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Particulate matter (PM) and NOx 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. NOx is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by NOx 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 NOx 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, NOx removal decreases with an increase in the oxygen concentration. The maximum NOx 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 NOx 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, NOx removal energy efficiency is larger, but the PM removal is lower in the case of catalyst packed-bed reactor. [ABSTRACT FROM PUBLISHER]

Air-pollutant and greenhouse gas emissions typically have high gas flow rates and low concentrations (in ppm ∼ % levels, 1% = 10 000 ppm). The bulky equipment required for direct treatment of high-flow-rate low-concentration exhaust gases result in high-energy consumption and prohibitive operating costs. As such, the objective of this study is to convert high-flow-rate low-concentration exhaust gases into low-flow-rate high-concentration gases. This is achieved by desorbing the gas from an adsorbent by applying an atmospheric plasma inside a nonthermal plasma (NTP) reactor. This paper focuses on carbon dioxide (CO2) concentration (condensation) via this method. The adsorbent consists of spherical ∼2-mm-diameter molecular-sieve pellets of zeolite. Plasma desorption is performed by applying nanosecond high-voltage pulses (peak voltage ∼35 kV, pulse frequency = 140–350 Hz, and pulse width ∼600 ns) to the plasma reactor. A gas flow rate of 4 L/min is used and the concentrations of CO2, O2, H2O, and N2 gases are 2.75%, 18%, 1%, and the balance, respectively. The results reveal that CO2 can be desorbed effectively and more rapidly in a repeated adsorption and NTP desorption process than during the thermal process. Moreover, for the same electric power, the peak concentrations (typically 13%) are higher in the NTP desorption process than in the thermal process at equal electric power. These results indicate that the efficient NTP dissociation of CO2 to CO, which can be utilized in the production of combustion fuels, is possible. [ABSTRACT FROM AUTHOR]

Due to the fact that it is difficult to fulfill the recent stringent regulations governing marine diesel engine emission by means of combustion improvement alone, an effective aftertreatment technology is required to achieve the efficient simultaneous removal of \NOx and particulate matter (PM) . In the present study, we designed and investigated an effective aftertreatment system that employs a combination of ozone injection and nonthermal plasma (NTP) reduction for a marine diesel engine. The proposed technology offers the advantage of not requiring precious-metal catalysts and harmful heavy-metal catalysts as well as urea solution. In this aftertreatment system, PM in the exhaust gas is first captured by a ceramic diesel particulate filter. Subsequently, the deposited PM is oxidized and removed by NTP-induced ozone injection. After the PM treatment, \NOx in the exhaust gas is treated by adsorption followed by NTP-combined desorption and reduction processes. These processes are repeated periodically, and total emission control is achieved. Since the deposited PM and the desorbed \NOx are treated at a high-concentration state by ozone and oxygen-lean NTP, a higher performance for total marine diesel emission control is recorded. The maximum efficiencies of \NOx and PM reduction were 94% and 95%, respectively. [ABSTRACT FROM PUBLISHER]

Atmospheric-pressure nonequilibrium nonthermal plasma hybrid exhaust gas aftertreatment systems that do not utilize precious metal catalysts, harmful ammonia, etc., have been developed by the authors. Two types of new environmental protection systems (a dry system and a wet system), which enable the production of ultralow \CO2, particulate matter and \NOx emissions as well as reduced fuel consumption and low cost, are investigated for diesel engines, marine engines, and combustion boiler applications. This paper reports the principles of the dry system and some recent experimental results of laboratory tests. The \NOx reduction comprises three flow processes: 1) adsorption, 2) heating, and 3) cooling processes. The heating process corresponds to the regeneration process. These processes are repeated in the following order: 1), 2), and 3). This dry system demonstrates excellent energy efficiencies that meet the most recent Japanese national regulations regarding automobile diesel engine exhaust gas. In this study, approximately 60% of the \NOx of the exhaust (\NOx: 240 \sim 325 ppm, \flow rate = 300\ \NL/min, N: standard state) can be treated for 35 h. An improved system energy efficiency of 143 \g\ (\NO2)/\kWh, which is the highest yet, is achieved for \NOx reduction. [ABSTRACT FROM AUTHOR]

The aim of this paper is to analyze the influence of plasma discharge reactor unit geometries on the efficiency of dry \NOx reduction process in nitrogen plasma environments. The experimental setup consists of the versatile plasma discharge reactor unit powered by 10-kHz pulse HV supply and supplied by mass flow controllers with a simulated (\NO + \N2) gas under different concentrations and flowing rates. The measurements are obtained by means of a gas analyzer for \NO/NOx concentration and a digital oscilloscope supplied with HV and current probes for discharge power computation. The number of surface discharge electrodes, the distance between them, their active area, the gas flow rate, and concentration are studied while aiming at 30 \g(\NO2)/\kWh energy efficiency and higher reduction efficiencies. These targets are the keys to industrial application of plasma discharge reactor, as a way of reducing \NOx from the regeneration phase in the next generation diesel exhaust aftertreatment system, and the results proved successful. [ABSTRACT FROM PUBLISHER]

A simultaneous reduction of particulate matter (PM) and \NOx 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 ( \sim10 000) are used as packed pellets, and carbon PM is loaded among the pellets. \NOx is reduced by N radicals, and PM is incinerated by oxygen radicals induced either by \NO \rm 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 \NOx. 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 \NOx. 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 \NOx reduction in the experiment. [ABSTRACT FROM AUTHOR]