Improving Combustion Intensity and Modulating Flame Behaviors Using Helical-Grooved Cones

2012 ◽  
Vol 29 (2) ◽  
pp. 273-280 ◽  
Author(s):  
S. C. Yen ◽  
C. L. Shih
Keyword(s):  
Angular Momentum ◽  
Bluff Body ◽  
Flame Length ◽  
Tangential Component ◽  
The Other ◽  
Body Effect ◽  
Jet Flame ◽  
Air Jet ◽  
Fuel Jet ◽  
Air Mixing

AbstractFour helical-grooved cones were installed behind an unconfined combustion nozzle to increase the bluff-body effect and turbulence intensity (T.I.). The cone configurations included a smooth cone and the other three cones cut with 1, 2 and 3 helical v-grooves. Experimental results showed that the helical v-grooves transformed the axial momentum (or the axial velocity) to the angular momentum (or the angular velocity). TheT.I.was enhanced by increasing the tangential component of fuel-jet momentum. The direct photography and thermocouple were utilized to observe the flame structures and to delineate the characteristic flame modes, flame length, temperature distribution, and combustion intensity. The flame modes were classified as jet flame, flickering flame, bubble flame, recirculation flame, lifted flame and ring flame. The flame length decreases as the groove number increases. The increasedT.I.and groove number (or bluff-body effect) improve the fuel-air mixing. The total combustion intensity increases with annular-air jet and with the groove number.

scholarly journals Morphology and Dynamics of a Premixed Hydrogen-Methane-Air Jet Flame in Hot Vitiated Turbulent Crossflow

2020 ◽  
Author(s):  
R. Solana-Pérez ◽  
L. Miniero ◽  
S. Shcherbanev ◽  
M. Bothien ◽  
N. Noiray
Keyword(s):  
Shear Layer ◽  
High Speed ◽  
Equivalence Ratio ◽  
Thermal Power ◽  
Atmospheric Condition ◽  
Flame Length ◽  
Fuel Blend ◽  
Time Resolved ◽  
Jet Flame ◽  
Air Jet

Abstract The effect of hydrogen enrichment of a premixed hydrogen-methane-air jet in hot vitiated crossflow was studied at atmospheric condition. The hot turbulent vitiated crossflow is generated by a symmetric array of 4 × 4 jet flames burning a lean mixture of natural gas and air in fully premixed condition at equivalence ratio φcf = 0.7 and total thermal power of 50 kW. This crossflow is then used to ignite the premixed perpendicular jet of hydrogen-methane-air at ambient temperature. Three jet parameters are varied to study the effect of hydrogen addition on the flame morphology and stabilization mechanism: the hydrogen mass fraction of the H2/CH4 fuel blend (ξ = 0 – 100%), the jet equivalence ratio (φ = 0.8 – 2.0) and the jet-to-crossflow momentum ratio (J = 3 – 12). High-speed hydroxyl (OH) chemiluminescence is used to obtain the time-resolved imaging of the reactive jet and to compute its time averaged morphology. OH planar laser induced fluorescence (OH-PLIF) is used to acquire OH concentration fields at the jet center plane. The jet morphology is analyzed by considering its mean trajectory, extracted from the experimental data and fitted with empirical correlations available from the literature. New correlations are proposed for the flame length, width and center of gravity as function of the hydrogen content. It is shown that with increasing hydrogen fraction, the flame is shortened and more compact, and it stabilizes close to the jet root. Another finding of this work is the reattachment of the flame at the base of the windward jet shear layer when hydrogen fraction is increased. Robust flame anchoring is observed for H2 mass fractions of the CH4/H2 fuel blend that exceed 50%. Moreover, it is shown using instantaneous OH-PLIF images that for these conditions of increasing hydrogen concentration, the windward shear layer features larger-scale coherent structures that govern the aerodynamics of the reactive premixed jet in turbulent vitiated crossflow.

Flame Structure and Combustion Capability of Non-Premixed Rifled Nozzles

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Kuo C. San ◽  
Hung J. Hsu ◽  
Shun C. Yen
Keyword(s):  
Flame Structure ◽  
Mixing Efficiency ◽  
Gas Analyzer ◽  
Jet Flame ◽  
Gas Concentration ◽  
Air Jet ◽  
Fuel Jet ◽  
Schlieren Photography ◽  
Flame Behavior ◽  
Jet Velocities

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the central-fuel jet and the annular swirled air-jet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gas-concentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling air-jet velocity (ua) improves the combustion capability. Five characteristic flame modes—jet-flame, flickering-flame, recirculated-flame, ring-flame and lifted-flame—were obtained using various annular air-jet and central fuel-jet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12-rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12-rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2005 ◽  
Vol 127 (1) ◽  
pp. 187-196 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven nonpremixed turbulent flames.

Orifice Diameter Effects on Diesel Fuel Jet Flame Structure

2001 ◽  
Author(s):  
Lyle M. Pickett ◽  
Dennis L. Siebers
Keyword(s):  
Diesel Fuel ◽  
Direct Injection ◽  
Flame Structure ◽  
Air Entrainment ◽  
Flame Length ◽  
Turbulent Flames ◽  
Orifice Diameter ◽  
Jet Flame ◽  
Fuel Jet ◽  
Lift Off

Abstract The effects of orifice diameter on several aspects of diesel fuel jet flame structure were investigated in a constant-volume combustion vessel under heavy-duty, direct-injection (DI) diesel engine conditions using Phillips research grade #2 diesel fuel and orifice diameters ranging from 45 μm to 180 μm. The overall flame structure was visualized with time-averaged OH chemiluminescence and soot luminosity images acquired during the quasi-steady portion of the diesel combustion event that occurs after the transient premixed burn is completed and the flame length is established. The lift-off length, defined as the farthest upstream location of high-temperature combustion, and the flame length were determined from the OH chemiluminescence images. In addition, relative changes in the amount of soot formed for various conditions were determined from the soot incandescence images. Combined with previous investigations of liquid-phase fuel penetration and spray development, the results show that air entrainment upstream of the lift-off length (relative to the amount of fuel injected) is very sensitive to orifice diameter. As orifice diameter decreases, the relative air entrainment upstream of the lift-off length increases significantly. The increased relative air entrainment results in a reduced overall average equivalence ratio in the fuel jet at the lift-off length and reduced soot luminosity downstream of the lift-off length. The reduced soot luminosity indicates that the amount of soot formed relative to the amount of fuel injected decreases with orifice diameter. The flame lengths determined from the images agree well with gas jet theory for momentum-driven, non-premixed turbulent flames.

MODELING OF A TURBULENT ETHYLENE/AIR JET FLAME USING HYBRID FINITE VOLUME/MONTE CARLO METHODS

2009 ◽  
Vol 1 (1) ◽  
pp. 37-53 ◽  
Author(s):  
Ranjan S. Mehta ◽  
Anquan Wang ◽  
Michael F. Modest ◽  
Daniel C. Haworth
Keyword(s):  
Monte Carlo ◽  
Finite Volume ◽  
Monte Carlo Methods ◽  
Jet Flame ◽  
Air Jet

Effects of Acoustic Excitation on a Swirling Diffusion Flame

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Michael E. Loretero ◽  
Rong F. Huang
Keyword(s):  
Flow Field ◽  
Bluff Body ◽  
Excitation Frequency ◽  
Excitation Amplitude ◽  
Mie Scattering ◽  
Flame Length ◽  
Laser Doppler Velocimeter ◽  
Scattering Method ◽  
Acoustic Excitation ◽  
Characteristic Modes

A swirling double concentric jet is commonly used for nonpremixed gas burner application for safety reasons and to improve the combustion performance. Fuel is generally spurted at the central jet while the annular coflowing air is swirled. They are normally separated by a blockage disk where the bluff-body effects further enhance the recirculation of hot gas at the reaction zone. This paper aims to experimentally investigate the behavior of flame and flow in a double concentric jet combustor when the fuel supply is acoustically driven. Laser-light sheet assisted Mie scattering method has been used to visualize the flow, while the flame lengths were measured by a conventional photography technique. The fluctuating velocity at the jet exit was measured by a two-component laser Doppler velocimeter. Flammability and stability at first fuel tube resonant frequency are reported and discussed. The evolution of flame profile with excitation level is presented and discussed, together with the reduction in flame length. The flame in the unforced reacting axisymmetric wake is classified into three characteristic modes, which are weak swirling flame, lifted flame, and transitional reattached flame. These terms reflect their primary features of flame appearances, and when the acoustic excitation is applied, the flame behaviors change with the excitation frequency and amplitude. Four additional characteristic modes are identified; e.g., at low excitation amplitudes, wrinkling flame with a blue annular film is observed because the excitation induces vortices in the central fuel jet and hence gives rise to the wrinkling of flame. The central jet vortices become larger with the increase in excitation amplitude and thus lead to a wider and shorter flame. If the excitation amplitude is increased above a certain value, the central jet vortices change the rotation direction and pacing with the annular jet vortices. These changes in the flow field induce large turbulent intensity and mixing and therefore make the flame looks blue and short. Further increase in the excitation amplitude would lift the flame because the flow field would be dramatically modified.

Modeling of Free Vertical Turbulent Diffusion Flames

1991 ◽  
Author(s):  
M. A. Gadalla ◽  
M. A. R. Sharif
Keyword(s):  
Temperature Distribution ◽  
Turbulent Diffusion ◽  
Diffusion Flames ◽  
Turbulent Diffusion Flame ◽  
Jet Mixing ◽  
Turbulent Diffusion Flames ◽  
Air Jet ◽  
Annular Jet ◽  
Fuel Jet ◽  
Model Predictions

Abstract A mathematical/empirical model compatible with the jet mixing theory for predicting the flow field properties, flame envelope, temperature distribution, and flame heights around a free vertical axi-symmetric turbulent diffusion flame has been developed. The model considers the effects of buoyancy force and the relative angle between the reactant jets. The flames are issued from a burner which consists of a central air jet and an annular fuel (commercial butane) jet. The annular jet is issued either vertically or at an angle to the flame axis. Experiments were performed earlier to measure the temperature distribution and concentration of carbon dioxide and oxygen in such flames. Three angular positions of the annular fuel jet and nine burner geometries were investigated. The model predictions in similar configurations are found to be in fair agreement with the experimental data.

Experimental investigation of isothermal and reacting flow characteristics downstream of axisymmetric bluff body stabilizers under stratified or fully premixed inlet mixture conditions

2020 ◽  
Author(s):  
Γεώργιος Πατεράκης
Keyword(s):  
Experimental Investigation ◽  
Turbulent Flow ◽  
Bluff Body ◽  
Operating Conditions ◽  
Reacting Flow ◽  
Wide Range ◽  
Flow Features ◽  
Air Mixing ◽  
The Impact ◽  
Stratified Flames

The current work describes an experimental investigation of isothermal and turbulent reacting flow field characteristics downstream of axisymmetric bluff body stabilizers under a variety of inlet mixture conditions. Fully premixed and stratified flames established downstream of this double cavity premixer/burner configuration were measured and assessed under lean and ultra-lean operating conditions. The aim of this thesis was to further comprehend the impact of stratifying the inlet fuelair mixture on the reacting wake characteristics for a range of practical stabilizers under a variety of inlet fuel-air settings. In the first part of this thesis, the isothermal mean and turbulent flow features downstream of a variety of axisymmetric baffles was initially examined. The effect of different shapes, (cone or disk), blockage ratios, (0.23 and 0.48), and rim thicknesses of these baffles was assessed. The variations of the recirculation zones, back flow velocity magnitude, annular jet ejection angles, wake development, entrainment efficiency, as well as several turbulent flow features were obtained, evaluated and appraised. Next, a comparative examination of the counterpart turbulent cold fuel-air mixing performance and characteristics of stratified against fully-premixed operation was performed for a wide range of baffle geometries and inlet mixture conditions. Scalar mixing and entrainment properties were investigated at the exit plane, at the bluff body annular shear layer, at the reattachment region and along the developing wake were investigated. These isothermal studies provided the necessary background information for clarifying the combustion properties and interpreting the trends in the counterpart turbulent reacting fields. Subsequently, for selected bluff bodies, flame structures and behavior for operation with a variety of reacting conditions were demonstrated. The effect of inlet fuel-air mixture settings, fuel type and bluff body geometry on wake development, flame shape, anchoring and structure, temperatures and combustion efficiencies, over lean and close to blow-off conditions, was presented and analyzed. For the obtained measurements infrared radiation, particle image velocimetry, laser doppler velocimetry, chemiluminescence imaging set-ups, together with Fouriertransform infrared spectroscopy, thermocouples and global emission analyzer instrumentation was employed. This helped to delineate a number of factors that affectcold flow fuel-air mixing, flame anchoring topologies, wake structure development and overall burner performance. The presented data will also significantly assist the validation of computational methodologies for combusting flows and the development of turbulence-chemistry interaction models.

Influence of Burner Material, Tip Temperature, and Geometrical Flame Configuration on Flashback Propensity of H2-Air Jet Flames

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Zhixuan Duan ◽  
Brendan Shaffer ◽  
Vincent McDonell ◽  
Georg Baumgartner ◽  
Thomas Sattelmayer
Keyword(s):  
Jet Flames ◽  
Comprehensive Overview ◽  
High Hydrogen ◽  
Jet Flame ◽  
Practical Applications ◽  
Geometric Configurations ◽  
Air Jet ◽  
Low Emission ◽  
Flame Burner ◽  
Negative Impacts

Flashback is a key operability issue for low emission premixed combustion systems operated on high hydrogen content fuels. Previous work investigated fuel composition impacts on flashback propensity and found that burner tip temperature was important in correlating flashback data in premixed jet flames. An enclosure around the jet flame was found to enhance the flame–burner rim interaction. The present study further addresses these issues using a jet burner with various geometric configurations and interchangeable materials. Systematic studies addressing the quantitative influence of various parameters such as tip temperature, burner material, enclosure size, and burner diameter on flashback propensity were carried out. A comprehensive overview of the flashback limits for all conditions tested in the current study as well as those published previously is given. The collective results indicate that the burner materials, tip temperature, and flame confinement play significant roles for flashback propensity and thus help explain previous scatter in flashback data. Furthermore, the present work indicates that the upstream flame propagation during flashback is affected by the burner material. The material with lower thermal conductivity yields larger flashback propensity but slower flame regression inside the tube. These observations can be potentially exploited to minimize the negative impacts of flashback in practical applications.

scholarly journals Experimental Study on Bluff-Body Stabilized Premixed Flame with a Central Air/Fuel Jet

Energies ◽  
2017 ◽  
Vol 10 (12) ◽  
pp. 2011 ◽  
Author(s):  
Yiheng Tong ◽  
Shuang Chen ◽  
Mao Li ◽  
Zhongshan Li ◽  
Jens Klingmann
Keyword(s):  
Experimental Study ◽  
Bluff Body ◽  
Premixed Flame ◽  
Fuel Jet
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