Chemical Morphology of Carbonaceous Particulates and Their Precursors in Diffusion Flames

George Washington University, Washington DC

Investigators

Abstract

A bright yellow glow is a ubiquitous feature of most fires and flames and is associated with combustion by anyone who has ever seen a candle or a fire in a fireplace or outside. This emission is from very hot, nanometer-sized particles of mostly carbon, along with smaller quantities of some other elements, especially hydrogen. Given the central role that these particles hold in the human experience with fires and combustion, it is remarkable that the details of how they are formed are not fully known. How can this be? One reason is that the processes that occur happen very quickly. These particles, that contain perhaps a million carbon atoms, are assembled in times of less than a second from molecules that contain only a few carbon atoms. Thus, this chemistry involves thousands (perhaps millions) of successive steps and just as many intermediates. To compound the problem, the suite of laboratory diagnostics that have been applied to the study of "soot" formation typically gives us information about very small or very large intermediates, leaving a great deal of uncertainty about what happens in between. In this grant, a team of researchers at George Washington University is applying a suite of laser-based diagnostics to a study of soot formation in simple and well-characterized, laboratory flames. In addition to "traditional" diagnostics available in this laboratory, a new suite of measurements will be introduced based on a class of emerging "super continuum" light sources. In essence, these sources are "white-light lasers" where a beam of light is created covering a wide range of colors. One of these sources produces visible light (and light just beyond the range of human perception) and will be used to study the behavior of electrons in the smallest soot particles. The second produces infrared light that provides additional information on particle structure; specifically how individual carbon atoms are bound to one another. Both types of diagnostics are intended to provide insight to the structure of "nascent" soot particles formed at the earliest stages of molecular growth. In addition to this experiment work, computational tools will be used to predict particle structures, with a goal of validation of the laboratory results. Soot formation on earth plays a critical role in energy generation (from the soot coating of furnace walls in a commercial boiler, to soot particle impingement on the turbine blades of a commercial aircraft engine) and in the environment (from increasing mortality in urban areas to contributing to climate change). Remarkably, the same types of species (perhaps formed through similar processes) are found throughout the universe and are thought to be responsible for some of the most intriguing (and elusive) astronomical observations. A primary focus of this and the Miller Lab's entire prior NSF supported work has been the education of doctoral students. There has been a proven record of success by laboratory alumni. Four of the last five Ph.D.s to be awarded from this research group applied for and were awarded prestigious government postdoctoral fellowships. At least three of the alumni have grown into senior management positions at laboratories of the Department of Defense, Commerce, and NASA. One now serves in the Office of Science and Technology Policy at the White House. Further, the laboratory has a proven record of education of traditionally underrepresented genders and races in STEM fields. In this grant, the tradition will be continued by providing research experience for doctoral students, undergraduates, and high school students drawn from District of Columbia high schools.