Simultaneous Rayleigh imaging and CH-PLIF measurements in a lifted jet diffusion flame

Watson, K.A.; Lyons, Kent; Donbar, Jeffrey M.; Carter, C.D

doi:10.1016/s0010-2180(00)00133-4

Cited by 73 publications

(38 citation statements)

References 21 publications

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“…Data from numerous experiments utilizing particle image velocimetry to determine the velocity of the stabilized flame were compared to the estimates provided by the Tieszen velocity relation (Watson et al [3], Su et al [25], and Muñiz and Mungal [1]). The published PIV measurements for each agree with the estimated velocities predicted by (2), especially as the flame stabilizes further downstream. Each of these experimental studies used planar laser-induced fluorescence to determine the axial and radial location of the flame edge.…”

Section: Analysis Of the Scalar Fieldsupporting

confidence: 73%

“…A diffusion flame has no burning velocity so it is the premixed flame front that is generally assumed to act as a stabilizing anchor. Many studies, like that of Muñiz and Mungal [1] and Watson et al [2][3][4], have investigated stable lifted flame reaction zone structures that settle at moderate downstream positions. If the reaction zone moves further downstream, it eventually enters a region that can no longer support combustion due to the low fuel concentration and all reaction abruptly ceases, a condition known as flame blowout (Kalghatgi [5], Pitts [6], Coats [7], Chao et al [8,9].…”

Section: Introductionmentioning

confidence: 99%

“…Since the blowout phenomenon happens typically in an abrupt and unpredictable manner, its transient characteristics are difficult to study experimentally. Additionally, the large width of the fuel jet, the small gradients in the scalar and velocity fields, and the relatively low values of fuel concentration make the situation, in many ways, more challenging to fully characterize than the situations described in the studies of Watson et al [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

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Observations on Jet-Flame Blowout

Moore

McCraw

Lyons

2008

International Journal of Reacting Systems

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The mechanisms that cause jet-flame blowout, particularly in the presence of air coflow, are not completely understood. This work examines the role of fuel velocity and air coflow in the blowout phenomenon by examining the transient behavior of the reaction zone at blowout. The results of video imaging of a lifted methane-air diffusion flame at near blowout conditions are presented. Two types of experiments are described. In the first investigation, a flame is established and stabilized at a known, predetermined downstream location with a constant coflow velocity, and then the fuel velocity is subsequently increased to cause blowout. In the other , an ignition source is used to maintain flame burning near blowout and the subsequent transient behavior to blowout upon removal of the ignition source is characterized. Data from both types of experiments are collected at various coflow and jet velocities. Images are used to ascertain the changes in the leading edge of the reaction zone prior to flame extinction that help to develop a physically-based model to describe jet-flame blowout. The data report that a consistent predictor of blowout is the prior disappearance of the axially oriented flame branch. This is witnessed despite a turbulent flames' inherent variable behavior. Interpretations are also made in the light of analytical mixture fraction expressions from the literature that support the notion that flame blowout occurs when the leading edge reaches the vicinity of the lean-limit contour, which coincides approximately with the conditions for loss of the axially oriented flame structure.

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Section: Analysis Of the Scalar Fieldsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Observations on Jet-Flame Blowout

Moore

McCraw

Lyons

2008

International Journal of Reacting Systems

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“…It is seen that the predicted flame propagation speeds are within AE5% of the local flow velocity at the flame stabilization point. Although these velocities are slightly less than 1 m=s, much higher flow velocities ($ 1-1.2 m=s) are experimentally measured by Muniz and Mungal (1997) and Watson et al (2000) upstream of the flame stabilization point. The existence of higher flow velocities ($ 1.0 m=s) at the flame stabilization point shows that that flame stabilization is governed by turbulent flame propagation rather than laminar flame propagation.…”

Section: Methane Jet Flamesmentioning

confidence: 81%

Prediction of Flame Liftoff Height of Diffusion/Partially Premixed Jet Flames and Modeling of Mild Combustion Burners

Kumar

Paul

Mukunda

2007

Combustion Science and Technology

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In this article, a new flame extinction model based on the k=e turbulence time scale concept is proposed to predict the flame liftoff heights over a wide range of coflow temperature and O 2 mass fraction of the coflow. The flame is assumed to be quenched, when the fluid time scale is less than the chemical time scale (Da < 1). The chemical time scale is derived as a function of temperature, oxidizer mass fraction, fuel dilution, velocity of the jet and fuel type. The present extinction model has been tested for a variety of conditions: (a) ambient coflow conditions (1 atm and 300 K) for propane, methane and hydrogen jet flames, (b) highly preheated coflow, and (c) high temperature and low oxidizer concentration coflow. Predicted flame liftoff heights of jet diffusion and partially premixed flames are in excellent agreement with the experimental data for all the simulated conditions and fuels. It is observed that flame stabilization occurs at a point near the stoichiometric mixture fraction surface, where the local flow velocity is equal to the local flame propagation speed. The present method is used to determine the chemical time scale for the conditions existing in the mild= flameless combustion burners investigated by the authors earlier. This model has successfully predicted the initial premixing of the fuel with combustion products before the combustion reaction initiates. It has been inferred from these numerical simulations that fuel injection is followed by intense premixing with hot combustion products in the primary zone and combustion reaction follows further downstream. Reaction rate contours suggest that reaction takes place over a large volume and the magnitude of the combustion reaction is lower compared to the conventional combustion mode. The appearance of attached flames in the mild combustion burners at low thermal inputs is also predicted, which is due to lower average jet velocity and larger residence times in the near injection zone.

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“…These leading edge flames are often present at the stabilization point of lifted spray investigated by a twodimensional laser-sheet imaging technique, as has been described earlier. The nature of the flamefront in the stabilization region of the spray-jet flame is vibrant topic of research [34][35][36], along with the corresponding work in gaseous flames [39][40][41][42][43][44][45][46][47]. Whether all spray flames exhibit "leading edge' flame structures as shown by our group for the gaseous and for some spray cases case is a major question to be addressed by our group in future work.…”

Section: Research Results In Spray Flames At Ncsumentioning

confidence: 84%

Stabilization and Blowout of Gaseous- and Spray-Jet Flames

Lyons¹

2004

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Simultaneous Rayleigh imaging and CH-PLIF measurements in a lifted jet diffusion flame

Cited by 73 publications

References 21 publications

Observations on Jet-Flame Blowout

Observations on Jet-Flame Blowout

Prediction of Flame Liftoff Height of Diffusion/Partially Premixed Jet Flames and Modeling of Mild Combustion Burners

Stabilization and Blowout of Gaseous- and Spray-Jet Flames

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