Flame Holding and Combustion Characteristics of a Geometrical Flame Holder

2008 ◽  
Author(s):  
K. A. Ahmed ◽  
D. J. Forliti
Keyword(s):  
Boundary Layer ◽  
High Speed ◽  
Equivalence Ratio ◽  
Recirculation Zone ◽  
Combustion Products ◽  
Flame Stabilization ◽  
Combustion Characteristics ◽  
Bluff Bodies ◽  
Trailing Edge ◽  
Flame Holder

Flame Stabilization in a high-speed premixed environment requires the presence of a mechanism to stabilize the flame. Bluff bodies or geometrical flame holders introduce a recirculation zone that anchor the flame. The current study considers the influence of equivalence ratio and the boundary layer state at the trailing edge of the flame holder on the flowfield and combustion characteristics. It was found that the recirculation zone is shortened as the equivalence ratio increases towards unity. A secondary shear region emerges downstream of the recirculation zone and is caused by the accelerated low-density combustion products. The emergence of the secondary shear region moves upstream with increasing equivalence ratio. Tripping the boundary layer causes a dramatic reduction in the length of the recirculation zone, and the secondary shear region is greatly augmented. Visualizations show that tripping the boundary layer resulted in a greatly disturbed flame near the trailing edge and large flame scales. Flowfield measurements suggest that the heat release is increased by approximately 50% when the boundary layer tripped.

Analysis of Lift off Height and Blow-Off Mechanism of Turbulent Flame by V-Gutter Bluff Body

2015 ◽  
Vol 787 ◽  
pp. 727-731 ◽  
Author(s):  
S. Boopathi ◽  
P. Maran ◽  
V. Caleb Eugene ◽  
S. Prabhu
Keyword(s):  
Bluff Body ◽  
Recirculation Zone ◽  
Turbulent Flame ◽  
Flame Stability ◽  
Bluff Bodies ◽  
Combustion Instabilities ◽  
Test Rig ◽  
Square Duct ◽  
Flame Holder ◽  
Lift Off

The experimental investigation has been carried out to study the stabilization and blowout mechanisms of turbulent flame stabilized by V-gutter bluff body in a square duct at reactive and non-reactive conditions. V-shaped bluff bodies made of stainless steel having 1.6 mm thicknessare used for stabilization of the flame.Experiments have been conducted at selective velocities of commercially available methane and oxygen with 60 degree V-gutter as flame holder. It is observed that at stoichiometric conditions, the V-gutter is dominated by shear layer stabilized flames. The flame stability is influenced by bluff body dimensions and mass flow rate which play a major role in combustion instabilities mixing of air fuel ratio and blow off. The lift off decreases at higher blockage ratios.A strong recirculation zone is found in this test rig immediately downstream of the V-Gutter which gradually subsides and disappears far downstream.The lift off height is not much affected by the velocity of the fuel-air mixture.

On Flame Stabilization by Bluff-Bodies

1980 ◽  
Vol 102 (1) ◽  
pp. 209-214 ◽  
Author(s):  
K. M. Kundu ◽  
D. Banerjee ◽  
D. Bhaduri
Keyword(s):  
Heat Exchange ◽  
Recirculation Zone ◽  
Flame Stabilization ◽  
Flame Stability ◽  
Bluff Bodies

Flame stabilization by bluff-bodies has been investigated to highlight the role of recirculation zone on the phenomenon. It has been observed that close correlations exist between heat exchange from recirculation zone and flame stability as controlled by recirculation strength.

Experimental and Numerical Investigations of MILD Combustion in a Model Combustor Applied for Gas Turbine

2018 ◽  
Author(s):  
Huan Zhang ◽  
Zhedian Zhang ◽  
Yan Xiong ◽  
Yan Liu ◽  
Yunhan Xiao
Keyword(s):  
Gas Turbine ◽  
Reaction Zone ◽  
High Speed ◽  
Equivalence Ratio ◽  
Low Noise ◽  
Combustion Characteristics ◽  
Doppler Velocity ◽  
Exhaust Gas ◽  
Mild Combustion ◽  
Jet Velocity

The Moderate or Intense Low-oxygen Dilution (MILD) combustion is characterized by low emission, stable combustion and low noise for various kinds of fuel. MILD combustion is a promising combustion technology for gas turbine. The model combustor composed of an optical quartz combustor liner, four jet nozzles and one pilot nozzle has been designed in this study. The four jet nozzles are equidistantly arranged in the combustor concentric circle and the high-speed jet flows from the nozzles will entrain amount of exhaust gas to make MILD combustion occur. The combustion characteristics of the model combustor under atmosphere pressure have been investigated through experiments and numerical simulations. The influence of equivalence ratio and jet velocity on flow pattern, combustion characteristics and exhaust emissions were investigated in detail, respectively. Laser Doppler velocity (LDV) was utilized to measure the speed of a series of points in the model combustor. The measurement results show that a central recirculation existed in the combustion chamber. As the jet velocity of the nozzles increases, the amount of entrained mass by the jet increases simultaneously, however, the central recirculation zone is similar in shape and size. The recirculation of the model combustor will remain self-similar when the jet velocity varies in the range. The calculation model and method were verified through comparing with experimentally LDV data and be used to optimize the model combustor. Planar laser-induced fluorescence of hydroxyl radical (OH-PLIF) approaches were adopted to investigate the flame structure, the reaction zone and the OH distribution. OH distribution of the paralleled and crossed sections in the model combustor were measured, the whole reaction zone have been analyzed. The results show that the OH distribution was uniform in whole combustor. The exhaust gas composition of the combustor was measured by the “TESTO 350” Exhaust Gas Analyzer. All measurements emission results were corrected to 15% O2 in volume. Experimental results showed that NOx and CO emissions were less than 10 ppm@15%O2 when the equivalence ratio ranges from 0.63 to 0.8.

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.

Study on lifted flame stabilization under different background pressures

2021 ◽  
pp. 1-19
Author(s):  
Qiushi Qin ◽  
Zhijun Wu ◽  
Alessandro Ferrari
Keyword(s):  
High Speed ◽  
Imaging System ◽  
Experimental Tests ◽  
Combustion Products ◽  
Jet Flow ◽  
Flame Stabilization ◽  
Lifted Flame ◽  
Jet Velocity ◽  
Lift Off ◽  
Pdf Model

Abstract A numerical experimental investigation is presented for a steady methane lifted-flame and a non-reaction jet flow in a co-flow of hot combustion products from lean premixed air/hydrogen combustion. A pressurized vitiated co-flow burner has been employed to study the methane lifted flame and non-reaction jet flow under different background pressures. The lift-off height has been measured with a high-speed camera, and the central jet flow velocity has been measured by means of a Schlieren imaging system. The experimental results show that the lift-off height decreases for an increment in the background pressure and in the co-flow temperature. As far as the experimental tests on the non-reaction jet flow is concerned, the jet velocity becomes extinct faster as the background pressure rises. The evolution of the jet velocity has been proved to be another important factor that affects the lift-off height under different background pressures, in addition to the fuel autoignition delay. The simulation data led with a RANS/PDF model show that an increment in the background pressure makes the temperatures increase and induces a brighter yellow part of lifted flame, which leads to more soot production. This proves that the flame is not completely premixed. On the other hand, the Schlieren images of a non-reaction jet flow highlight that the flame is partially premixed, since the edge of the jet is not well defined, as the jet penetration increases with time.

scholarly journals Counter-hairpin vortices in the turbulent wake of a sharp trailing edge

2011 ◽  
Vol 689 ◽  
pp. 317-356 ◽  
Author(s):  
Sina Ghaemi ◽  
Fulvio Scarano
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Coherent Structures ◽  
High Speed ◽  
High Speed Flow ◽  
Trailing Edge ◽  
Hairpin Vortices ◽  
Low Speed ◽  
Speed Flow ◽  
Low Speed Streaks

AbstractThe unsteady organization and evolution of coherent structures within the turbulent boundary layer and subsequent wake of the sharp symmetric trailing edge of a NACA0012 aerofoil are investigated. The experiments are conducted in an open test-section wind tunnel at ${\mathit{Re}}_{c} = \text{386\hspace{0.167em}000} $ based on the aerofoil chord and ${\mathit{Re}}_{\theta } = 1300$ based on the boundary layer momentum thickness. An initial characterization of the flow field using two-component particle image velocimetry (PIV) is followed by the investigation of the unsteady organization and evolution of coherent structures by time-resolved three-dimensional PIV based on a tomographic approach (Tomo-PIV). The inspection of the turbulent boundary layer prior to the trailing edge in the region between 0.15 and $0. 8\hspace{0.167em} {\delta }_{99} $ demonstrated streaks of low- and high-speed flow, while the low-speed streaks are observed to be more coherent along with strong interaction with hairpin-type vortical structures similar to a turbulent boundary layer at zero pressure gradient. The wake region demonstrated gradual deterioration of both the low- and the high-speed streaks with downstream progress. However, the low-speed streaks are observed to lose their coherence at a faster rate relative to the high-speed streaks as the turbulent flow develops towards the far wake. The weakening of the low-speed streaks is due to the disappearance of the viscous sublayer after the trailing edge and gradual mixing through the transport of the remaining low-speed flow towards the free stream. This transport of low-speed flow is performed by the ejection events induced by the hairpin vortices as they also persist into the developing wake. The higher persistence of the high-speed streaks is associated with counter-hairpin vortical activities as they oppose the deterioration of the high-speed streaks by frequently sweeping the high-speed flow towards the wake centreline. These vortical structures are regarded as counter-hairpin vortices as they exhibit opposite characteristics relative to the hairpin vortices of a turbulent boundary layer. They are topologically similar to the hairpins as they appear to be U-shaped but with inverted orientation, as the spanwise portion is in the vicinity of the wake centreline and the legs are inclined at an approximately $6{0}^{\ensuremath{\circ} } $ to the wake axis in the downstream direction demonstrating a strain-dominated topology. The counter-hairpin vortices are partially wrapped around the high-speed streaks and contribute to the wake development by transporting high-speed flow towards the wake centreline. Similar to the hairpin vortices of a turbulent boundary layer, the occurrence of a complete counter-hairpin vortex is occasional while its derivatives (portions of spanwise or quasi-streamwise vortices) are more frequently observed. Therefore, a pattern recognition algorithm is applied to establish characterization based on an ensemble-averaged counter-hairpin vortex. The formation of the counter-hairpin vortices is due to an additional degree of interaction between the low- and high-speed streaks after the trailing edge across the wake centreline. The shear layer produced along the wake centreline by neighbouring low- and high-speed streaks promotes the formation of spanwise vortices that form the counter-hairpin vortices by connection to quasi-streamwise vortices. Finally, a conceptual model is proposed to depict the three-dimensional unsteady organization and evolution of coherent structures in the wake region based on the hairpin and counter-hairpin vortex signatures.

scholarly journals Combustion Study on Methane-Fuel Laboratory Scaled Ram Combustor

1992 ◽  
Author(s):  
Y. Kinoshita ◽  
J. Kitajima ◽  
M. Shiraha ◽  
A. Tatara
Keyword(s):  
Mach Number ◽  
Natural Gas ◽  
Pressure Loss ◽  
Equivalence Ratio ◽  
Combustion Efficiency ◽  
Flame Stabilization ◽  
Basic Design ◽  
Design Data ◽  
Flame Holder ◽  
Combustion Tests

Fundamental flameholding and combustion tests using simple V-gutters for the flame holders were investigated in order to obtain basic design data of a natural gas fueled ram combustor. Then Laboratory Scaled Ram Combustor (LSRC) was designed and fabricated in the first phase of the HYPR project using the fundamental flameholding and combustion tests results. Various tests were conducted to study combustion performance, such as flame stabilization, combustion efficiency, pressure loss and so on, of the LSRC at the simulated conditions of flight Mach number 3. The results indicate that high combustion efficiency is attainable with controlling the concentration of methane air mixture flowed into a flame holder even at a low equivalence ratio.

Dynamics of Non-Premixed Bluff Body-Stabilized Flames in Heated Air Flow

2010 ◽  
Author(s):  
Caleb Cross ◽  
Aimee Fricker ◽  
Dmitriy Shcherbik ◽  
Eugene Lubarsky ◽  
Ben T. Zinn ◽  
...  
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
High Speed ◽  
Bluff Body ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Inlet Temperature ◽  
Fuel Injectors ◽  
Flame Holder ◽  
Process Heat

This paper describes a study of the fundamental flame dynamic processes that control bluff body-stabilized combustion of liquid fuel with low dilatation. Specifically, flame oscillations due to asymmetric vortex shedding downstream of a bluff body (i.e., the Be´nard/von-Ka´rma´n vortex street) were characterized in an effort to identify the fundamental processes that most affect the intensity of these oscillations. For this purpose, the spatial and temporal distributions of the combustion process heat release were characterized over a range of inlet velocities, temperatures, and overall fuel-air ratios in a single flame holder combustion channel with full optical access to the flame. A stream of hot preheated air was supplied to the bluff body using a preburner, and Jet-A fuel was injected across the heated gas stream from discrete fuel injectors integrated within the bluff body. The relative amplitudes, frequencies, and phase of the sinusoidal flame oscillations were characterized by Fourier analysis of high-speed movies of the flame. The amplitudes of the flame oscillations were generally found to increase with global equivalence ratio, reaching a maximum just before rich blowout. Comparison of the flame dynamics to the time-averaged spatial heat release distribution revealed that the intensity of the vortex shedding decreased as a larger fraction of the combustion process heat release occurred in the shear layers surrounding the recirculation zone of the bluff body. Furthermore, a complete transition of the vortex shedding and consequent flame stabilization from asymmetric to symmetric modes was clearly observed when the inlet temperature was reduced from 850°C to 400°C (and hence, significantly increasing the flame dilatation ratio from Tb/Tu ∼ 2.3 to 3.7).

The Effects of a Tripped Turbulent Boundary Layer on Vortex Shedding from a Blunt Trailing Edge Hydrofoil

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Philippe Ausoni ◽  
Amirreza Zobeiri ◽  
François Avellan ◽  
Mohamed Farhat
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Vortex Shedding ◽  
High Speed ◽  
Boundary Layer Transition ◽  
Trailing Edge ◽  
Layer Transition ◽  
Blunt Trailing Edge ◽  
Turbulent Transition ◽  
Reference Length

Experiments on vortex shedding from a blunt trailing edge symmetric hydrofoil operating at zero angle of attack in a uniform high speed flow, Reh=16.1·103-96.6·103, where the reference length h is the trailing edge thickness, are reported. The effects of a tripped turbulent boundary layer on the wake characteristics are analyzed and compared with the condition of a natural turbulent transition. The foil surface is hydraulically smooth and a fully effective boundary layer tripping at the leading edge is achieved with the help of a distributed roughness. The vortex shedding process is found to be strongly influenced by the boundary layer development: the tripped turbulent transition promotes the re-establishment of organized vortex shedding. In the context of the tripped transition and in comparison with the natural one, significant increases in the vortex span-wise organization, the vortex-induced hydrofoil vibration, the wake velocity fluctuations, and the vortex strength are revealed. Although the vortex shedding frequency is decreased, a modified Strouhal number based on the wake width at the end of the vortex formation region is constant and evidences the similarity of the wakes in terms of spatial distribution for the two considered boundary layer transition processes.

Ignition and Flame Stabilization of a Premixed Jet in Hot Cross Flow

2013 ◽  
Author(s):  
Denise Schmitt ◽  
Michael Kolb ◽  
Johannes Weinzierl ◽  
Christoph Hirsch ◽  
Thomas Sattelmayer
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Equivalence Ratio ◽  
Large Scale ◽  
Large Diameter ◽  
Flame Temperature ◽  
Cross Flow ◽  
Flame Stabilization ◽  
Wide Range ◽  
Cold Case

At the Institute of Thermodynamics, Technical University of Munich a large scale atmospheric combustion test rig has been designed and set up. The experimental setup is comprised of two burning zones: A first zone consists of 16 burners providing vitiated air at 1776K, into which a secondary fuel-air mixture jet is injected and ignited by the hot cross flow. The phenomenon is known in the literature as a reacting jet in hot cross flow. The hot data is compared to the cold case in order to show differences in the flow field due to flame propagation. For evaluating the flow field several experimental analyses have been applied so far (OH*, High-Speed PIV, Mixture Analysis). The focus of this paper is on the momentum ratios J = 4–10 with Jet Reynolds Numbers between 20,000 and 80,000. For the cold case the flow field is measured and compared with the reacting jet. In the injector the air and the natural gas are perfectly premixed. The equivalence ratio of the jet is varied over a wide range of mixtures (ϕ = 0.05–0.77) resulting in an adiabatic flame temperature of the jet between 800 and 2200K. As the pictures of the chemiluminescence analysis show the jet gas ignites immediately upon entering the hot cross flow. The distinct influence of the equivalence ratio on the flame length and shape can be seen in the data. The trajectory of the flame penetrates further into the channel compared to the trajectory of the cold case caused by the reaction in the flame and its resulting gas expansion. Due to the large diameter of the jet in the experiment the origins of the dominant flow patterns are obtained with high spatial resolution. Following this, flame anchoring mechanisms at different operation points are derived.

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