Study On The Performance Of National ? Emission Post-treatment System

After entering the new century,China's engine industry has developed rapidly.Diesel engines have been paid more and more attention by virtue of their high combustion efficiency,power,economy and reliability,and their application scope has become wider and wider.With the improvement of people's living standards,the requirements for living environment have become stricter and stricter.However,in recent years,the environment has been deteriorating,especially the frequent occurrence of haze.One of the main factors causing this phenomenon is the emission of pollutants from automobiles.Therefore,restricting and controlling the emission of harmful pollutants from diesel engines has become one of the important factors affecting the design and operation of diesel engines.At the same time,the sixth phase of the national emission standards for motor vehicles will soon be implemented,which puts forward more stringent specific requirements for the emission of diesel engines.At present,it is difficult for a single post-treatment technology to meet the emission requirements,so it is necessary for several emission treatment technologies to work together to achieve the purification of tail gas.Firstly,this paper summarizes the main post-treatment control technology of diesel engine emissions,and introduces the hazards and formation mechanism of the main pollutants from diesel engine emissions.Based on the performance requirements of the six-stage diesel engine post-processing system,the structure parameters of the post-processing system are designed and the selection of the carrier is completed,then the calculation model of the post-processing system is established.By comparing the simulation and experimental data of the system temperature field under specific conditions,a more accurate temperature boundary condition is obtained and applied to the CFD calculation of the exhaust gas flow area.The simulation results of the post-processing system are analyzed from the aspects of velocity field,pressure field and atomization effect.The velocity streamline diagram of the system is analyzed,and the flow direction distribution in the inner watershed and the velocity uniformity in front of the carrier are obtained.The pressure field of the system is analyzed,and the pressure loss of the system mainly comes from the partial pressure loss of the catalysts,while the pressure loss along the pipeline.The local pressure drop caused by the abrupt change of the diversion and spoiler devices is relatively small.The atomization process and distribution law of urea droplets are analyzed through the particle size distribution of urea spray.Following the optimum design theory of the mixer,the mixer structure of the exhaust aftertreatment system is optimized to further improve the uniformity of NH₃ and ensure that the pressure loss of the system is not higher than the design requirements.The simulation results show that the effect of the optimized mixer on the internal air flow in the post-processing system is greater,which increases the eddy current intensity in the later basin,makes the velocity uniformity coefficient and ammonia uniformity coefficient higher,and after optimization,the thickness of liqLuid film on the wall of mixer under low working conditions is less than that before optimization,and there is little difference between medium and high working conditions.