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

With the increasingly serious global environmental pollution,many countries have issued new emission standards to limit the emission of pollutants from automobile exhaust.The emission limits and measurement methods for heavy diesel vehicles issued by China?the sixth stage of China?indicate that the emission standards for heavy diesel vehicles in China are about to enter a new stage.Selective catalytic reduction technology is one of the most important methods to reduce emissions of heavy-duty diesel engine.Therefore,it is of great practical significance to study the mixer and technical route in SCR system of heavy-duty diesel engine.Based on the Sixth National Standard,the SCR mixer and system routes of heavy-duty diesel engine were tested.The power and economic performance of different mixers and their effects on conversion efficiency were tested in the bench laboratory.This thesis emphatically analyzed the selection of double-SCR after-treatment system and traditional single SCR system,and verified the emission performance of double-SCR system.Firstly,the causes of diesel engine pollutants were introduced theoretically.Several after-treatment schemes used at the present stage were elaborated and the importance of SCR conversion efficiency was illustrated based on the structure and the latest research status of SCR system;Secondly,a new type of mixer which is different from the traditional mixer was used to carry out the experiment.The performance of the new mixer was explored by comparing the SCR system with the old mixer in the aspects of fuel consumption,back pressure,power and conversion efficiency;Thirdly,the double-SCR route was compared with the traditional high-efficiency SCR after-treatment route in terms of economic power and NOx conversion efficiency;Finally,the performance of the double-SCR system and its control effect on NH₃ emission were verified by the WHTC cycle emission test.The following conclusions were drawn:after using the new mixer,the conversion efficiency was improved compared with the old mixer,the atomization effect reaches the ideal requirement,and the urea crystallization problem in the exhaust pipe was well solved;The conversion efficiency of the after-treatment system using box double-SCR was about 2%higher than that of the single SCR after-treatment system and the impact on power performance and fuel economy can be neglected;Using box DOC+DPF+double-SCR+ASC system,the emission of PM,NOx,CO and other pollutants meets the six national standards,and ammonia leakage was significantly reduced compared with single SCR system.