EAGER: Raman Analysis of Thermophoretically Sampled Soot Particulate

George Washington University, Washington DC

Investigators

Abstract

1142284 Miller Intellectual Merit: Soot is the term given to small particles that are mostly composed of carbon, and that result from incomplete combustion processes. Soot formation plays both positive roles (radiation from hot particles is the dominant mechanism for heat transfer in boilers) and negative (in the same boilers, soot may coat furnace walls and soot particle impingement on the turbine blades of a commercial airline engine leads to wear) in energy generation. Soot is also important in the environment as it increases mortality in urban areas and contributes to climate change. In the laboratory, what we understand about soot formation comes from measurements near the beginning (through the measurements of concentrations of small precursor molecules) and near the end (through optical measurements in flames and/or microscopic analysis of collected particulate matter) of the process. As a consequence, there are several fundamental questions that have gone unanswered: What is the mechanism for the transition from flat, planar molecules to three-dimensional particles? What is the nature of the carbon bonding in the youngest particles? The goal of this project is to answer these questions through a study of particles sampled from several types of flames. By understanding the detailed chemistry and physics of soot formation and destruction in flames, we enable combustion system engineering that can enhance the positive effects of soot in flames (heat transfer) and while minimizing deleterious heath effects and environmental impacts. The project's principal investigator has been a leader in the science of soot formation for more than 20 years. In the 1980s, he proposed that soot particles are composed of aggregates of flat, and extremely stable, molecules known as polynuclear aromatic hydrocarbons (PAH). His calculations suggest that the binding energy that holds clusters of PAH together is strong enough for them to survive even at flame temperatures. To prove this hypotheses, in this project particles are studied using Raman spectroscopy, in which laser light is "scattered" from the carbon particles, providing information about the optical and electronic properties of the particles, which can then be used to infer structure and morphology. Analysis is performed on particles that are rapidly extracted from laboratory flames that mimic a wide range of conditions found in practical combustion devices. Broader Impacts: In addition to the technical motivation for the project described above, an additional outcome of this award will be the education of a doctoral student in the Chemistry Department of GWU. The GWU Ph.D. program is smaller than most US doctoral chemistry programs. However, its size has been an attribute in attracting top-quality students who are looking for the type of individual attention that is available there. Its small size has catalyzed interdisciplinary research that links the chemistry program with scientists and engineers with mutual interests at GW, at other US academic campuses and laboratories, and at partner institutions throughout the world. This strategy has been a successful recipe in insuring that their graduates find employment in both the public and private sectors. George Washington University is ranked among the top few universities in the country in the population of women in science and engineering graduate programs. In line with this fact, the chemistry department's graduate program and the PI's lab have majority female populations.