The Experts below are selected from a list of 306 Experts worldwide ranked by ideXlab platform
Thomas Sattelmayer - One of the best experts on this subject based on the ideXlab platform.
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Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process
Fluids, 2019Co-Authors: Aaron Endres, Thomas SattelmayerAbstract:Boundary layer Flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined Flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0.5 bar and 3 bar. It was found that the Flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at Flashback conditions decrease with increasing pressure, which decreases Flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases Flashback propensity. It is not possible to predict the occurrence of boundary layer Flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer Flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer Flashback.
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Boundary Layer Flashback in Premixed Hydrogen-Air Flames With Acoustic Excitation
Journal of Engineering for Gas Turbines and Power, 2017Co-Authors: Vera Hoferichter, Thomas SattelmayerAbstract:Lean premixed combustion is prevailing in gas turbines to minimize nitrogen oxide emissions. However, this technology bears the risk of flame Flashback and thermoacoustic instabilities. Thermoacoustic instabilities induce velocity oscillations at the burner exit which, in turn, can trigger flame Flashback. This article presents an experimental study at ambient conditions on the effect of longitudinal acoustic excitation on Flashback in the boundary layer of a channel burner. The acoustic excitation simulates the effect of thermoacoustic instabilities. Flashback limits are determined for different excitation frequencies characterizing intermediate frequency dynamics in typical gas turbine combustors (100–350 Hz). The excitation amplitude is varied from 0% to 36% of the burner bulk flow velocity. For increasing excitation amplitude, the risk of flame Flashback increases. This effect is strongest at low frequencies. For increasing excitation frequency, the influence of the velocity oscillations decreases as the flame has less time to follow the changes in bulk flow velocity. Two different Flashback regimes can be distinguished based on excitation amplitude. For low excitation amplitudes, Flashback conditions are reached if the minimum flow velocity in the excitation cycle falls below the Flashback limit of unexcited unconfined flames. For higher excitation amplitudes, where the flame starts to periodically enter the burner duct, Flashback is initiated if the maximum flow velocity in the excitation cycle is lower than the Flashback limit of confined flames. Consequently, Flashback limits of confined flames should also be considered in the design of gas turbine burners as a worst case scenario.
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Predicting Flashback Limits of a Gas Turbine Model Combustor Based on Velocity and Fuel Concentration for H2–Air Mixtures
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2016Co-Authors: Matthias Utschick, Daniel Eiringhaus, Christian Kohler, Thomas SattelmayerAbstract:This study investigates the influence of the fuel injection strategy on safety against Flashback in a gas turbine model combustor with premixing of H2–air mixtures. The Flashback propensity is quantified and the Flashback mechanism is identified experimentally. The A2EV swirler concept exhibits a hollow, thick-walled conical structure with four tangential slots. Four fuel injector geometries were tested. One of them injects the fuel orthogonal to the air flow in the slots (jet-in-crossflow injector (JICI)). Three injector types introduce the fuel almost isokinetic to the air flow at the trailing edge of the swirler slots (trailing edge injector (TEI)). Velocity and mixing fields in mixing zone and combustion chamber in isothermal water flow were measured with high-speed particle image velocimetry (PIV) and high-speed laser-induced fluorescence (LIF). The Flashback limit was determined under atmospheric pressure for three air mass flows and 673 K preheat temperature for H2–air mixtures. Flashback mechanism and trajectory of the flame tip during Flashback were identified with two stereoscopically oriented intensified high-speed cameras observing the OH* radiation. We notice Flashback in the core flow due to combustion-induced vortex breakdown (CIVB) and turbulent flame propagation (TFP) near the wall dependent on the injector type. The Flashback resistance (FBR) defined as the ratio between a characteristic flow speed and a characteristic flame speed measures the direction of propagation of a turbulent flame in the flow field. Although CIVB cannot be predicted solely based on the FBR, its distribution gives evidence for CIVB-prone states. The fuel should be injected preferably isokinetic to the air flow along the entire trailing edge in order to reduce the RMS fluctuation of velocity and fuel concentration. The characteristic velocity in the entire cross section of the combustion chamber inlet should be at least twice the characteristic flame speed. The position of the stagnation point should be tuned to be located in the combustion chamber by adjusting the axial momentum. Those measures lead to safe operation with highly reactive fuels at high equivalence ratios.
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Analytic Prediction of Unconfined Boundary Layer Flashback Limits in Premixed Hydrogen-Air Flames
Combustion Theory and Modelling, 2016Co-Authors: Vera Hoferichter, Christoph Hirsch, Thomas SattelmayerAbstract:Flame Flashback is a major challenge in premixed combustion. Hence, the prediction of the minimum flow velocity to prevent boundary layer Flashback is of high technical interest. This paper presents an analytic approach to predicting boundary layer Flashback limits for channel and tube burners. The model reflects the experimentally observed Flashback mechanism and consists of a local and global analysis. Based on the local analysis, the flow velocity at Flashback initiation is obtained depending on flame angle and local turbulent burning velocity. The local turbulent burning velocity is calculated in accordance with a predictive model for boundary layer Flashback limits of duct-confined flames presented by the authors in an earlier publication. This ensures consistency of both models. The flame angle of the stable flame near Flashback conditions can be obtained by various methods. In this study, an approach based on global mass conservation is applied and is validated using Mie-scattering images from a ch...
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Prediction of Confined Flame Flashback Limits Using Boundary Layer Separation Theory
Journal of Engineering for Gas Turbines and Power, 2016Co-Authors: Vera Hoferichter, Christoph Hirsch, Thomas SattelmayerAbstract:Premixed combustion is a common technology applied in modern gas turbine combustors to minimize nitrogen oxide emissions. However, early mixing of fuel and oxidizer opens up the possibility of flame Flashback into the premixing section upstream of the combustion chamber. Especially, for highly reactive fuels, boundary layer Flashback (BLF) is a serious challenge. For high preheating and burner surface temperatures, boundary layer Flashback limits for burner stabilized flames converge to those of so-called confined flames, where the flame is stabilized inside the burner duct. Hence, the prediction of confined Flashback limits is a highly technically relevant task. In this study, a predictive model for Flashback limits of confined flames is developed for premixed hydrogen–air mixtures. As shown in earlier studies, confined Flashback is initiated by boundary layer separation upstream of the flame tip. Hence, the Flashback limit can be predicted identifying the minimum pressure rise upstream of a confined flame causing boundary layer separation. For this purpose, the criterion of Stratford is chosen which was originally developed for boundary layer separation in mere aerodynamic phenomena. It is shown in this paper that it can also be applied to near-wall combustion processes if the pressure rise upstream of the flame tip is modeled correctly. In order to determine the pressure rise, an expression for the turbulent burning velocity is derived including the effects of flame stretch and turbulence. A comparison of the predicted Flashback limits and experimental data shows high prediction accuracy and wide applicability of the developed model.
Ahsan Choudhuri - One of the best experts on this subject based on the ideXlab platform.
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effects of syngas composition on combustion induced vortex breakdown civb Flashback in a swirl stabilized combustor
Fuel, 2011Co-Authors: Bidhan Dam, Gilberto Corona, Mir M Hayder, Ahsan ChoudhuriAbstract:Abstract Flame Flashback attributed to combustion induced vortex breakdown (CIVB) is a major design challenge for swirl stabilized burner combustors. This paper presents an experimental investigation of combustion induced vortex breakdown (CIVB) Flashback propensity for flames yielded from Hydrogen (H 2 )–Carbon Monoxide (CO) fuel blends and actual synthesized gas (syngas) mixtures. A two-fold experimental approach, consisting of a high definition digital imaging system and a high speed PIV system, was employed. The main emphasis was on the effect of concentration of different constituents in fuel mixtures on Flashback limit. In addition, the effect of Swirl Number on Flashback propensity was discussed. The percentage of H 2 in fuel mixtures played the dominant role when CIVB Flashback occurred. For a given air mass flow rate, the mixture containing a higher percentage of H 2 underwent Flashback at much leaner conditions. Flashback maps for actual syngas fuel compositions showed a distinct behavior when various concentrations of diluents were introduced in the mixture. For the two major diluents tested, carbon dioxide (CO 2 ) and nitrogen dioxide (NO 2 ), CO 2 was more dominant. The effect of Swirl Number on the Flashback propensity was also tested and showed a decrease with an increase in Swirl Number. The final portion of this paper also provides an analysis of flow field of reacting flames which revealed complex vortex–chemistry interactions leading to vortex breakdown and Flashback. Based on the experimental results a parametric model similar to Peclet Number approach was developed employing a flame quenching concept. A value of the quench parameter, C quench was obtained from the correlation of flow Peclet Number and flame Peclet Number, which was observed to be dominated by the fuel composition rather than Swirl Number.
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Investigation of Flashback Propensity in Turbines with Syngas Fuels
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010Co-Authors: Ahsan Choudhuri, Bidhan Dam, Gilberto CoronaAbstract:The paper presents experimental measurements of combustion induced vortex breakdown (CIVB) Flashback propensity for hydrogen (H2)-carbon Monoxide (CO) flames. The effects of H2 concentration, diluents and swirl number on the Flashback propensity of H2-CO flames are discussed. For a given Ubulk, the stoichiometric ratio (%F) at which the CIVB Flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However, the Flashback propensity decreases with the increase in the swirl number. Combustor Flashback maps for syngas compositions derived from different coal source shows the distinct behavior due to the presence of various diluents in fuel mixtures.
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Flashback Propensity in Swirl Stabilized Burner With Syngas Fuels
ASME 2010 Power Conference, 2010Co-Authors: Bidhan Dam, Gilberto Corona, Ahsan ChoudhuriAbstract:In swirl stabilized burner, combustion induced vortex breakdown (CIVB) Flashback is a significant phenomenon. This paper presents experimental measurements of CIVB Flashback propensity for hydrogen (H2 )-carbon monoxide (CO) flames. The effects of H2 concentration, and swirl number on the Flashback propensity of H2 -CO flames are discussed. For a given air mass flow rate, the stoichiometric ratio (%F) at which the CIVB Flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However it appears that near the CIVB Flashback limit, the swirl strength plays a more dominating role over the H2 concentration in the fuel mixture. The Flashback propensity decreases with the increase in swirl number. An analysis of the nonreacting flow field (Air 6 g/s) as well as reacting (CH4 -Air and H2 -CO-Air) flame near the CIVB transient velocity field was conducted. The analysis revealed that a complex vortex-chemistry interaction leading to vortex breakdown and Flashback occurred. The vector flow field showed that the high swirling flow generates a more stabilized and wider recirculation zone. It also showed that the presence of H2 dictates the intensity of the Flashback process.Copyright © 2010 by ASME
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Flashback Propensity of Syngas Fuels
ASME 2009 Power Conference, 2009Co-Authors: Bidhan Dam, Ahsan ChoudhuriAbstract:The paper presents experimental measurements of Flashback propensity of H2 -CO mixtures (primary constituents of syngas fuels). Effects of H2 concentration, external excitation and swirl on the Flashback propensity of H2 -CO flames are discussed. The Flashback behavior of H2 -CO flames changes nonlinearly with the increase in H2 contents in the mixture. The critical velocity gradient (gF ) values of 5%–95% and 15%–85% H2 -CO mixtures somewhat agree with the scaling relation (gF = c(SL 2 /α)) and yield an average c value of 0.035. However, the gF values of 25%–75% H2 -CO mixture show higher order variations with the SL 2 /α ratio (especially for SL 2 /α < 19,000 s−1 ). At a lower SL 2 /α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher SL 2 /α ratio. The effect of external excitation on the Flashback propensity of H2 -CO flames with more than 5% H2 is not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H2 -CO flames.Copyright © 2009 by ASME
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Investigation of combustion instability effects on the flame characteristics of fuel blends
5th International Energy Conversion Engineering Conference and Exhibit (IECEC), 2007Co-Authors: Mahesh Subramanya, Ahsan ChoudhuriAbstract:The Flashback propensity and flame extinction combustion instabilities are investigated in hydrogen based fuel blends (ranging from 0 ‐ 25% volumetric composition) of CH 4 ‐ H 2 and CO ‐ H2. A one-dimensional counterflow twin flame burner is engineered to investigate the flame extinction trends. A burner system with interchangeable burner exits of various diameters is designed to investigate the Flashback propensity. S uch a system allows in analyzing the effect of burner exit diameter on the Flashback propensity of fuel blends. The high burning velocity of hydrogen increases the Flashback propensity in fuel blends. However, the presence of hydrogen in fuel blends strengthens the flame surfaces and prov ides greater flame stability. These flames tend to extinct at much leaner air-fuel ratios at a given s tretch rate. The presence of external oscillations enhances the flame instabilities, both in Flashback propensity and flame extinction processes. Higher the frequency or amplitude of these external oscill ations, greater is the flame instabilities.
Emily A Holmes - One of the best experts on this subject based on the ideXlab platform.
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low emotional response to traumatic footage is associated with an absence of analogue Flashbacks an individual participant data meta analysis of 16 trauma film paradigm experiments
Cognition & Emotion, 2015Co-Authors: Ian A Clark, Clare E Mackay, Emily A HolmesAbstract:Most people will experience or witness a traumatic event. A common occurrence after trauma is the experience of involuntary emotional memories of the traumatic event, herewith "Flashbacks". Some individuals, however, report no Flashbacks. Prospective work investigating psychological factors associated with an absence of Flashbacks is lacking. We performed an individual participant data meta-analysis on 16 experiments (n = 458) using the trauma film paradigm to investigate the association of emotional response to traumatic film footage and commonly collected baseline characteristics (trait anxiety, current depression, trauma history) with an absence of analogue Flashbacks. An absence of analogue Flashbacks was associated with low emotional response to the traumatic film footage and, to a lesser extent, low trait anxiety and low current depression levels. Trauma history and recognition memory for the film were not significantly associated with an absence of analogue Flashbacks. Understanding why some individuals report an absence of Flashbacks may aid preventative treatments against Flashback development.
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The neural basis of Flashback formation: the impact of viewing trauma
Psychological medicine, 2012Co-Authors: C. Bourne, Clare E Mackay, Emily A HolmesAbstract:BACKGROUND: Psychological traumatic events, such as war or road traffic accidents, are widespread. A small but significant proportion of survivors develop post-traumatic stress disorder (PTSD). Distressing, sensory-based involuntary memories of trauma (henceforth 'Flashbacks') are the hallmark symptom of PTSD. Understanding the development of Flashbacks may aid their prevention. This work is the first to combine the trauma film paradigm (as an experimental analogue for Flashback development) with neuroimaging to investigate the neural basis of Flashback aetiology. We investigated the hypothesis that involuntary recall of trauma (Flashback) is determined during the original event encoding. Method A total of 22 healthy volunteers viewed a traumatic film whilst undergoing functional magnetic resonance imaging (fMRI). They kept a 1-week diary to record Flashbacks to specific film scenes. Using a novel prospective fMRI design, we compared brain activation for those film scenes that subsequently induced Flashbacks with both non-traumatic control scenes and scenes with traumatic content that did not elicit Flashbacks ('potentials'). RESULTS: Encoding of scenes that later caused Flashbacks was associated with widespread increases in activation, including in the amygdala, striatum, rostral anterior cingulate cortex, thalamus and ventral occipital cortex. The left inferior frontal gyrus and bilateral middle temporal gyrus also exhibited increased activation but only relative to 'potentials'. Thus, these latter regions appeared to distinguish between traumatic content that subsequently flashed back and comparable content that did not. CONCLUSIONS: Results provide the first prospective evidence that the brain behaves differently whilst experiencing emotional events that will subsequently become involuntary memories - Flashbacks. Understanding the neural basis of analogue Flashback memory formation may aid the development of treatment interventions for this PTSD feature. Language: en
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can playing the computer game tetris reduce the build up of Flashbacks for trauma a proposal from cognitive science
PLOS ONE, 2009Co-Authors: Emily A Holmes, Ella L James, Thomas Coodebate, Catherine DeeproseAbstract:Background Flashbacks are the hallmark symptom of Posttraumatic Stress Disorder (PTSD). Although we have successful treatments for full-blown PTSD, early interventions are lacking. We propose the utility of developing a ‘cognitive vaccine’ to prevent PTSD Flashback development following exposure to trauma. Our theory is based on two key findings: 1) Cognitive science suggests that the brain has selective resources with limited capacity; 2) The neurobiology of memory suggests a 6-hr window to disrupt memory consolidation. The rationale for a ‘cognitive vaccine’ approach is as follows: Trauma Flashbacks are sensory-perceptual, visuospatial mental images. Visuospatial cognitive tasks selectively compete for resources required to generate mental images. Thus, a visuospatial computer game (e.g. “Tetris”) will interfere with Flashbacks. Visuospatial tasks post-trauma, performed within the time window for memory consolidation, will reduce subsequent Flashbacks. We predicted that playing “Tetris” half an hour after viewing trauma would reduce Flashback frequency over 1-week. Methodology/Principal Findings The Trauma Film paradigm was used as a well-established experimental analog for Post-traumatic Stress. All participants viewed a traumatic film consisting of scenes of real injury and death followed by a 30-min structured break. Participants were then randomly allocated to either a no-task or visuospatial (“Tetris”) condition which they undertook for 10-min. Flashbacks were monitored for 1-week. Results indicated that compared to the no-task condition, the “Tetris” condition produced a significant reduction in Flashback frequency over 1-week. Convergent results were found on a clinical measure of PTSD symptomatology at 1-week. Recognition memory between groups did not differ significantly. Conclusions/Significance Playing “Tetris” after viewing traumatic material reduces unwanted, involuntary memory Flashbacks to that traumatic film, leaving deliberate memory recall of the event intact. Pathological aspects of human memory in the aftermath of trauma may be malleable using non-invasive, cognitive interventions. This has implications for a novel avenue of preventative treatment development, much-needed as a crisis intervention for the aftermath of traumatic events.
Jens Klingmann - One of the best experts on this subject based on the ideXlab platform.
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visualization of different Flashback mechanisms for h2 ch4 mixtures in a variable swirl burner
Journal of Engineering for Gas Turbines and Power-transactions of The Asme, 2015Co-Authors: Parisa Sayad, Alessandro Schönborn, Jens KlingmannAbstract:Flame Flashback from the combustion chamber to the premixing section is a major operability issue when using high H-2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, Flashback can be triggered by different mechanisms. In this work, three Flashback mechanisms of H-2/CH4 mixtures were visualized in an atmospheric variable-swirl burner using high speed OH* chemiluminescence imaging. The H-2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of Flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown (CIVB) occurred at swirl numbers >= 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer (BL) and flame propagation in the premixing tube caused by auto-ignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during Flashback was studied and Flashback speed for different mechanisms was estimated. The flame propagation speed during Flashback was significantly different for the different mechanisms. (Less)
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influence of precessing vortex core on flame Flashback in swirling hydrogen flames
International Journal of Hydrogen Energy, 2014Co-Authors: Alessandro Schönborn, Parisa Sayad, Jens KlingmannAbstract:This study examines the influence of vortex core precession on flame Flashback of swirl-stabilised hydrogen flames. Theoretical considerations suggest that the angular velocity of a swirling flow is reduced as vortex precession causes it to acquire an eccentric motion around the central axis of the burner. The eccentric motion of the vortex generates a secondary flow, which is thought to reduce the angular velocity and tangential momentum available to the primary flow, and thereby reduce the Flashback propensity at the centre of the vortex core. Experiments measuring the influence of the eccentric motion of the flame tip on flame Flashback behaviour were conducted using high-speed sequences of OH*-chemiluminescence images. Temporal analysis of a large sample of images revealed the existence of a systematic rotational frequency of the flame tip around the central axis of the burner. Analysis of the radial position of the flame tip in relation to its axial propagation velocity showed that Flashback velocity increased as the flame tip eccentricity approached zero and Flashback velocity decreased as the eccentricity amplitude of the flame tip reached larger values. This suggested that flame eccentricity caused by vortex core precession may be detrimental to upstream flame propagation and may be effective in inhibiting flame Flashback in swirl-stabilised flames. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. (Less)
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Visualization of Different Flashback Mechanisms for H2/CH4 Mixtures in a Variable-Swirl Burner
Journal of Engineering for Gas Turbines and Power, 2014Co-Authors: Parisa Sayad, Alessandro Schönborn, Jens KlingmannAbstract:Flame Flashback from the combustion chamber to the premixing section is a major operability issue when using high H-2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, Flashback can be triggered by different mechanisms. In this work, three Flashback mechanisms of H-2/CH4 mixtures were visualized in an atmospheric variable-swirl burner using high speed OH* chemiluminescence imaging. The H-2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of Flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown (CIVB) occurred at swirl numbers >= 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer (BL) and flame propagation in the premixing tube caused by auto-ignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during Flashback was studied and Flashback speed for different mechanisms was estimated. The flame propagation speed during Flashback was significantly different for the different mechanisms. (Less)
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Visualization of Different Flashback Mechanisms for H2/CH4 Mixtures in a Variable-Swirl Burner
Volume 3A: Coal Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration, 2014Co-Authors: Parisa Sayad, Alessandro Schönborn, Jens KlingmannAbstract:Flame Flashback from the combustion chamber to the premixing section is a major operability issue when using high H-2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, Flashback can be triggered by different mechanisms. In this work, three Flashback mechanisms of H-2/CH4 mixtures were visualized in an atmospheric variable swirl burner using high speed OH chemiluminescence imaging. The H-2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of Flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown occurred at swirl numbers >= 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer and Flashback due to autoignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during Flashback was studied and Flashback speed for different mechanisms was estimated. The flame propagation speed during Flashback was significantly different for the different mechanisms. (Less)
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visualization of different Flashback mechanisms for h2 ch4 mixtures in a variable swirl burner
Volume 3A: Coal Biomass and Alternative Fuels; Cycle Innovations; Electric Power; Industrial and Cogeneration, 2014Co-Authors: Parisa Sayad, Alessandro Schönborn, Jens KlingmannAbstract:Flame Flashback from the combustion chamber to the premixing section is a major operability issue when using high H-2 content fuels in lean premixed combustors. Depending on the flow-field in the combustor, Flashback can be triggered by different mechanisms. In this work, three Flashback mechanisms of H-2/CH4 mixtures were visualized in an atmospheric variable swirl burner using high speed OH chemiluminescence imaging. The H-2 mole fraction of the tested fuel mixtures varied between 0.1 and 0.9. The flow-field in the combustor was varied by changing the swirl number from 0.0 to 0.66 and the total air mass-flow rate from 75 to 200 SLPM (standard liters per minute). The following three types of Flashback mechanism were observed: Flashback caused by combustion induced vortex breakdown occurred at swirl numbers >= 0.53 for all of the tested fuel mixtures. Flashback in the boundary layer and Flashback due to autoignition were observed at low swirl numbers and low total air mass-flow rates. The temporal and spatial propagation of the flame in the optical section of the premixing tube during Flashback was studied and Flashback speed for different mechanisms was estimated. The flame propagation speed during Flashback was significantly different for the different mechanisms. (Less)
Bidhan Dam - One of the best experts on this subject based on the ideXlab platform.
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effects of syngas composition on combustion induced vortex breakdown civb Flashback in a swirl stabilized combustor
Fuel, 2011Co-Authors: Bidhan Dam, Gilberto Corona, Mir M Hayder, Ahsan ChoudhuriAbstract:Abstract Flame Flashback attributed to combustion induced vortex breakdown (CIVB) is a major design challenge for swirl stabilized burner combustors. This paper presents an experimental investigation of combustion induced vortex breakdown (CIVB) Flashback propensity for flames yielded from Hydrogen (H 2 )–Carbon Monoxide (CO) fuel blends and actual synthesized gas (syngas) mixtures. A two-fold experimental approach, consisting of a high definition digital imaging system and a high speed PIV system, was employed. The main emphasis was on the effect of concentration of different constituents in fuel mixtures on Flashback limit. In addition, the effect of Swirl Number on Flashback propensity was discussed. The percentage of H 2 in fuel mixtures played the dominant role when CIVB Flashback occurred. For a given air mass flow rate, the mixture containing a higher percentage of H 2 underwent Flashback at much leaner conditions. Flashback maps for actual syngas fuel compositions showed a distinct behavior when various concentrations of diluents were introduced in the mixture. For the two major diluents tested, carbon dioxide (CO 2 ) and nitrogen dioxide (NO 2 ), CO 2 was more dominant. The effect of Swirl Number on the Flashback propensity was also tested and showed a decrease with an increase in Swirl Number. The final portion of this paper also provides an analysis of flow field of reacting flames which revealed complex vortex–chemistry interactions leading to vortex breakdown and Flashback. Based on the experimental results a parametric model similar to Peclet Number approach was developed employing a flame quenching concept. A value of the quench parameter, C quench was obtained from the correlation of flow Peclet Number and flame Peclet Number, which was observed to be dominated by the fuel composition rather than Swirl Number.
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Investigation of Flashback Propensity in Turbines with Syngas Fuels
48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition, 2010Co-Authors: Ahsan Choudhuri, Bidhan Dam, Gilberto CoronaAbstract:The paper presents experimental measurements of combustion induced vortex breakdown (CIVB) Flashback propensity for hydrogen (H2)-carbon Monoxide (CO) flames. The effects of H2 concentration, diluents and swirl number on the Flashback propensity of H2-CO flames are discussed. For a given Ubulk, the stoichiometric ratio (%F) at which the CIVB Flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However, the Flashback propensity decreases with the increase in the swirl number. Combustor Flashback maps for syngas compositions derived from different coal source shows the distinct behavior due to the presence of various diluents in fuel mixtures.
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Flashback Propensity in Swirl Stabilized Burner With Syngas Fuels
ASME 2010 Power Conference, 2010Co-Authors: Bidhan Dam, Gilberto Corona, Ahsan ChoudhuriAbstract:In swirl stabilized burner, combustion induced vortex breakdown (CIVB) Flashback is a significant phenomenon. This paper presents experimental measurements of CIVB Flashback propensity for hydrogen (H2 )-carbon monoxide (CO) flames. The effects of H2 concentration, and swirl number on the Flashback propensity of H2 -CO flames are discussed. For a given air mass flow rate, the stoichiometric ratio (%F) at which the CIVB Flashback occurs decreases with the increase in H2 concentration in fuel mixtures. However it appears that near the CIVB Flashback limit, the swirl strength plays a more dominating role over the H2 concentration in the fuel mixture. The Flashback propensity decreases with the increase in swirl number. An analysis of the nonreacting flow field (Air 6 g/s) as well as reacting (CH4 -Air and H2 -CO-Air) flame near the CIVB transient velocity field was conducted. The analysis revealed that a complex vortex-chemistry interaction leading to vortex breakdown and Flashback occurred. The vector flow field showed that the high swirling flow generates a more stabilized and wider recirculation zone. It also showed that the presence of H2 dictates the intensity of the Flashback process.Copyright © 2010 by ASME
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Flashback Propensity of Syngas Fuels
ASME 2009 Power Conference, 2009Co-Authors: Bidhan Dam, Ahsan ChoudhuriAbstract:The paper presents experimental measurements of Flashback propensity of H2 -CO mixtures (primary constituents of syngas fuels). Effects of H2 concentration, external excitation and swirl on the Flashback propensity of H2 -CO flames are discussed. The Flashback behavior of H2 -CO flames changes nonlinearly with the increase in H2 contents in the mixture. The critical velocity gradient (gF ) values of 5%–95% and 15%–85% H2 -CO mixtures somewhat agree with the scaling relation (gF = c(SL 2 /α)) and yield an average c value of 0.035. However, the gF values of 25%–75% H2 -CO mixture show higher order variations with the SL 2 /α ratio (especially for SL 2 /α < 19,000 s−1 ). At a lower SL 2 /α ratio, burner diameters have small effects on critical velocity gradient measurements; however, the effect is significant at higher SL 2 /α ratio. The effect of external excitation on the Flashback propensity of H2 -CO flames with more than 5% H2 is not significant. Flashback through two mechanisms and their dependence on combustor parameters were also identified for swirl stabilized H2 -CO flames.Copyright © 2009 by ASME