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MEASUREMENT OF SOOT MORPHOLOGY, CHEMISTRY, AND OPTICAL PROPERTIES IN THE VISIBLE AND NEAR-INFRARED SPECTRUM IN THE FLAME ZONE AND OVERFIRE REGION OF LARGE JP-8 POOL FIRES

2007; Taylor & Francis; Volume: 179; Issue: 12 Linguagem: Inglês

10.1080/00102200701484266

1563-521X

Kirk A. Jensen, Jill Suo-Anttila, Linda Gail Blevins,

Rocket and propulsion systems research

Abstract The dimensionless extinction coefficient, K e , was measured for soot produced in 2 m JP-8 pool fires. Light extinction and gravimetric sampling measurements were performed simultaneously at 635 and 1310 nm wavelengths at three heights in the flame zone and in the overfire region. Measured average K e values of 8.4 ± 1.2 at 635 nm and 8.7 ± 1.1 at 1310 nm in the overfire region agree well with values from 8–10 recently reported for different fuels and flame conditions. The overfire K e values are also relatively independent of wavelength, in agreement with recent findings for JP-8 soot in smaller flames. K e was nearly constant at 635 nm for all sampling locations in the large fires. However, at 1310 nm, the overfire K e was higher than in the flame zone. Chemical analysis of physically sampled soot shows variations in carbon-to-hydrogen (C/H) ratio and polycyclic aromatic hydrocarbon (PAH) concentration that may account for the smaller K e values measured in the flame zone. Rayleigh–Debye–Gans theory of scattering for polydisperse fractal aggregate (RDG-PFA) was applied to measured aggregate fractal dimensions and found to under-predict the extinction coefficient by 17–30% at 635 nm using commonly accepted refractive indices of soot, and agreed well with the experiments using the more recently published refractive index of 1.99–0.89i. This study represents the first measurements of soot chemistry, morphology, and optical properties in the flame zone of large, fully-turbulent pool fires, and emphasizes the importance of accurate measurements of optical properties both in the flame zone and overfire regions for models of radiative transport and interpretation of laser-based diagnostics of soot volume fraction and temperature. Keywords: AbsorptionFireLight extinctionOptical propertiesPAHPolycyclic aromatic hydrocarbonsPool fireRadiative transportRDG-PFAScatteringSoot This work was supported by the Sandia Engineering Sciences Research Foundation and Campaign 6 Abnormal Thermal Environments Program and was performed at Sandia National Laboratories, a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy's National Nuclear Safety Administration under Contract DE-AC04-94AL85000. The authors would like to acknowledge the contributions of Pat Drozda for design and fabrication of the TCRN, Tom Headley for TEM imaging of the soot samples, and David Ho for setting up the laminar burner. Special thanks are extended to the Lurance Canyon Burn Site team, consisting of Dann Jernigan, Armando Saenz, Dan Hester, and Adrian Baca. Denise Bencoe, James Hochrein, and Christine White are gratefully acknowledged for their contributions to the chemistry analysis. Discussions with Chris Shaddix, Sheldon Tieszen, John Hewson, and Tom Blanchat during preparation and internal review are also gratefully acknowledged. Mun Choi of Drexel University was instrumental in this study with helpful technical discussions, aid in the design of the transmission cell, and supplying the laminar burner. Notes Combined uncertainity: 11.9%. 1BP = Boiling point. ∗Most stable isomer at flame temperatures (Stein and Fahr, Citation1985). 1Measured or reported standard deviations are shown in parentheses, (). 2Calculated standard deviations from specific extinction coefficient are shown in brackets, []. 3Average value for acetylene, ethene, propylene, butadiene, benzene, cyclohexane, toluene, and n-heptane. Density not specified. 4Density of 1.74 g/cm3 referenced from (Choi et al., Citation1995). 5Uncertainties calculated from 5% of the mean value shown in curly braces, {}. Type A reported as 2–5%. 6Density not specified; 1.74 g/cm3 from (Choi et al., Citation1995) used.