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In recent years, the rapid growth of China's automobile industry, car to provide people with convenient, the impact on the environment are becoming increasingly serious. Especially automobile exhaust pollution of the air, a serious threat to human health and life; also pose a huge challenge in addition to the further development of the automotive industry. Harmful emissions of diesel engines, NOx emissions are the highlight of many pollution. The face of increasingly demanding emissions regulations, relying solely on the machine the purification difficult to meet, must be assisted to rely on exhaust after-treatment technology. Research at home and abroad to reduce harmful emissions of the diesel engine has two main technical route. EGR technology, i.e., by the exhaust gas recirculation to reduce NOx generated in the machine, then through the machine outside the particle capture technology to reduce the emission of PM; SCR technology, first by strengthening reduce PM generation internal combustion engine machine, and then machine outside the selective catalytic reduction technology to reduce NOx emissions. SCR technology-based fuel economy to meet the Euro IV and Euro Ⅴ stage emission regulations can share a test platform, the sulfur content of the fuel is not sensitive to other factors, the research focus has moved to the SCR technology. SCR technology will be the most effective measures to reduce harmful emissions of the diesel engine. This paper describes the composition of the SCR electronic control system, work and reaction principle, the introduction of SCR electronic control system open-loop control strategy, which according to engine speed, load query the urea injection steady-state MAP of to calculate the basic injection quantity of urea solution, and then exhaust temperature, the catalytic converter the ammonia storage model for the basic injection amount is corrected. Control strategy elaborated on the urea injection computing model, the ammonia storage model of the exhaust temperature correction model and catalytic converters. The present study is to build the SCR power control system, completion of the SCR power control unit hardware and software design, including the choice of the microprocessor, the sensor signal acquisition, urea pump of urea nozzle and heating valve drive, CAN communication interface design and so on. The software program introduced in the the urea control state management mechanism, the urea injection control system is divided into ready, pressure control, pressure control, pressure unloading and counter, emptying state, in order to meet the needs of the urea solution is measured accurately. Finally, the engine bench NOx emission test, emission test results show that the self-developed SCR electronic control system in the exhaust temperature of 250 ° C or more NOx conversion efficiency of up to 50%, the ratio of NOx emissions of less than g / kWh. The results of this paper has a certain reference value to the development of diesel engines to meet the State IV emission regulations with the reality of the social significance of reducing diesel engine emissions, reducing air pollution.
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