| The development of urbanization brings in increasingly serious environmental pollution and energy shortage problems; meanwhile NOx pollution has attracted much attention recently. Diesel engine with its advantages of low fuel consumption and high power is widely used in heavy-duty vehicles. And it leads to serious NOx emission, which has been widely studied in the field of post-processing technology. In the study of NOx post-processing technology, selective catalytic reduction of SCR, catalyst activity, domestic and foreign scholars have made a series of theoretical and experimental research, and have made great progress. While there are few studies on low-temperature operating characteristics of SCR system, so this paper introduces the low-temperature characteristics of urea tank, pump module, dosing module; explores different factors influencing thawing, discusses urea thaw parameters under different conditions, such as urea tank state, coolant flow, heating tube; through the analysis of the thawing time and temperature in urea tank to find a optimal heating scheme; proposes new criterion for urea successfully thawing. It has great significance in the application of SCR technology in cold regions.First of all, design and set SCR low-temperature experiment platform. SCR system requires a constant supply of heat and energy, which consists two parts, one is supplied by high-temperature coolant for urea thawing, another is provided by24V power for pump module, dosing module and urea pipes. The coolant is heated to a certain temperature (about353K) by the electrical heater, while the heater power is determined by the desired heating power based on urea thawing. So establish a mathematical model for urea thawing, estimate the amount of heat dissipation of the coolant along the pipeline, to provide a theoretical basis for the selection of the heater.Secondly, introduce the pipe connection and electrical connection of experiment platform. Pipe connections include coolant circulation and urea circulation. In real vehicles, coolant circulations of dosing module are not controlled by the heating valve, while the coolant circulations are all controlled by the heater outlet valve in the experiment platform. Electrical connections include heating circuit, control circuit and communication connection. Data acquisition software can collect the inlet and outlet temperature of the coolant, coolant flow, temperature of16measuring points in urea tank, temperature of pump suction point. The coolant flow can be regulated according to the need of the experiment.Thirdly, based on different factors that affecting the urea thawing, arrange series of experimental. Analyze the test data via Matlab software, and draw the temperature distribution of urea inside the tank. Obtained the following conclusions:The heating effect of helical is better than that of U-shaped tube under the same conditions; Urea thawing effect of tank under vibration state is superior to tank in a stationary state; Urea thawing time decreases with increasing coolant flow through U-shaped tube; Compared with coolant flow, shape of heating tube does more to urea thawing. In order do more comprehensive analysis of the solid-liquid distribution of the urea tank, establish the simulation model of urea thawing, change of urea temperature is consistent with the experimental result. This paper summarizes a new criterion for urea thaw, that urea temperature near the urea temperature sensor reaches-10℃. It’s reliable and can reduce NOx emissions by diesel vehicles in the warm-up process.Finally, in order to tests the performance of the main components of SCR system with messages on the vehicle\engine as few as possible, carry out the strategy optimization of urea injection. Based on ECU unit of Bosch Denoxtronic(?)2.2, design and develop an injection unit controller, instead of DCU. Variable resistors on controller board are used to simulate engine speed and torque, button switch is used to simulate vehicle key. Through debugging of program, it is found that the controller can monitor pump and urea tank in real time, receive injection mass from ECU accurately, complete the entire workflow with pump and dosing module. |
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