Research On Matching Performance Of Automotive Diesel Engine Aftertreatment Device

Diesel engines,which are widely used in the field of motor vehicles,have attracted a lot of attention for their pollutant emissions.As motor vehicle emission regulations become more stringent,SCR,as the most effective device for reducing nitrogen oxide emissions from diesel engines,has a higher standard for upgrading.The matching design of SCR carrier specifications and the optimization of reaction conditions affect the performance of diesel engines and aftertreatment devices.Its good flow and mixing characteristics are the key to the Urea-SCR packaging system with high efficiency NO_x conversion and low ammonia leakage.This article has launched a detailed study for this.Firstly,the SCR transient model of copper-based molecular sieve was optimized and calibrated based on the AVL-BOOST software,combined with the technical parameters of a specific automotive diesel engine and the measured operating data,the matching of the SCR carrier structure and the ammonia nitrogen ratio,space velocity,and DOC oxidation were studied.The impact of sex on the performance of SCR catalysts.The results show that the NO_x conversion efficiency and carrier pressure drop of the catalytic converter show an upward trend with the increase of the carrier volume,and the ammonia escape volume will decrease accordingly.The SCR carrier volume is generally twice the diesel engine displacement;the carrier length-to-diameter ratio has a significant effect on the pressure drop.Importantly,the catalytic converter with a smaller length-to-diameter ratio has better performance.Nitrogen oxides can be almost completely converted when the ammonia-nitrogen ratio is maintained at 1 in the middle temperature stage,and the ammonia leakage at the outlet is almost zero;in the high temperature range,due to the large amount of NH3 oxidation reaction,excessive ammonia gas needs to be introduced to improve the conversion efficiency,and the ammonia leakage is negligible.The space velocity affects the conversion efficiency,ammonia leakage and pressure drop of the catalyst in the low temperature stage.The oxidation reaction of DOC increases the exhaust temperature while increasing the ratio of NO₂/NO_xin the exhaust gas,which increases the NO_x conversion efficiency of SCR and greatly reduces the amount of ammonia escape.Use the AVL-FIRE platform to establish a three-dimensional model of the straight-tube integrated post-processing device,change the number of spirals in the mixing section,to explore the effect of ammonia uniformity on the NO_x conversion efficiency;adjust the urea injection volume to analyze the change in the ammonia-nitrogen ratio on the SCR flow mixing The impact of characteristics.The main conclusions are as follows:the flow field generated in the mixing section with different spiral turns is similar.After the exhaust gas flows through the spiral section,it is fully mixed to form a swirling flow.The NH3 distribution of the SCR inlet section is affected by this.The change is divided into three stages.The increasing trend of NO_x conversion efficiency changes with the change of ammonia uniformity.The ammonia-nitrogen ratio has no effect on the distribution of ammonia concentration,the index of ammonia uniformity remains unchanged,and the radial distribution of NO concentration in the catalyst is affected by the air flow.When the ammonia-nitrogen ratio is 1,1.1 and 1.2,the conversion efficiency of NO_x and the amount of N₂O produced increase with it.