Year of Publication

2018

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Michael Winter

Second Advisor

Dr. Kozo Saito

Abstract

Flame synthesis is a growing field of research aiming at forming new materials and coatings through injection of seed materials into a flame. Accurate prediction of the thermal structure of these flames requires detailed information on the radiative properties and a thorough understanding of the governing combustion processes. The objective of this work is to establish a basic optical diagnostic characterization of different methane-air diffusion flames of different complexity. The basic principles are developed and demonstrated at a rotational symmetric co-flow burner and finally applied to a burner consisting of six clustered microflames which is designed for future flame synthesis work. This work focuses on the demonstration of the optical techniques for characterizing the optical emissions from diffusion flames and of the proposed method for the determination of radiating species properties from these optical measurements.

In the co-flow diffusion flame setup, the fuel of methane diluted with nitrogen is provided through an inner tube while the air is applied through an outer duct surrounding the fuel nozzle. Filtered imaging and spectrally resolved measurements of the chemiluminescence of CH* and C2* and of water emission were conducted. A procedure for using the HITRAN database to support the spectroscopic analysis of the water emission was developed.

In the six clustered microflames burner setup, the burner consisted of six micro-nozzles arranged in a circle surrounding a central nozzle through which air and TaN seed particles with sizes between 0.3 and 3 μm were injected. Spectrally resolved measurements of the chemiluminescence of CH* and C2* were conducted for temperature measurements. Imaging results obtained from a spectral integration of the molecular emission were compared to results from Japanese collaborators who applied a tomographic analysis method to filtered emission measurements of CH* emission which can yield spatially resolved three dimensional mapping of the flame front. The analysis of the spatial distribution of the integrated band emission of CH* and C2* showed that the emission of both species is generated at the same locations in the flame which are the thin flame sheets shown in the tomography results of CH*. The ratio of the C2* and the CH* emission from the emission spectroscopy measurements was used to determine a local equivalence ratio through empirically derived correlations for premixed flames reported in literature. Rotational and vibrational temperature distributions of CH* and C2* radicals throughout the entire flame were determined from the spectrally resolved emission from CH* and C2*. The temperatures of TaN seed particles were characterized using VIS-NIR emission spectra while varying fuel-air flow rates. The temperature profiles of the particles at various heights above the base of the central nozzle, obtained by their VIS-NIR continuum emission, showed a well-defined constant temperature region that extended well beyond the actual flame front and changed as fuel and oxidizer flow rates were varied. The results demonstrate the ability to control the duration to which seed particles are subjected to high temperature reactions by adjusting fuel and oxidizer flow rates in the clustered microflames burner.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2018.324

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