Characteristics of a Laminar Diffusion Flame in a Cross-Flow of Combustion Products

2005 ◽  
Author(s):  
M. A. Simon ◽  
B. D. Baird ◽  
S. R. Gollahalli
Keyword(s):  
Diffusion Flame ◽  
Equivalence Ratio ◽  
Cross Flow ◽  
Combustion Products ◽  
Flame Length ◽  
No Production ◽  
Flat Flame ◽  
Laminar Diffusion ◽  
Flame Burner ◽  
The Cross

This study was an investigation of the characteristics of a horizontal laminar diffusion flame established from a tubular burner in a buoyant vertical flow vitiated with combustion products created by a flat flame. The effects of varying flat flame equivalence ratio on these characteristics were studied. Applications of this study include exhaust gas recirculation (EGR), staged combustion in furnaces, and afterburners in jet engines. The fuel used for both the horizontal (cross-flow flame) and the flat flame in this study was propane. For a range of flat flame burner equivalence ratio (0.6 to 0.9), measurements of cross-flow flame length, and global emissions of NO were made. The mass flow rate of propane delivered to the cross-flow flame was held constant during these measurements. The flames were photographed with a digital camera. Profiles of combustion species concentrations and temperature were taken at 25% and 50% of the cross-flow flame length for flat flame burner equivalence ratios of 0.6 and 0.8, and for a non-combustion case (air flow only) in the flat flame. It was found that increasing the flat flame burner equivalence ratio caused an increase in the length of the cross-flow flame. The maximum temperature of the cross-flow flame decreased with increasing flat flame burner equivalence ratio. The introduction of the cross-flow flame increased the NO production in a flat flame with an equivalence ratio of 0.6, but did not significantly affect the NO production in a flat flame of an equivalence ratios of 0.7 or 0.8, and reduced it (by as much as 25%) in a flat flame of equivalence ratio of 0.9. This reduction of NO production and flame temperature and increase in flame length with increasing flat flame equivalence ratio was attributed to the reduction of oxygen available to the cross-flow flame. These results were supported with the in-flame combustion species concentration profiles.

Comparison of the Flame Characteristics of Circular and Elliptic Jets in a Cross-Flow

2000 ◽  
Author(s):  
S. R. Gollahalli ◽  
D. Pardiwalla
Keyword(s):  
Cross Flow ◽  
Major Axis ◽  
Minor Axis ◽  
No Production ◽  
Sampling System ◽  
Computer Data ◽  
Rate Of Increase ◽  
Jet Velocity ◽  
The Cross ◽  
Lower Limits

Abstract This study was directed to understand the coupling effects of the noncircular geometry of the burner and a cross-flow on the combustion of gas jets. This paper compares the characteristics of propane jet flames from circular (diameter = 0.45 cm) and elliptic (major axis = 0.75 cm, minor axis = 0.26 cm) burners of equivalent exit area in a cross-flow. The elliptic burner was oriented with its major axis or minor axis aligned with the cross-flow. Experiments were conducted in a wind-tunnel provided with optical and probe access and capable of wind speeds up to 12.5 m/s. The burners were fabricated with metal tubes. Instrumentation included a Pt-Pt/13%Rh thermocouple, a quartz-probe gas sampling system, chemiluminescent and non-dispersive infrared analyzers, a video-recorder, and a computer data acquisition system. The measurements consisted of the upper and lower limits of jet velocity for a stable flame, flame configuration, and visible length. Flame structure data including temperature profiles and concentration profiles of CO2, O2, CO, and NO were obtained in a two-zone flame configuration where a planar recirculation exists in the wake of the burner tube followed by an axisymmetric tail. Emission indices of CO and NO were estimated from the composition data. Results indicate that the upper and lower limits of the fuel jet velocity increase with the cross-flow velocity for all burners, and the rate of increase is highest for the elliptic burner with its minor axis aligned with the cross-flow. That burner configuration also produces the longest flame. The emission indices show that the CO production is lower and NO production is higher for elliptic burners than for circular burners in cross-flow. Also, aligning the minor axis of the elliptic burner with the cross-stream is superior in terms of flame stability and emissions of NO and CO.

Numerical Studies on Flames Established in Reacting Film-Cooling Experiment

2014 ◽  
Author(s):  
Viswanath R. Katta ◽  
David Blunck
Keyword(s):  
Heat Transport ◽  
Film Cooling ◽  
Equivalence Ratio ◽  
Mass Transfer Rate ◽  
Cross Flow ◽  
Combustion Products ◽  
Local Heat ◽  
Equal Mass ◽  
Blowing Ratio ◽  
Numerical Studies

Integration of turbine turning vanes into a combustor is needed for the development of ultra-compact combustors. A viable approach for protecting the combustor from the high-temperature fuel-rich environment is to inject air through the holes drilled on surfaces. However, it is possible that air intended to cooling may react with the fuel rich combustion products and increase the heat flux. Air Force Research Laboratory has initiated several experimental/numerical studies for investigating the flames that might develop between the injected air and fuel-rich flows in the combustor and their impact on film cooling. A time-dependent, detailed-chemistry computational-fluid-dynamics model is used in the present study for understanding the flames formed in reacting film cooling. Combustion of propane fuel with air is modeled using a chemical-kinetics mechanism involving 52 species and 544 reactions. Both laminar and turbulent flow simulations are performed. Effects of blowing ratio, equivalence ratio and sidewall cooling are investigated. Simulations have reproduced various flame characteristics observed in the experiments. Numerical results are used for explaining the non-intuitive shift in flame anchoring location to the changes in blowing ratio and equivalence ratio. The higher diffusive mass transfer rate of hydrogen in comparison to the local heat transport enhances cooling of cross-flow combustion products, which, in turn, affects the autoignition process. While increasing the blowing ratio abates the differences resulting from non-equal mass and heat transport rates, higher concentrations of hydrogen in the fuel-rich cross-flows accelerate those differences.

Investigation of a Flame Anchored in Crossflow Stream of Vitiated Air at Elevated Pressures

2012 ◽  
Author(s):  
Flavio Cesar Cunha Galeazzo ◽  
Chockalingam Prathap ◽  
Matthias Kern ◽  
Peter Habisreuther ◽  
Nikolaos Zarzalis ◽  
...  
Keyword(s):  
Combustion Zone ◽  
Equivalence Ratio ◽  
Turbulent Flame ◽  
Cross Flow ◽  
Flux Ratio ◽  
Combustible Mixture ◽  
Stage Combustion ◽  
Secondary Stage ◽  
The Cross ◽  
Flow Stream

The objective was to study the effect of equivalence ratio of secondary stage combustible mixture injected into the cross flow stream of vitiated air in a two staged combustion system on the characteristics of the secondary stage combustion zone. The primary cylindrical combustor equipped with low swirl air blast nozzle operating with kerosene generates vitiated air. A methane injector was flush mounted to the inner surface of the secondary combustor. It was used to inject the premixed methane-air mixtures perpendicular into the crossflow of vitiated air. An optical, double shell, secondary combustor with three optical windows on its outer shell was used to image the secondary stage flames. The inner shell was a quadratic fused quartz tube which acts as a thermal barrier and the outer thick quartz windows mounted in the quadratic stainless steel chamber withholds the pressure. Chemiluminescence imaging technique equipped with ICCD camera was used to image the OH* emissions of the secondary stage flame. The vitiated air was generated at 2 bar and 1700 K. The velocity of the vitiated air in the secondary combustor was 57 m/s. A premixed methane air mixture was injected into the cross flow stream of vitiated air. The momentum flux ratio between the jet and the vitiated air was maintained at 1.4. The equivalence ratio of the premixed methane-air mixture was varied from 0.5 to 1.0. As the equivalence ratio of the secondary stage combustible mixture moves towards stoichiometric condition, the secondary stage combustion zone becomes compact and also the distance between the burner and the combustion zone decreases. The turbulent flame stabilized in the secondary combustor exhibited large scale structures and other unsteady phenomena that require time-resolved computational methods. Large eddy simulations (LES) are well suited to the calculation of such complex flows. The flame was embedded in a strong turbulent flow where auto-ignition and quenching are important, which poses a significant challenge for the reaction modeling. The presumed JPDF turbulent reaction model, which has been proven to be a reliable model for these challenging conditions, was successfully coupled with the LES simulation. The qualitative agreement between the results of simulations and measurements was quite satisfactory.

Comprehensive JP8 Mechanism for Vitiated Flows

2010 ◽  
Vol 4 (1) ◽  
Author(s):  
K.M. Hall ◽  
X. Fu ◽  
K. Brezinsky
Keyword(s):  
Combustion Process ◽  
Combustion Products ◽  
Chemical Kinetic ◽  
Fused Silica ◽  
Liquid Fuels ◽  
Outer Diameter ◽  
Jet Engines ◽  
Flat Flame ◽  
Major Species ◽  
Flame Burner

With the intent of optimizing the combustion process of complex hydrocarbon liquid fuels such as JP8 in internal combustion jet engines and their afterburners, simpler surrogate hydrocarbon compounds were used in a counterflow diffusion flat flame burner to validate the chemical kinetic modeling process. The combustion products sampled from the flame produced during the burning of the validation fuels methane and n-heptane were analyzed using a Varian CP3800 gas chromatograph. The effects of sampling with a 350 micron outer diameter (OD) fused-silica tube were compared to those of a 3.5 mm quartz probe in order to minimize sampling effect on the flame. Simulations of the sampled species were performed using the OPPDIF package of CHEMKIN with chemistry models provided by UIC. Concentrations of major species (e.g. CO, CH4, CO2, O2) were found to be well simulated with the models, with the best fit occurring for methane and n-heptane, and wider variation occurring with some species in all validation fuels.

scholarly journals Laser-Induced Breakdown Spectroscopy (LIBS) For The Characterization Of Methane-Air Laminar Diffusion Flame

2021 ◽  
Vol 42 (4) ◽  
Author(s):  
Meirong Dong
Keyword(s):  
Spatial Distribution ◽  
Diffusion Flame ◽  
Flame Temperature ◽  
Combustion Products ◽  
Laser Induced Breakdown Spectroscopy ◽  
Laminar Diffusion Flame ◽  
Breakdown Spectroscopy ◽  
Laminar Diffusion ◽  
Laser Induced Breakdown

Laser-induced breakdown spectroscopy (LIBS) was applied for the characterization of the methane-air laminar diffusion flame, revealing the spatial distribution of its composition. From the measurement, it was found that distribution of the atomic and ionic N emissions produced by the flame had obvious differences, which were mainly distributed in the air area and flame area, respectively. A comparison of the LIBS spectra of air, methane gas, and methane-air laminar diffusion flame showed that the atomic N emissions were mainly produced by the excitation of N2, and the ionic N emissions were more related to the N-containing combustion products. In addition, the correlation between typical emissions and the flame temperature measured by thermocouple was estimated to show that the tendency of the changes in temperature can be characterized by C2 emission intensities. This work provides a new method for real-time online flame temperature measurement, and also provides a reference for revealing the formation process and conversion pathway of each component in the flame.

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