Design Of SCR Controller For Diesel Engine

With the wide application of diesel engine,the exhaust pollution is becoming more and more serious.In order to meet the requirements of emission regulations,it is no longer feasible to clean the engine in a simple way,and more advanced exhaust aftertreatment technology must be combined with.Because the better fuel economy and more simple structure of the engine,the technology of Selective Catalytic Reduction(SCR)has become the mainstream technology of reducing NOx emission for diesel engine,and the NOX conversion efficiency is up to 95%.SCR performance mainly depends on the control system,but the SCR control system in current domestic is almost monopolized by foreign,and there is a big gap between them in performance,therefore,it is necessary to study the SCR controller which can achieve the efficient conversion of NOx.Based on the analysis of the advanced SCR control technology at home and abroad,combined with the design requirements of the diesel exhaust aftertreatment control system,the controller was designed for the non air assisted SCR system.The main research contents were as follows:(1)Controller hardware design.Based on the analysis of the configuration requirements of sensors and actuators in the SCR system of diesel engine,the overall scheme of the controller hardware system was designed.Based on the 16 bit dual core micro controller of NXP,the SCR controller was designed,which include MCU minimum system module,power management module,analog and digital signal processing module,output control module and CAN bus communication module etc..(2)Controller software design.Based on the principle of hierarchy and modularization,the overall structure of the embedded software which includes the underlying driver software and application layer software was designed.On the Codewarrior platform,the initial configuration of the microcontroller was carried out,and the driving software of the electronic control unit was developed.After the executable code is generated,it can be encapsulated into a function library.Based on sensor NOx feedback control,the application layer software was designed from the appropriate control strategy,which include access to SCR catalytic converter and engine state information,the calculation of the amount of urea,urea pump pressure control and heating of SCR system.(3)Management software development.SCR monitoring and management software was developed based on VB.NET programming environment.Which communicate with the SCR controller by CAN bus,the system can not only get the change of the state parameters of the SCR system during the working process,but also can record and monitor the parameters of the SCR controller.(4)Controller test verification.The hardware and software performance of the controller were tested by the hardware test platform and the bench test platform.The experimental results show that the hardware of the SCR controller is stable,and the underlying driver is reliable.The conversion efficiency of NOx is up to 84% under the ESC test cycle,which meets the limits of NOx emission limits for the national V emission standard.