Urea Dosing Strategy Study For The Heavy-duty Diesel Engine SCR System

As the emission regulation becomes more and more strict, The Selective CatalystReduction of the heavy-duty diesel engine has become the main stream of the after-treatmenttechnique to meet increasingly stringent emissions regulations. The paper is based on theresearch of the SCR urea dosing control strategy, which is the core of the SCR technology. Itgives a design of control system of the SCR manage software, it also has accomplished theurea dosing strategy on calibration of the map and the SCR model,as well as experimentalverification on test bed.A control strategy based on the map has been designed and were verified throughsoftware simulation.,which including the estimation of the original NOx emission withtransient correction of the algorithm, the design of the NOx conversion efficiency Map; thecalculation algorithm of the urea injection, and the correction algorithm of temperature,storage ammonia,aging parameters on the injection quantity, The above dosing strategyarithmetic verified by MATLAB/SIMULINK software.The paper also designed a model of catalytic converter on the basis of the chemicalkinetics and heat transfer theory,and also given a model based urea dosing controlstrategy.The strategy takes advantage of the observer to calculate the internal storage ofammonia and temperature of the SCR model, obtains the amount of the urea injectionaccording to the results of the state observer and the target of NH3concentration to achievemodel-based feedforward algorithm, the simulation results show that the algorithm can bemore effective on the leak of NH3.In order to verify the algorithm on test bed, The SCR management software system hasbeen designed based on the documentations from home and abroad. The system is consistedof three layers: the upper is the state machine module, the middle is the monitoringcomponent module and the lower is equipment control module. The state machine modulecontrols the the SCR system under different states.The monitoring component module is responsible for the collecting the variety of message from the lower equipment module,assembling them as the prerequisite of the state transformation, at the same time controllingthe actions of the lower equipment module according to the state of the state machinemodule.The lower equipment control module mainly drives the actuator, and adjusts sensorsignal. According to the calculated amount of urea injection control strategy it controls thedosing system on the urea dose volume in meteringcontrol state.In order to testify the effectiveness of the algorithm, the engine test bench was set up.the SCR urea dosing control strategy and software management system were downloadedinto RCP based on the dSPACE. And the RCP was taken as the DUC instead of the originalECU to control the SCR components. The ESC steady-state test cycling and ETC transienttest cycling were carried out respectively. The results show that the concentration of NOxand NH3on the SCR downstream have been well controlled with the application of the ureadosing strategy system proposed here, and it can meet the requirements of State Ⅴemission regulations.