INVESTIGATION OF THE FACTORS AFFECTING NOx REMOVAL PERFORMANCE FOR DIESEL ENGINE EXHAUST GASES BY SILENT DISCHARGE

第一年，在实验室建立了实验系统。作为第一个实验，研究了无声放电的电极效应。结果表明，平板型电极对NO的去除效果优于各种网状电极，电极面积对NO的去除效果几乎没有影响。接着，研究放电装置的放电功率密度、放电能量密度和气体滞留时间的影响。结果表明，前两个因素几乎没有影响，但气体停留时间显示出相当大的影响，效率。最佳停留时间为50 ~ 150 ms。碳氢化合物（HC）添加到废气中的效率有很大的影响，并发现与大分子尺寸的HC是更好的。在实验过程中发现NO去除效果变差的现象，分析其原因是放电装置的介质板上结露所致。将TiO_2涂层置于放电装置的下游，经紫外线活化后，其效果较好。多级布置显示出更好的性能。作为直接放电法的一种替代技术，对废气中注入臭氧进行了研究。结果表明，臭氧注入法具有直接放电法无法比拟的优点，如NO去除率高、无烟尘和水分污染等。然而，HC的添加对效率改善没有效果甚至是不良的效果。研究结果表明，氧强化是提高脱硝效率的有效方法，并提出了低温等离子体脱硝的应用和比较方法。

In the first year, the experimental system was set up in the laboratory. As the first experiment, the effect of electrode of silent discharge was investigated. It was found that NO removal efficiency using flat type electrode is better than various meshed electrodes and electrode area has almost no effect on the efficiency. Next, influence of discharge power density, discharge energy density and gas residence time of the discharge device were investigated. It was found that the first two factors have almost no influence, however the gas residence time shows considerable influence to the efficiency. The optimum residence time was in between 50 to 150ms. Hydrocarbon (HC) addition into exhaust gases showed big effect on the efficiency and the HCs with big molecular size were found to be better. During the experiments, the phenomenon that NO removal performance becomes very poor was found. The reason was analyzed and found that it came from the moisture condensation on the dielectric plate of discharge device.In the second year, the photo-catalyst was investigated. Ti0_2 coated filter activated by ultraviolet ray was found to be effective if it was placed down stream of discharge device. Multi-stage arrangement showed better performance. As an alternative technology of direct discharge method, ozone injection into exhaust gases was investigated. It was found that the ozone injection method has many advantages to the direct discharge method, such as high NO removal rates and contamination free process by soot and moisture in exhaust gases. However the HC addition has no or even bad effect for efficiency improvement. Oxygen enhancement was found to be good method for efficiency improvement.The application and a way of comparison method of non-thermal plasmas to NOx removal were proposed as a final achievement of this investigation.