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Synergistic Approach to Reduce Nitrogen Oxides and Particulate Emissions from Diesel Engines, 08-9051

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Principal Investigators
Magdi K. Khair
Partha P. Paul
Michael G. Grothaus

Inclusive Dates: 10/01/97 - 07/01/99

Background - Controlling oxides of nitrogen (NOx) and particulate emissions (PM) is a formidable challenge to the diesel engine industry. Catalyst suppliers are improving traditional devices such as oxidation catalysts and particulate filters as well as developing novel aftertreatment devices such as lean NOx catalysts, lean NOx adsorbers, and selective catalytic reduction of NOx emissions. Despite a substantial development effort in lean NOx catalysts, they have a NOx conversion efficiency of only 30 percent. An insufficient number of negatively charged species may be a possible limiting factor in the efficiency for these catalysts. Recent SwRI research in nonthermal plasmas provided a means of supplying the necessary electrons to enhance the lean NOx catalyst conversion efficiency. The use of nonthermal plasmas with lean NOx catalyst systems may provide a NOx reduction efficiency greater than the 50 percent required to meet future standards.

Approach - A series of short, high-voltage electrical pulses generates an atmospheric-pressure nonthermal plasma in a cylindrical vessel known as a pulsed corona reactor. After determining the baseline emissions emanating from a representative diesel engine, the exhaust is introduced into this reactor tube to determine the effects of the nonthermal plasma acting alone. The change in concentration of the relevant gaseous species (for example, NOx, CO, or total hydrocarbons) was recorded for comparison to the case in which nonthermal plasma is used in concert with a lean NOx catalyst. Three different lean NOx catalytic formulations were individually applied to reactor tubes identical to the tube used in the plasma acting alone case. Exhaust from the same diesel engine was introduced into the three catalyst-coated tubes, and the resulting concentrations of relevant gases were compared with that of the plasma only experiments.

Accomplishments - The results of the plasma-assisted catalysis experiments in diesel exhaust have shown that increased removal efficiency is possible over that of either nonthermal discharge or a passive (without reductant) lean NOx catalyst acting alone. As a result of these experimental observations, the research team has drawn several significant conclusions. This internal research effort has resulted in external funding to continue development of this promising technology.

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