Research And Development Of SCR System To Meet Vehicle Diesel Engine Emission Standard Of China Ⅵ

As one of the main power sources of road transport vehicles,diesel engine has high fuel economy and high torque at low speed.But it also brings pollutants,especially NO_x（Nitrogen Oxide）and PM（Particle Matter）,increasingly stringent emission regulations limit purification in cylinder of internal combustion engine,especially emission limits and measurement methods for the heavy duty diesel（China Ⅵ）has been implemented,improving larger than China Ⅴregulation.SCR（Selective Catalyst Reduction）is widely used because can effectively reduce diesel engine NO_x emission,the principle is supplying a certain amount of urea solution to urea nozzle,atomized by the nozzle,evaporated,pyrolyzed and hydrolyzed to form ammonia（NH₃）in the exhaust pipe,the NO_x converted to nitrogen gas（N₂）and water（H₂O）on SCR catalyst surface.NH₃ uniformity and fluid velocity uniformity before catalytic converter have a great influence on the conversion efficiency of SCR system,the injection control of urea solution is one of the important factors affecting the conversion efficiency and the closed-loop correction of ammonia storage.In this paper,the aftertreatment system of the China Ⅵ road vehicle diesel engine is studied.Begin from the China Ⅵ road vehicle diesel engine SCR system perspective,this paper proposes an aftertreatment system layout,the aftertreatment system structure designed,especially the design of the exhaust mixer,the flow and urea injection,atomization and diffusion models of the catalytic converter were established,the full-scale CFD（Computational Fluid Dynamics）exhaust flow field simulation analysis was carried out,the velocity uniformity,NH₃ concentration distribution and pressure drop loss of the mixer studied,feature size is optimized,and the results show the uniformity of NH₃ can reach 0.996 with the pressure drop of 4.17kPa.The test was carried out on a Yunnei China Ⅵ 3.0L heavy duty diesel engine bench,verified that the newly developed and optimized aftertreatment system had less resistance,and the NH₃ uniformity measured reached over 98%under rated working conditions.The mixer without spoiler performed better at different Space Velocities and temperatures.The results of WHTC（World harmonised Transient Cycle）and WHSC（World harmonised Steady State Cycle）meet the requirements of China Ⅵ,the mixer has good anti-crystallization performance,and it is confirmed that the newly developed aftertreatment system and exhaust mixer can be used in China Ⅵ road vehicle diesel engines.Secondly,SCR control strategy developed,followed the automobile electronic control system based on the model of V development process,modeling and simulation analysis of the SCR system based on Simulink,including the SCR carrier temperature model,SCR open-loop control model,especially ammonia storage closed-loop control model,according to the bench test data to identify the parameter and the software simulation.The.mod file in Simulink through Code Generation generated embedded HS12 kernel C language Code,the completed underlying driver coupled with the embedded C code is swiped into the DCU（Dosing Control Unit）.Test and calibration carried on a Yunnei China Ⅵ 3.6L heavy-duty diesel engine bench,testing the NO_xcontrol capability and strategy of the SCR system,including WHTS and WHSC cycle emission tests.The aftertreatment controller was a DCU jointly developed with FAI.Then a FOTON N1 type light vehicle carried a QUANCHAI China Ⅵ 2.3L diesel engine verified again the NO_x control capability and strategy of the SCR system,took the WLTC（Worldwide Light-duty Test Cycle）cycle as the core to carry out the vehicle revolving drum emission test.The aftertreatment controller was also a DCU jointly developed with FAI.The results show that the emission test conducted in accordance with the requirements,all the results are in full compliance with the China Ⅵ emission regulations,the completed SCR closed-loop control system based on ammonia storage can significantly reduce the NO_x emission and ammonia slip of diesel engines,confirming that the newly developed aftertreatment control system can be applied to the China Ⅵ road vehicle diesel engines.