【作者】 王攀；

【导师】 蔡忆昔； 孙平；

【作者基本信息】 江苏大学 ， 动力机械工程， 2009， 博士

【摘要】 随着人们环保意识的不断增强和汽车排放法规的日益严格,柴油机有害排放成为制约其进一步发展的重要课题。目前的柴油机排放处理技术难以满足未来更加严格的汽车排放标准,开发新的柴油机排气后处理技术以进一步降低柴油机NO_x和PM排放显得尤为重要。低温等离子体技术是20世纪90年代兴起的柴油机排放后处理控制技术,它涉及等离子体物理、高压电源技术、发动机排放控制、化学反应动力学等多种学科。研究表明,低温等离子体辅助催化剂技术可以有效降低柴油机的有害排放。近年来,很多专家和学者以模拟气体为对象,对低温等离子体降低柴油机排放进行了研究,并取得了不少成果。本文在前人研究基础上,以柴油机实际排放气体为研究对象,首先对介质阻挡放电等离子体发生器及电源性能进行了静态试验,分析了低温等离子体发生器的特征参数（结构参数和工作参数）的变化关系以及对介质阻挡放电的影响规律,优化了低温等离子体发生器的设计;然后利用多种表面分析测试方法,对低温等离子体作用后的颗粒物进行表征和成分测试,以研究低温等离子体对颗粒物形貌以及燃料中硫元素的影响;最后以碱族金属元素和金属氧化物为主要活性成分,分别制备了三种具有介孔结构的复合催化剂,在同样的台架试验条件下,使碳颗粒和HC与NO_x互为氧化还原剂,研究了低温等离子体辅助催化技术同时转化NO_x和PM排放的作用机理及影响规律。具体研究工作如下:第一,基于介质阻挡放电理论,采用V-Q lissajous图形法对NTP发生器结构参数（内径,放电间隙）和工作参数（电压、电流和频率）的变化关系以及对介质阻挡放电的影响规律进行了研究,并以此为基础,设计了NTP体发生器装置。第二,根据化学反应动力学等理论,分析了柴油机有害气体各组分在低温等离子体气相反应区内发生的物理化学基元反应,以进一步研究低温等离子体与催化剂共同去除柴油机有害排气的反应机理,然后确立一条可行的尾气去除技术路线。第三,利用自制的介质阻挡放电试验装置,采用交流高频高压电源产生等离子体,对柴油机排放物进行后处理净化试验。初步实验结果表明:单独使用低温等离子体技术可有效转化柴油机PM排放,转化效率可以达到60%（质量比m计）,THC转化效率将近20%,但是NO_x总量变化不明显。第四,针对柴油机颗粒物微观形貌和化学成分分析,引入SEM/EDS分析方法以检测分析柴油机排放颗粒物的理化特性。本研究以燃用不同燃料的柴油发动机尾气作为颗粒物发生源,利用低温等离子体净化处理排放物,在不同工况条件下对颗粒物进行采集取样,然后对样品进行SEM/EDS分析。结果表明:a.低温等离子体作用后,不同燃料颗粒物样品的粒径都有所减小。b.EDS半定量分析结果表明,在颗粒物所含有的化学成分中,除了主要成分C、O外,还有微量的Mg、Al、Ca、Cu、Zn等元素。NTP作用前后对颗粒物中硫的影响较小,不易发生硫中毒现象。较之传统的后处理方法,低温等离子体是一种更为理想的柴油机后处理技术。第五,以碱族金属元素和金属氧化物为主要活性成分,用等体积浸渍方法制备成了CeO₂-CuO/γ-Al₂O₃、Na-Rh/γ-Al₂O₃和Ag/γ-Al₂O₃复合金属氧化物催化剂,并利用XRD、SEM、BET等表征方法,探讨了催化剂、催化剂载体的结构和形貌等特性,以及催化剂的浸渍涂覆工艺对其结构和性能的影响,证明形成的催化剂晶型结构符合试验需要。其中:a.活性成分Ag在载体γ-Al₂O₃表面的附着性好,涂覆量大,增大了催化剂和反应气体的接触面积,有利于在催化剂表面有效进行催化反应;b.CeO₂-CuO/γ-Al₂O₃催化剂晶粒细小均匀,与另外两种催化剂相比,其比表面积更大。第六,通过台架试验,研究了低温等离子体对催化转化NO_x和PM活性的影响,并对其反应机理进行分析。研究表明,等离子体作用促使气体中产生高能活性物种,再通过催化剂作用,进一步提高NO和O₂共存下NO转化为NO₂的能力,把PM中的SOF氧化为含氧碳氢化合物,促使NO₂和含氧碳氢化合物的反应生成CO₂和N₂。第七,以柴油机实际排出气体为研究对象,分别从化学动力学模拟计算和实验的角度出发,讨论了催化剂成分、温度、转速、转矩等参数对有害气体去除率的影响,得出了一些具有指导性的结论。更多还原

【Abstract】 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.更多还原