Micro-Plasmas Through Porous Media

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Porous media may be thought of as material that is essentially transparent to fluid flow (e.g. gas or liquid). The internal surface area of such materials is substantial, making the material excellent for chemical processing applications. Porous media play an important role in modern society with applications ranging from water filtration, such as activated charcoal filters, to air filtration. Indeed, a catalytic converter exploits porous media's high surface area to volume ratio to achieve high emission reduction efficiency in automobile exhausts. New and emerging applications of porous media include fuel cells and clean combustion. Porous media combustion in particular takes place in the pores. The energy released there elevates the medium temperature so that injected fuel automatically ignites upon entry. This technology has the potential to reduce auto emissions and significantly increase fuel efficiency by enabling very lean fuel burns. The introduction of small amounts of ionized gas, a micro-plasma, inside the pores can further reduce ignition temperature thereby allowing for further increases in efficiency. Additionally, reactive micro-plasmas produced in the pores have the potential to decompose toxic combustion byproducts as well as to clean the pores to greatly improve service lifetime. Currently, the micro-plasma production in porous media is not well understood. This effort aims to improve the understanding and optimize the production of micro-plasmas in porous media by using a combination of experiments and simulations. The goal of the effort is to bridge the gap between scientific understanding of plasma production in porous media and actual applications. The understanding obtained from this effort contributes to the development and realization of clean burning, highly efficient, low emission automobiles, advanced fuel cells and advanced industrial smoke stack scrubbers. A fundamental understanding of the physical conditions that lead to interconnected plasma propagation from pore to pore is necessary before one can credibly control and thus exploit micro-plasmas in porous media (MPPM). We expect that a combination of diffusive transport between pores and plasma avalanche within the pores, augmented by surface charging and radiation transport, play key roles in establishing plasma interconnectivity between adjacent pores. However there is now little experimental or theoretical confirmation of these or other theories. In this research project, we will investigate the basic properties of atmospheric pressure plasmas propagating into and through porous media in chemically reacting environments. The goals are to improve our understanding of plasma-surface interactions, which lead to MPPM, through a collaborative investigation combining comprehensive experimental measurements and first-principles, fluid, hybrid and kinetic modeling. Two configurations will be studied. The first is a structured porous material represented by a pack-bed reactor consisting of dielectric beads or rods having a controlled radius, permittivity, conductivity and layout placed between metal electrodes. The second configuration will be a truly randomly structured porous material, ceramic and/or metal foam, as is commercially available. The project also includes a K-12 outreach effort targeting low-income students. The effort aims to introduce the students to plasma science and the emerging field of plasma-aided combustion through both hands on experiments and science lesson modules.