Combustion Structures in Lifted Ethanol Spray Flames

2004 ◽  
Vol 126 (2) ◽  
pp. 254-257 ◽  
Author(s):  
Stephen K. Marley ◽  
Eric J. Welle ◽  
Kevin M. Lyons
Keyword(s):  
Reaction Zone ◽  
Flame Structure ◽  
Leading Edge ◽  
Laser Induced Fluorescence ◽  
Premixed Combustion ◽  
Diffusion Mode ◽  
Spray Flames ◽  
Partially Premixed Combustion ◽  
Planar Laser ◽  
Single Reaction

The development of a double flame structure in lifted ethanol spray flames is visualized using OH planar laser-induced fluorescence (PLIF). While the OH images indicate a single reaction zone exists without co-flow, the addition of low-speed co-flow facilitates the formation of a double flame structure that consists of two diverging flame fronts originating at the leading edge of the reaction zone. The outer reaction zone burns steadily in a diffusion mode, and the strained inner flame structure is characterized by both diffusion and partially premixed combustion exhibiting local extinction and re-ignition events.

The Structure of Two-Stage Counterflow n-Heptane-Air Flames

2000 ◽  
Author(s):  
S. K. Aggarwal ◽  
H. S. Xue
Keyword(s):  
Strain Rate ◽  
Reaction Zone ◽  
Equivalence Ratio ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Premixed Flame ◽  
Partially Premixed Combustion ◽  
Reaction Zones ◽  
Partially Premixed ◽  
Partially Premixed Flame

Partially premixed flames are formed by mixing air (in less than stoichiometric amounts) into the fuel stream prior to the reaction zone, where additional air is available for complete combustion. Such flames can occur in both laboratory and practical combustion systems. In advanced gas turbine combustor designs, such as a lean direct injection (LDI) combustor, partially premixed combustion represents an impotent mode of burning. Spray combustion often involves partially premixed combustion due to the locally fuel vapor-rich regions. In the present study, the detailed structure of n-heptane/air partially premixed flame in a counterflow configuration is investigated. The flame is computed by employing the Oppdif code and a detailed reaction mechanism consisting of 275 elementary reactions and 41 species. The partially premixed flame structure is characterized by two-stage burning or two distinct but synergistically coupled reaction zones, a rich premixed zone on the fuel side and a ‘nonpremixed zone on the air side. The fuel is completely consumed in the premixed zone with ethylene and acetylene being the major intermediate species. The reactions involving the consumption of these species are found to be the key rate-limiting reactions that characterize interactions between the two reaction zones, and determine the overall fuel consumption rate. The flame response to the variations in equivalence ratio and strain rate is examined. Increasing equivalence ratio and/or strain rate to a critical value leads to merging of the two reaction zones. The equivalence ratio variation affects the rich premixed reaction zone, while the variation in strain rate predominantly affects the nonpremixed reaction zone. The flame structure is also characterized in terms of a modified mixture fraction (conserved scalar), and laminar flamelet profiles are provided.

scholarly journals Observations on Jet-Flame Blowout

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
N. J. Moore ◽  
J. L. McCraw ◽  
K. M. Lyons
Keyword(s):  
Reaction Zone ◽  
Mixture Fraction ◽  
Flame Structure ◽  
Leading Edge ◽  
Transient Behavior ◽  
Turbulent Flames ◽  
Ignition Source ◽  
Jet Flame ◽  
Physically Based ◽  
Air Diffusion

The mechanisms that cause jet-flame blowout, particularly in the presence of air coflow, are not completely understood. This work examines the role of fuel velocity and air coflow in the blowout phenomenon by examining the transient behavior of the reaction zoneat blowout. The results of video imaging of a lifted methane-air diffusion flame at near blowout conditions are presented. Two types of experiments are described. In the first investigation, a flame is established and stabilized at a known, predetermined downstream location with a constant coflow velocity, and then the fuel velocity is subsequently increased to cause blowout. In the other, an ignition source is used to maintain flame burning near blowout and the subsequent transient behavior to blowout upon removal of the ignition source is characterized. Data from both types of experiments are collected at various coflow and jet velocities. Images are used to ascertain the changes in the leading edge of the reaction zone prior to flame extinction that help to develop a physically-based model to describe jet-flame blowout. The data report that a consistent predictor of blowout is the prior disappearance of the axially oriented flame branch. This is witnessed despite a turbulent flames' inherent variable behavior. Interpretations are also made in the light of analytical mixture fraction expressions from the literature that support the notion that flame blowout occurs when the leading edge reaches the vicinity of the lean-limit contour, which coincides approximately with the conditions for loss of the axially oriented flame structure.

Effects of leading edge entrainment on the double flame structure in lifted ethanol spray flames

2004 ◽  
Vol 29 (1) ◽  
pp. 23-31 ◽  
Author(s):  
S.K. Marley ◽  
E.J. Welle ◽  
K.M. Lyons ◽  
W.L. Roberts
Keyword(s):  
Flame Structure ◽  
Leading Edge ◽  
Spray Flames

scholarly journals Measurements in swirling spray flames at blow-off

2018 ◽  
Vol 10 (3) ◽  
pp. 185-210 ◽  
Author(s):  
Ruoyang Yuan ◽  
James Kariuki ◽  
Epaminondas Mastorakos
Keyword(s):  
Heat Release ◽  
Recirculation Zone ◽  
Laser Induced Fluorescence ◽  
Sauter Mean Diameter ◽  
Phase Doppler Anemometry ◽  
Planar Laser Induced Fluorescence ◽  
Spray Flames ◽  
Mean Diameter ◽  
Planar Laser ◽  
Lift Off

Various characteristics of swirling spray flames of ethanol, n-heptane, n-decane, and n-dodecane have been measured at conditions far from and close to blow-off using phase Doppler anemometry and OH* chemiluminescence, OH-planar laser-induced fluorescence, and Mie scattering at 5 kHz. The blow-off transient has also been examined. The OH* showed that the two main heat release regions lie around the spray jet at the inner recirculation zone and along the outer shear layer between the inner recirculation zone and the annular air jet. The heat release region is shortened and more attached as the flame approached blow-off. Mie images and phase Doppler anemometry data showed a wider dispersion of the ethanol spray compared to the other fuels. Similar spatial distributions of the Sauter mean diameter were observed for the four fuels for identical flow conditions, with the Sauter mean diameter value increasing with decreasing fuel volatility, but with the exception of significant presence of droplets in the nominally hollow cone for the ethanol spray. The OH-planar laser-induced fluorescence measurements showed an intermittent lift-off from the corner of the bluff body and the average lift-off height decreased with increasing air velocity, with less extinction along the inner flame branch especially for the heavier fuels. At the blow-off conditions, local extinctions appeared at both flame branches. The blow-off process followed a gradual reduction of the size of the flame, with the less volatile fuels showing a more severe flame area reduction compared to the condition far from blow-off. The average blow-off duration, [Formula: see text], calculated from the evolution of the area-integrated OH* signal, was a few tens of milliseconds and for all conditions investigated the ratio [Formula: see text] /( D/ UB) was around 11, but with large scatter. The measurements provide useful information for validation of combustion models focusing on local and global extinction.

Analysis of flame structure by isotope shift-planar laser induced fluorescence spectrometry of trace OH and OD Radicals

2013 ◽  
Vol 106 ◽  
pp. 334-339 ◽  
Author(s):  
Tsuyoshi Kajimoto ◽  
Eisuke Yamada ◽  
Masahisa Shinoda ◽  
Nelfa Desmira ◽  
Kuniyuki Kitagawa ◽  
...  
Keyword(s):  
Isotope Shift ◽  
Flame Structure ◽  
Laser Induced Fluorescence ◽  
Fluorescence Spectrometry ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

Measurement of Flame Structure by OH/CH Planar Laser Induced Fluorescence

2002 ◽  
Vol 2002 (0) ◽  
pp. 123-124
Author(s):  
Toshihiko SAITO ◽  
Shunsuke TSUKINARI ◽  
Gyung Min CHOI ◽  
Mamoru TANAHASHI ◽  
Toshio MIYAUCHI
Keyword(s):  
Flame Structure ◽  
Laser Induced Fluorescence ◽  
Planar Laser Induced Fluorescence ◽  
Planar Laser

scholarly journals Investigation of Dilution Effect on CH4/Air Premixed Turbulent Flame Using OH and CH2O Planar Laser-Induced Fluorescence

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 325
Author(s):  
Li Yang ◽  
Wubin Weng ◽  
Yanqun Zhu ◽  
Yong He ◽  
Zhihua Wang ◽  
...  
Keyword(s):  
Reaction Zone ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Dilution Effect ◽  
Dilution Ratio ◽  
Lean Combustion ◽  
Mild Combustion ◽  
Planar Laser ◽  
Premixed Turbulent Flame ◽  
The Given

Diluting the combustion mixtures is one of the advanced approaches to reduce the NOx emission of methane/air premixed turbulent flame, especially with high diluents to create a distributed reaction zone and mild combustion, which can lower the temperature of reaction zone and reduce the formation of NOx. The effect of N2/CO2 dilution on the combustion characteristics of methane/air premixed turbulent flame with different dilution ratio and different exit Reynolds number was conducted by OH-PLIF and CH2O-PLIF. Results show that the increase of dilution ratio can sharply reduce the concentration of OH and CH2O, and postpone the burning of fuel. Compared with the ultra-lean combustion, the dilution weakens the combustion more obviously. For different dilution gases, the concentration of OH in the combustion zone varies greatly, while the concentration of CH2O in the unburned zone is less affected by different dilution gas. The CO2 dilution has a more significant effect on OH concentration than N2 with the given dilution ratio, but a similar effect on the concentration of CH2O in the preheat zone of flame. However, dilution does not have much influence on the flame structure with the given turbulent intensity.

Solid Propellant Flame Structure

1995 ◽  
Vol 418 ◽  
Author(s):  
T. P. Parr ◽  
D. M. Hanson-Parr
Keyword(s):  
Spatial Resolution ◽  
Solid Propellant ◽  
Diffusion Flames ◽  
Flame Structure ◽  
Laser Induced Fluorescence ◽  
Flame Length ◽  
Dark Zone ◽  
Planar Laser ◽  
Burn Rate ◽  
Laser Flux

AbstractPlanar Laser Induced Fluorescence (PLIF), UV/Vis Absorption, and thermocouple measurements were done for HNF, RDX, HMX, and XM39 deflagration with and without CO2 laser-support. RDX and especially HNF have very short self-deflagration flame length scales. HMX and XM39 have taller self-deflagration flames. XM39 has a marked dark zone with plateau temperature about 1400K. RDX's dark zone, present under laser supported deflagration, collapses when the external laser flux is removed. PLIF was used to measure the 2D NH, OH, and CN species profiles for these materials and OH temperature profile for RDX and HNF under non-laser supported conditions. The best spatial resolution for the RDX PLIF was about 4μm. Sandwiches of HNF and various binders were studied with PLIF and while obvious diffusion flames were present at low pressure, they are weak and are not expected to be burn rate controlling.

scholarly journals Analysis of the partially premixed combustion in a labscale swirl-stabilized burner fueled by a methane-hydrogen mixture

2021 ◽  
Vol 312 ◽  
pp. 11004
Author(s):  
Michele Stefanizzi ◽  
Saverio Stefanizzi ◽  
Vito Ceglie ◽  
Tommaso Capurso ◽  
Marco Torresi ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Flame Structure ◽  
Premixed Combustion ◽  
Combustion Model ◽  
Cold Flow ◽  
Partially Premixed Combustion ◽  
Energy Scenario ◽  
Partially Premixed ◽  
Technical Solutions ◽  
Combustion Processes

Nowadays hydrogen is gaining more and more attention by Industry, Academia and Politics. Being a carbon free fuel, it is supposed to have a key role in the future energy scenario, especially if produced by renewable sources. The use of mixtures of hydrogen and conventional hydrocarbons in gas turbines is one of the most promising technical solutions for obtaining a sustainable combustion during the transition toward a full decarbonization. For this reason, it is fundamental to investigate the behaviour of fuels enriched with hydrogen in combustion processes. In this work, a lab-scale swirled premixed burner has been investigated by means of a fully 3D URANS approach. Firstly, a numerical simulation with cold flow has been performed to validate the model against experimental data. Then, reactive flow simulations have been performed. Initially, a combustion with 100% methane was considered. Then, a 30% by volume hydrogen blending has been investigated. The partially premixed combustion model has been implemented to take into account the inhomogeneities of the mixture at the chamber inlet. The variation of the flame structure due to the hydrogen enrichment will be described in terms of the temperature and species concentration distributions.

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