Study On CDPF Regeneration Technology Based On HC-dosing

With the increasing requirements for emissions in domestic and overseas,the field of diesel exhaust after-treatment is facing more severe challenges.At present,the main goal in the domestic field of diesel engine after-treatment is to comprehensively upgrade and optimize the emission system to meet CN-VI standards.Because of its simplicity and safety and no interference with the normal operation of diesel engine,the hydrocarbon dosing(HC-dosing)system is the mainstream exhaust heating method for medium and heavy duty diesel engines,gained extensive attention and application in domestic and overseas.The main purpose of precise exhaust temperature control is to periodically regenerate the Catalyzed Diesel Particulate Filter(Hereinafter referred to as CDPF),and meet the stability and safety of regeneration.Therefore,it is of great significance to research on CDPF temperature-controlled regeneration technology based on HC-dosing.In this paper,flow and chemical kinetic model for a diesel oxidation catalyst(Hereinafter referred to as DOC)with HC-dosing is constructed and validated to obtain its thermodynamic characteristics.Meanwhile,a CDPF trap and regeneration model is constructed and validated.Taking CDPF as regeneration control object,the regeneration start-stop judgment and ash strategy based on the soot load calculation method are designed.The working condition selection method and target temperature calculation for regeneration are also designed.Taking DOC with HC-dosing as temperature control method,a temperature control strategy with feedforward and feedback module is designed.Then,under the synergistic effect of the DOC temperature control strategy and the CDPF regeneration target strategy,the CDPF regeneration strategy based on HC-dosing is verified through simulation and experiment,which proves the effectiveness and stability of the model-based regeneration control strategy.The main work of the thesis are as follows:(1)Research on DOC model with HC-dosing.Aiming at the thermodynamic characteristics of DOC with HC-dosing,flow,heating,and evaporation-pyrolysis from diesel droplets to gaseous hydrocarbons are considered inside DOC,meanwhile,the Arrhenius form is utilized to describe the evaporation-pyrolysis rate equation of diesel droplets.Gaseous hydrocarbons generated by evaporation-pyrolysis process are diffused and transferred on the surface of DOC,heating DOC by catalytic oxidation and feed back to the exhaust through convective heat transfer.The whole process is a coupling process of chemical reaction,energy conversion and mass transfer,and this thesis constructs a detailed thermodynamic model to describe and analyze.After experimental calibrated and validated,this model can simulate the actual temperature rise under various working conditions,which is suitable for offline control simulation and subsequent strategy design of model-based temperature control.(2)Model research for CDPF trap and regeneration.This thesis constructs the model of CDPF trap and regeneration process.In addition to the traditional mechanism of CDPF trap and regeneration,the model also adds the catalytic oxidation process of unreacted hydrocarbons from DOC to CDPF.The result shows that unreacted hydrocarbons will increase the substrate temperature of CDPF,which promotes the regeneration of carbon particulates.After calibration and validation,the model can simulate the actual trap and regeneration process of CDPF,which is suitable for offline control simulation and subsequent strategy design of regeneration target.(3)Model-based temperature control regeneration strategy.In this thesis,a calculation method for carbon loading is designed based on the CDPF trap and regeneration model.The method consists of three parts: the accumulated carbon integral method,the wall temperature calculation method,and the Darcy flow resistance method.This method is utilized for regeneration start-stop judgment and ash maintenance.Based on DOC+CDPF coupling model,the selection method of regeneration conditions and the calculation method of regeneration target are designed.After determination of regeneration target,the specific temperature control strategy is designed based on the model of DOC with HC-dosing.First,the feedforward control algorithm is designed from DOC thermodynamic model.Then according to experimental order identification of DOC as third-order characteristics,PI feedback control algorithm is designed from stable boundary locus(SBL)method combined with intelligent weighting and selfoptimizing.The regeneration target strategy gives a specific control target,and the DOC temperature control strategy realizes the temperature control process.Finally,these two strategies are combined,constructing an integrated temperature control regeneration strategy.(4)Simulation and experimental research of temperature control regeneration.Based on DOC model and CDPF model,this thesis simulates the regeneration strategy of temperature control on Matlab Simulink offline.The model simulates the effect of DOC temperature control strategy under different interferences and the regeneration effect of CDPF temperature control.The regeneration strategy of temperature control validated by simulation,has been carried out on diesel engine bench under different conditions,conducting the experiments of temperature control,carbon trap and regeneration.The experiment results prove that the control strategy of DOC temperature is robust and stable,prove that the trap and regeneration process of CDPF controlled by temperature control regeneration strategy has a good effect.The strategy can provide a research basis for the development of the CDPF regeneration technology with HCdosing.