The Research On System Performance For SCR To Reduce NO_x Emission From Diesel Engine

As a main power unit, diesel engine has been widely used in many fields, such astransportation, energy power, agriculture machine and so on. Although diesel engine hashigh thermal efficiency and high fuel economy, a large proportion of NO_x emission hasattracted great public attention. With strict emission regulation and debut of EuropeⅣ,SCR control technology has been regarded as a best method to reduce NO_x emission fromdiesel engine. This technology is gradually becoming a main research direction.This paper mainly includes three research aspects, and they are theory research,experimental research and simulation research.The first is theory research, and the structure and technology principle of SCR systemare introduced. Then the functional properties of various reducing agents and catalysts arealso described. Different factors of NO_x reduction from SCR system, such as reactiontemperature, space velocity, NH₃/NO_x concentration ratio and urea spray are elaborated.Theory research can provide theoretical basis for all-state diesel test and simulationanalysis of SCR reaction factors.The second is experimental research, and this research mainly focuses on emissioncharacteristics of diesel ESC tests. On this condition, original diesel tests in all operationstates are carried out. Speeds of rotation in all tests are at the range from700r/min to2200r/min, and the throttle values are at the range from10%to100%. During all-statediesel tests，with the increase of rotational speed, the changes of NO_x concentration, COconcentration, HC concentration, exhaust pressure, exhaust temperature, intake pressure,torque value, power value and specific fuel consumption are analyzed in detail. Comparingthe NO_x emission values in all-state tests and those with SCR system, the amount of NO_xreduction and NO_x reduction rate are analyzed in detail. This research can provideexperimental basis and data reference for simulation analysis of SCR factors. The last is simulation research. During all-state diesel tests, since huge amount ofNO_x emission occurs in1200r/min condition, the simulation research mainly fouces onthis condition, and analysis of SCR reaction factors are focused on important parameters,such as urea spray, reaction temperature, space velocity and NH₃/NO_x concentration ratio.The simulation images are converted to relative curves and values for further explanation.All these researchs show that, the application of SCR system in diesel test is effectivefor NO_x reduction and environmental protection.