Effect of Flow Unsteadiness on Soot Morphology

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dc.contributor.advisor Dr. william Roberts, Committee Chair en_US
dc.contributor.author Xiao, Jidong en_US
dc.date.accessioned 2010-04-02T19:06:35Z
dc.date.available 2010-04-02T19:06:35Z
dc.date.issued 2005-04-07 en_US
dc.identifier.other etd-01052005-230458 en_US
dc.identifier.uri http://www.lib.ncsu.edu/resolver/1840.16/5040
dc.description.abstract The morphology of combustion-generated soot is of fundamental interest, but is difficult to measure. A new planar diagnostic technique was developed for morphology measurements in simple laminar flames. Additionally, Polycyclic Aromatic Hydrocarbons, (PAH) the precursors to soot formation, were measured non-intrusively in an unsteady laminar flame to determine the characteristic time scales of their formation. An existing point-wise laser scattering technique to determine soot morphology was extended to a planar technique and applied to a laminar ethylene air co-flow flame. An Nd:YAG laser (532 nm) was used to illuminate the soot particles and the resulting scattered light was collected over a wide range of angles. A low power laser was used to eliminate fluorescence and incandescence interferences. Simultaneous laser induced incandescence measurements were used to determine the soot volume fraction. Six morphological parameters, including primary spherule size and mass fractal dimension, were derived using this new planar measurement technique based on RDG/PFA theory. The results clearly show the soot formation processes, including inception, agglomeration, and oxidization. A two-angle approximate method was also demonstrated and shown to be applicable for instantaneous measurements in unsteady flames. The approximate method can provide limited soot morphology information including primary particle size and number of primary particles per aggregate, when the fractal dimension and distribution are assumed. The approximate method was not suitable over the entire region of this flame because the fractal dimension varies significantly from the assumed value of 1.8, particularly in the soot inception zone. Three different size classes of PAH were measured qualitatively via laser induced fluorescence by detecting fluorescence in different spectral regions. The relative concentrations of these PAH were measured in counterflow diffusion flames subjected to both steady and oscillating strain. With increasing strain rate, the PAH concentration was observed to decrease dramatically, though unequally, among the three size classes measured. With an unsteady strain rate, the PAH concentration oscillates in phase for frequencies below 50 Hz. At frequencies above 100 Hz, the PAH zone no longer responds to the imposed oscillations. Smaller PAH continue to respond to the instantaneous strain rate at a higher frequency than larger PAH. en_US
dc.rights I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. en_US
dc.subject PAH PLIF en_US
dc.subject soot morphology en_US
dc.subject LII en_US
dc.subject Laser scattering en_US
dc.title Effect of Flow Unsteadiness on Soot Morphology en_US
dc.degree.name PhD en_US
dc.degree.level dissertation en_US
dc.degree.discipline Mechanical Engineering en_US

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