Interaction of Flame Flashback Mechanisms in Premixed Hydrogen-Air Swirl Flames

2014 ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen-air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed PIV/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approx. 1/3 of the typical flow velocities in gas turbine burners. In that range the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approx. 0.45 and delivers NOx-emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

Interaction of Flame Flashback Mechanisms in Premixed Hydrogen–Air Swirl Flames

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Thomas Sattelmayer ◽  
Christoph Mayer ◽  
Janine Sangl
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Turbulent Flame ◽  
Quantitative Information ◽  
Flow Speed ◽  
Flame Stabilization ◽  
Bulk Flow ◽  
Wall Region

An experimental study is presented on the interaction of flashback originating from flame propagation in the boundary layer (1), from combustion driven vortex breakdown (2) and from low bulk flow velocity (3). In the investigations, an aerodynamically stabilized swirl burner operated with hydrogen–air mixtures at ambient pressure and with air preheat was employed, which previously had been optimized regarding its aerodynamics and its flashback limit. The focus of the present paper is the detailed characterization of the observed flashback phenomena with simultaneous high speed (HS) particle image velocimetry (PIV)/Mie imaging, delivering the velocity field and the propagation of the flame front in the mid plane, in combination with line-of-sight integrated OH*-chemiluminescence detection revealing the flame envelope and with ionization probes which provide quantitative information on the flame motion near the mixing tube wall during flashback. The results are used to improve the operational safety of the system beyond the previously reached limits. This is achieved by tailoring the radial velocity and fuel profiles near the burner exit. With these measures, the resistance against flashback in the center as well as in the near wall region is becoming high enough to make turbulent flame propagation the prevailing flashback mechanism. Even at stoichiometric and preheated conditions this allows safe operation of the burner down to very low velocities of approximately 1/3 of the typical flow velocities in gas turbine burners. In that range, the high turbulent burning velocity of hydrogen approaches the low bulk flow speed and, finally, the flame begins to propagate upstream once turbulent flame propagation becomes faster than the annular core flow. This leads to the conclusions that finally the ultimate limit for the flashback safety was reached with a configuration, which has a swirl number of approximately 0.45 and delivers NOx emissions near the theoretical limit for infinite mixing quality, and that high fuel reactivity does not necessarily rule out large burners with aerodynamic flame stabilization by swirling flows.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2001 ◽  
Author(s):  
Jassin Fritz ◽  
Martin Kröner ◽  
Thomas Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying High Speed Video recordings, the Laser Doppler Anemometry and the Laser Induced Fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechansim of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

Flashback in a Swirl Burner With Cylindrical Premixing Zone

2004 ◽  
Vol 126 (2) ◽  
pp. 276-283 ◽  
Author(s):  
J. Fritz ◽  
M. Kro¨ner ◽  
T. Sattelmayer
Keyword(s):  
Flame Propagation ◽  
Gas Turbines ◽  
High Speed ◽  
Vortex Breakdown ◽  
Swirling Flow ◽  
Laser Doppler Anemometry ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Measurement Techniques ◽  
Mean Flow

Flame flashback from the combustion chamber into the mixing zone is one of the inherent problems of lean premixed combustion and essentially determines the reliability of low NOx burners. Generally, flashback can be initiated by one of the following four phenomena: flashback due to the conditions in the boundary layer, flashback due to turbulent flame propagation in the core flow, flashback induced by combustion instabilities and flashback caused by combustion induced vortex breakdown. In this study, flashback in a swirling tubular flow was investigated. In order to draw maximum benefit from the tests with respect to the application in gas turbines, the radial distribution of the axial and circumferential momentum in the tube was selected such that the typical character of a flow in mixing zones of premix burners without centerbody was obtained. A single burner test rig has been designed to provoke flashback with the preheating temperature, the equivalence ratio and the mean flow rate being the influencing parameters. The flame position within the mixing section is detected by a special optical flame sensor array, which allows the control of the experiment and furthermore the triggering of the measurement techniques. The burning velocity of the fuel has been varied by using natural gas or hydrogen. The characteristics of the flashback, the unsteady swirling flow during the flame propagation, the flame dynamics and the reaction zones have been investigated by applying high-speed video recordings, the laser Doppler anemometry and the laser induced fluorescence. The presented results show that a combustion induced vortex breakdown is the dominating mechanism of the observed flashback. This mechanism is very sensitive to the momentum distribution in the vortex core. By adding axial momentum around the mixing tube axis, the circumferential velocity gradient is reduced and flashback can be prevented.

Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

2006 ◽  
Author(s):  
Pratap Sathiah ◽  
Andrei N. Lipatnikov
Keyword(s):  
Bluff Body ◽  
Burning Velocity ◽  
Rectangular Channel ◽  
Turbulent Flame ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Turbulent Diffusivity ◽  
Flame Thickness ◽  
Premixed Turbulent Flames ◽  
Premixed Turbulent Flame

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.

Investigation of Fuel and Load Flexibility in a SGT-600/700/800 Burner Under Atmospheric Pressure Conditions Using High-Speed Oh-Plif and Oh Chemiluminescence Imaging

2021 ◽  
Author(s):  
Arman Ahamed Subash ◽  
Haisol Kim ◽  
Sven-Inge Möller ◽  
Mattias Richter ◽  
Christian Brackmann ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Gas Turbines ◽  
High Speed ◽  
Recirculation Zone ◽  
Burning Velocity ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Optical Measurements ◽  
Experimental Investigations ◽  
Pilot Fuel

Abstract Experimental investigations were performed using a standard 3rd generation dry low emission (DLE) burner under atmospheric pressure to study the effect of central and pilot fuel addition, load variations and H2 enrichment in a NG flame. High-speed OH-PLIF and OH-chemiluminescence imaging were employed to investigate the flame stabilization, flame turbulence interactions, and flame dynamics. Along with the optical measurements, combustion emissions were recorded to observe the effect of changing operating conditions on NOX level. The burner is used in Siemens industrial gas turbines SGT-600, SGT-700 and SGT-800 with minor hardware differences. This study thus is a step to characterize fuel and load flexibility for these turbines. Without pilot and central fuel injections in the current burner configuration, the main flame is stabilized creating a central recirculation zone. Addition of the pilot fuel strengthens the outer recirculation zone (ORZ) and moves the flame slightly downstream, whereas the flame moves upstream without affecting the ORZ when central fuel injection is added. The flame was investigated utilizing H2/NG fuel mixtures where the H2 amount was changed from 0 to 100%. The flame becomes more compact, the anchoring position moves closer to the burner exit and the OH signal distribution becomes more distinct for H2 addition due to increased reaction rate, diffusivity, and laminar burning velocity. Changing the load from part to base, similar trends were observed in the flame behavior but in this case due to the higher heat release because of increased turbulence intensity.

Fuel Variation Effects in Propagation and Stabilization of Turbulent Counter-Flow Premixed Flames

2018 ◽  
Author(s):  
Ehsan Abbasi-Atibeh ◽  
Sandeep Jella ◽  
Jeffrey M. Bergthorson
Keyword(s):  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Mass Diffusion ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Flame Surface ◽  
Differential Diffusion ◽  
Turbulent Flame Speed

Sensitivity to stretch and differential diffusion of chemical species are known to influence premixed flame propagation, even in the turbulent environment where mass diffusion can be greatly enhanced. In this context, it is convenient to characterize flames by their Lewis number (Le), a ratio of thermal-to-mass diffusion. The work reported in this paper describes a study of flame stabilization characteristics when the Le is varied. The test data is comprised of Le ≪ 1 (Hydrogen), Le ≈ 1 (Methane), and Le > 1 (Propane) flames stabilized at various turbulence levels. The experiments were carried out in a Hot exhaust Opposed-flow Turbulent Flame Rig (HOTFR), which consists of two axially-opposed, symmetric turbulent round jets. The stagnation plane between the two jets allows the aerodynamic stabilization of a flame, and clearly identifies fuel influences on turbulent flames. Furthermore, high-speed Particle Image Velocimetry (PIV), using oil droplet seeding, allowed simultaneous recordings of velocity (mean and rms) and flame surface position. These experiments, along with data processing tools developed through this study, illustrated that in the mixtures with Le ≪ 1, turbulent flame speed increases considerably compared to the laminar flame speed due to differential diffusion effects, where higher burning rates compensate for the steepening average velocity gradient, and keeps these flames almost stationary as bulk flow velocity increases. These experiments are suitable for validating the ability of turbulent combustion models to predict lifted, aerodynamically-stabilized flames. In the final part of this paper, we model the three fuels at two turbulence intensities using the FGM model in a RANS context. Computations reveal that the qualitative flame stabilization trends reproduce the effects of turbulence intensity, however, more accurate predictions are required to capture the influences of fuel variations and differential diffusion.

Experimental Study of Flame Stretch Under Engine-Like Conditions

2017 ◽  
Author(s):  
Behdad Afkhami ◽  
Yanyu Wang ◽  
Scott A. Miers ◽  
Jeffrey D. Naber
Keyword(s):  
Flame Front ◽  
Flame Propagation ◽  
High Speed ◽  
Combustion Engine ◽  
Turbulent Flame ◽  
Experimental Studies ◽  
Flame Velocity ◽  
Turbulent Flame Speed ◽  
Stretch Rate ◽  
Flame Stretch

Since fossil fuels will remain the main source of energy for power generation and transportation in next decades, their combustion processes remain an important concern for the foreseeable future. For liquid or gaseous fuels, flame velocity that propagates normal to itself and relative to the flow into the unburned mixture is one of the most important quantities to study. In a non-uniform flow, a curved flame front area changes continually which is known as flame stretch. The concept becomes more important when it is realized that the stretch affects the turbulent flame speed. The current research empirically studies flame stretch under engine-like conditions since there has not been enough experimental studies in this area. For this reason, a one-cylinder, direct-injection, spark-ignition, naturally-aspirated optical engine was utilized to image the flame propagation process inside an internal combustion engine cylinder on the tumble plane. The flame front was found by processing high speed images which were taken from the flame inside the cylinder. Flame front propagation analysis showed that after the flame kernel was developed, during flame propagation period, the stretch rate decreased until the flame front touches the piston surface. This trend was common among stoichiometric, lean, and rich mixtures. In addition, the fuel-air mixture with λ = 0.85 showed lower stretch rate compared to stoichiometric or lean mixture with λ = 1.2. However, based on previous studies, further enrichment may result in the flame stretch rate become greater than that of the stretch rates for stoichiometric or lean mixtures. Also, comparing the stretch rate at two different engine speeds revealed that as the speed increased the stretch rate also increased; especially during the early flame development period. Therefore, according to previous studies which discussed flame stretch as a mechanism for flame extinguishment, the probability of the flame extinction is higher when the engine speed is higher.

Experimental Study on Laminar Flame Speeds and Markstein Length of Methane-Air Mixtures at Atmospheric Conditions

2014 ◽  
Vol 699 ◽  
pp. 714-719
Author(s):  
Alaeldeen Altag Yousif ◽  
Shaharin Anwar Sulaiman
Keyword(s):  
High Speed ◽  
Equivalence Ratio ◽  
Laminar Flame ◽  
Burning Velocity ◽  
Ambient Pressure ◽  
Flame Speed ◽  
Laminar Flame Speed ◽  
Atmospheric Conditions ◽  
Laminar Burning Velocity ◽  
Markstein Length

Accurate value of laminar flame speed is an important parameter of combustible mixtures. In this respect, experimental data are very useful for modeling improvement and validating chemical kinetic mechanisms. To achieve this, an experimental characterization on spherically expanding flames propagation of methane-air mixtures were carried out. Tests were conducted in constant volume cylindrical combustion chamber to measure stretched, unstretched laminar flame speed, laminar burning velocity, and flame stretch effect as quantified by the associated Markstein lengths. The mixtures of methane-air were ignited at extensive ranges of lean-to-rich equivalence ratios, under ambient pressure and temperature. This is achieved by high speed schlieren cine-photography for flames observation in the vessel. The results showed that the unstretched laminar burning velocity increased and the peak value of the unstretched laminar burning velocity shifted to the richer mixture side with the increase of equivalence ratio. The flame propagation speed showed different trends at different equivalence ratio for tested mixtures. It was found that the Markstein length was increased with the increase of equivalence ratio.

scholarly journals Explosion-Suppression Characteristics of Nonmetallic Spherical Spacers on Propane-Air Mixtures in Confined Space

2021 ◽  
Vol 11 (19) ◽  
pp. 9238
Author(s):  
Yangyang Yu ◽  
Lehai Liu ◽  
Junhong Zhang ◽  
Jun Wang ◽  
Xiangde Meng ◽  
...  
Keyword(s):  
Flame Propagation ◽  
High Speed ◽  
Laminar Flame ◽  
Turbulent Flame ◽  
Confined Space ◽  
Effective Prevention ◽  
Jet Flame ◽  
Explosion Suppression ◽  
Explosion Overpressure ◽  
Suppression Effects

The explosion-suppression effects of NSSs on overpressures, flame propagation and flame tip velocities were explored under the initial pressures of 0.2 MPa, 0.3 MPa and 0.4 MPa. All experiments tested in a constant volume combustion bomb (CVCB). Explosion reaction of premixed propane–air gas in a new designed CVCB filled with nonmetallic spherical spacers (NSSs) was analyzed. The results showed that overpressures decreased under the different initial pressures. With the increase of filling density, the overpressure decreased, the time to reach explosion overpressure decreased, and the decay rate of explosion overpressure increased. It was also found that the explosion-suppression effects of NSSs on pressures. Flame front could be captured by high-speed schlieren photography. Combustion phenomena were captured including flame propagation, corrugated laminar flame, jet flame, corrugated turbulent flame as well as tulip flame under different initial pressures. Flame tip velocities also were captured. The results demonstrate that flame tip velocities decreased with the increase of filling densities. However, compared with unfilled CVCB, flame tip velocities increased after filling NSSs in CVCB under different initial pressures. NSSs suppressed the explosion overpressure in the cylinder, and promoted the flame propagation. In both cases, NSSs played a dual role. The suppression effect of NSSs was affected by both its suppression and promotion effect on the explosion. This work provides a scientific basis for the effective prevention of explosion accidents with propane–air premixtures and the development of explosion-suppression products.

scholarly journals Dynamic-Stability Characteristics of Premixed Methane Oxy-Combustion

2011 ◽  
Author(s):  
Andrew P. Shroll ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Dynamic Stability ◽  
High Speed ◽  
Vortex Breakdown ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Wave Mode ◽  
Oxygen Mixture ◽  
Quarter Wave ◽  
Fuel Mixtures

This work explores the dynamic stability characteristics of premixed CH4/O2/CO2 mixtures in a 50kW swirl stabilized combustor. In all cases, the methane-oxygen mixture is stoichiometric, with different fractions of carbon dioxide used to control the flame temperature (Tad). For the highest Tad’s, the combustor is unstable at the five-quarter wave mode. As the temperature is reduced, the combustor jumps to the three quarter mode and then to the quarter wave before eventually reaching blowoff. Similar to the case of CH4/air mixtures, the transition from one mode to another is predominantly a function of the Tad of the reactive mixture, despite significant differences in laminar burning velocity and/or strained flame consumption speed between air and oxy-fuel mixtures for a given Tad. High speed images support this finding by revealing similar vortex breakdown modes and thus similar turbulent flame geometries that change as a function of flame temperature.

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