Feasibility of Plasma Aftertreatment for Simultaneous Control of NOx and Particulates 1999-01-3637

Plasma reactors can be operated as a particulate trap or as a NO_x converter. Particulate trapping in a plasma reactor can be accomplished by electrostatic precipitation. The soluble organic fraction of the trapped particulates can be utilized for the hydrocarbon-enhanced oxidation of NO to NO₂. The NO₂ can then be used to non-thermally oxidize the carbon fraction of the particulates. The oxidation of the carbon fraction by NO₂ can lead to reduction of NO_x or backconversion of NO₂ to NO. This paper examines the hydrocarbon and electrical energy density requirements in a plasma for maximum NO_x conversion in both heavy-duty and light-duty diesel engine exhaust. The energy density required for complete oxidation of hydrocarbons is also examined and shown to be much greater than that required for maximum NO_x conversion. The reaction of NO₂ with carbon is shown to lead mainly to backconversion of NO₂ to NO. These results suggest that the combination of the plasma with a catalyst will be required to reduce the NO_x and oxidize the hydrocarbons. The plasma reactor can be operated occasionally in the arc mode to thermally oxidize the carbon fraction of the particulates.