Research On Matching And Control Strategy Of NH₃-SCR System For Diesel Engine

Due to urea can’t be hydrolyzed to NH3at low temperature, the NOx conversionefficiency will be reduced and the sedimentary will block the exhaust pipe in the actuallUrea-SCR system. In this dissertation a NH3-SCR system which inject NH3directly intothe exhaust pipe instead of injecting urea to improve the effect of purification. The mainresearches of this dissertation include matching of NH3-SCR system and the effcts bydifferent factors by steady-state experiments; research of NOx emission and to be correctedpredicted with a quardratic polynomial by transient condition experiments;put forwardNH3dosing strategy on calibration of the mapverification on test bench.Thisdissertation researches the differences between Urea-SCR and NH3-SCR systemin steady-state by engine test bench exeperiments. The results show that the average NOxconversion efficiency of the NH3-SCR system is better than that of Urea-SCR system,especially average gap is15.67%at three low load operation conditions; NH3-SCR systemapplied can improve NOx emission of SCR system and be affected negligible by spacevelocity; at low temperature zone (200℃~300℃) the NOxconverstion effiency ofmolecular sieve based ctalystis higher than that of vanadia catalylst,but as the increase oftemperature,the latter catch up with and surpass the former;Saturated storage amount ofammonia in catalylst be influences by temperature and space velocity obviously.It mayeasily lead toammonia slipespecially from low temperature and low load conditions to hightemperature and high load condtions within a short time.Use transient conditiontest system to do diesel operations transient performedexperimentsi.e. fixed engine speed during transients in torque and fixed torque duringtransients in engine speed.The results shows that respond time of parametershas closerelationship with transient time, speed change and torque change.Analyse the reason andproposed a “lag multiple”which is an evaluation index to estimate the delay of theperformances in the transient process. Choose a quardratic polynomial to correct andpredict transient NOx emission by MATLAB/Model-Base Calibration.Design a dosing strategy on calibration of the map which include the correctionmodule to engine origin NOx transient emission, arithmetic of ammonia injection quantityand corrected by temperature and Saturated storage amount of ammonia.