Experimental Study of Soot Nanoparticle Formation and Oxidation at Elevated Pressures

Yale University, New Haven CT

Investigators

Abstract

Proposal Number: CBET-0651906 Principal Investigator: Gomez, Alessandro Affiliation: Yale University Proposal Title: Experimental Study of Soot Nanoparticle Formation and Oxidation at Elevated Pressures PUBLIC ABSTRACT This research focuses on the fundamentals of soot nanoparticle formation at elevated pressures, a challenge because many practical systems operate at such conditions but few fundamental data are available there. Emission of soot particles from combustion systems has been a long-standing environmental problem because of the health effects associated with particulate matter and the polycyclic aromatic hydrocarbons adsorbed on their surfaces. Soot formation is also an issue of technical relevance for the potential engineering problems that may ensue; e.g., erosion of turbine blades. Despite considerable progress made in recent years, a fundamental understanding of soot formation in practical systems is still a daunting challenge. The present research examines soot formation of gaseous and liquid fuels in a counterflow burner operated at high pressures, up to 40 atm, that are relevant to practical applications such as gas turbines and engines. Fuels to be studied include ethylene, acetylene, heptane and toluene, a set of gaseous and liquid fuels with significantly different sooting propensities. One of the main difficulties of studying soot formation with these fuels is that they are very prone to soot, a problem that is exacerbated at high pressures. If the soot yield is too abundant, a number of experimental complications ensue that make it difficult to perform fundamental studies. A counterflow diffusion flame was selected as an optimal environment for the research because of the unparalleled level of control that it provides on the soot formation process, the suppression of buoyancy instabilities that typically plague co-flow flames at high pressures, and the opportunity of modeling the system in subsequent studies as one-dimensional. The flame is operated as a reactor in which the soot loading can be ?dialed? at will from the onset of the nucleation stage to significant surface growth and oxidation. As an additional novelty, by experimenting with a high diffusivity diluent such as helium, sufficiently thick flames can be stabilized, despite the high-pressure conditions, to enable the probing of the flame structure with adequate resolution. Particular emphasis is placed on the nanoparticle, early-nucleation stage. Chemical species are characterized that reflect the flame structure and participate in the growth process. Among impacts of the work, the effort is intended to yield a database for general use in validation of detailed computational models. Data sets will be made available on the web to allow convenient access to researchers for subsequent modeling. The research will also spill over into teaching and outreach activities. Soot research at high pressure does not lend itself easily to experimentation by inexperienced hands. However, with the supervision of graduate students and the PI, simple projects, such as on SEM/TEM analysis and data reduction software, will be tackled by undergraduate and upper high-school students.