Measurement of soot concentration and bulk fluid temperature and velocity using modulated laser-induced incandescence

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DOIResolve DOI: http://doi.org/10.1007/s00340-015-6107-z
AuthorSearch for: ; Search for: ; Search for: ; Search for:
TypeArticle
Journal titleApplied Physics B: Lasers and Optics
ISSN0946-2171
Volume119
Issue4
Article number6107
Pages697707; # of pages: 11
SubjectCoherent scattering; Cooling; Laser excitation; Laser theory; Modulation; Raman spectroscopy; Refractive index; Soot; Volume fraction; Absorption co-efficient; Excitation sources; Fluid temperatures; Higher frequencies; Laminar diffusion flames; Line-of-sight attenuations; Modulation frequencies; Soot volume fraction; Dust
AbstractThe use of a modulated LII two-colour technique to measure soot temperature in a laminar diffusion flame is described, and the results compared to CARS experiments. A sinusoidal modulated diode laser is used to excite the soot, and both the modulated LII intensity and its relative phase to the excitation source are measured with a lock-in amplifier and recorded. Modulation frequencies from 25 to 200,000 Hz were employed. The temperature is derived from the ratio of the modulated LII radiation signal at 445 and 750 nm, and the results compared to values obtained by CARS spectroscopy. The modulated LII temperatures were largely independent of modulation frequency and agreed well with the CARS temperatures. A theory is developed to explain the dependence of the phase delay of the modulated LII signal (with reference to that of the laser excitation source) on gas replacement time in the sample volume, soot cooling rate and soot volume fraction. The theory is shown to give a reasonable fit to the experimental results at all frequencies. At lower frequencies, the phase delay is dominated by the gas replacement time in the sample volume and at higher frequencies by the cooling rate of the heated soot. Time constants for both processes and the soot volume fraction are derived from the data and shown to be largely in agreement with the expected values. Using modulated LII-determined soot volume fraction and inverted and scatter corrected line-of-sight attenuation-determined absorption coefficients, the soot refractive index absorption function E(m) was measured to be between 0.45 and 0.42 over the wavelength range of 436–825 nm.
Publication date
PublisherSpringer International Publishing
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); Measurement Science and Standards
Peer reviewedYes
NPARC number21275846
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Record identifierad56fe74-f06f-4913-b0c4-e04c8c0453ea
Record created2015-07-14
Record modified2016-05-09
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