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，考察了无声放电电极的作用。结果表明，平板型电极的脱氮效果优于各种网状电极，电极面积对脱除效率几乎没有影响。其次，研究了放电功率密度、放电能量密度和气体停留时间对放电装置性能的影响。结果表明，前两个因素对效率几乎没有影响，但气体停留时间对效率有较大影响。最佳停留时间为50~150ms。尾气中添加碳氢化合物(HC)对效率有较大影响，且分子尺寸较大的HC效果较好。在实验过程中，发现了NO去除性能变得很差的现象。分析了原因，发现是由于放电装置介质板上的水汽凝结造成的。第二年，对光催化剂进行了研究。在放电装置下游放置紫外光活化的TiO_2涂层滤光片是有效的。多阶段布置表现出较好的效果。作为直接放电法的替代技术，对废气中注入臭氧进行了研究。结果表明，臭氧喷射法与直接排气法相比，具有脱氮率高、废气中无碳烟和水分污染等优点。然而，HC的加入对效率的提高没有甚至是不利的影响。氧强化被认为是提高效率的好方法。作为本研究的最终成果，提出了低温等离子体在脱除NOx中的应用和比较方法。

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.