Study On Plasma-Catalysis Synergistic Removal Of Diesel Particulate Matter

Diesel engines emit particulate matter(PM),which causes the deterioration of air quality and is harmful to human health.A new and efficient technology for removing PM from diesel engine exhaust is required in our country.Compared with the traditional diesel particle filter(DPF)technology,a plasma-catalytsis synergistic technology has obtained great attention in recent years as it has following advantages:(1)no influence of sulfur content in the diesel fuel,(2)high PM removal efficiency and,(3)no need to rectify the diesel engine.In this study,the plasma-catalytic technology is used to remove the PM from the exhaust of a diesel engine.The PM removal performance of the catalysts was evaluated under different reaction conditions using plasma-catalytic evaluation systems feeded with simulated diesel exhaust gas and real diesel engine exhaust gas.The catalyst species include alumina balls,Au-loaded alumina balls,CaSO4-loaded alumina balls,and Au/CaSO4-loaded alumina balls.In order to accurately measure the concentration of PM emission,this study develops a method which uses polytetrafluoroethylene(PTFE)sintered tube to filter PM for the measurement of PM concentration in the diesel engine exhaust.The main results obtained using the plasma-catalytic evaluation system feeded with the simulated gas are as follows:(1)DBD(dielectric barrier discharge)can remove the PM.(2)The PM removal performance of Au/CaS04 alumina balls is the best,Au alumina balls and CaSO4 alumina balls take the middle,alumina balls are the lowest.(3)With the increase in reaction temperature,the PM removal performace of plasma-catalytic technology is improved greatly.This indicates that the reaction temperature is one of the most important factors influencing the PM removal efficiency.With the increase in oxygen concentration,the PM removal performance of plasma-catalytic technology is improved.This indicates that the oxygen concentration is also an important factor which affects PM removal performance.(4)The products of PM plasma-catalytic oxidation are CO and C02.PM oxidation with alumina balls has the lowest C02 selectivity,CaS04 alumina balls do not improve C02 selectivity,Au/CaS04 alumina balls improve the selectivity of C02 greatly.This suggests that CaS04 have no obvious catalytic effect on the selectivity of C02,and Au plays a catalytic role in improving the selectivity of C02.(5)With the increase of reaction temperature,the alumina balls and the CaSO4 alumina balls can not improve the selectivity of CO2,Au alumina balls improve the selectivity of C02,Au/CaS04 balls improve the selectivity of CO2 greatly.This indicates that Au can improve the selectivity of C02 under the condition of increasing reaction temperature.The main results obtained using the plasma-catalytic evaluation system feeded with the real exhaust gas of the diesel engine are as follows:(1)When diesel engine output power is fixed,CaS04 alumina balls improve the PM removal efficiency more significantly than alumina balls;Au/CaSO4 alumina balls are most favorable to diesel PM removal.(2)The exhaust temperatures are 150 0C,180 ?,200 ?,and 230 0C when the output powers of the diesel engine are 0 kW,0.8 kW,1.2 kW,and 2 kW,respectively.The PM removal efficiency of Au/CaS04 alumina balls increased with the increase in the output power of the diesel engine(reaction temperature).(3)The PIM diameter is mainly within in the range of 50?200 nm.After the plasma-catalytic oxidation,the PM diameter at maximum number concentration becomes smaller.(4)Au/CaS04 alumina balls can improve the removal of NOx,while CaSO4 alumina balls can not improve the removal of NOx.This indicates that only Au plays a catalytic role in the removal of NOx.The results show that Au/CaS04 alumina balls can promote the removal of NOX under the condition of different diesel generator outputs,the higher the output power,the better the catalytic effect.(6)Both CaSO4 alumina balls and Au/CaSO4 alumina balls can improve the HC removal.When the output power of the diesel engine is 1.2 kW(the exhaust gas temperature:200 °C),HC is completely removed on both catalysts.The main results obtained from measurement of PM concentration in the exhaust of the diesel engine using TFEE filter are as follows:(1)For the PM with a diameter larger than 30 nm,the filtration efficiency using PTFE sintered tube is above 98.5%and the total PM filtration efficiency is over 99.4%.(2)The mass concentrations of PM in the exhaust gases are 5.40,7.47,8.73,and 19.4 mg/m3 when the diesel output powers are 0,0.8,1.2,and 2 kW,respectively.