Development Of Diesel Engine SCR Urea Injection System And Experimental Study

With environmental pollution becoming more serious, The exhaustemissions of automobile is an enormous source of environmentalpollution.in order to alleviate the environmental problems, all countriesformulate related policies and regulations to limit emissions from motorvehicles.As one of the most effective technologies of Dieselafter-treatment technology,the SCR injection system reduce NO_x emissionof exhaust effectively through injecting Urea solution to the exhaustpipe.The Urea solution mass fraction of32.5%is also called Adblue.Therefore, the studies on the Urea injection system development andInjection control strategy have far-reaching significance.BOSCH has applied two generations of SCR Urea injection system in themarket and some enterprises like kailong and yuchai,have their own Ureainjection system.The SCR Urea injection system developed need to becoupled with diesel engine ECU to realize the quantitative of the ureasolution spray.In this study, we have independently developed a set of SCR ureasolution injection system,and studied the characteristic of two kinds ofmolecular sieve SCR catalysts by experiment. We have specific studied:（1） We put forward the working principle of SCR injection systemdesigned and expound the designed principle of the sensor signalacquisition system,power drive device system and the Urea injectionmeasurement system.We discussed the designed principle of Multi-channeltemperature acquisition system based on K-Thermocouple and MAX6675,the signal acquisition hardware circuit diagram and program flow chart ofmagnetoelectric speed sensor.As well as the signal acquisition methodof the knock sensor and level sensor.（2）We present the diagram of the power drive system and expounds theworking principle of the power drive system and flow chart of theprogram.The hardware circuit and measurement principle of the Urea SCRdevice measuring injection system were introduced in detail.In addition,the OBD functions of SCR system, the system management software based onLabview are also designed.（3） Urea solution viscosity gets great changes with the change of itstemperature and density,and when the environment temperature and thetemperature of the exhaust pipe change, it will produce certain effecton the injection quantity of the nozzle. We determine the injection volumecorrection coefficient of ρ1,through the analysis of the change of ureasolution density with temperature.We define the threshold value of theinjection quantity through the combination of experiment and statistics.Combined with regression analysis,we define the urea solution sprayvolume correction coefficient of ρ2.（4）On the CA6DL diesel engine,the activity of two molecular sievecatalysts with the given NSR was researched by the ESC experiment.Thelow-temperature activity of two molecular sieve catalysts and theinfluence of temperature,air speed and HC on NO_x conversion efficiencywere analyzed.The results show that the air speed has little influenceon NO_x conversion at the temperature of250℃.The highest efficienciesof NO_x conversion for Cu-based and Fe-based molecular sieve are88%and78%respectively at the NSR of1.0,and hence Cu-based SCR catalyst hasa better low-temperature performance than Fe-based SCRcatalyst.Furturemore,Cu-based molecular catalyst has the better abilityof anti-hydrogen poisoning.At the temperature of350℃,the efficiency of NO_x conversion is influenced by air speed and temperature and efficienciesfor two molecular sieve catalyst reach the highest respectively at theair speed of115060h^-1and90400h^-1.Fe-based molecular catalyst is moresensitive to HC than Cu-based molecular catalyst.