A minimally-intrusive optical sensing system for
high-temperature/high-velocity gas-generator exhaust plumes has been developed.
The overall goal of this effort is to perform a feasibility assessment of the
associated non-intrusive measurement technologies and to establish a roadmap
for the most effective practice. For this application glass fiber-optic cables,
acting as radiation conduits, are inserted through the combustion chamber or
nozzle wall and look directly into the flow core. The cable transmits data from
the flame zone to externally-mounted spectrometers. In order to capture the
full-optical spectrum, a blended dual-spectrum system was employed, with one
spectrometer system tuned for best-response across the visible-light and
near-infrared spectrum, and one spectrometer tuned for best-response in the
near- and mid-infrared spectrum. The dual-band sensors are
radiometrically-calibrated and the sensed-spectra are spliced together using an
optimal Wiener filtering algorithm to perform the deconvolution. The merged
spectrum is subsequently curve-fit to Planck's black-body radiation law, and
flame temperature is calculated from associated curve maxima (Wien's law). The
presented fiber-optic sensing systems performs a function that is analogous to
Raman spectroscopy. The system is non-contact and does not interfere with the
heat transfer processes. In this report data collected from a lab-scale (200 N)
hybrid rocket system are analyzed using the described method. Optically-sensed
flame-temperatures are correlated to analytical predictions, and shown to
generally agree within a few degrees. Additionally, local maxima in the optical
spectra are shown to correspond to emission frequencies all species known to
exist in the hybrid combustion plume. The presented data makes clear that the
approach works equally when the fiber optic protrudes from a solid boundary
into the flow field. This result opens up the possibility for the presented
fiber-optic techniques to be applied for a wide swath of gas-generators, including
gas turbine engines.
Author(s) Details:
Stephen A. Whitmore,
Department of Mechanical and Aerospace Engineering, Utah State
University, 4130 Old Main Hill, Logan UT, 44322, USA.
Please see the link here: https://stm.bookpi.org/CAERT-V1/article/view/14156
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