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Measurement of Dimensionless Extinction Constant of Soot Generated Using Various Fuels.


pdf icon Measurement of Dimensionless Extinction Constant of Soot Generated Using Various Fuels. (410 K)
Zhou, Z.; Choi, M. Y.

Combustion Institute/Central and Western States (USA) and Combustion Institute/Mexican National Section and American Flame Research Committee. Combustion Fundamentals and Applications. Joint Technical Meeting. Proceedings. April 23-26, 1995, San Antonio, TX, Gore, J. P., Editor(s), 87-91 pp, 1995.

Sponsor:

National Institute of Standards and Technology, Gaithersburg, MD

Keywords:

combustion; soot; fuels; extinction; premixed flames; light extinction

Abstract:

Even though the soot volume fraction is a key property for describing soot both in the flame and above the flame, there has been little work to verify the accuracy of measurements by light extinction techniques. Choi et al studied the effects of source wavelength, scattering by soot particles, light extinction by 'large' molecules and the use of different indices of refraction reported in the literature on the measurement of soot volume fraction. The experiments indicated that the measured soot volume fractions were sensitive to the absorption constant (which was calculated using the reported refractive indices). For example, at a wavelength of 632.8 nm, the absorption constant can vary by a factor of two depending on the choice of indices of refraction. The focus of this paper is on the use of an independent method for characterizing soot volume fraction to assess the accuracy and to calibrate the light extinction method for soot generated using rich premixed flames. In short, the method consists of isokinetically sampling the soot at a known flow rate, measuring the mass of soot collected, and determining the density of the soot by helium pycnometry. The optical measurements can then be calibrated with the gravimetric measurements. In this manner, the dimensionless extinction constant can be determined without making assumptions regarding the optical properties of soot which can introduce significant uncertainties. The accurate measurement of the dimensionless extinction constant can improve the usefulness of the optical extinction technique.