A Study Of Urea-scr Control System In Diesel Engine Based On Dsp

SCR technology is one of the most effective after-treatment techniques to meet Euro 4 emissions and above. The technology focus of the study is:First, the advanced catalyst and reductant technology; Second, precisely control technology of inject reductant.In this paper, the chemical reaction principle on the urea-SCR system is analyzed. Then the whole system is analyzed. The whole system is builded on the basis of existing technology and conditions of experiment. After the analysis of urea-SCR system at home and abroad, the control strategies of the urea-SCR system are designed. According to requirement of this system built calibration system, and the calibration system is practical and simple. Hardware of the urea-SCR control system is designed for the system control objects and control strategies. The hardware urea-SCR control system includes:main controller and data acquisition card. The main controller is responsible for signal acquisition, actuators control, calibration system, communicate with automotive ECU and data acquisition card. The data acquisition card is in charge of receiving GPS signals and storing in the SD card at the same time, communicating with the master controller. As the complexest of the calculations of the main controller, so it should choose DSP chip TMS320F2812 as controller chip in the main controller. Data acquisition card controller chip select the cost-effective high ATmegal28 chip. According to automotive electromagnetic environment on the actual, the filter circuit is designed to avoid some specific interference in vehicle for enhancing robustness of the urea-SCR control system.The urea-SCR control system and the catalyst of provided by cooperator are installed in the WD615.96 heavy-duty diesel to build test bench. The test bench is used to calibrate dosing module and MAPs. The dosing module is a key factor to realize precisely dosing reductant. So this paper determines its frequency and pressure by experimental study and calibrate at last. When calibrate MAPs, the first step is determine rough MAPs by analyzing test data and theories. Then, the MAPs are corrented by experiment. The 4 MAPs are calibrated, namely, NOx concentration MAP, exhaust flow MAP, NOX conversion efficiency MAP and urea supply coefficient MAP. In accordance with the Euro 4 and 5 requirements of heavy-duty diesel engines with the exhaust after-treatment technology in GB17691-2005, the WD615.96 heavy-duty diesel with the urea-SCR system should test ESC and ETC cycles. The results of ESC and ETC show that the the WD615.96 heavy-duty diesel engine with the urea-SCR system meet Euro 4 and Euro 5 emission requirements.