【作者】 韩文赫；

【导师】 蔡忆昔；

【作者基本信息】 江苏大学 ， 动力机械及工程， 2014， 博士

【摘要】 随着汽车保有量的增加,机动车废气排放引起的环境污染问题已经引起了社会的广泛关注。随着技术的不断革新,现代柴油机具有能量密度高、结构紧凑、CO2排放低等优点,因此发展高效清洁的柴油利用技术有助于降低汽车CO2的总排放量。柴油机排气中包含多种危害较大的污染物,如NOx、PM、PAHs等；但目前已有的后处理技术尚存在缺点,因此有必要对其进行改进或开发新型的后处理技术。近年来兴起的利用低温等离子体降低柴油机有害排放技术成为研究热点。本文协同利用发射光谱、气相色谱质谱联用、高效液相色谱、热重谱、拉曼光谱、X射线光电子能谱及PM BSUs特征参数谱对DNTP柴油机排气中NOx、PM、多环芳烃及醛酮类污染物与INTP氧化PM的机理进行了较为系统的研究。设计了一台介质阻挡放电型NTP反应器并搭建了D/INTP实验平台。为便于改变气体组分进行机理研究,采用模拟气代替真实排气对DNTP处理过程中的发射光谱进行了分析,考察了工作电压峰峰值、02初始浓度、NO初始浓度、C3H6初始浓度等因素对发射光谱及NOx去除率的影响；并结合化学模型对产物浓度的变化进行了分析。结果表明：02和C3H6均可以促进模拟气中NO的转化；模拟排气中02会削弱NOx去除效果,对C3H6的分解及HC向CO、CO2转化也有抑制效应；放电功率一定的情况下,降低工作频率有助于NOx去除率的提高；C3H6对NOx去除的促进作用明显,还可以调节NOx中NO和N02的比例。利用气相色谱质谱联用与高效液相色谱技术分别对]DNTP降低柴油机排气中多环芳香烃和醛酮类物质的效果进行了研究。结果表明：DNTP对PAHs排放总量降低作用明显,除100%负荷下二环PAHs浓度高于原机,其余各环PAHs的浓度均明显下降。DNTP对屈的去除效果最好；排气中检出的醛、酮类污染物中甲醛含量最高；DNTP作用后,所选的大部分工况下多种醛、酮类污染物能完全去除,醛、酮类污染物的总臭氧生成反应活性明显降低；因此,DNTP可有效降低柴油机醛、酮类污染物排放,减轻其对环境的危害。为了研究DNTP降低PM的机理,首先利用热重谱考察了PM中HVF、LVF、EC含量与PM氧化过程的放热规律在DNTP作用下的变化,然后利用SEM、TEM和HRTEM技术获取了DNTP作用前后PM的形貌及特征参数谱,并进行了对比分析。结果表明：原机PM样品中EC含量随着负荷的增加逐渐升高,HVF含量随着负荷的增加逐渐降低,LVF含量随负荷的增加则呈现先升高后降低的趋势；DNTP作用后,PM样品中各组分含量随负荷变化的趋势与原机PM样品组分含量随负荷变化的趋势大致相似,只有一个样品的DSC曲线出现两个放热峰,表明DNTP处理后PM中固体碳氧化活性的差异减小；DNTP处理后,SEM观测到的样品形貌随负荷的变化规律与原机相似,TEM观测到的初级颗粒积聚形态并未发生显著变化；DNTP在PM初级颗粒BSUs的数量长度分布与数量曲率分布过于平缓或集中时,可以发挥平抑作用。因此减小了不同工况下PM的物理化学特性的差异。为了研究DNTP作用后PM碳结构有序性、碳团簇含量的变化,测取了各样品的拉曼光谱并用五带模型对光谱进行拟合,得到了G、D1带FWHM及D3带相对强度；然后利用X射线光电子能谱技术研究了PM样品表面C、O元素比,官能团种类及比例在DNTP作用下的变化。结果表明：随着柴油机负荷的增加,原机样品中石墨结构有序性逐渐降低；DNTP处理后,样品的石墨结构有序性维持在一个相对较平稳的水平；原机PM样品中碳团簇的比例在低负荷时较低,中高负荷时有所升高,但随着负荷的进一步增加变化并不明显,DNTP作用后的PM样品中碳团簇比例较原机样品均有所升高,因此PM样品的氧化活性较原机样品有所增加；所有负荷下缺陷石墨碳键的比例均比原机样品中的高,表明DNTP处理后样品的表面活性有所增强；样品表面含氧官能团中O1s谱主要包含类醌类结构的羰基、普通的羰基、类醚类结构的碳氧单键及羧基中的碳氧键,DNTP处理后样品表面O1s的结合能整体上有向高位移动的趋势,可能是由于类醌类结构在放电产生大量活性物质的撞击下断裂,与OH自由基形成类醚类、羧基等官能团形成的。为了研究INTP再生DPF机理及PM在不同氛围中加热的氧化机理,对柴油机PM样品进行了空气氛围加热、氧气氛围加热、空气INTP、氧气INTP处理,并对处理过程中排气组分浓度随时间的变化及处理后PM碳结构、表面元素比例和官能团种类的变化进行了分析。结果表明：加热处理对PM碳结构有序性的削弱效应明显强于INTP,氧气INTP对碳结构有序性的削弱效应强于空气INTP空气加热、空气INTP;氧气INTP处理后样品中碳团簇含量高于原机样品,氧气加热处理后样品中碳团簇含量低于原机样品；空气INTP处理后的样品中碳团簇含量高于氧气INTP样品,表明N02氧化PM过程中更易于生成碳团簇；处理后各样品表面O元素含量高于原机样品,空气INTP处理后的样品O元素含量高于氧气加热处理后的样品；原机样品和空气加热处理后的样品中O元素不含类醌类碳氧结构；这是由于空气加热处理时样品经历剧烈氧化过程,碳氧双键、单键被直接氧化,无需经历醌类碳氧结构过渡；而氧气加热处理、空气INTP和氧气INTP处理过程中温度较低,类醌类碳氧结构成为固体碳氧化为气态氧化物的过渡态。更多还原

【Abstract】 The environmental issue caused by vehicle exhaust gas has aroused wide attention with the growing of automobile holdings. Meanwhile, technology inovation has brought about many merits for modern diesel engines like high energy density, compact structrure, and low CO2emission and consequently developing efficient and clean diesel technology would be helpful to decrease total carbon dioxide emission of vehicles. Diesel exhaust gas contains various hazardous substances, including NOx, PM, PAHs, aldoketones and so on. However, the existing aftertreatment techniques against those harmful emissions are barely satisfactory, which make it essential to develop new amd more effective technoly. In this paper, synergentic application of emission spectrum, TG, GC-MS, HPLC, SEM, TEM, HRTEM, raman spectrum and X-ray photonelectrons spectrum is adopted to study the mechanism of NOx, PAHs, aldehydes and ketones, and PM decomposition by nonthermal plasma, aiming for supply experimental basis for direct and indirect application of nonthermal plasma in diesel aftertreatment field.A dielectric barrier discharge nonthermal plasma reactor was designed and then the experimental platform was established. In order to survey NOx removal mechanism by direct nonthermal plasma, simulated gas were used, whose components can be changed more easily. The influence of voltage peak-to-peak value and frequency of power supply and the intial concentration of oxygen, nitrogen monoxides and propene on the spectrum and NOx removal efficiency were investigated. The results indicates that oxygen and propene can both promote the convertion of NO and oxygen can attenuate NOx removal rate and hamper the decomposition of propene and the oxidation of hydrogen carbon to CO and CO2. The exisiting of propene has an obvious positive effect on NOx removal. In addition, Lowing frequency of power supply could help to improve NOx removal rate under the same power.PAHs and carbonyl emission in diesel exhaust gas before and after the treatment of DNTP were detected via GC-MS and HPLC respectively. The result indicates that DNTP has the strongest removal capability towards chrysene and the total PAHs emission decreased obviously with reduction of most PAHs emission except a abrupt growing of two-ring PAHs at100%load. Methanal has the highest pencentage among aldehydes and ketons detected in the exhaust gas. Several aldehydes and ketones was completely removed at most loads and the total ozone reactivity of aldehydes and ketones was brought down and thus alleviate the hazard caused by the aldehydes and ketones emission from diesel engine exhaust gas.To investigate the variation of HVF, LVF and EC content, the heat release process and the morphology during oxidation of PM, the samples before and after the treatment of DNTP was analysed via TG, DSC, SEM, TEM and HRTEM. The results show that EC content grows with the increasing of loads while HVF content sees the opposite trends and LVF content rise first before get down with the growing of loads. Contents variation of samples after the treatment was approximately similar with that before the treatment, and the SEM and TEM observation shows the result alike. Only one sample’s DSC curve has two heat release peaks, indicating the differentiation of elemental carbon reactivity of samples is weakened by the DNTP treatment. HRTEM observation shows that DNTP plays a balance role as the length and curvature distribution of primary particle BSUs are too concentrated or dispersive, and thus reduce the differentiation of physical and chemical characteristic of PM samples.The relative intensity of D3band and the FWHM of G and D1bands were obtained to survey the carbon structure ordering and molecule carbon contents after analyzing the spectrums of PM samples, which is fitted via a five-band model. Then XPS was used to investigate the variation of the elemental ratio of carbon and oxygen and the species of functional group after the treatment of DNTP. The results show that the graphene structure is less ordered as loads grow. After the treatment of DNTP, the graphene structure ordering could keep at a relative stable level. The molecular carbon content of PM samples after treatment is higher than that before treatment which increases gently at low and medium loads and has no obvious growing with the further load rising. So the treatment brought the PM higher oxidation reactivity. The proportions of defective carbon bonds of treated PM samples are all higher than that of raw samples, indicating PM samples have more reactive surfaces after the treatment of DNTP. The O1s spectrum of the oxygenie functional groups in the surface of PM samples mainly includes quinonoid carbonyl, common carbonyl, single C-0bonds in ethers and single C-0bonds in carboxyl. The O1s bond energy move to higher position holistically after the DNTP treatment, which is probably caused by the formation of additional ethers and quinonoid functional groups after the decomposing of quinonoid carbonyl under the collision of reactive particles generated during discharge and combination with OH radicals. Four kinds of treatment was administered toward PM samples including heating in air atmosphere, heating in oxygen atmosphere, air INTP and Oxygen INTP, so as to survey the mechanism of DPF regeneration by INTP and PM oxidation in different condition. The carbon structure, elemental proportion, functional group species and the variation of exhaust gas component were also compared. The results show that air and oxygen atmosphere heating could weaken the carbon structure ordering more effectively than INTP, and oxygen INTP more effectively than air INTP. The molecular carbon content of PM samples is higher after the treatment of air atmosphere heating, air INTP and oxygen INTP while that is lower after the treatment of oxygen atmosphere heating. PM samples treated by air INTP have higher molecular carbon content than that treated by oxygen INTP, implying that molecular carbon is more likely to form during the PM oxidation by NO2. The oxygen elemental proportion in the surface of PM samples treated by air atmosphere heating, oxygen atmosphere heating, air INTP and oxygen INTP is higher than that of raw PM samples, and air INTP treated is higher than oxygen atmosphere heating treated samples. The oxygen element in samples treated by oxygen atmosphere heating, air INTP and oxygen INTP is from quinonoid carbonyl, C=O bonds, single C-O bonds in ethers, single C-O bonds in hydroxyl and absorbed oxygen or water molecular. But the raw and air atmosphere treated samples has no oxygen element from quinonoid structure. The probable reason is that C-O and C=O bonds are directly oxidized to CO or CO2when heated in high temperature air atmosphere while C-O and C=O bonds are firstly converted to quinnoid structure as intermediate state before oxidized to CO or CO2.更多还原