Effect of Diluent on the Blowout Limits of Jet Diffusion Flames

2001 ◽  
Author(s):  
N. Papanikolaou ◽  
I. Wierzba ◽  
V. W. Liu
Keyword(s):  
Carbon Dioxide ◽  
Experimental Investigation ◽  
Flow Field ◽  
Diffusion Flames ◽  
Jet Fuel ◽  
Field Structure ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Lifted Flames

Abstract The paper will describe the results of an experimental investigation on the effect of diluents premixed with either the jet or co-flowing air stream on the blowout limits and flow field structure of jet diffusion flames. Experiments were conducted for a range of co-flowing air stream velocities with methane as the primary jet fuel, and nitrogen and carbon dioxide as diluents in the jet fuel; carbon dioxide was also used in the co-flowing air stream. The addition of a diluent to the surrounding air stream had a much stronger effect on the blowout limits than the addition of the diluent to the jet fuel. The effect of partially premixing air with the jet fuel on the blowout limits was also investigated. The addition of air (to up to 30%) to the methane jet significantly reduced the blowout limits of lifted flames, but it had little effect on the blowout limits of attached flames, which was rather unexpected.

Prediction and Validation of Blowout Limits of Co-Flowing Jet Diffusion Flames—Effect of Dilution

1998 ◽  
Vol 120 (2) ◽  
pp. 167-171 ◽  
Author(s):  
M. Karbasi ◽  
I. Wierzba
Keyword(s):  
Carbon Dioxide ◽  
Time Scale ◽  
Diffusion Flames ◽  
Mixing Time ◽  
Stability Limit ◽  
Jet Fuel ◽  
Stream Velocity ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Scale Ratio

The blowout limits of a co-flowing turbulent methane jet diffusion flame with addition of diluent in either jet fuel or surrounding air stream is studied both analytically and experimentally. Helium, nitrogen, and carbon dioxide were employed as the diluents. Experiments indicated that an addition of diluents to the jet fuel or surrounding air stream decreased the stability limit of the jet diffusion flames. The strongest effect was observed with carbon dioxide as the diluent followed by nitrogen and then by helium. A model of extinction based on recognized criterion of the mixing time scale to characteristic combustion time scale ratio using experimentally derived correlations is proposed. It is capable of predicting the large reduction of the jet blowout velocity due to a relatively small increase in the co-flow stream velocity along with an increase in the concentration of diluent in either the jet fuel or surrounding air stream. Experiments were carried out to validate the model. The predicted blowout velocities of turbulent jet diffusion flames obtained using this model are in good agreement with the corresponding experimental data.

Effect of Burner Geometry on the Blowout Limits of Jet Diffusion Flames in a Co-Flowing Oxidizing Stream

1996 ◽  
Vol 118 (2) ◽  
pp. 134-139 ◽  
Author(s):  
N. Papanikolaou ◽  
I. Wierzba
Keyword(s):  
Diffusion Flames ◽  
Flame Stabilization ◽  
Stream Velocity ◽  
Discharge Area ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Lifted Flames ◽  
Nozzle Shape ◽  
The Stability ◽  
Flowing Stream

The effects of changes in the jet nozzle geometry, i.e., nozzle shape and lip thickness, on the blowout limits of jet diffusion flames in a co-flowing air stream were experimentally investigated for a range of co-flow air stream velocities. Circular and elongated nozzles of different axes rations were employed. Preliminary results showed that nozzles with low major-to-minor axes ratios improved, while high ratios reduced, the blowout limit of attached flames compared with that for an equivalent circular nozzle. The nozzle shape had no apparent influence on the blowout limits lifted flames and the limiting stream velocity. The experimental blowout limits of lifted flames were found to be a function of the co-flowing stream velocity and jet discharge area. On the other hand, the stability of attached flames was a function of the co-flowing stream velocity, jet discharge area as well as the nozzle shape. The effect of premixing a fuel with the surrounding air was also studied. Generally, the introduction of auxiliary fuel into the surrounding stream either increased or decreased the blowout limit depending on the type of flame stabilization mechanism prior to blowout. The stability mechanism of the flame was found to be a function of the co-flow stream velocity and the auxiliary fuel employed.

Stability Limits of Biogas Jet Diffusion Flames

2007 ◽  
Author(s):  
T. Leung ◽  
I. Wierzba
Keyword(s):  
Carbon Dioxide ◽  
Diffusion Flames ◽  
Carbon Dioxide Concentration ◽  
Operating Conditions ◽  
Small Range ◽  
Jet Diffusion Flames ◽  
Air Stream ◽  
Jet Nozzle ◽  
The Stability ◽  
Stability Limits

An investigation of the stability limits of biogas jet diffusion flames in a co-flowing air stream was conducted. Stability limits were determined experimentally for two different methane-carbon dioxide mixtures that are of typical biogas composition. Moreover, the effect of jet nozzle diameter was also investigated. It was found that with the presence of a significant amount of CO2 in the fuel as in the case of biogas, the stability limits were very low and the flames can only be stabilized over a very small range of coflowing velocities. As expected, an increase in carbon dioxide concentration resulted in the narrowing of the region of the stable flames. However, it was shown that the flame stability of such mixtures can be enhanced very significantly and over a much wider range of co-flowing air velocities by introducing a small amount of hydrogen in the fuel. Results indicate an increase in the stability limits by approximately fourfold when 10% (by vol.) of hydrogen is added under the same operating conditions. The effect of addition of hydrogen on enhancement of biogas stability is most significant with the initial addition of 10%. The degree of enhancement diminishes with further increase in hydrogen addition from 10% to 30%.

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

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.

scholarly journals The Effect of Co-Flowing Stream Velocities on the Flow Characteristics of Jets Issuing From Elliptic Nozzles

1997 ◽  
Author(s):  
N. Papanikolaou ◽  
I. Wierzba
Keyword(s):  
Diffusion Flames ◽  
Flow Characteristics ◽  
Nozzle Geometry ◽  
Laser Doppler Velocimeter ◽  
Circular Nozzle ◽  
Jet Diffusion Flames ◽  
Aspect Ratios ◽  
Air Stream ◽  
Lifted Flames ◽  
Flowing Stream

The flow structure of cold and ignited jets issuing into a co-flowing air stream was experimentally studied using a laser Doppler velocimeter. Methane was employed as the jet fluid discharging from circular and elliptic nozzles with aspect ratios varying from 1.29 to 1.60. The diameter of the circular nozzle was 4.6 mm and the elliptic nozzles had approximately the same exit area as that of the circular nozzle. These non-circular nozzles were employed in order to increase the stability of attached jet diffusion flames. The time-averaged velocity and r.m.s. value of the velocity fluctuation in the streamwise and transverse directions were measured over the range of co-flowing stream velocities corresponding to different modes of flame blowout that are identified as either lifted or attached flames. On the basis of these measurements, attempts were made to explain the existence of an apparent optimum aspect ratio for the blowout of attached flames observed at higher values of co-flowing stream velocities. The insensitivity of the blowout limits of lifted flames to nozzle geometry observed in our previous work at low co-flowing stream velocities was also explained.

An Experimental Investigation of the Blowout Limits of a Jet Diffusion Flame in Co-Flowing Streams of Different Velocity and Composition

1993 ◽  
Vol 115 (2) ◽  
pp. 142-147 ◽  
Author(s):  
I. Wierzba ◽  
K. Kar ◽  
G. A. Karim
Keyword(s):  
Carbon Dioxide ◽  
Experimental Investigation ◽  
Laminar Flow ◽  
Turbulent Flow ◽  
Diffusion Flame ◽  
Detrimental Effect ◽  
Stream Velocity ◽  
Air Stream ◽  
Methane Diffusion ◽  
Flow Stream

The blowout limits of a methane diffusion flame in a co-flowing air-fuel or air-diluent stream were determined for a range of surrounding co-flow stream velocities, both laminar and turbulent, up to ~ 1.50 m/s. Methane, ethylene, propane and hydrogen were used as the fuels in the surrounding co-flow stream while nitrogen and carbon dioxide were used as diluents. The experimental results show that the velocity of the surrounding stream affects the blowout phenomena significantly. An increase in the stream velocity has a detrimental effect on the blowout limits at very low velocities up to 0.30 m/s (essentially laminar flow) and at velocities higher than 1.50 m/s (turbulent flow). The addition of a fuel to the air stream in most cases enhances the blowout limit of a methane diffusion flame. However, different trends in the variation of the blowout limits with the surrounding fuel concentration were observed, depending on the type of fuel used and on whether the surrounding coflow stream was laminar or turbulent. The addition of nitrogen or carbon dioxide to the air stream results in decreasing the blowout limits. The effect is more severe at the higher velocities.

The Liftoff Properties of Dimethyl Ether Jet Diffusion Flames With Preheating

2013 ◽  
Author(s):  
Jie Zhou ◽  
Yuhua Ai ◽  
Wenjun Kong
Keyword(s):  
Ambient Temperature ◽  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Diffusion Flames ◽  
Thermal Buoyancy ◽  
Jet Diffusion Flames ◽  
Lifted Flames ◽  
Low Mass ◽  
Jet Velocity

Liftoff properties of DME laminar axisymmetric diffusion flames were investigated experimentally with emphasis on the preheating effects. At room temperature, DME presented a different liftoff phenomenon from the non-oxygenated hydrocarbon fuels. It could not be lifted off directly by increasing the jet velocity except for far field ignition at relatively low mass flow rate. When fuel and dilution were preheated, the DME flame could be lifted off directly by increasing the jet velocity. The range of the mass flow rate of stabilized DME liftoff flames became much narrower and the liftoff height became much smaller at fuel preheating than that at ambient temperature. With the increase of the jet temperature, the DME liftoff flames exhibited as one of the following three types: stationary lifted flames, stable oscillating lifted flames and unstable oscillating lifted flames. Stationary lifted flames existed when the initial temperature was relatively low (less than 350 K). Stable oscillating lifted flames were observed at relatively high preheated temperature (about 350 K ∼ 750 K), and the trajectory of the liftoff flame base was nearly sinusoidal. Both the oscillating frequency and amplitude increased with the preheating temperature. The oscillating lifted flames were caused by thermal buoyancy effect, inertia and the instability in the inner flow. When the jet temperature exceeded 750 K, the oscillating lifted flames became unstable and easily to be blown out. The flame base of the stabilized DME liftoff flame had a tribrachial structure at both ambient temperature and elevated temperature.

Subatmospheric Extinction of Opposed-Jet Diffusion Flames of Jet Fuel and Its Surrogates

AIAA Journal ◽  
2010 ◽  
Vol 48 (1) ◽  
pp. 158-165 ◽  
Author(s):  
Srinivasan Dattarajan ◽  
Okjoo Park ◽  
Elizabeth M. Fisher ◽  
Frederick C. Gouldin ◽  
Joseph W. Bozzelli
Keyword(s):  
Diffusion Flames ◽  
Jet Fuel ◽  
Jet Diffusion Flames ◽  
Opposed Jet

The Effects of Burner Geometry and Fuel Composition on the Stability of a Jet Diffusion Flame

1997 ◽  
Vol 119 (4) ◽  
pp. 265-270 ◽  
Author(s):  
N. Papanikolaou ◽  
I. Wierzba
Keyword(s):  
Diffusion Flames ◽  
Flame Stabilization ◽  
Nozzle Geometry ◽  
Stream Velocity ◽  
Fuel Composition ◽  
Jet Diffusion Flames ◽  
Aspect Ratios ◽  
Air Stream ◽  
The Stability ◽  
Flowing Stream

The effect of the burner configuration and fuel composition on the stability limits of jet diffusion flames issuing into a co-flowing air stream is presented. Circular and elliptic nozzles of various lip thicknesses and aspect ratios were employed with methane as the primary fuel and hydrogen, carbon dioxide, and nitrogen as additives. It was found that the effects of nozzle geometry, fuel composition, and co-flowing stream velocity on the blowout limits were highly dependent on the type of flame stabilization mechanism, i.e., whether lifted or rim-attached, just prior to blowout. The blowout behavior of lifted flames did not appear to be significantly affected by a change in the nozzle shape as long as the discharge area remained constant, but it was greatly affected by the fuel composition. In contrast, attached flame stability was influenced by both the fuel composition and the nozzle geometry which had the potential to extend the maximum co-flowing stream velocity without causing the flame to blow out. The parameters affecting the limiting stream velocity were studied.

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