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Proceedings Paper

Absorption spectroscopy of RDX monopropellant flames: CN and NH concentrations
Author(s): B. E. Homan; John A. Vanderhoff
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Paper Abstract

UV-visible multi-channel absorption spectroscopy has been used to probe the self-sustained combustion of pressed RDX, a main energetic ingredient found in modern day propellants and explosives. The two dimensional feature of an intensified CCD detector allowed simultaneous recording of multiple, spatially distinct absorption spectra. Between 10 and 12 equally spaced absorption spectra with spatial resolution as small as 0.163 mm have been obtained during 1 ms exposure. The number of absorption spectra and the spatial resolution can easily be set by the detector software, size of the excitation sheet and the focal length of the collection lens. Temporal resolution in the UV region has been increased to 1 ms by pulsing the light source. A 0.54 joule pulse with a duration of 0.75 ms was added to a simmering Xenon arc lamp for the measurement of combustion species. The increase in light intensity of 30 and 70 times the non-pulsed output provided the necessary light flux to achieve single pulse, multiple absorption spectra. To increase the species concentration sensitivity of the experiment, a triple pass optical arrangement was adopted. Partially silvered windows were installed at an angle to the beam providing for three passes across the samples. The corresponding path length was increased by a factor of 2.8 times the sample diameter. Least squares analysis of absorption spectra provide mole fraction profiles for OH, CN and NH along with temperature. Profiles for NC and HN have been determined for self-sustained combustion of RDX in 1.0, 1.5 and 2.0 atm air. Peak CN mole fractions of about 200 ppm are observed at 1 atm pressure and the NH mole fraction is about a factor of two lower. As the pressure is increased the reactive CN and HN species peak closer to the combusting surface and reside over a smaller spatial extent. Peak concentrations drop for these higher pressures, but may be due, at least in part, to limitations of the spatial resolution of the absorption experiment.

Paper Details

Date Published: 21 November 1997
PDF: 10 pages
Proc. SPIE 3172, Optical Technology in Fluid, Thermal, and Combustion Flow III, (21 November 1997); doi: 10.1117/12.293415
Show Author Affiliations
B. E. Homan, U.S. Army Research Lab. (United States)
John A. Vanderhoff, U.S. Army Research Lab. (United States)


Published in SPIE Proceedings Vol. 3172:
Optical Technology in Fluid, Thermal, and Combustion Flow III
Soyoung Stephen Cha; James D. Trolinger; Masaaki Kawahashi, Editor(s)

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