【作者】 王伟；

【导师】 颜伏伍；

【作者基本信息】 武汉理工大学 ， 车辆工程， 2008， 博士

【摘要】 柴油机以其优越的动力性和燃油经济性，近年来得到更普遍的应用。柴油机排气的主要有害成分包括微粒、NO_x、HC、CO，其中HC与CO浓度较低且易在富氧环境中氧化，所以柴油机排气控制的重点是微粒与NO_x。目前，柴油机机内控制技术已经使柴油机排放降低到较低的水平，但仍不能满足未来严格的排放法规，迫切需要排气后处理新技术，以及多种现有技术的有机集成来同时对柴油机的有害排放物进行净化。本文首先分析了国内外车用柴油机四效催化转化装置的研究进展，认为国内外已经发展了许多用于柴油机排气后处理的技术，但各自又都面临一些问题，尚没有开发出较好的排气后处理技术。低温等离子体技术与催化转化技术的集成技术，因其理论上有可能达到较好的效果，而且避免了其他四效催化转化装置的主要问题，诸如要求排气温度较高，需要复杂的还原剂供应装置等，具有重要的研究价值。本文研究了催化剂的制各，结果显示，烧结法和溶胶-凝胶法都能制备La_0．9K_0．1CoO₃钙钛矿型复合氧化物。通过提高烧结温度，都能进一步提高产物的纯度，同时晶粒粒度会增大，比表面积减小。在相同烧结温度下，溶胶-凝胶法生成的产物与烧结法相比更纯一些，粒度更小，比表面积和孔径更大。因而，溶胶-凝胶法是制备La_0．9K_0．1CoO₃钙钛矿型复合氧化物的较理想方法。在小样试验中，发现用溶胶-凝胶法在1050℃烧结温度下制备的La_0．9K_0.1CoO₃钙钛矿型复合氧化物催化剂，具有更低的碳烟点火温度、更低的NO_x起始反应温度，更低的反应副产物CO浓度，因而催化性能优于烧结法制备的催化剂；通过适当提高烧结温度和采用溶胶-凝胶法可以提高催化剂净化PM和NO_x的性能。然后尝试分别利用贵金属Pt、La_0．9K_0.1CoO₃、Pt和La_0．9K_0．1CoO₃共同，三种方案作为PM和NO_x反应的催化剂。结果Pt和La_0．9K_0．1CoO₃共同应用则效果不佳；Pt催化剂在各反应温度指标上都略优于La_0．9K_0．1CoO₃，但它也有一定的缺陷，包括对NO_x的转化效率较低，最后残余CO、HC等污染气体没有反应，使用贵金属，成本较高等；因而综合考虑溶胶-凝胶法在1050℃烧结温度下制备的La_0．9K_0．1CoO₃是较理想的净化PM和NO_x的催化剂。最后研究了这种催化剂的工作条件，与发动机高速大负荷运转时的排气状况相符合。在柴油机台架试验中，La_0．9K_0．1CoO₃催化剂在一定温度下不仅能够同时降低柴油机排气中的PM和NO_x，还可以降低HC和CO的排放，但是对PM和NO_x的转化效率还比较低，在最好的情况下只有15％～20％;需与低温等离子体技术技术协同作用，以提高净化效果。在对低温等离子体技术的理论分析中，重点分析了低温等离子体技术的能耗问题，设计了并联式的介质阻挡放电反应器，以及确定了与之相匹配的高压脉冲电源参数，用经验公式计算了反应器的功率。研究了等离子体技术与钙钛矿型催化剂技术的协同作用，与单独用催化剂技术相比，可提高对柴油机排气净化效果，但对反应温度降低较小，仍然在300℃左右。在低温等离子体台架实验中，所设计的并联式的介质阻挡放电反应器，可正常工作，并达到净化柴油机排气的效果；采用催化剂后置，低温等离子体发生器前置的布置形式，难以达到催化剂工作温度；催化剂前置，低温等离子体发生器后置的布置形式，有利于满足催化剂的工作条件，使催化剂有效发挥作用。低温等离子体辅助柴油机四效催化转化技术对NO_x和微粒有较好的净化效果，尤其是对NO_x，净化率最蒿可达81．2％。对于固定式柴油机改进后基本具备实际应用的条件；对于车载柴油机，在解决高压脉冲电源小型化、可移动的问题后，也具有较广阔的应用前景。更多还原

【Abstract】 Because of its excellent power and economy in fuel, diesel is widely applied in recentl years. The main noxious contents of diesel emission are particles, CO, HC, and NO_x, and the concentration of HC and CO is relatively slow and they can easily be oxidized when oxygen is enough. So the focous of diesel emission control is NO_x and particles. At present, internal measures can reduce the emission to be relatevely low, but it can not meet the regulation in future. The after-treatment and combining various technoque together to purify the diesel exhausts are needed.The development of four-way catalyst all over the world is analyzed. Many purifying techniques in diesel have been developed but there still exist some shortcomings. Combine the technology of low-temperature plasma technology with catalytic conversion technology can obtain better effect theoretically, and the main problems existed in other four-way catalyst can be overcome, such as high emission temperature,complex supply equipment for reducer, which is of important value.Then the catalyst the perovskite type La_0.9K_0.1CoO₃ was prepared through bothcalcination and sol-gel method. The purity of La_0.9K_0.1CoO₃ powders can be increasedby raising the calcining temperature, at the same time, the particle diameter increased,BET surface area decrease. Under the same calcining temperature, the charactic properties of the La_0.9K_0.1CoO₃ powders synthesized by sol-gel, method is better than those synthesized by solid state reaction method, such as purer phase, smaller particle diameter, which can be used as a satisfactory catalyst in diesel waste gas cleaning.In small sample experiment, the catalytic performance of the La_0.9K_0.1CoO₃ Perovskite Composite Oxide catalyst synthesized by sol-gel, method sintered at 1050℃is better than that of the catalyst synthesized by solid state reaction method catalyst, such as lower ignition temperature of the diesel soot particulates, lower start temperature of NO_x treatment, creating lower concentration of byproduct CO, so it has better catalyzing effect. By increasing the sintering tempetature appropriately and using the sol-gel method, the effect of catalyst to purify PM and NO_x can be improved. Three measures, i e ,using Pt and La_0.9K_0.1CoO₃ respectively and both as catalyst to clear PM and NO_x were taken. It is indicated that it is not efficient using Pt and La_0.9K_0.1CoO₃ both, the effcet of Pt is a little superior to La_0.9K_0.1CoO₃,but the conversion rate to NO_x is slow and it can not treat with CO and HC, at the same time ,it is expensive. Considering the whole conditions, the better catalyst was chosen as La_0.9K_0.1CoO₃ prepared by sol-gel method and sintered at 1050℃. The working conditions of the catalyst was investigated, which is coincident with the exhaust gas when the engine is in high speed and large load.In the diesel test bench experimental, La_0.9K_0.1CoO₃ catalyst can not only reduce the PM and NO_x, but also reduce HC and CO emission. The conversion rate to PM and NO_x is still low, which is about 15%-20% on the optinum condition, so it is nessissary to combine with low-thermal plasms technique to improve the purifying effect.Then energy, consumption of low-thermal plasma technique was analyzed as focous, and the shunt dielectric barrier discharge plasma reactor was designed, then the corresponding high-pulse power parameters were determined. The power of the reactor was calculated by experiential formula. The calculation results indicate the reactor’s power is in the lower range of the diesel engine.The low-thermal plasma technique was combined with the La_0.9K_0.1CoO₃ Perovskite Composite Oxide catalyst for the first time. Compared with using single catalyst, the combined technique can improve the clearing effect, but it reduce the reaction temperature little, which is still at about 300℃.In the emplace bench experimental, the designed shunt dielectric barrier discharge plasma reactor can work well-balanced, and the diesel exhaust can be treated. When catalyst were emplaced behind and low-thermal plasma reactor were emplaced frontal, the temperature was not high enough for the catalyst to work. While When catalyst were emplaced frontal and low-thermal plasma reactor were emplaced behind, the catalyst can work efficiently. Four-way catalyst technique combimed with low-thermal plasms technique can purify PM and NO_x more efficiently, especially for PM, the purifying rate can reach 81.2%. This technique is feasible for improved fixed diesel engine,’and for mobile diesel engine, when the volume of the high voltage pulse power can be reduced and it can be locomotive, the technique may be widely applied in the future.更多还原