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New perspectives of turbulent flame structure via CH PLIF in prevaporized liquid fuels

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Gandomkar, Amirreza 
Svoboda, Aidan 
McManus, Thomas A 
Carter, Campbell 


This effort investigates flame topology, curvature, and flame surface density (FSD) measurements, using CH planar laser-induced fluorescence (PLIF) in prevaporized, premixed liquid fuel jet flames. A McKenna burner with a central jet port, fueled by methane, n-heptane, and n-dodecane is utilized in these experiments, using the flat flame as a methane-air pilot to maintain the stabilization of the jet flame. The measurements were conducted at Re = 10,000 at equivalence ratios of 0.8, 1, and 1.2. CH PLIF experiments were performed using the C-X band with excitation and fluorescence near 314 nm. A novel image processing methodology has been developed to capture flame structure and identify the product and reactant side of observed CH contours. This method allows for the determination of the sign of curvature to calculate curvature statistics and distributions for all cases studied. The effect of non-unity Le number is examined by analyzing fluorescence signal-curvature correlations for heavy hydrocarbon fuels compared to methane cases. The correlation reveals a relationship between the curvature of liquid fuel flames and CH fluorescence signals, particularly in high negative curvature regions. The signal-curvature correlation is stronger for larger Le fuels. In addition, the flame images are binarized to obtain a map of the average progress variable contours and flame surface density. Compared to OH PLIF, where the product and reactant sides are oriented and distinguished, CH PLIF requires more detailed binarization and side detection processing due to flame fragmentation and local extinctions. Observations of simultaneous OH-CH PLIF in these flames often show layers of extinguished CH while localized OH signal remains, which suggests the imaging of OH alone may not capture in-plane extinction and may lead to an over-prediction of flame surface density. Estimates of this over-prediction are determined by calculating flame surface density using artificially connected edges where a local extinction in CH images has occurred to simulate results from pseudo-OH PLIF imaging. Furthermore, the flame surface density, conditioned on local progress variable, is calculated for all cases comparing the effects of fueling, and equivalence ratio. Lastly, to determine potential differences in imaging methodologies between the CH PLIF and OH PLIF, the flame surface density is measured for pseudo-OH PLIF and is compared to the CH PLIF derived measurements.



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12th U. S. National Combustion Meeting

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