Mechanism Analysis And Experimental Study Of Removing No_x And Particulate Emissions From Diesel Engines By NPAC Technologies

With the raise of the environmental protection and the stringent of vehicle emission standards,the automotive and truck manufactures were compelled to focus on developing more efficient exhaust after-treatment devices to lower harmful emissions from diesel engines for further development.Through the current technology was difficult to deal with diesel engine emissions to meet increasingly stringent emission standards.There was a need to develop new diesel engine exhaust after treatment technology,to further reduce NO_x and PM emissions from diesel engines.Studies had shown that low-temperature plasma-assisted catalyst technology can effectively reduce harmful emissions from diesel engines. The technique using non-thermal plasma was a novel emission control method emerging in the 1990s,covering plasma physics,high voltage power supply,engine emission control,chemical reaction dynamics and others.Studies had shown that non-thermal plasma assisted catalyst technology could effectively reduce harmful emissions from diesel engine.In recent years,many experts and academics had studied the non-thermal plasma assisted catalytic technology to reduce diesel emissions using simulate gases,and had achieved many results.First of all, the reaction mechanism of analyzing the transformation of pollutants in non-thermal plasma,the simulation test of dielectric barrier discharge plasma generator and power performance was conducted based on the previous studies,and the characteristics of non-thermal plasma generator parameters(structural parameters and operating parameters) were analyzed,as well as changes in relations between the dielectric barrier discharge on the impact of the law.And the use of a variety of surface analytical testing methods,the characterization and composition of particulate matter test were carried out to study the impact of non-tthermal plasma on the particle morphology,as well as sulfur fuel elements.The catalyst were made using alkali metal elements and metal oxides as the main active ingredient.The mechanism and the laws of on-thermal plasma assisted catalytic technology simultaneously removing NO_x and PM emissions were studied in the actual environment of diesel engine emissions.In this paper,a systematic research was carried out as follows:First,based on the analysis of the dielectric barrier discharge theory, the characteristics of non-thermal plasma generator parameters(structural parameters and operating parameters) were analyzed using different methods,as well as changes in relations between the dielectric barrier discharge on the impact of the law.And on this basis,the dielectric barrier discharge non-thermal plasma reactor was designed.Second,According to the theories of chemical reaction kinetics,the physical and chemical elementary reaction of diesel engine of harmful gases in the atmosphere of non-thermal plasma were analyzed during the design process,In order to further study the common non-thermal plasma with the catalyst to remove harmful diesel exhaust catalytic mechanism. The viable technological route of removing diesel engine emissions was established.Third,AC power with high-voltage and high-frequency was used to produce non-thermal plasma.The experimental investigation on processing harmful emissions from diesel engine by dielectric barrier discharge device was carried out.Preliminary experimental results showed that only using dielectric barrier discharge non-thermal plasma technology could be effective removal of diesel engine particulate matter,and the removal efficiency could reach 79%.THC removal efficiency of nearly 20%, However,the total NO_x did not change significantly.Fourth,the methods of detecting particulate physico-chemical characteristics from diesel engine emissions was introduced to analyze particle microstructure and chemical composition.Diesel engine was fueled with different types of fuel as a source of particulate matter.The non-thermal plasma technology was used to deal with harmful emissions. And the SEM/EDS analysis were used to analyze the samples of particulate matter corresponding gold spray treatment.The results showed that:a.the way using scanning electron microscopy analyze to analyze and compare of diesel engine particulate matter emissions before and after non-thermal plasma treatment were very effective,with an intuitive,accurate and cost-effective advantage.Scanning electron microscopy observation showed that particulate matter sample size had been decreased after non-thermal plasma,b.EDS semi-quantitative analysis showed that there were Mg,Al,Ca,Cu,Zn and other elements contained in the chemical composition of Particulate matter,in addition to major components of C,O. The samples of 0 # diesel particulate matter had been detected the existence of sulfur.It showed that the sulfur was less affected before and after the NTP and was difficult to happen sulfur poisoning.NTP was a promising after treatment technology for diesel engine.Fifth,CeO₂-CuO/γ-Al₂O₃,Na-Rh/γ-Al₂O₃ and Ag/γ-Al₂O₃ catalysts were prepared by incipient wetness impregnation method,using alkali metal elements and metal oxides as the main ingredient.And using XRD,SEM,BET and other testing methods,the structure and morphology characteristics of the Catalyst and catalyst carrier were studied,As well as the catalyst impregnated coating process for its structure and properties.It proved that the formation of the catalyst crystal structure was needed.The coated quantity of Ag onγ-Al₂O₃ carrier was larger and the crystal structure of Ag/γ-Al₂O₃ catalyst was better than other catalysts.As a result,the contact condition between catalyst and Reaction gas was better for Ag/γ-Al₂O₃ case,which would benefit the Catalytic reaction between PM and gases on the surface of catalyst.Sixth,the plasma-assisted catalysis process improved the simultaneously catalytic removal of NO_x and PM.The mechanism of plasma-assisted catalysis for simultaneous removal of NO_x and PM was discussed based on a series of experiment results.The plasma process produced high active species that promoted a number of oxidation reactions,such as the oxidation of NO to NO₂ and partially oxidation of SOF(soluable organic fraction) to oxygenated hydrocarbons.Seventh,based on the actual diesel engine exhaust gas source for the experimental device,the catalyst composition,temperature,speed,torque and other parameters on the removal of harmful gases were discussed, separately from the chemical kinetics simulation and experimental point of view,and some guiding conclusions were drawn.