Research On Model-based Failure Diagnostic Strategy Of Diesel Particulate Filter

With the increasingly stringent emission regulation of every country all over the world,diesel particulate filter(DPF),with its ability of filtering soot in the exhaust efficiently,has been widely used in the field of post-processing.However,due to improperly use or use for long time,DPF can go out of action,such as channel blockage or carrier damaging,to affect it functionality and reliability.Therefore,it is particularly important to monitor the condition of the DPF in real time and estimate fault.At present,the research on the characteristics of the DPF is very comprehensive,but the fault diagnosis research on the DPF is few.To ensure that the filter is able to reduce PM levels of the diesel exhaust below regulated limits,On Board Diagnostics(OBD)of the DPF is required to provide alerts in the case of filter malfunction or failure.Therefore,this research chooses the DPF as the research object,setting up DPF model with the help of GT-Power,1D simulation software,and having research on DPF failure diagnostic strategy based on the model.The main research work of this paper is as follows:1.DPF model was established based on GT-Power software,which includes soot filtration model,flow pressure drop model and one-dimensional regeneration model.According to the theory of packed beds filtration,to discrete layers of the DPF carrier wall and deduce the formula of the DPF wall filtration efficiency each layer and the value of soot loading.This research has studied the four main sources of DPF pressure loss through the formula deduction and finds out the key parameters that affecting the pressure drop.According to the three fluid conservations laws including mass conservation,momentum conservation and energy conservation equation,the fluid flow control equation is deduced.According to the model theory of one dimensional-two layer,this research describes reaction equations and the reaction rate equations of C and NO2 in the different reaction layers and NO translated into NO2 in the presence of catalyst.2.According to the measured pressure drop data of the DPF,this research realized calibration of DPF filtration parameters and chemical reaction kinetics parameters in the condition of selected of steady-state loading.Finally,it realized the verification of DPF simulation model after calibration through an engine bench test.The results show that simulation results from the model and test results have good agreements.3.Two main types of the DPF failure are studied,and the method of fault injection is presented.The DPF failure model is established through the GT-Power model injected the fault.With the help of fault model,this research has carried on the simulation research of the DPF on two main failure modes: channel plugging and carrier damaged.The research also has analyzed the sensitivity,which of the main exhaust parameters shows with different failure effects.It is concluded that both of the DPF pressure drop and trapping efficiency can be used as characteristic parameters of the fault for the establishment of diagnostic strategy.The DPF pressure drop and trapping efficiency of the wall section will be obviously increasing when channel plugging happens.And it will be decreasing in some degree when carrier damage happens.When the damage degree of the substrate is higher than 30%,the filtration efficiency of the DPF will be down to around 50%;when its damage reaches 50%,the DPF pressure drop drops rapidly and is close to zero,the DPF can’t continue to use at this time.Due to passive regeneration of the DPF can also lead to the change of the pressure drop and trapping efficiency as well,in order to eliminate interference on fault diagnosis as much as possible caused by changing parameter of passive regeneration,this research chose high temperature and low load conditions as the diagnostic conditions of an engine,coupled with pressure drop and trapping efficiency monitored,as the basis of fault diagnosis of the DPF.4.This research has established diagnosis scheme according to effective exhaust parameters.It sets a differential pressure sensor on two ends of the DPF,performing real-time acquisition of the pressure drop data and transfers to the ECU for analyzing and calculation.According to the new OBD regulations,making a diagnosis strategy based on model of the DPF.With the help of a sensor,obtaining the measured data of pressure drop real-time.And then using the data to make a comparison and analysis with a prediction result in the ECU.In the experimental data and simulation data of the fault model,I made classified validation on diagnosis strategy which has been put forward in the end.The results show that the diagnosis strategy can effectively distinguish the state of the DPF and has feasibility and usefulness in some degree based on model proposed in this research.