New Condensed-Phase Approaches for Soot Formation, Aging, and Burnout

Brown University, Providence RI

Investigators

Abstract

This project on combustion-generated soot focuses on the complex carbonaceous condensed phases present in flames using concepts and tools developed for other carbon materials in the P.I.'s laboratory. The new tools include direct measurement of dynamic active-site loss at high temperatures and short times, the use of distributed activation energy formulations to understand and model both reactivity loss (aging) and oxidation, and the use of atomic pair-potential simulations to investigate higher polycyclic aromatic hydrocarbon (PAH) interactions. New distributed-site kinetic models are being applied to soot oxidation to resolve the long-standing paradox in the field of apparent power-law kinetics and to unify the kinetic database at high and low temperatures. A key modeling concept is the description of the condensed phases not as solids or liquids, but as polymeric glassy phases with variable nanostructural mobility that governs the transition from coalescence to agglomeration. The project includes a novel experimental task employing new aromatic-rich C/H nanoparticles synthesized in the P.I.'s laboratory as the first physicochemical models for young soot particles in flames. Combustion-generated soot is a respirable, ultrafine particulate material that carries known carcinogens and mutagens and is thus a key atmospheric pollutant. The reduction of soot emissions from diesel engines is a particularly challenging goal for U.S. vehicle manufacturers. Attempts to reduce soot emission from vehicles and furnaces focus on control of the flame chemistry and structure or on capture of particulates and subsequent low-temperature oxidation. For the design of both types of soot-control measures, a better understanding is needed of the structure, properties, and reactivity of the soot particles themselves from their first detection as recognizable condensed organic matter in the early stages of flames to their final release as fractal aggregates of fully carbonized and partially oxidized nanoparticles. This project applies the most modern approaches in carbon science to the understanding and characterization of the various stages of soot formation, evolution, and burnout.