A Study on Diesel Emission Reduction using a High-frequency Dielectric Barrier Discharge Plasma

The aim of this study is to develop a plasma-assisted after-treatment system for simultaneous reduction of NOx and PM in diesel exhaust, which is less sensitive to the fuel sulfur. The work presented focuses on development of a high-frequency dielectric barrier discharge reactor for oxidation of NO to NO₂ in diesel exhaust and low-temperature oxidation of diesel soot with NO₂. The first part of this paper describes the combustion characteristics of carbonaceous matters with pure NO₂ and discusses the difference when oxygen is used as oxidation agent. The second part focuses on the development of a high-frequency dielectric barrier plasma reactor and describes the effects of plasma reactor configuration, energy density and gas composition on the NO conversion into NO₂, and last part describes the soot oxidation with the plasma gas. The results reveal that NO can be efficiently oxidized into NO₂ using the developed plasma reactor. NO₂ formation is greatly affected by the energy density, gas composition and temperature. Hydrocarbons show positive effects on NO conversion into NO₂ by increasing the conversion rate, lowering the required electrical energy and preventing the formation of byproducts. Diesel soot oxidation experiments reveal that oxidation of soot with NO₂ begins at temperature of about 270°C that is 200°C lower than that of O₂. This result show that NO₂, which is produced by the plasma assisted conversion of NO can be used for continuous regeneration of PM filter at low temperature range, which is usually available in diesel exhaust.