Experimental Study On Selective Catalytic Reduction(SCR) Of Diesel Engine Based On China 6 Standard

Compared with gasoline engines,diesel engines have the advantages of high compression ratio,strong power,and good fuel economy.Therefore,they are widely used as construction machinery.As the exhaust emissions have become more and more polluting the environment on which humans depend,all countries in the world have formulated corresponding emission laws,regulations and standards according to their national conditions.China has formulated the《Limits and Measurement Methods for Pollutant Emissions from Heavy Duty Diesel Vehicles(China’s Sixth Phase)》since July 1,2019.Urea selective catalytic reduction(Urea-SCR)is one of the most effective technologies in the world to reduce NOx emissions.Therefore,based on the exhaust gas treatment requirements of heavy-duty diesel engines,this paper explores the impact of key structural parameters of heavy-duty diesel SCR systems on emission performance and internal combustion engine operating characteristics,and performs structural optimization design.It also provides support for SCR catalyst optimization and product development Engineering value.The thesis first introduces the pollution sources and control methods of the internal combustion engine.According to the development trend of the aftertreatment technology of the heavy-duty diesel engine,according to the working environment and combustion characteristics of the heavy-duty diesel engine,it is proposed to use a double SCR series aftertreatment system to improve its exhaust gas treatment effect.The performance of three dual-SCR catalysts with different structural parameters was studied in the experiment,and their effects on internal combustion engine power,exhaust gas conversion efficiency and exhaust back pressure were analyzed.The SCR catalyst with excellent performance was selected as the prototype for further structural optimization.The effects of key parameters such as the diameter,length,wall thickness of the carrier and the number of carrier holes on the prototype dual SCR series catalyst on NOx conversion efficiency and exhaust back pressure were studied.The results show that the larger the SCR catalyst diameter,the shorter the length,the thinner the carrier wall thickness,the better the performance of the catalyst;the change in the number of carrier holes will make the catalyst’s NOx conversion efficiency and exhaust back pressure show the opposite the trend of.Based on the above research,the prototype SCR catalyst was optimized and a bench test was conducted.And under the WHTC testcycle conditions,the average emission value of NOx volume fraction and the average emission volume of NH3 of the heavy-duty diesel engine using the optimized SCR catalyst meet the national sixth emission standard;The test data of thirteen working conditions under the WHSC test cycle conditions meet the national six emission standards.In summary,the thesis carried out a double-SCR series test study of heavy-duty diesel engines,explored the influence of SCR key parameters on performance,and optimized the design parameters of SCR catalyst structure.The queuing has reached the national six emission standard.The research provided experimental basis and theoretical reference for the design and optimization of SCR catalyst in the future,and promoted the engineering application of double SCR series products.