Development SCR Control System For Diesel Engine And Its Experiment Study

The world's attention now is focused on environmental pollution problem. In China, the source of pollutants in some big cities are convert from the fuliginous pollution to the car pollution. In order to alleviate the pressure of the environment,the more stringent emission regulations will be gradually implemented. For satistifying with the increasingly stringent emission regulations,it is the necessary to use the after-treatment technology to achieve the national ?or above emissions regulations.The one of developing directions of diesel engine technology is on the basis of existing purification technology of the diesel engine combined with efficient after-treatment measurements. Selective catalytic reduction(SCR) technology is a technical route to reduce engine NOx emissions. According to our country's basic national conditions, at present, the field of heavy-duty diesel engine uses SCR technical route.In this paper, a six-cylinder turbocharged diesel engine, with the SCR after-treatment technology, is selected as the research object. In order to reduce diesel engine NOx emission, SCR controller and control strategy is designed and developed, and implemented based on an engine test bench.Firstly, the functional requirements of SCR controller are analyzed, and the MC9S12XS128 is chosen as the core processor. According to the requirements, the controller area network(CAN) module, A/D conversion module, and pulse width modulation(PWM) module are used in the processor. The power supply module and driving module are designed. The Code Warrior integration development envirnment is used for each function module of the software configuration. With the developed SCR controller, the relative experiments can be carred out.Using VB development tool and based on SAE J1939 protocol, a SCR calibration and diagnostic tool is developed. With CAN bus engine state parameters, SCR after-treatment related parameters and OBD fault diagnosis information can be read. The OBD fault diagnosis strategy and programming in SCR controller is developed. The developed debugging the tool can run normally and the design requirements are met. The injection control strategies are developed in this SCR system. The base urea injection quantity is calculated through looking up NOx emission map and target NOx conversion efficiency map. The NOx sensor is used to calculate the actual NOx conversion efficiency, and the incremental PID control method is used for closed-loop to correct theurea injection quantity. The transient operating conditions are determinded with the throttle angle changing rate, and the delay of temperature and ammonia storage strategy is established.Through experiment, the NOx emission map exhaust flow map and target NOx conversion efficiency map are obtained. These maps provide basis data for realizing the control strategy.The ESC 13 test mode is used to verify the effect of SCR system. The test results show that, NOx emission of the diesel engine from 10.29 g/kw.h reduced to 2.02 g/kw.h with developed SCR control system.