Research On Particle Structure And Optical Properties Of Soot Agglomeration

Soot aggregation particles is clustered particles, which is mainly due to incomplete combustion of fuel or the mixture of combustion-generated gaseous pollutants and dust, and also it is the main factor that contribute to global warming. Research on the structure and optical characteristics for soot aggregation particles is of great significance on the field of optical properties of atmospheric chemistry, physics, optics, environmental medicine and so on. Therefore, based on the above background, this thesis carried out the following research work:Mie theory and discrete dipole approximation (DDA) method were introduced, and the shape parameters of several typical single particles were characterized, and also the scattering properties of single particles of different shapes with different size parameters were calculated. The study found that the scattering properties of single particle increased with the increase of size parameters. When the size parameter of plate and drip crystal particle was 5.5, the extinction factor and scattering factors appeared extremes, and also the scattering properties was inversely proportional to the refractive index.Cluster-cluster aggregation (CCA) model was used to simulate the randomly oriented soot aggregation particles. The state of aggregation of aggregated particles, unit particle shape, the size of the primary particles, the incident wavelength and the chemical composition of adhesion of large particles were taken into account. The changes of scattering properties of soot aggregation particles were calculated by using the discrete dipole approximation (DDA) method. The results showed that, as for different types of units arranged rule aggregated particles, the parallel scattering intensity and vertical scattering intensity changed inconsistently, and also when the parallel scattering intensity was 90°, the minimum value appeared, but the vertical scattering intensity did not happen this phenomenon. For the randomly oriented soot aggregation particles, under the different incident wavelength, the forward scattering intensity was stronger than the backscatter intensity, also its extinction and absorption coefficient decreased with the increase of the diameter of primary particles. For the comparison of a variety of aggregate particle size with single particle size of scattering properties agglomerates, there existed obvious discrepancies between the optical coefficient and different change of the incident wavelength. When the incident wavelength was small, the scattering effect was mainly determined by the forward scattering. When different chemical composition of large particles adhered to the surface of soot aggregation particles, the size of large particle size was much larger, the change in chemical composition of large particle had great significance on scattering characteristics of aggregation particles.In the design experimental, when the wavelength was 635nm and 532nm respectively, the relative extinction coefficient was calculated (0.8543) by using transmission rate comparison method, and the simulation results also confirmed its reliability.