Visualization of blow-off events in bluff-body stabilized turbulent premixed flames

Dawson, James; Gordon, Robert L.; Kariuki, J. M.; Mastorakos, Epaminondas; Masri, Assaad R.; Juddoo, Mrinal

doi:10.1016/j.proci.2010.05.044

Cited by 97 publications

(68 citation statements)

References 17 publications

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“…In Fig. 4b, one can also see that when U a is increased to 34.5 m/s in BO3, τ BO is decreased to about 0.03 s, a trend consistent with the observations from premixed flame blow-off experiments [37,38]. Furthermore, the peaks of Q time series after t = 0.014 s are intermittently discernible before BO3 extinguishes completely.…”

Section: Blow-off Characterizationsupporting

confidence: 85%

“…Global extinction is a transient process in which the localized extinction area on the flame front gradually expands until complete extinction occurs. It has been shown recently that the blow-off transient is long relative to estimates of the residence time in the combustor and that empirical correlations of the blow-off condition do not give very accurate results [15,[37][38][39]. Therefore, in the context of turbulent combustion modeling, the following question can be posed: does a combustion model that can predict reasonably well the degree of local extinction also possesses the ability to predict the global extinction conditions and dynamics in a flame in a realistic geometry?…”

Section: Introductionmentioning

confidence: 99%

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Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

Zhang

Mastorakos

2015

Flow Turbulence Combust

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The Large Eddy Simulation (LES)/three-dimensional Conditional Moment Closure (CMC) model with detailed chemistry is applied to predict the operating condition and dynamics of complete extinction (blow-off) in swirling non-premixed methane flames. Using model constants previously selected to provide relatively accurate predictions of the degree of local extinction in the piloted jet flames Sandia D−F, the error in the blow-off air velocity predicted by LES/3D-CMC in short, recirculating flames with strong swirl for a range of fuel flow rates is within 25 % of the experimental value, which is considered a new and promising result for combustion LES that has not been applied before for the prediction of the whole blow-off curve in complex geometries. The results also show that during the blow-off transient, the total heat release gradually decreases over a duration that agrees well with experiment. The evolution of localized extinction, reactive scalars and scalar dissipation rate is analyzed. It has been observed that a consistent symptom for flames approaching blow-off is the appearance of high-frequency and high-magnitude fluctuations of the conditionally filtered stoichiometric scalar dissipation rate, resulting in an increased fraction of local extinction over the stoichiometric mixture fraction iso-surfaces. It is also shown that the blow-off time changes with the different blow-off conditions.

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Section: Blow-off Characterizationsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

Zhang

Mastorakos

2015

Flow Turbulence Combust

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“…In contrast to flames far from extinction, whose behaviour is well summarised by Driscoll [7], flames close to blow-off have been studied little. Previous investigations of such flames were performed using fast OH-PLIF (5 kHz) to study changes in the flame structure at conditions approaching blow-off, and during the extinction transient [8,9]. Lean premixed methane-air flames stabilized on a bluff body were studied.…”

Section: The Application Of This Diagnostic Technique To Turbulent Rementioning

confidence: 99%

Heat release imaging in turbulent premixed methane–air flames close to blow-off

Kariuki

Dowlut

Yuan

et al. 2015

Proceedings of the Combustion Institute

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Estimates of the heat release (HR) of unconfined lean premixed methane-air flames stabilized on an axisymmetric bluff body have been measured for conditions increasingly closer to blowoff. Simultaneous imaging of OH-and CH 2 O-PLIF was performed, and HR measurements obtained using the pixel-by-pixel multiplication of the OH-and CH 2 O-PLIF images. Blow-off was approached by slowly reducing the fuel flow rate. At conditions far from blow-off, HR occurred along the shear layer, whereas at conditions near blow-off, HR was also observed inside the recirculation zone (RZ). Localised extinctions along the flame front were seen at conditions away from blow-off, and increased in frequency and size as blow-off was approached. At conditions near blow-off, HR was detected on the boundary of flame pockets inside the RZ which had detached from the fragmented flame at the attachment point. Regions void of OH in the RZ near blow-off were often seen to be filled with CH 2 O. Regions void of both OH and CH 2 O were also observed, but less often, indicating the presence of both preheated gases and fresh reactants inside the RZ. Such images do not show a connection with the annular air jet, implying the cold reactants entered the RZ from the top. HR was observed to increase as a function of the absolute value of flame front curvature for the near unity Lewis number flames investigated. The measurements reported here are useful for model validation and for exploring the changes in turbulent premixed flame structure as extinction is approached.

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“…When bluff body is used as a flame holder, the incoming fuel and oxidizer mixture is ignited by the hot combustion products recirculating in a wake structure formed behind the bluff body. This stabilization mechanism has been investigated extensively by many researchers [6][7][8][9][10][11][12]. Many studies associated with bluff body stabilization mechanism focus on premixed combustion systems, where premixed fuel and oxidizer are provided to the combustion zone and thus complex physics that controls mixing process can be neglected.…”

Section: Ppbb Burnermentioning

confidence: 99%

Application of a Central Composite Design for the Study of NOx Emission Performance of a Low NOx Burner

2015

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Abstract:In this study, the influence of various factors on nitrogen oxides (NOx) emissions of a low NOx burner is investigated using a central composite design (CCD) approach to an experimental matrix in order to show the applicability of design of experiments methodology to the combustion field. Four factors have been analyzed in terms of their impact on NOx formation: hydrogen fraction in the fuel (0%-15% mass fraction in hydrogen-enriched methane), amount of excess air (5%-30%), burner head position (20-25 mm from the burner throat) and secondary fuel fraction provided to the burner (0%-6%). The measurements were performed at a constant thermal load equal to 25 kW (calculated based on lower heating value). Response surface methodology and CCD were used to develop a second-degree polynomial regression model of the burner NOx emissions. The significance of the tested factors over their respective ranges has been evaluated using the analysis of variance and by the consideration of the coefficients of the model equation. Results show that hydrogen addition to methane leads to increased NOx emissions in comparison to emissions from pure methane combustion. Hydrogen content in a fuel is the strongest factor affecting NOx emissions among all the factors tested. Lower NOx formation because of increased excess air was observed when the burner was fuelled by pure methane, but this effect diminished for hydrogen-rich fuel mixtures. NOx emissions were slightly reduced when the burner head was shifted closer to the burner outer tube, whereas a OPEN ACCESSEnergies 2015, 8 3607 secondary fuel stream provided to the burner was found to have no impact on NOx emissions over the investigated range of factors.

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Visualization of blow-off events in bluff-body stabilized turbulent premixed flames

Cited by 97 publications

References 17 publications

Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

Prediction of Global Extinction Conditions and Dynamics in Swirling Non-premixed Flames Using LES/CMC Modelling

Heat release imaging in turbulent premixed methane–air flames close to blow-off

Application of a Central Composite Design for the Study of NOx Emission Performance of a Low NOx Burner

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