to premixed flame configurations motivated by power generation and propulsive gas turbine applications. In the present research effort, an investigation into the response of atmospheric, non-premixed swirling flames to acoustic perturbations at various frequencies (f[subscript p] = 0-315Hz) and swirl intensities (S=0.09 and S=0.34) is carried out. The primary objective of the research effort is to broaden the scope of fundamental understanding in flame dynamics in the literature to include non-premixed swirling flames. Applications of the research effort include control strategies to mitigate the occurrence of combustion instabilities in future power generation gas turbines. Flame heat release is quantitatively measured using a photomultiplier with a 430nm bandpass filter for observing CH* chemiluminescence which is simultaneously imaged with a phase-locked CCD camera. Acoustic perturbations are generated with a loudspeaker at the base of an atmospheric co-flow burner with resulting velocity oscillation amplitudes, [vertical line]u'/U[subscript avg][vertical line] in the 0.03-0.30 range. The dependence of flame dynamics on the relative richness of the flame is investigated by studying various constant fuel flow rate flame configurations. The effect of varying fuel flow rates on the flame response is also examined using with dynamic time-dependent fuel supply rates over the data acquisition period. The Particle Image Velocimetry (PIV) method is used to study the isothermal flow field associated with acoustic pulsing. The acoustic impedance, wavelet analysis, Rayleigh criteria and phase conditioning methods are used to identify fundamental mechanisms common to highly responsive flame configurations.

Swirling Flows and Flames

Swirling Flows and Flames
Author : Toufik Boushaki
Publisher : BoD – Books on Demand
Release Date : 2019-06-26
Category : Science
Total pages :118
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Swirl flows are used in a wide range of industrial applications. In non-reacting cases, examples of applications include vortex amplifiers and reactors, heat exchangers, jet pumps, and cyclone separators. In reacting cases, swirlers are widely used in combustion systems, such as gas turbines, industrial furnaces, boilers, gasoline and diesel engines, and many other practical heating devices. Effects of using swirl on flow and combustion are significant and varied, and concern, for example, aerodynamics, mixing, flame stability, intensity of combustion, and pollutant emissions. The purpose of this book is to present recent research efforts to understand and characterize swirling flows of different types and in different applications. These include gaseous, liquid, and solid fuels in order to enhance combustion systems and their energy efficiency. Swirl flows are very complex and the studies proposed in this project are based on different means, including theoretical calculations, numerical modeling, and experimental measurements.

Combustion Dynamics of Swirl-stabilized Lean Premixed Flames in an Acoustically-driven Environment

Combustion Dynamics of Swirl-stabilized Lean Premixed Flames in an Acoustically-driven Environment
Author : Yun Huang
Publisher : Unknown
Release Date : 2008
Category : Combustion
Total pages :252
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In a similar fashion, increasing the pressure was found to alter the flame shape and flame extent, but the thermo-acoustic coupling and induced large scale structure persisted to 0.34MPa, the highest pressure tested.

ASME Technical Papers

ASME Technical Papers
Author : Anonim
Publisher : Unknown
Release Date : 2001
Category : Mechanical engineering
Total pages :129
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International Aerospace Abstracts

International Aerospace Abstracts
Author : Anonim
Publisher : Unknown
Release Date : 1999
Category : Aeronautics
Total pages :129
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Energy Research Abstracts

Energy Research Abstracts
Author : Anonim
Publisher : Unknown
Release Date : 1992
Category : Power resources
Total pages :129
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Includes all works deriving from DOE, other related government-sponsored information and foreign nonnuclear information.

Flame Structure and Stabilization in Premixed Swirl-stabilized Combustion

Flame Structure and Stabilization in Premixed Swirl-stabilized Combustion
Author : Craig L. Beyler
Publisher : Unknown
Release Date : 1981
Category : Combustion
Total pages :138
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AIAA Aerospace Sciences Meeting and Exhibit, 42nd

AIAA Aerospace Sciences Meeting and Exhibit, 42nd
Author : Anonim
Publisher : Unknown
Release Date : 2004
Category : Aeronautics
Total pages :129
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34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit

34th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit
Author : Anonim
Publisher : Unknown
Release Date : 1998
Category : Airplanes
Total pages :129
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Impact of Fuel and Oxidizer Composition on Premixed Flame Stabilization in Turbulent Swirling Flows

Impact of Fuel and Oxidizer Composition on Premixed Flame Stabilization in Turbulent Swirling Flows
Author : Soufien Taamallah
Publisher : Unknown
Release Date : 2016
Category :
Total pages :214
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The world relies on fossil fuels as its main energy source (86.7% in 1973, 81.7% in 2012). Several factors including the abundance of resources and the existing infrastructure suggest that this is likely to continue in the near future (potentially 75% in 2040). Meanwhile climate change continues to be a pressing concern that calls for the development of low CO2 energy systems. Among the most promising approaches are pre-combustion capture technologies, e.g., coal gasification and natural gas reforming that produce hydrogen-rich fuels. Another approach is oxy-combustion in which air is replaced by a mixture of O2/CO2/H2O as the oxidizer stream. However, modern gas turbines have been optimized to operate on methane-air combustion and several challenges, notably thermo-acoustic instability, arise when using other fuels or oxidizers because of their different thermochemical and transport properties. While these phenomena constitute a major challenge under conventional operations, using hydrogen-rich fuels or CO2-rich oxidizer exacerbates the problem by modifying the combustor stability map in ways that are not well understood. In this thesis, we identify combustion modes most prone to dynamics, predict the onset of thermo-acoustic instability over a wide range of fuel and oxidizer compositions, and define parameters that can scale the data. To this end, a combination of experimental and numerical tools were deployed. We carried out a series of experiments in an optically accessible laboratory-scale swirl-stabilized combustor typical of those found in modern gas turbines, using high-speed chemiluminescence to examine the flame macrostructure; high-speed Particle Image Velocimetry and OH Planar Laser Induced Fluorescence to probe the flow and flame microstructure. Numerical simulations were used to complement experiments and examine the complex three-dimensional two-way interaction between the flame and the turbulent swirling flow. Experimental data were used to construct the stability maps for different CH4-H2 mixtures and analyze the dynamic flame macrostructures and their transitions. A comparison with acoustically uncoupled combustion shows that the onset of thermo-acoustic instability is concomitant with a specific transition associated with the intermittent appearance of the flame in the outer recirculation zone (ORZ) and stabilization along the outer shear layer (forming between the swirling jet and the ORZ, as revealed by the PIV-PLIF data). The sudden onset of large amplitude limit cycle oscillations and the observed hysteresis suggest the existence of a sub-critical Hopf bifurcation typically characterized by a bistable or "triggering" zone; the flame intermittency in the ORZ can potentially provide the disturbance required to trigger these oscillations. Using a dual-camera method to track chemiluminescence in space and time, this flame transition was found to originate from a reacting kernel that detaches from the inner shear layer flame (forming between the jet and the vortex breakdown zone), reaching the ORZ and spinning at a specific frequency; its characteristic Strouhal number is independent of the Reynolds number and the fuel/oxidizer, only a function of the swirl strength. We propose a new Karlovitz number based criterion that defines the transition on a flow time - flame time space, the former being the inverse of the spinning frequency and the latter being the flame extinction strain rate. According to this scaling, the flame survives in the ORZ if and when it can overcome the region's bulk strain rate. This criterion is valid over a wide range of operating, fuel and oxidizer composition, covering a wide range of fast to slow chemistry scenarios. Given the role of this flame transition in triggering the instability, the same criterion is applicable to predicting the onset of thermo-acoustics. The interaction of the turbulent swirling flow with the flame is further examined using large eddy simulations. Numerical simulations show that the experimentally observed large scale flame structures along the inner shear layer are due to a helical vortex core that originates at the swirler's centerbody. This vortical structure stays aligned with the centerline in the combustor upstream section, but bends and reaches the inner shear layer-stabilized flame around the sudden expansion where it causes the flame wrinkling. We propose that the flame kernel igniting the ORZ/ OSL observed in the experiment may be related to the interaction between the helical vortical structure and the outer shear layer.

40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit July 11-14, 2004, Fort Lauderdale, FL.: 04-4000 - 04-4049

40th AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit July 11-14, 2004, Fort Lauderdale, FL.: 04-4000 - 04-4049
Author : Anonim
Publisher : Unknown
Release Date : 2004
Category : Airplanes
Total pages :129
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Chemical Abstracts

Chemical Abstracts
Author : Anonim
Publisher : Unknown
Release Date : 2002
Category : Chemistry
Total pages :129
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40th AIAA Aerospace Sciences Meeting & Exhibit

40th AIAA Aerospace Sciences Meeting & Exhibit
Author : Anonim
Publisher : Unknown
Release Date : 2002
Category : Aeronautics
Total pages :129
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