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Coupled Dipole Calculation of Extinction Coefficient and Polarization Ratio for Smoke Agglomerates.


pdf icon Coupled Dipole Calculation of Extinction Coefficient and Polarization Ratio for Smoke Agglomerates. (1322 K)
Mulholland, G. W.; Mountain, R. D.

Combustion and Flame, Vol. 119, 56-68, 1999.

Keywords:

smoke; agglomerates; extinction

Abstract:

The mass specific extinction coefficient and the polarization ratio at 90 deg of simulated smoke agglomerates are computed for clusters with 3 to 1390 primary spheres and for size parameter from 0.05 to 0.6 using the coupled electric and magnetic dipole (CEMD) method. For the size parameter range of interest for post-flame smoke, the specific extinction coefficient computed by CEMD is 21% to 36% greater than Rayleigh prediction, and for this size range for clusters with 100 - 1,000 primary spheres, the range in the specific extinction coefficient is about 12%. Aggrement between measured and predicted specific extinction coefficient would require selection of a refractive index outside the range of values wiedly used by the combustion community. The polarization ratio at 90 deg is found to be a monotonic function of primary sphere size and relatively independent of agglormerate size. Comparison with the limited experimental resutls indicates potential for polarization ratio as a diagnostic for primary sphere size.