|M.Sc Student||Shtift Matty|
|Subject||Characterization of Black Carbon Airborne Nano-|
Particulates by Cavity-Ring-Down Spectroscopy
|Department||Department of Chemistry||Supervisor||PROF. Israel Schechter|
|Full Thesis text|
Nano-sized airborne Black Carbons (BCs) are easily inhaled and are known to be hazardous. BCs are associated with relatively high amount of organic carbon such as Polycyclic Aromatic Hydrocarbons (PAHs) which are known carcinogenic or mutagenic agents. Therefore, the study of soot and coal particulates is important for their reduction in the environment and minimizing their release in industrial processes. As representatives of BC particulates we characterized soot in premixed flames and coal particulates in air/or water suspension.
This work applies Cavity-Ring-Down Spectroscopy (CRDS) method for on line determination of size distribution of nano-metric coal particulates under atmospheric conditions. It was found that flow rates significantly affect the time of aggregation in the nano-scale ranges (and less in other ranges). Subsequently it affects the measured distribution of the ultrafine particulates. The influence on the larger particulates was minor. Our fast measurements of the size-distribution is significant, since it comes out that the distribution is time dependent and changes rapidly. Moreover, by controlling the flow rates we could measure size distributions in the ultrafine-range in water suspensions, where other methods actually failed.
A CRDS based method was also proposed to determine the soot volume fraction in sooting flames along the centerline of the flame (i.e. the combustion time line). By using a stainless steel burner, which produced a line of stable flames, the system could isolate the influences of the sooting parameters such as: initial C/O ratios (which is critical for soot formation), gas/air flow rates and the burner geometry. It allowed for identifying the fast polymerization zone in the early combustion, and determining the extinction coefficients and the volume fractions of PAHs and Condensed Hydrocarbon Species (CHS) in this zone. Moreover, we showed for the first time how the extinction coefficients and the volume fractions develop as a function of the initial C/O ratio (C/O = 0.44-2.5). The extinction coefficients decreased from to for the low C/O flames, but increased for the richer flames. This was attributed to PAH absorption. The volume fraction (at this zone) decreases exponentially as a function of the initial C/O ratio, but has a polynomial increase as the flame becomes richer.