Improvement of NOx Reduction Efficiency in Diesel Emission Using Nonthermal Plasma - Exhaust Gas Recirculation Combined Aftertreatment

Atmospheric-pressure nonequilibrium nonthermal plasma (NTP) hybrid exhaust gas aftertreatment systems have been developed by the authors without using precious metal catalysts and harmful ammonia, etc. Two types of new environmental protection systems (a dry system and a wet system), which enable to produce ultra low CO₂, PM (Particulate Matter), NOx emissions, fuel consumption and low cost, are investigated for diesel engine, marine engine and combustion boiler applications. These systems are now at the stage of pilot-scale plants tests supported by Japan Science and Technology Agency (JST) and carried out for four years as a national program. This paper mainly reports the principles of the dry system and some recent experimental results of laboratory tests. The NOx reduction comprises three flow processes: (a) adsorption, (b) heating and (c) cooling processes. The heating process corresponds to the regeneration process. These processes are repeated in the following order: (a), (b) and (c). This dry system demonstrates excellent energy efficiencies to meet the most recent Japanese national regulation of automobile diesel engine exhaust gas. In this study, approximately 60% of the NOx of the exhaust (NOx: 240 ~ 325 ppm, flow rate = 300 NL/min, N: standard state) can be continuously treated for 20 hrs. A improved and highest system energy efficiency of 154 g(NO₂)/kWh is achieved for NOx reduction.