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Optical Diagnostics Development for Soot Detection Michelsen, Hope Small (sub-micron) particulates are believed to pose a greater health risk than larger soot particles, are expected to have a significant impact on the Earthís climate, and are commonly produced during combustion. A growing concern about adverse health and environmental effects of small particles has prompted strict regulations of fine particulate emissions and has intensified research on the formation and impact of combustion-generated particles. Studies of particle formation and evolution, however, are hindered by a lack of sensitive, accurate, noninvasive measurements of their physical characteristics. Research in the Particle Diagnostics Laboratory at Sandia's Combustion Research Facility focuses on the development of optical diagnostics for particles, primarily soot particles, in combustion environments and combustion exhaust plumes. The goal of this work is in situ measurements of volume fraction, size, composition, and morphology of such particles with fast time response and high sensitivity. Optical techniques used include Laser-Induced Incandescence (LII), Elastic Laser Scattering (ELS), and multi-pass extinction via Cavity Ringdown Spectroscopy (CRDS). 
Soot particles in exhaust plumes are often coated with unburned fuel, sulfuric acid, water, ash, and other combustion by-products. Diesel particles, for example, can be comprised of as much as 50% volatile compounds. We are involved in studies to understand the effects of these coatings on particle characteristics, diagnostics, and chemical evolution. The ability to generate inhomogeneous particles and to deposit controlled volatile coatings on them is a critical component of this work. Equally important is the development of new capabilities to probe the physical and chemical properties of these particles. |
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