Single-Stage Simultaneous Reduction of Diesel Particulate and $\hbox {NO}_{\rm x}$ Using Oxygen-Lean Nonthermal Plasma Application

A simultaneous reduction of particulate matter (PM) and NO_x emitted from diesel engines has been realized by means of a barrier-type packed-bed nonthermal plasma (NTP) application driven by a pulse high-voltage power supply under oxygen-lean conditions. BaTiO₃ particles having a large dielectric constant ( ~ 10 000) are used as packed pellets, and carbon PM is loaded among the pellets. NO_x is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by NO_x or by ozone (O₃) reduction under elevated local temperatures among the pellets. From the photographs of the pellets, it can be confirmed that the carbon PM or soot is removed under the condition of lean oxygen, resulting in the simultaneous removal of the PM and NO_x. An optimal value for the mass of the loaded PM exists, and when the loaded PM mass is greater than a threshold value, the effect of the NTP induced by the partial discharge is too weak to simultaneously reduce the PM and NO_x. Under the optimized plasma condition, the experiment yields energy efficiencies of 2.2 g/kWh for the PM incineration and 4.3 g(NO₂)/kWh for the NO_x reduction in the experiment.