Structural Optimization And Experimental Study On Integrated Aftertreatment System Of Diesel Engine

Diesel engine is widely used in large vehicles and heavy machinery at home and abroad because of its advantages of power performance,fuel economy and reliability.But there are a lot of harmful substances in the exhaust of diesel engine,which is one of the main source of air pollution.With the introduction of China VI emission regulations,the emission limit of diesel engine pollutants is greatly tightened,and the use of DOC+DPF+SCR integrated aftertreatment system can effectively reduce pollutant emissions,which is the mainstream technical route of diesel engine emission control.And the flow of exhaust gas in the aftertreatment system has a great impact on its workability,stability and reliability.Therefore,it is of great engineering significance to study the uniformity of exhaust flow in integrated aftertreatment system.In this research,by analyzing the working principle of each catalytic converter of integrated aftertreatment system,the numerical model of DOC+CDPF system was established,and the modeling and simulation was carried out on AVL-FIRE software.The structure was optimized based on the layout of the test bench,and the flow field distribution of different structures was compared and analyzed.Finally,the test verification and performance research were carried out on the bench.According to the simulation results,the distribution of pressure and speed of exhaust in the aftertreatment system is uneven,especially in the interior of the expansion pipe and at the inlet of the catalytic converter,the distribution uniformity of flow field of the optimal structure is significantly higher than that of the benchmark structure,and the exhaust uniformity index in the DOC catalytic converter and CDPF catalytic converter is 7.17%and 3.29%higher than that of the benchmark structure,respectively.Simultaneously,the optimal structure was simulated under two conditions of soot loading and regeneration.According to the experimental study,DOC catalytic converter can basically completely oxidize the CO and HC in the exhaust,but it has no obvious effect on the NO_Xemission reduction.Its oxidation capacity for HC increases with the rise of temperature.The conversion efficiency at 200?was only 6.14%,and it reached 97.62%at 280?.After that,the oxidation capacity remained unchanged.The temperature characteristic curve and pressure drop characteristic curve of CDPF catalytic converter under different regeneration conditions have roughly the same trend,which rises sharply to the peak and then drops slowly,and drops sharply at the end of regeneration.With the increase of regeneration temperature and time,the regeneration efficiency also keeps rising.The regeneration efficiency can reach 100%when the regeneration temperature is 500?.During the regeneration process,the HC content in the exhaust increased greatly due to the occurrence of secondary backspray.The integrated aftertreatment system can effectively reduce the emission of various pollutants in the exhaust,especially for NO_Xemissions.The conversion efficiency is more than 94%.The HC and NO_Xemissions and ammonia leakage are high under the cold state condition in WHTC cycle test,but it generally meets the China VI emission requirements.