Effects of swirl on the stability and turbulent structure of jet diffusion flames

1990 ◽  
Author(s):  
F. TAKAHASHI ◽  
W. SCHMOLL ◽  
M. VANGSNESS
Keyword(s):  
Diffusion Flames ◽  
Turbulent Structure ◽  
Jet Diffusion Flames ◽  
The Stability

Effects of finite-rate chemistry and detailed transport on the instability of jet diffusion flames

2014 ◽  
Vol 745 ◽  
pp. 647-681 ◽  
Author(s):  
Yee Chee See ◽  
Matthias Ihme
Keyword(s):  
Transport Properties ◽  
Diffusion Flames ◽  
Diffusive Transport ◽  
Mean Flow ◽  
Stability Behaviour ◽  
Jet Diffusion Flames ◽  
One Step ◽  
The Mean ◽  
Modelling Assumptions ◽  
The Stability

AbstractLocal linear stability analysis has been shown to provide valuable information about the response of jet diffusion flames to flow-field perturbations. However, this analysis commonly relies on several modelling assumptions about the mean flow prescription, the thermo-viscous-diffusive transport properties, and the complexity and representation of the chemical reaction mechanisms. In this work, the effects of these modelling assumptions on the stability behaviour of a jet diffusion flame are systematically investigated. A flamelet formulation is combined with linear stability theory to fully account for the effects of complex transport properties and the detailed reaction chemistry on the perturbation dynamics. The model is applied to a methane–air jet diffusion flame that was experimentally investigated by Füriet al.(Proc. Combust. Inst., vol. 29, 2002, pp. 1653–1661). Detailed simulations are performed to obtain mean flow quantities, about which the stability analysis is performed. Simulation results show that the growth rate of the inviscid instability mode is insensitive to the representation of the transport properties at low frequencies, and exhibits a stronger dependence on the mean flow representation. The effects of the complexity of the reaction chemistry on the stability behaviour are investigated in the context of an adiabatic jet flame configuration. Comparisons with a detailed chemical-kinetics model show that the use of a one-step chemistry representation in combination with a simplified viscous-diffusive transport model can affect the mean flow representation and heat release location, thereby modifying the instability behaviour. This is attributed to the shift in the flame structure predicted by the one-step chemistry model, and is further exacerbated by the representation of the transport properties. A pinch-point analysis is performed to investigate the stability behaviour; it is shown that the shear-layer instability is convectively unstable, while the outer buoyancy-driven instability mode transitions from absolutely to convectively unstable in the nozzle near field, and this transition point is dependent on the Froude number.

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.

Turbulent Structure Dynamics of Buoyant and Non-Buoyant Pulsed Jet Diffusion Flames

2010 ◽  
Vol 182 (3) ◽  
pp. 309-330 ◽  
Author(s):  
Mathieu Fregeau ◽  
James C. Hermanson ◽  
Dennis P. Stocker ◽  
Uday G. Hegde
Keyword(s):  
Diffusion Flames ◽  
Turbulent Structure ◽  
Pulsed Jet ◽  
Structure Dynamics ◽  
Jet Diffusion Flames

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.

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