| Motorcycle industry in China is developing rapidly. But motorcycle causes serious atmospheric pollution at the same time. Our country have been paying high attention to motorcycle emissions and publishing more and more strict regulations to limit motorcycle emissions. The work of meeting international standards is in progress. However, emission control technology in China remains to be further developed. There are many of methods which can control vehicle emissions pollution. One of them is reducing exhaust by improving or changing the operating mode of internal combustion engine when it is in running condition. But this method is conflict with dynamic property and economical efficiency. The technology of exhaust after-treatment is the preferred method of exhaust cleaning because its structure is simple, its cost just rises a little, but its effect is positive. The technology of catalytic converters is an important measure to less the noxious emissions of engines. It has already become the predominant technique of tail gas clean-up and been well developed in some foreign countries. However, it just began to be taken on domestic motorcycles and it is seldom used on small and medium displacement motorcycles. So there are a lot of technical problems need to be improved and adapted by us.To meet the strict emission limit regulations, the technology of catalytic converters is usually used with the technology of secondary air supply together. A motorcycle exhaust gas purification system with two-stage catalyzing and secondary air supply is designed on the basis of a deep research on catalytic converter and on secondary air supply. The upstream catalyst is used for increasing temperature of exhaust gas rapidly, and the downstream catalyst is used for reducing the remaining exhaust. The emissions of motorcycle contain a lot of HC and CO but contain little oxygen. Putting fresh air into the exhaust pipe one more can lower the HC and CO. This technology ensures a high purification rate, and doesn't waste engine power at the same time. The first part of this paper analyses the emission condition of domestic motorcycle, compares the emission control methods which are most used. The emission cleaning solutions of this paper is selected according to above analysis and comparison. The design process of motorcycle emission control system with catalytic converter and secondary air supply is detailed described in the second section of this paper. The third part of this paper studies impact on the conversion rate of the catalytic converter with a test by changing supply way, supply location and supply volume of secondary air, verifies the real effect of motorcycle emission control system by testing a sample motorcycle with UDC.After the research, we get below results: 1.beside a good quality catalytic converter, a reasonable layout design is helpful to the work of catalyzer. 2. The emission volume of HC and CO can be reduced by supplying enough oxygen to the catalytic reaction with a secondary air supply system. 3. Suitable oxygen volume supply according to different speed and different load condition can furthest reduce the harmful emissions but don't weak the engine power. 4. When supplying secondary air, on one hand, the secondary air entrance should be designed near the engine hole of exhaust to make sure the HC and CO in the emissions can get enough ignition temperature and rekindle. On the other hand, pressure distribution in the exhaust pipe should be taken into consideration to make sure the supply time can be prolonged. The active supply way with air pump is better than the passive supply way. 5. The UDC test shows that such a designed system can effectively reduce motorcycle emissions and reach the standard of china stage III. |
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