Development Of Control Technology Of Non-air Assisted Urea-SCR Injection System For Diesel Engine

The particulate matter (PM) and nitrogen oxides (NO_x) of Diesel emissions will causeserious environmental problems, and almost all countries have enacted stringent emissionregulations to limit diesel’s emissions. There are two routes can reduce diesel engineemissions effectively: one route is with the exhaust gas recirculation (EGR) technology toreduce in-cylinder NOxformation first, and then reduce particulate matter emissionsthrough the exhaust particulate filter (DPF); another is to optimize the in-cylindercombustion to reduce the generation of particulate matter first, and then through theselective catalytic reduction (SCR) technology, to reduce the emissions of NOx. SCRtechnology is widely regarded as the main line of the response to the emissions regulationsof the State Ⅴ for its advantages of fuel economy and the low sensitivity to sulfur. In thispaper, for the urea injection system of the StateⅤ-oriented non-air assisted SCR forheavy-duty diesel, the corresponding hardware circuit is developed, and the fuzzy PIDcontroller of the pump pressure is designed to improve the stability of the urea injectionpressure. The main researches in this study are as follows:The components and advantages and disadvantages of the air-assisted spray and no-airspray of the urea injection system are analyzed respectively. The non-air assisted injectionsystem program is chosen in this paper. The composition and the hardware features ofnon-air assisted urea injection system are detailed analyzed, and for the configuration of thedSPACE MicroAutoBox and RapidPro, the interface circuits of the various components aredesigned.The urea nozzles peak-hold circuit is designed with the Operational Amplifiercharacteristics of the analog circuit. Due to the smaller inductance value of urea nozzle, avery high control frequency of the PWM is required, which will greatly consume computingresources of the digital controller, and therefore, this study adopts the analog circuit forclose loop control. As the complexity of the waveform of the peak hold circuit, the circuitdesign use two Operational Amplifiers and a series of resistors, capacitors andsemiconductor devices to achieve the circuit design. In order to ensure the correctness of thecircuit design, this paper determine the circuit parameters though the circuit simulationanalysis with the dedicated power electronic circuit simulation software–Pspice. Based on the preliminary design, the PCB design is completed using Protel software, and functiondebugging is completed on the dSPACE experimental platform.Urea pressure Fuzzy PID control algorithm is designed. The stability of the Ureapressure directly affects the accuracy of the urea injection. As the urea pressure has a strongnon-linear, it is difficult to optimize its controller in full working condition; and the segmentPID algorithm is used in the traditional control. In order to achieve better urea pressurecontrol, this paper designs a fuzzy PID controller for urea pipeline characteristics. Thoughthe rapid prototyping experiments on the dSPACE, compared with the segmented PIDcontrol, the fuzzy PID can effectively reduce the pressure overshoot and improve thestability of the pressure control.