Flame height and lift-off of turbulent buoyant jet diffusion flames in a reduced pressure atmosphere

Abstract The present study deals with the augmentation of the turbulent shear effect on transport in turbulent jet diffusion flames due to the presence of air-suction flow and the possibility of extending the flame blow-off limits through augmentation. The experimental apparatus employed here comprises a fuel nozzle placed at the center of a concentric annulus with an outer cylinder encompassing the nozzle. The fuel jet is allowed to eject upwards and turbulent jet diffusion flames are formed by igniting the jet, then by increasing the volume flow rate of the fuel. The annular counterflow technique was employed to augment the turbulent shear effect. It is found that (1) the augmentation of turbulent shear effect exerted on the shear layer formed between the jet flames and the opposed flow of air causes an increase in temperature of the cold fuel gas at the flame center and an extension of flame blowoff limits; (2) flame lift-off heights are suppressed; (3) the lift-off propensity of the diffusion flame is alleviated by such augmentation.

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Lift-Off Stability of n-Heptane Jet Diffusion Flames in Homogeneous Environments of Fuel and Air

Journal of Energy Resources Technology ◽

10.1115/1.2794221 ◽

1997 ◽

Vol 119 (1) ◽

pp. 45-48

Author(s):

P. Samuel ◽

G. A. Karim

Keyword(s):

Liquid Fuel ◽

Diffusion Flames ◽

Jet Fuel ◽

Small Concentration ◽

Stream Velocity ◽

Jet Flame ◽

Jet Diffusion Flames ◽

Discharge Velocity ◽

Lift Off ◽

Made In

The lift-off of jet diffusion flames of a liquid fuel in coflowing streams of air was established experimentally for a range of jet discharge and stream velocities. The improvement in the lift-off stability of the flame due to the presence of a small concentration of an auxiliary gaseous fuel in the surrounding air was established. Liquid n-heptane was the jet fuel while methane, ethylene, propane, and hydrogen were employed individually in small concentrations as the auxiliary fuels. It is shown that the lift-off distance and the corresponding ignition delay of the jet flame can be correlated for all the observations made in terms of derived dimensionless grouping of the main parameters varied, which included the jet discharge velocity, the surrounding stream velocity, and the concentration of the fuel added to the surroundings of the flame.

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Lift-Off, Reattachment and Blowout Limits of Co-Flow Jet Diffusion Flames

Engineering Technology Conference on Energy, Parts A and B ◽

10.1115/etce2002/cae-29018 ◽

2002 ◽

Author(s):

M. Karbasi ◽

I. Wierzba

Keyword(s):

Diffusion Flames ◽

Flame Stabilization ◽

Nozzle Geometry ◽

Stream Velocity ◽

Jet Diffusion Flames ◽

Air Stream ◽

Lifted Flames ◽

Lift Off ◽

The Stability ◽

Flowing Stream

The stability behaviour of jet diffusion flames in a co-flowing stream of air was examined. Their lift-off, reattachment and blowout limits were established for methane, propane, ethylene and hydrogen. The co-flowing air stream velocity affected significantly the mechanism of flame stabilization. Different flow regimes where the blowout of lifted flames or attached flames can occur were recognized. A transition region in which both the blowout of lifted flames as well as that of attached flames was observed and identified with respect to the value of the air stream velocity. It was found that the blowout limits for lifted flames in this region were much smaller than for the attached flames. The effects of changes in the nozzle geometry and co-flowing stream composition were also considered.

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