Research On SCR Electronic Controlunit For Diesel Engine

It is extremely difficult for diesel engine to meet the state IV emission regulation bymerely adopting inside-cylinder purifying treatment. By optimizing inside-cylinder fuelinjection strategy to resolve PM pollution and applying SCR afterward treatment system toreduce NOx emission, the state IV emission regulation can possibly be met.In this paper, a SCR control strategy was formulated by basing on the workingprinciple of SCR system, and a SCR electronic control unit which fulfills the strategy wasdeveloped. The major work of this paper consist of three parts (1) Designing controlstrategy for urea injection. First, the urea injection basic amount in the steady-state isdetermined according to the engine speed and the accelerator pedal position. Then, theactual urea injection amount is determined by two-dimensional look-up table algorithmaccording to both NOx conversion efficiency and NH3storage corrections.(2) Indeveloping phase, at first, the SCR electronic control unit is divided into differentfunctional blocks (sensors block, input signal conditioning block, control driving signalconditioning block, micro-controller block). Then, based on the dSPACE developmentplatform, the hardware processing of I/O signals are completed in accordance with I/Osignals’characteristic of different functional blocks. The auto-control urea injection in SCRsystem is eventually achieved by the informational interaction between software of ureainjection control strategy and hardware development platform in Matlab environment.(3)In testing phase, the maps of major parameters are firstly calibrated and the urea injectionbasic amount map in the steady-state is then formulated. All the fluctuations of NOx andNH3concentration in exhaust gas are monitored and analysed by the steady-state ESC testcycle both in the origin diesel engine and the engine equipped with SCR systemBy the testing, it is showed that the self-designed SCR electronic control unit canadjust control strategy by request to meet different NOx emission regulations. It is alsoshowed that the unit runs stable and reliable. The structure of the unit is rational.