| In recent years, some parts of China frequently have regional air pollution problems, such as haze; those problems are closely linked with atmospheric particulate matter (PM). The PM with a diameter not higher than2.5μm (PM2.5) and the PM with a diameter not higher than10μm (PM10), due to their low deposition speeds and long residence time in the atmosphere, can be transferred over a long distance across countries or over seas, and have influence over not only its own region but also the world. PM in the atmosphere of a city is mainly from local industrial processes and diesel exhaust gases. PM from diesel exhaust gases can be removed using diesel particlutae filter (DPF) and plasma discharges. DPF works on the base of PM filtration, and is useful for the diesel with sulphur less than10ppm. PM removal by plasma dischargs is on the principle of PM deposition in the discharge reactor and the oxidation of PM to CO2and H2O with reactive oxygen species generated by the plasma discharges. As the efficiency of PM removal using plasma dishcarges is not influenced by the sulphur in the diesel fuel, the geometry structure of the plasma reactor is simple, and the use of plasma PM removal does not require to rectify the diesel engine, PM removal using plasma discharges has potential as a new after-treatment technology for PM removal from diesel exhaust gases.In this study, a dielectric barrier discharge (DBD) reactor with or without a catalyst was used to oxidatively remove diesel exhaust PM. At first, the effects of Au, Pt, and Ag catalysts on PM removal were investigated using a simulated exhaust gas system. With the real exhaust exhaust gas system, DBD reactors and DBD-catalyst reactors were then used to find the influence of discharge parameters and the geometry of the DBD reactors on PM removal and gaseous components (O2, COx, and NOx) in the exhaust gases.Using the simulated exhaust gas system, the effects of catalysts on PM removal is investigated, main results are as follows:(1)The DBD reactors with catalysts of Au, Pt, and Ag can enhance PM removal efficiency in comparison with the DBD reactor without a catalyst.(2) Under a condition of exhaust temperature200℃and discharge power4W, the PM removal efficiency is5.58g/kWh when using the DBD reactor without a catalyst; the PM removal efficiencies were6.01,6.14, and5.72g/kWh, respectively, when using the DBD reactors with Au, Pt, and Ag catalysts (0.1μg/cm2).(3) The DBD reactor with Au catalyst has the maximum PM removal efficiency (6.10g/kWh) at Au concentration of1μg/cm2. The DBD reactor with Pt catalyst has the highest PM removal efficiency (6.14g/kWh) at Pt concentration of0.1μg/cm2. The DBD reactor with Ag catalyst has a peak PM removal efficiency (5.82g/kWh) at Ag concentration of1μg/cm2.The PM removal effects were evaluated using the real diesel exhaust gas system, main results are as follows:(4) When the engine output power increased, the exhaust gas temperature, the total number of PM concentration, and NOX (NO+NO2), and COx (CO+CO2) concentrations increased, but O2concentration decreased.(5) With increasing the numbers of reaction units, PM removal ratio increases. PM removal ratio increased from61%to88%when the reaction units increased10to40; when the reaction units are greater than15, the increase in PM removal ratio is not obvious.(6) With the increase in discharge power, PM removal ratio increased significantly. When the discharge power increased from0to43.4W, PM removal ratio increased from0%to93%; when the discharge power was greater than20W, a remarkable difference in PM removal ratios were not found.(7) DBD reactor can efficiently remove the PM with a diameter less than200nm, the PM efficiency decreased slightly for the PM larger than200nm. (8) The energy injection to the DBD reactor increased with increasing discharge voltage, pulse frequency, and discharge spaces, but the increase in discharge gap distance dose not contribute the increase in energy injection. The maximum energy injection was50W. The energy injection promotes PM removal.(9) With the increase in elapsed discharge time, PM removal ratio decreased obviously when using the DBD reactor without a catays. This finding suggested that PM removal should be improved by using a catalyst.The PM removal by the DBD reactor with Au, Pt, or Ag catalyst was evaluated using the real exhaust gas system. The results are summaried as follows:(10) When the engine output power is0W, the PM removal ratio with Pt catalyst is highest; when the engine power output of800,1200, and2000W, the PM removal ratio with Au catalyst is highest.(11) Au, Pt, and Ag catalysts have no influence on the energy injection to the DBD reactors.(12) The mechanism of Au, Pt, and Ag catalysts on PM removal is discussed. The PM removal promotion is possibly due to the effective use of reactive speciese produced by discharges on catalysts. |
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