Pilot-Scale Combined Reduction of Accumulated Particulate Matter and NO _x Using Nonthermal Plasma for Marine Diesel Engine

High-Throughput NOx Removal by Two-Stage Plasma Honeycomb Monolith Catalyst

“…In exhaust gas, most of the NO x exists in the form of NO, and the SCR of NO x would be promoted by increasing the ratio of NO 2 /NO x in the feed gas . In this regard, the advantage of plasma is that it facilitates the partial oxidization of NO to NO 2 by the plasma discharge of NO feed gas or by injecting O 2 plasma into the feed gas. − Consequently, the presence of plasma, either directly or indirectly, is useful in terms of the NO x removal efficiency and energy efficiency. In our previous work, for instance, we showed that supplying the energy to generate the plasma is more advantageous for NO x removal than heating the feed gas in a one-stage plasma–catalyst system operated at temperatures ≤250 °C .…”

Enhancing the Selective Catalytic Reduction of NOx at Low Temperature by Pretreatment of Hydrocarbons in a Gliding Arc Plasma

“…For instance, the use of the catalyst Ag/γ-Al 2 O 3 in conjugation with dielectric barrier discharge (DBD) at 60 J/L increased the removal efficiency by approximately 50% at an operating temperature of 250 °C. 8 The reasons for the improvement of NO x removal by a plasma catalyst process can be classified into several groups: oxidization of NO to form NO 2 , 16 oxidization of HCs to form oxygenated hydrocarbons (OHCs), 17,18 more reactive chemicals owing to the plasma state, and an enhanced interface between the plasma and catalyst. 19 All these advanced plasma catalyst processes can be realized by combining the plasma catalyst reaction in one stage, that is, plasma generation in the presence of a packed catalyst; consequently, the plasma and the catalyst act synergistically to accomplish NO x removal.…”

“…This is a promising practical approach to process diesel exhaust gases and requires less input energy for the plasma stage. 16 Enhancing the removal efficiency of NO x by the pretreatment of HCs with plasma to generate OHCs is another promising technology for practical plasma applications. The technical key is that OHCs would be more effective than the original HCs for the HC-SCR process in the low-temperature range.…”

“…However, the large volume of diesel exhaust gas presents a significant challenge, in that it requires a large amount of air plasma to be generated. Recently, Nguyen et al introduced a sandwich-type honeycomb plasma with the ability to generate large air plasma; however, their approach still needs to be refined to enable it to be used for the treatment of actual diesel exhaust gas, considering that diesel engines emit exhaust gas of the order of cubic meters per min. , Moreover, during plasma generation from the entire amount of diesel exhaust gases, energy loss could occur via self-heating of the diesel exhaust gas by the plasma, but the temperature increase is insufficient to render the catalyst reactive at a low temperature. For instance, an increase in the temperature of diesel exhaust gas from 180 to 200 °C is still insufficient to activate the catalyst, and the energy consumption is approximately 24 J/L (∼1.2 J/L K; specific heat capacity of air).…”

“…Interestingly, part of the feed gas can be treated by plasma instead of treating the entire amount of diesel exhaust gas. This is a promising practical approach to process diesel exhaust gases and requires less input energy for the plasma stage …”