Coupled Dipole Calculation of Extinction Coefficient and Polarization Ratio for Smoke Agglomerates.
Coupled Dipole Calculation of Extinction Coefficient and
Polarization Ratio for Smoke Agglomerates.
Mulholland, G. W.; Mountain, R. D.
Combustion and Flame, Vol. 119, 56-68, 1999.
smoke; agglomerates; extinction
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.