Investigation of stagnation-flow diamond-forming flames using advanced laser diagnostics
Bertagnolli, Kenneth Eugene
This item is only available for download by members of the University of Illinois community. Students, faculty, and staff at the U of I may log in with your NetID and password to view the item. If you are trying to access an Illinois-restricted dissertation or thesis, you can request a copy through your library's Inter-Library Loan office or purchase a copy directly from ProQuest.
Permalink
https://hdl.handle.net/2142/20181
Description
Title
Investigation of stagnation-flow diamond-forming flames using advanced laser diagnostics
Author(s)
Bertagnolli, Kenneth Eugene
Issue Date
1996
Doctoral Committee Chair(s)
Lucht, Robert P.
Department of Study
Mechanical Science and Engineering
Discipline
Mechanical Engineering
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Chemical
Engineering, Mechanical
Language
eng
Abstract
Gas phase temperature and atomic-hydrogen concentration profiles were measured near the deposition substrate in atmospheric-pressure, stagnation-flow diamond-forming flames. In these flames, a rich acetylene/oxygen/hydrogen mixture accelerates through a nozzle and impinges on a water-cooled molybdenum substrate, stabilizing a flat-flame approximately 1 mm below the substrate. A thin, polycrystalline diamond film is deposited on the substrate under appropriate conditions of flame stoichiometry and substrate temperature. Scanning electron microscopy and surface Raman spectroscopy verified the quality and uniformity of the diamond films deposited with this flame. Coherent anti-Stokes Raman scattering (CARS) spectroscopy of hydrogen was used to measure temperature profiles between the substrate and the incoming premixed jet. Hydrogen atom concentration profiles were measured using three-photon-excitation laser-induced fluorescence (LIF). The CARS measurements showed peak flame temperatures of 3300 K, approximately 200 K above the adiabatic equilibrium temperature for these flames. Temperatures were measured to within approximately 50 $\mu$m of the molybdenum substrate, sufficient to capture most of the steep temperature gradient near the substrate. The LIF measurements showed peak atomic hydrogen concentrations on the order of 6%, well below computed adiabatic equilibrium concentrations. The superadiabatic flame temperatures are believed to occur because of insufficient time for complete dissociation of unburned acetylene in these rich flames. Since atomic hydrogen is one of the dissociation products of acetylene, the observation of subequilibrium atomic hydrogen concentrations is to be expected. Measured temperature and hydrogen atom concentration profiles are in good agreement with a numerical flame model developed by Meeks and coworkers at Sandia National Laboratories, except that the measured distance between the substrate and the reaction zone is much less than predicted. The measurements show that the flame stand-off distance is approximately 0.6 to 0.8 mm along the stagnation streamline, while the model predicts a flame stand-off distance of 1.2 mm. The difference between the measured and predicted stand-off is probably due to differences between the actual and modeled velocity flowfield.
Use this login method if you
don't
have an
@illinois.edu
email address.
(Oops, I do have one)
IDEALS migrated to a new platform on June 23, 2022. If you created
your account prior to this date, you will have to reset your password
using the forgot-password link below.