Jet flames from noncircular burners

Gollahalli, S. R.

doi:10.1007/bf02744478

Cited by 9 publications

(4 citation statements)

References 15 publications

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“…Different bandsof OH [(2, 0), (1, 0), (3,2), and (0, 0)] are detected in the emission spectra. It is observed that the OH radical formation is higher in the elliptic co ow ames than in the circular co ow ame.…”

Section: Radiation Spectral Measurementsmentioning

confidence: 99%

Elliptic Coflow Effects on a Circular Gas Jet Flame

Choudhuri

Luna

Gollahalli

2002

Journal of Propulsion and Power

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The effects of elliptic co ow on the structure of a propane jet ame are presented. The interaction of a fuel jet and a co ow in the shear layer enhances the mixing behavior of the ow eld and affects the combustion characteristics of diffusion ames. Nonaxisymmetric exit jet geometries are characterized by better mixing and increased uid entrainment into the jet core, which is desirable for low pollution from a diffusion-controlled combustion environment. In the present study the interaction of an elliptic co ow with a propane jet ame issued from a circular tube burner has been studied. Pollutant emission, ame radiation, ame structure, and soot concentration have been measured. The fuel jet exit Reynolds number is 2.7 £ £ 10 3 , and the exit Reynolds number for the co ow is 4.01 £ £ 10 3 and 8.02 £ £ 10 3 based on the minor and major axis, respectively. The results are compared with the measurements from the experiments on the same burner in a circular co ow. The pollution characteristics and the ame structure of the ame in the elliptic co ow are signi cantly different from those in the circular co ow. The nitric-oxide emission is higher, and the carbon-monoxide emission is lower in the elliptic co ow than in the circular co ow. The elliptic co ow ame produces less soot than the circular co ow ame. Nomenclature d cfc = circular co ow diameter d j = burner diameter F = radiative heat loss fraction Re = Reynolds number Re j = jet exit Reynolds number r = radial distance U c = co ow velocity U j = fuel jet velocity w = soot concentration Introduction M ANY practical combustor systems employ a diffusioncontrolled ame con guration for energy release. In this con guration generally the fuel is injected as a jet, and the surrounding air is entrained into the fuel core through turbulent mixing and molecular mixing. Hence, the combustion process is uid dynamically controlled, and instead of chemical kinetics mixing rate of fuel and air limits the rate of combustion. The emissions of combustion pollutants such as CO and NO x from these combustion systems largely depend on the reactant mixing characteristics. The CO and NO x emissions from combustion systems can be reduced if fuel-air mixing rates at different zones of the ame are controlled rationally. This generally requires a more complicated combustion system design such as staged combustion. On the other hand, postcombustion removal of pollutants is possible through catalytic conversion or exhaust gas-processing techniques. These, however, require a high setup and maintenance cost. A costeffective way is to modify the burner geometry to enhance mixing through an alteration of the near-burner ow eld characteristics. One such approach is to use nonaxisymmetric geometries. Several previous investigations conducted in the Combustion and Flame Dynamics Laboratory of the University of Oklahoma have shown promising improvements of combustion systems through the use of nonaxisymmetric burner con gurations. 1¡4 The manipulation of co ow to improvethe combustioncharacteristicsof d...

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Section: Radiation Spectral Measurementsmentioning

confidence: 99%

Elliptic Coflow Effects on a Circular Gas Jet Flame

Choudhuri

Luna

Gollahalli

2002

Journal of Propulsion and Power

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“…The effects of burner shape and orientation of elliptic burner on flame characteristics were analyzed. The most previous research set the fuel orifice as a circle or ellipse, and the flame characteristic is different between those two burners’ shapes. − Papanikolaou et al suggested the fuel exit shape holds an important effect on flame characteristics including flame size and radiation. Akbarzadeh and Birouk conducted experiments to study the effect of fuel nozzle orifice geometry including circular and rectangular on liftoff of coflowing nonpremixed turbulent methane flame.…”

Section: Introductionmentioning

confidence: 99%

Radiant Heat Flux Profile of Horizontally Oriented Rectangular Source Fuel Jet Fires

Huang

Dong

2018

Ind. Eng. Chem. Res.

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A series of numerical simulations were performed to investigate the flame radiant heat flux of horizontally oriented jet fires by rectangular source fuel with the same orifice area (400 mm 2 ) but different aspect ratios (1, 2, 4). The natural gas was carried out as fuel, of which the jet velocity varied from 27.5 to 205.8 m/s. The nondimensional radiant heat flux was defined to reveal the effect of fuel jet velocity and orifice aspect ratio on radiant heat flux. Results show that the flame size increases with the increasing fuel jet velocity and the larger orifice aspect ratio results in shorter flame length. The radiant heat flux is affected by the orifice aspect ratio as the different soot particle distribution. The predicted model to characterize the radiant heat flux is proposed by taking the orifice aspect ratio into account. The prediction results of proposed model agree well with the simulated data and previous experimental results.

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“…Gutmark and Grinstein 17 highlighted the favorable impact of flow ellipticity on the turbulence development and combustion performance by indicating the vortical flow pattern associated with the axis switching. The elliptical jets reduce the soot and NOx emissions from partially premixed flames, 18 while increasing the aspect ratio (defined as the major to the minor diameter ratio) enhances the flow stretch and provides more increase in the combustion efficiency of nonpremixed flames. 19 These features are favorably coupled to the strain rate corresponding to the jets' mutual impingement in both flame modes.…”

Section: Introductionmentioning

confidence: 99%

Development of a cylindrical burner comprising multiple pairs of opposing partially premixed or inverse diffusion flames

Kamal

2015

Proceedings of the Institution of Mechanical Engineers, Part A:

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A cylindrical burner was developed to combine extensive firing limits, high combustion efficiencies, and low NOx emissions from partially premixed or inverse diffusion flames by setting multiple pairs of circumferentially opposing jets (of concentric fuel and air streams). Normal strain rates as high as 1600 s−1 in addition to transverse strain rates of 640 s−1 were combined with a cross-flow impact and elliptical jet dispersion such that a turbulent kinetic energy peak of 15.4 m2/s2 was produced. The fuel/air mixing was enhanced and the peak temperature was reduced due to the stimulation of cross-flow wake zones and the axis switching of the elliptical jets. Partially premixed methane/air combustion of 12 opposing mixtures at Φ=1.5 led to NOx reduction to 0.36 g/kg fuel via controlling the flow residence time and adjusting the separation between the premixing and diffusion zones of each flame. As elliptical ports are used, the NOx concentrations decreased to 4 ppm with an aspect ratio of 3.0. Increasing the ratio between the diameter of the jets and their axial separation decreased the CO and HC emissions respectively to 489 ppm and 0.019%. Upon having opposing inverse diffusion flames, the blowout stability limit reached a maximum value of 53.2 m/s. With a separation of 4.0 cm, the NOx emissions reached a minimum level of 25 ppm by increasing the momentum flux ratio between the cross-flow air jet and the opposing jets to 1.5. By optimizing the cross-flow/primary air velocity ratio and the primary air/fuel jet diameter ratio, the CO and HC emissions were respectively minimized to 721 ppm and 0.039%. The velocity fluctuations indicated that increasing the opposing jets increases the turbulent kinetic energy and decreases the smallest scales of turbulence.

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Jet flames from noncircular burners

Cited by 9 publications

References 15 publications

Elliptic Coflow Effects on a Circular Gas Jet Flame

Elliptic Coflow Effects on a Circular Gas Jet Flame

Radiant Heat Flux Profile of Horizontally Oriented Rectangular Source Fuel Jet Fires

Development of a cylindrical burner comprising multiple pairs of opposing partially premixed or inverse diffusion flames

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