Particulate matter (PM) and NO_x emitted from diesel engines is simultaneously reduced by a barrier-type catalyst-packed nonthermal plasma (NTP) application, driven by a pulse high-voltage power supply under oxygen-lean conditions. Catalyst particles of γAl₂O₃ and Ag/γAl₂O₃ with a diameter of 2–4 mm are used as packed pellets and carbon PM is loaded among the pellets. The reduction results are compared with those in a previous study using a noncatalytic BaTiO₂ pellet packed bed reactor. NO_x is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by NO_x or ozone (O₃) reduction at elevated local temperatures among the pellets. Since CO and CO₂ are generated, the carbon PM is actually combusted under oxygen-lean conditions, resulting in the simultaneous removal of PM and NO_x with NTP-assisted catalysts. It is found that in the presence of the catalysts, PM removal calculated from CO and CO₂ generation increases with an increase in the oxygen concentration. The maximum PM removal energy efficiency of 0.92 g(C) /kWh is observed for O₂ = 2%. Furthermore, NO_x removal decreases with an increase in the oxygen concentration. The maximum NO_x removal energy efficiency of 14.2 g(NO₂ ) /kWh is observed for O₂ = 0%. Compared with the experimental results obtained without the catalyst pellets, the NO_x removal energy efficiency increases by a maximum of 47% for O₂ = 2%. When comparing the present results with those in the previous study using BaTiO₃ pellets, NO_x removal energy efficiency is larger, but the PM removal is lower in the case of catalyst packed-bed reactor.

An effective NO _x -reduction aftertreatment system for a marine diesel engine that employs combined nonthermal plasma (NTP) and adsorption is investigated. The system can also treat particulate matter (PM) that employs a diesel particulate filter (DPF) and its regeneration by NTP-induced ozone. The effect of the combined reduction of accumulated PM and NO _x is studied. The marine diesel engine of interest provides an output power of 1 MW at 100% of the engine load. The NO _x reduction is composed of repeated adsorption and desorption flow processes using NTP combined with NO _x adsorbents. With a view toward practical use, experiments on a higher number of cycles are carried out. The amount of adsorbents is 105 kg, which is greater than that in the authors’ previous study. As a result, NO _x reduction efficiency by NTP is higher than in the previous study and is greater at higher amounts of adsorbents owing to higher NO _x desorption. Furthermore, DPF regeneration with plasma-induced O ₃ injection is achieved simultaneously. This aftertreatment system demonstrates an excellent energy efficiency of 114 g(NO ₂ )/kWh. The present aftertreatment can generate a synergistic effect of PM and NO _x reduction.

The collection and incineration mechanisms in the particulate matter (PM) aftertreatment technique proposed by the author were investigated. An experiment for actual exhaust gas was performed by sampling 10 NL/min of exhaust gas from the flue gas from a stationary diesel engine generator. The reactor for PM aftertreatment comprised a glass tube with surrounding corona needles that projected negative charges. Various combinations of voltages applied to each of the corona needles and the surface electrodes were compared. The results enhanced the hypothesis that negatively charged PM is attracted by the dielectric surface that is positively charged by positive ions supplied by the electrode on the glass surface. Subsequently, conditions for carbon incineration by nonthermal plasma were investigated using a simulated dielectric barrier discharge electrode and carbon black particles applied to the surface. It was found that the gap length over which the carbon-adhered area and the surface electrode face each other is the key factor for the rate of incineration.

An efficient NO_x reduction aftertreatment technology for a marine diesel engine that combines nonthermal plasma (NTP) and NO_x adsorption/desorption is investigated. The aftertreatment technology can also treat particulate matter using a diesel particulate filter and regenerate it via NTP-induced ozone. In this study, the NO_x reduction energy efficiency is investigated. The investigated marine diesel engine generates 1 MW of output power at 100% engine load. NO_x reduction is performed by repeating adsorption/desorption processes with NO_x adsorbents and NO_x reduction using NTP. Considering practical use, experiments are performed for a larger number of cycles compared with our previous study; the amount of adsorbent used is 80 kg. The relationship between the mass of desorbed NO_x and the energy efficiency of NO_x reduction via NTP is established. This aftertreatment has a high reduction efficiency of 71% via NTP and a high energy efficiency of 115 g(NO₂)/kWh for a discharge power of 12.0 kW.