Diffusion-flame shape in the wake of a falling droplet.

AIAA Journal ◽  
1967 ◽  
Vol 5 (11) ◽  
pp. 1984-1988 ◽  
Author(s):  
FRANCIS E. FENDELL ◽  
EDWARD B. SMITH
Keyword(s):  
Diffusion Flame ◽  
Flame Shape

Nitrogen Diluted Jet Flames in the Presence of Coflowing Air

2011 ◽  
Author(s):  
James D. Kribs ◽  
Tamir S. Hasan ◽  
Kevin M. Lyons
Keyword(s):  
Diffusion Flame ◽  
Axial Position ◽  
Flammability Limit ◽  
Jet Flames ◽  
Flow Rates ◽  
Nitrogen Dilution ◽  
Flame Shape ◽  
Methane Flow

The purpose of this study is to observe methane jet flames under varying levels of nitrogen dilution and coflowing air. The jet flames were examined in order to determine the conditions for which liftoff and blowout occur under conditions that strain the flame. Methane flow rates were varied, corresponding to intermediate lifted positions to blowout. A sequence of images were taken at each level of dilution and coflow, and were used to determine the lowest radial and axial position of the flammability limit. These flammability regions were compared to the lean flammability limit. It was observed that flame shape and liftoff were considerably more influenced by the effects of the coflowing air compared to the presence of the diluents, and that flames under coflow lost the trailing diffusion flame earlier, which has been shown to be a marker for flame blowout.

Theoretical and numerical study of a symmetrical triple flame using the parabolic flame path approximation

2000 ◽  
Vol 415 ◽  
pp. 227-260 ◽  
Author(s):  
SANDIP GHOSAL ◽  
LUC VERVISCH
Keyword(s):  
Activation Energy ◽  
Heat Release ◽  
Diffusion Flame ◽  
Mixture Fraction ◽  
The Body ◽  
Approximate Theory ◽  
Characteristic Structure ◽  
Rate Of Increase ◽  
Path Approximation ◽  
Flame Shape

In non-premixed turbulent combustion the reactive zone is localized at the stoichiometric surfaces of the mixture and may be locally approximated by a diffusion flame. Experiments and numerical simulations reveal a characteristic structure at the edge of such a two-dimensional diffusion flame. This ‘triple flame’ or ‘edge flame’ consists of a curved flame front followed by a trailing edge that constitutes the body of the diffusion flame. Triple flames are also observed at the edge of a lifted laminar diffusion flame near the exit of burners. The speed of propagation of the triple flame determines such important properties as the rate of increase of the flame surface in non-premixed combustion and the lift-off distance in lifted flames at burners. This paper presents an approximate theory of triple flames based on an approximation of the flame shape by a parabolic profile, for large activation energy and low but finite heat release. The parabolic flame path approximation is a heuristic approximation motivated by physical considerations and is independent of the large activation energy and low heat release assumptions which are incorporated through asymptotic expansions. Therefore, what is presented here is not a truly asymptotic theory of triple flames, but an asymptotic solution of a model problem in which the flame shape is assumed parabolic. Only the symmetrical flame is considered and Lewis numbers are taken to be unity. The principal results are analytical formulas for the speed and curvature of triple flames as a function of the upstream mixture fraction gradient in the limit of infinitesimal heat release as well as small but finite heat release. For given chemistry, the solution provides a complete description of the triple flame in terms of the upstream mixture fraction gradient. The theory is validated by comparison with numerical simulation of the primitive equations.

scholarly journals Characteristics of Flame Shapes and Map For LPG and Hydrogen Inverse Confined Diffusion Flames at High Level of Fuel Excess

2012 ◽  
Vol 12 (1) ◽  
pp. 1
Author(s):  
Yazid Bindar ◽  
Anton Irawan
Keyword(s):  
Diffusion Flame ◽  
Laminar Flame ◽  
Turbulent Flames ◽  
Flame Height ◽  
Strong Base ◽  
Air Jet ◽  
Inverse Diffusion ◽  
Flame Shape ◽  
High Level ◽  
Inverse Diffusion Flame

A combustion flame can be generated by locating the air jet supply inside the fuel jet supply. This flame is referred as an inverse diffusion flame. The size and structure of inverse diffusion flame were studied experimentally. The experiment was conducted for LPG and Hydrogen fuels. The inlet fuel and air flow rates are supplied at high level of fuel excess for its combustion reaction. These two fuels generated the flame shape having two parts. At lower part, the flame is wider and serves as a base of the flame. The upper part is longer and acts as a flame tower. The base flame was a weak flame resulted by a rich fuel-air mixture. The tower flame is formed by mixing between the entrained fuel and the air. The flame length decreases with the increase on the momentum ration between fuel and air. The flame height correlates to the fuel and air Reynold number ratio, Refu/Rea. The development of the flame shapes from continues to strong base-tower flame shape is mapped by air and fuel inlet momentum rate. Very low fuel and air momentum rates result laminar flame and continuous shapes. The turbulent flames having base-tower shape are formed at high air momentum rate. The oxygen profiles shows that the oxygen concentration decays from the burner tip, vanishes at some distance from the burner tip and increase again after this distance. The hydrogen is completely consumed before the flame tip is reached

Analysis of LPG diffusion flame in tube type burner

2019 ◽  
Vol 13 (3) ◽  
pp. 5278-5293
Author(s):  
Vipul Patel ◽  
Rupesh Shah
Keyword(s):  
Diffusion Flame ◽  
Emission Characteristic ◽  
Flame Stability ◽  
Liquefied Petroleum Gas ◽  
Air Velocity ◽  
Length Fraction ◽  
Low Emission ◽  
Tube Type ◽  
Stability Limits ◽  
Co Emission

The present research aims to analyse diffusion flame in a tube type burner with Liquefied petroleum gas (LPG) as a fuel. An experimental investigation is performed to study flame appearance, flame stability, Soot free length fraction (SFLF) and CO emission of LPG diffusion flame. Effects of varying air and fuel velocities are analysed to understand the physical process involved in combustion. SFLF is measured to estimate the reduction of soot. Stability limits of the diffusion flame are characterized by the blowoff velocity. Emission characteristic in terms of CO level is measured at different equivalence ratios. Experimental results show that the air and fuel velocity strongly influences the appearance of LPG diffusion flame. At a constant fuel velocity, blue zone increases and the luminous zone decreases with the increase in air velocity. It is observed that the SFLF increases with increasing air velocity at a constant fuel velocity. It is observed that the blowoff velocity of the diffusion flame increases as fuel velocity increases. Comparison of emission for flame with and without swirl indicates that swirl results in low emission of CO and higher flame stability. Swirler with 45° vanes achieved the lowest CO emission of 30 ppm at Φ = 1.3.

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