| Diesel engine emissions of oxides of nitrogen and particulate matter can be reduced simultaneously through the non-thermal plasma (NTP) assisted catalyst, which is considered as one of the most potential method in the field of exhaust after-treatment for diesel engines. The catalytic effect of the catalyst largely depends on the exhaust gas temperature. The catalyst shows no activity at low temperature of the diesel engine running under low and medium speed and load operating conditions, and it is hard to achieve the high efficiency of catalytic removal NOx and PM.In this paper, the nano-catalysts are prepared through improving the catalyst coating process to obtain the higher BET surface area and catalytic activity. Then the NTP-NC system is established by combining the NTP reactor with nano-catalysts. With regard to the advantages of the NTP activation, the low-temperature catalytic activity of the nano-catalysts are improved, and the low-temperature combustion activity is enhanced, which can provide benefits for NOx and PM removal. The main research in this work was carried out as follows:(1) The NTP reactor was designed on the basis of the dielectric barrier discharge theory, which has the advantages of discharge stable and good safety performance. A compound NTP reactor was formed by combining several NTP reactors arranged in parallel. Based on the static test, results showed that such structure can not only ensure the NTP reactor work stable but also can increase the exhaust flow.(2) The composite metal oxide catalyst LKMCO, LKFMCO and Fe/Ce-K-O prepared by the sol-gel assisted dip-coating method, the metal oxide loaded on the carrier was9.0wt%,10wt%and10wt%separately, and the coating thickness both was30μm. By characterizing the catalyst powders with X-ray diffraction (XRD), BET and scanning electron microscope (SEM), the structure of the catalysts and the transformation of crystal configuration were discussed as well. The results suggest that the LKMCO, LKFMCO and Fe/Ce-K-O catalysts have a porous structure. The average diameter of the catalysts were16.27nm、26nm and32nm, and the surface area of the catalyst were221.7m2/g、208.5m2/g and213.4m2/g. (3) Based upon the bench test, the effects of NTP SED on the variation of the exhausts components and working voltage were investigated. The results found that the NTP SED increased with the working voltage increasing under the different NTP discharge frequency. Under the treatment of NTP technology, the total amount of NOx changed little. However, soot emission was significantly reduced after NTP treatment and tended to decline with the increasing of NTP SED.(4) The effect of temperature on NOx removal under the treatment of NTP and NTP-LKMCO were studied by temperature programming method. According to the experiment results the mechanism of NOx conversion was analyzed. Comparing with the NTP treatment, the total amount of NOx reduced after NTP-LKMCO treatment. And the catalyst began to exhibit higher catalytic reactivity when temperature was higher than280℃.(5) By combining LKFMCO and Fe/Ce-K-O nano-catalysts with NTP reactor the NTP-NC system were established. NO、NO2、NOx and by-product N2O emissions were measured online with Photon infrared gas analyzer. The effect of engine load on NOx removal was studied on the basis of bench test. Meanwhile, NOx removal and the activity influence factors of the catalysts were also analyzed and discussed. The formation and variation rule of by-product N2O was tested and evaluated during the process of NTP-NC technology. Under the treatment of NTP, by-product N2O caused with the rise in temperature. Compared with the reference test, N2O concentration efficiently reduced after NTP-LKFMCO and NTP-Fe/Ce-K-O treatment.(6) By comparing the effect of load on soot removal with NTP、NTP-LKFMCO and NTP-Fe/Ce-K-O technology were studied based upon the bench test, it is shown that the major role in soot removal was NTP processing during the NTP-NC treatment, but not the LKFMCO and Fe/Ce-K-O catalyst.(7) SOF is extracted from PM using soxhlet extraction method. And the mass fraction variation of the SOF components in PM was investigated with NTP technology. The results revealed that the main components were organic acids and the mass fraction of SOF was reduced after NTP treatment. The distribution range of main components in PM samples were C14～C24and Cl1～C24before and after NTP treatment, and the amount of low carbon atoms increased considerably after NTP treatment. (8) The physical structure and the chemical composition of PM samples with NTP technology were investigated by SEM and EDS. Comparing without the NTP treatment, the particulates in PM samples arranged more loosely and the particles size became smaller after NTP treatment, and the content of C was also obviously decreased. In the different conditions of2000r/min speed75%load and2800r/min speed100%load, PM samples were obtained by using the MOUDI device. Then the thermogravimetry analysis and derivative thermogravimetric analysis were used to study the thermal properties of PM samples in N2and O2atmosphere, in order to analyze the reasons for PM components loss. By comparing the differences at the end of combustion temperatures, the NTP effects on the low temperature combustion properties of PM was evaluated. |
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