| The low fuel consumption and strong power of modern diesel engine make it widely used. The size of diesel exhaust particulate matter is small and its large specific surface area make it not easy to subside. Furthermore it can adsorb heavy metal element and other harmful organisms easily. The emission of diesel exhaust particulate matter has brought serious environmental pollution. The smaller the particle matter, the easier flow through a diesel particulate filter(DPF) and entering into the atmosphere. Controlling nanoscale diesel particulate matter emissions has been an international technology problem. Charging and agglomerating technology is a kind of methods to promote the growth of fine particulate matter and it’s a research hotspot in the field of aerosol at home and abroad, but there are few studies in the treatment of the diesel particulate matter.In this article, the charging and agglomerating method is used to pretreatment of diesel particulate matter. The online charging test bench was set up for researching the charge efficiency of diesel engine exhaust particulate matter under corona discharge. Particulate matter contained in the sample gas was charged by a wire-cylinder negative DC high-voltage electrode corona discharge device then collected by a Faraday Cup. EST111 Coulomb meter which connected to the Faraday Cup is used for measuring the charge efficiency of the particulate matter.The micro-structure morphology of exhaust particulate matter was observed by a scanning electronic microscopy to investigate their difference in micro-structure morphology in the condition of the power supply turn on or off. The charge efficiency of particulate matter under different charging parameters and different diesel working conditions was studied. The results show that diesel particulate matter can be charged obviously. In the condition of-15 k V DC voltage, controlling the sample exhaust gas velocity as 0.12 m/s, 0.24 m/s, 0.36 m/s, 0.48 m/s, 0.60 m/s, the charge carried by particulate matter which measured by the Faraday Cup increased with gas velocity and sampling time. The charge to mass ratio of particulate matter collected by the Faraday Cup increases with theas velocity first and then decreased, it reaches the maximum value at the velocity of 0.36 m/s, and the maximum charge to mass ratio of diesel particulate is-118.2μC/g. Charge to mass ratio increased with voltage,furthermore the growth rate increase with voltage. Compared the weight of particulate matter collected from the Faraday Cup before and after corona discharge, it can be found that a portion of the charged particles were trapped by high voltage corona discharge wire-cylinder device. Diesel particulate matter forms a large particle without corona discharge while it forms a porosity and dendrite structure in the presence of corona discharge.Furthermore, the online agglomerating test bench was set up for researching the charged particles coagulation. Micro-Orifice Uniform Deposition Impactor was used to split and compare the particle size range before and after charged agglomeration. Within the range of 0.18 to 10μm, the particle size distribution is similar to unimodal normal distribution, and the peak is located in the range of 0.56 to1.0μm. When engine speed at 2700 r / min with 100%, 75%, 50% and 25% of full load conditions. The size of particulate matter after charged agglomeration was increased. Compared with the original diesel particulate matter, the mass concentration accumulation mode particles less than 1.8μm decreased by 15.9%、17.1%、17.8% and 16.8%, while the mass concentration of coarse size particle mode more than 1.8μm increased by 49.1%、42.3%、51.3% and 44.3%. It showed that charging and agglomerating technology is effect for increasing the size of diesel exhaust particles. |
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