AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Physicochemical Characterization of Cerium Particles Generated by Combustion of Ce-Doped Diesel Fuel
ROBERT WILLIS, Kristin Bunker, Traci Lersch, Gary Casuccio, Eric Grulke, Natalia Mandzy, Joseph Conny, Michael Lewandowski, Jason Weinstein, Jonathan Krug, Kasey Kovalcik, U.S. EPA
Abstract Number: 549 Working Group: Combustion
Abstract Diesel engines emit large amounts of soot which degrades air quality and harms public health. Nanoscale metal-oxide fuel-borne catalysts (FBCs) have been shown to reduce soot emissions and improve fuel efficiency. FBCs utilizing nano-sized cerium oxide (ceria) particles are used in other countries, but are not currently approved for on-road use in the US. The EPA’s Nanomaterial Research Strategy has targeted ceria as a nanomaterial of concern due to the potential for human and ecosystem exposure to nanoceria particles released to the atmosphere.
In order to understand the exposure potential and environmental fate of nanoceria particles from the use of FBCs, the EPA is conducting research to characterize the morphology, composition, and size distribution of cerium-rich particles generated by combustion of ceria-doped fuel. We will discuss results obtained using a nano-MOUDI™ cascade impactor to collect size-resolved particulate samples on filters (analyzed by ICP-MS) and TEM grids (analyzed with high-resolution electron microscopy).
Analyses of “aged” diesel exhaust showed Ce-rich particles ranging in size from ~12-80 nm, some enclosed within a Ca-rich shell, embedded in or decorating soot particles; no isolated ceria particles were observed. The smooth, rounded morphologies of most of the Ce-rich nanoparticles combined with their sizes, suggest a two-step process during combustion, in which the catalyst ceria particles quickly form aggregates which then fuse together or melt during high-temperature combustion. Experiments are underway to characterize fresh diesel emissions using a dilution manifold to simulate real-world tailpipe emissions. Size distribution data show that, compared to fresh undoped emissions, the nanoceria FBC results in the appearance of a nuclei mode dominated by ceria particles < 30nm in size accompanied by a decrease in accumulation mode soot particles. Results of the characterization of the Ce-rich particles emitted from fresh diesel exhaust generated by combustion of ceria-doped diesel fuel will be presented.