Simultaneous measurement of localized heat-release with OH/CH2O–LIF imaging and spatially integrated OH∗ chemiluminescence in turbulent swirl flames

Röder, Markus; Dreier, Thomas; Schulz, Christof

doi:10.1016/j.proci.2012.06.102

Cited by 59 publications

(16 citation statements)

References 19 publications

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“…Uncertainties arising from collisional quenching rates of OH LIF are typically reported to be below 20 % [13,14]. However, limited information is available on collisional quenching rates for CH 2 O LIF.…”

Section: Resultsmentioning

confidence: 99%

Heat Release Imaging in Turbulent Premixed Ethylene-Air Flames Near Blow-off

Kariuki

Dowlut

Balachandran

et al. 2016

Flow Turbulence Combust

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The focus of this work is to visualise the regions of CH 2 O and heat release (HR) of an unconfined turbulent premixed bluff body stabilised ethylene-air flame at conditions approaching lean blow-off using simultaneous imaging of OH-and CH 2 O-PLIF. The HR regions are estimated from the product of the OH and CH 2 O profiles. At conditions near blow-off, wide regions of CH 2 O are observed inside the recirculation zone (RZ). The presence of CH 2 O and HR inside the RZ is observed to follow fragmentation of the downstream flame parts near the top of the RZ. The presence of wide regions void of both OH and CH 2 O inside the RZ at conditions very close to blow-off indicates the possible entrainment of un-reacted gases into the RZ. The behaviour of the lean ethylene-air flame with Lewis number (Le) greater than 1 is compared to that of a lean methane-air flame with Le of approximately 1. For both fuels, qualitatively similar observations of flame fragmentation downstream followed by build-up of CH 2 O and HR inside the RZ are observed at conditions near lean blow-off. Also, a similar trend of flame front curvature conditioned on HR was observed for both the ethylene-air and methane-air flames, where the magnitude of HR was observed to increase with the absolute value of curvature.

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Section: Resultsmentioning

confidence: 99%

Heat Release Imaging in Turbulent Premixed Ethylene-Air Flames Near Blow-off

Kariuki

Dowlut

Balachandran

et al. 2016

Flow Turbulence Combust

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“…The reaction zone thickness is defined to be the width of the CH 2 O-OH overlap layer at 50% of its maximum value (FWHM). Previous studies [27][28][29][30][31][32][33][34][35][36][37][38][39][40] have also used the overlap of OH and CH 2 O or HCO to define the reaction layer. This is because the primary pathway for HCO production (and subsequently heat release) involves reactions with CH 2 O and OH.…”

Section: A Burner Design and Diagnosticsmentioning

confidence: 99%

Measurements to Determine the Regimes of Turbulent Premixed Flames

Skiba

Wabel

Temme

et al. 2015

51st AIAA/SAE/ASEE Joint Propulsion Conference

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Structural features of highly turbulent piloted flames were acquired from simultaneous PLIF images of formaldehyde (CH 2 O) and OH. The lean (equivalence ratio = 0.75) methane-air flames were studied under eight different flow conditions and at two different interrogation regions. The non-reacting conditions for these flames consist of turbulent Reynolds numbers (Re T ), turbulence intensities (u'/S L ), and integral length scales that range from 520 to 80,000, 5 to 184, and 6 mm to 29 mm, respectively. Preheat and reaction zone thicknesses were measured for flames subjected to these range of values. The preheat zone thickness was deduced from the CH 2 O PLIF images and the reaction zone thicknesses were obtained from the profiles produced by the pixel-by-pixel product of the OH and CH 2 O PLIF images. The reaction or preheat zones associated with a particular condition were classified as being "thickened" if the mean thickness for that condition exceeded two but not four times the laminar value. If the average thickness was greater than four times the laminar value that preheat or reaction zone was deemed "primarily distributed." Eight of the eleven cases possessed "primarily distributed" preheat zones, while the other three were "thickened." A reaction zone was further characterized as being "moderately distributed" if more than 20% but less than 40% of it was identified as being "locally distributed." A particular portion of a reaction zone is found to be "locally distributed" if that portion is both four times thicker than the laminar value and its length to thickness ratio is less than four. All of the reaction zones near the burner's exit were "thickened" and, except in one case, were also deemed "moderately distributed." Additionally, all of the reaction layers in the downstream interrogation region were "primarily distributed." Yet, regardless of being categorized as "moderately" or "primarily distributed," each case's reaction zones exhibited regions of both relatively thin and distributed reactions. In fact the appearance of the observed reaction zones can best be described as resembling "chicken noodle soup." That is, in any given instantaneous image relatively thin, "noodle-like" reaction layers are generally accompanied by thicker "chunky-chicken-like" reaction regions. Furthermore, the observed reaction zone structures in a particular case typically fail to correspond to those predicted by the turbulent premixed combustion regime diagram. This suggests that the regime diagram requires alterations if it is to properly forecast the appearance of a flame based on a simple set of operating conditions. The data set presented here is currently too limited to enable a thorough re-mapping of the regime diagram. However, based on their structural features, the cases considered here were classified into appropriate regimes of combustion.

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“…Generally, chemiluminescence of natural excited species, e.g., OH*, CH*, (where *denotes an electronically excited state) and Laser-Induced Fluorescence (LIF) techniques (Najm et al, 1998a,b;Paul and Najm, 1998;Röder et al, 2013;Sidey and Mastorakos, 2015) are used to identify the reaction zone and its topology. However, the choice of the scalars able to identify the reaction region can be influenced by the specific chemical-physical behavior of the combustion process, determined in turn both by operative conditions and fuel mixture (Najm et al, 1998a,b;Nikolaou and Swaminathan, 2014).…”

Section: Introductionmentioning

confidence: 99%

Heat Release Rate Markers for the Adelaide Jet in Hot Coflow Flame

et al. 2020

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In the present work, the correlation between the Heat Releaser Rate (HRR) and species mole fractions and net reaction rates is studied. The PaSR closure model is employed in a RANS framework to implement a detailed kinetic scheme, including the excited species OH*, used as a HRR marker. The effect of oxygen dilution on the combustion regime is investigated, as it can lead to Moderate or Intense Low-Oxygen Dilution (MILD) conditions. Two cases with different levels of oxygen concentration are analyzed. The results suggest the possibility of combining chemical species to construct an appropriate scalar to achieve better correlation with the HRR. It is found that typical markers such as radicals O, OH, OH* correlate fairly well with the HRR but improved correlations can be achieved with appropriate species mole fractions combinations, particularly for the MILD region of the flame.Keywords: heat release rate, heat release rate markers, OH*, laser induced fluorescence, jet in hot coflow, Moderate or Intense Low-Oxygen Dilution Frontiers in Mechanical Engineering | www.frontiersin.org

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Simultaneous measurement of localized heat-release with OH/CH2O–LIF imaging and spatially integrated OH∗ chemiluminescence in turbulent swirl flames

Cited by 59 publications

References 19 publications

Heat Release Imaging in Turbulent Premixed Ethylene-Air Flames Near Blow-off

Heat Release Imaging in Turbulent Premixed Ethylene-Air Flames Near Blow-off

Measurements to Determine the Regimes of Turbulent Premixed Flames

Heat Release Rate Markers for the Adelaide Jet in Hot Coflow Flame

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