Development Of FAI_SCR Calibration System And Research On Ammonia Storage Characteristics Of SCR Converter

With the increasing requirement of diesel engine emission control,in-cylinder optimization technology has been found not enough to meet the increasingly stringent emission regulations.To achieve the China?or higher emission standards,exhaust after treatment technology is necessary.Selective catalytic reduction?SCR?after treatment technology has good economy and sulfur tolerance,and it is considered as the main technical route to decrease diesel engine NO_x emission.SCR system uses urea aqua?DEF?as reducing agent,and urea will be changed to NH₃ via hydrolysis reaction inside the engine exhaust pipe after it is injected by the DEF dosing system.The NH₃,which covers the catalyst surface,will react with the engine exhausted NO_x,reducing diesel engine NO_x emissions and meeting regulatory requirements as a result.In this paper,calibration software for FAI_SCR system was developed and the ammonia storage model was studied.Firstly,LabVIEW is used to develop the calibration software DATAVIEW,which can acquire and display real-time SCR data,read and write the FLASH or EEPROM data inside the slave computer?DCU,Doser Control Unit?.This calibration software is a basic but strong tool for FAI_SCR system development and application.The calibration system was tested and verified in engine emission bench tests.Secondly using the function about ammonia storage experiment developed in the SCR calibration tool,the relationship between ammonia storage and temperature,NO_x conversion efficiency and ammonia storage saturation of a SCR catalyst converter was studied by bench test.The results showed that the maximum ammonia storage would decrease with the increase of SCR temperature.The decreasing trend at high temperature is much lower than that at low temperature,which is consistent with the assumption in the dosing control strategy.At low temperature,the NO_x conversion efficiency is proportional to the ammonia saturation degree.When the temperature is over 300°C,the effect of ammonia storage on NO_x conversion efficiency is much smaller.