Development And Experiment On Electronic Control System Of Solid SCR For Diesel Engine

Urea Selective catalyst reduction (SCR) has been considered as one of the mostpromising techniques to reduce nitrogen oxide (NOX) emitted from diesel engines and hasbeen widely used on diesel vehicles in the world. However there are still some problemswith Urea-SCR system. Urea solution may crystallize and sometimes even freeze underlow-temperature conditions, which also makes conversion rate of the catalyst at a low level.To solve this problem, a new system which is called the solid SCR system has beendeveloped. It injects NH3directly into the exhaust pipe instead of urea solution. Theproblems mentioned above can be well resolved by this method.This paper has referred to many advanced development schemes of control systemsand analyzed the function requirements and working principles, and come up with acomplete set of system platform design scheme. The solid SCR control system has beendesigned based on microprocessor MC9S12DP256. The primary works are presented asfollows：1. The thesis has analyzed the function requirements and working principles of thesolid SCR control system and worked out the control strategy for NH3injection. Thesystem calculates NH3injection amount via referring NH3injection MAP under steadyconditions based on engine speed and load. The temperature and ammonia storage model ofcatalyst are used to revise the NH3injection amount. The nozzle is controlled to injectaccurate amount of NH3into the exhaust pipe.2. Taking advantages of on-chip resources of Freescale MC9S12DP256, this thesis hasdesigned the hardware circuit of the development platform. The hardware circuit includesnot only MCU basic circuit such as the clock circuit, power supply circuit and A/Dconversion circuit, but also the nozzle driving circuit, temperature measurement circuit,serial communication circuit and CAN bus communication circuit.3. The control module of the solid SCR control system is designed and optimized withthe help of Matlab/Simulink. Then convert the control module into C code suitable forMC9S12DP256after the RTW toolbox has been configured correctly. And then import theC code into the target area of the main program built by Code Warrior. After completing theprocess of debugging and compilation, download the program into the microcontroller. 4. Build the functional test environment within the equipments and conditions in thelaboratory and verify the control effect of the solid SCR control system on NOx reductionunder ESC test cycles. The results show that this control system is capable to meet therequirements.