Deposited diesel soot oxidation and removal characteristics by nonthermal plasma

Particulate matter (PM) emissions generated by vehicles and transports can reduce the effectiveness of environmental control devices such as exhaust gas recirculation (EGR) heat exchangers due to fouling of the heat transfer surface and fins. This experimental study examines a non-thermal plasma system to remove deposited soot on a 25.4 mm diameter exhaust pipe during periods when the engine is not in operation. The results suggest that Ox radicals, metastables, positive ions and negative ions in the flow stabized corona process can reduce the soot deposition downstream on the pipe wall. Both soot oxidation and ash reduction gaseous by-products were observed. The application of nonthermal plasma in the absence of exhaust gas flow resulted in minimal generation of NO and NO2 while the removal of sulphur content in the soot was observed through measured concentrations of H2S and SO2 in the range of 1-5 ppm. Transient concentration measurements of CO and hydrocarbons (HC) were observed downstream during the plasma cycles suggesting oxidation of the soot layer. This was demonstrated by soot thickness measurement comparisons of the test and control sections that show a modest reduction in thickness in the proximity to the corona discharge plasma stream.