Collaborative Research: Plasma-enhanced Electrostatic Precipitation of Diesel Particulates using High Voltage Nanosecond Pulses

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The adverse health effects of diesel engine particulate emissions have been firmly established by many toxicological studies over the past few decades. These fine particulates smaller than 2.5 microns have been linked to premature cardiovascular and respiratory deaths, as well as lung cancer. While electrostatic precipitation was first demonstrated in 1824, thus far, use of the technology to remove combustion particulates has been limited to large power plants that can accommodate large secondary treatment devices. Reducing the overall size of this technology is necessary to open up new applications for electrostatic precipitation in mobile sources, such as ships and trucks. Our approach to electrostatic precipitation using plasma (a superheated state of matter) together with ultra-high frequency high voltage pulsing represents a novel application of an old technology. Preliminary results have shown significant promise in reducing particulate emissions, but the underlying mechanisms are poorly understood. The goal of this project is to address these knowledge gaps and identify the mechanisms for particulate removal in plasma enhanced electrostatic precipitation. If successful, this approach will enable development of much more compact electrostatic precipitators that could potentially transform diesel particulate mitigation technology for mobile sources. Further benefits to society result from outreach to high school teachers in the Los Angeles area to improve STEM teaching for underrepresented students. Outreach through professional societies will improve chemistry teaching and provide research opportunities for undergraduate students, thus improving scientific literacy.Preliminary results by the research team show that nanosecond high voltage pulsed plasma provides significant enhancement over conventional electrostatic precipitators in removing diesel engine particulates. However, the fundamental mechanism(s) underlying this enhancement remain poorly understood. The overall goal of this research is to explore the application of plasma enhanced nanosecond high voltage pulsed discharges as a novel approach for electrostatic precipitation. The specific research objectives designed to achieve this goal include: i) spectroscopic examination of ion mobilities and species generated by nanosecond high voltage pulse discharge, ii) characterization of size-dependent particle charge distributions, iii) multi-physics computational fluid dynamics modeling of nanosecond high voltage pulse electrostatic precipitation, and iv) investigation of the role of streamers in the ESP process. Results from this systematic study will provide mechanistic insight into the plasma enhanced electrostatic precipitation process. Such information is necessary to design systems to overcome current limitations and further improve particle removal efficiency. The nature of this work is inherently interdisciplinary, involving high voltage electronics, electrostatics, and fluid-dynamics, as well as combustion and aerosol science. This project brings together researchers with complimentary expertise to perform the research, as well as provide collaborative training opportunities for the student researchers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.