Study On The Effects Of Ash Deposition On DPF And Diesel Engine Performance

In this paper,the preliminary test of the D30 TCI diesel engine with DOC and DPF has been carried out,which provides the basic test data for the construction of the model and its reliability verification,and the test of the DPF has been carried out and performed destructive active regeneration experiments on the DPF.The models of diesel engine post-processing system and diesel engine complete model with post-processing system are built respectively by using one-dimensional thermodynamic software,and the basic performance parameters of China 6 DPF are optimized and selected under the condition of ash deposition,the effect of ash and DPF on the performance of diesel engine was also studied,and the matching DPF was selected.A model of DPF with ash was built by using 3D CFD software to study the effect of ash on the pressure and velocity of airflow in the duct,and the law of particle migration and deposition in the duct was also studied.The results show that the higher the ash distribution coefficient,the more the layer ash distributed on the wall,the lower the airflow area and the higher the DPF pressure drop;at the same time,the increase of the ash layer on the wall is beneficial to the improvement of the ash layer trapping effect on the particles,so the trapping efficiency increases with the ash distribution coefficient.Increasing the number and the ratio of carriers can improve the ash capacity under the same DPF pressure drop.At present,the ratio of inlet and outlet aperture is 1.25 ～ 1.35,and the ratio of inlet and outlet aperture is 1.2 ～ 1.5,which are commonly used in engineering DPF.The optimized DPF was tested in the China 6 transient cycle test and the destructive active regeneration test was carried out.The results show that the optimized 300 mesh asymmetrical cell structure carrier can meet the emission limit requirement of China 6when the DPF ratio is 1.2.Incomplete regeneration of DPF may affect the migration and deposition of soot,and multiple incomplete regenerations may lead to excessive local carbon load and increase the risk of uncontrolled regeneration.The results show that the outlet pressure decreases uniformly from front to back,and the air velocity increases continuously when the ash content is removed from the outlet,and the outlet pressure decreases gradually when the ash content is removed from the outlet until the exit is at full capacity.The larger the ash distribution coefficient,the larger the pressure difference between inlet and outlet,the larger the energy loss and the smaller the air outlet velocity.The ash loading reduces the effective filter length but improves the collection efficiency of the wall layer,which is beneficial to the whole collection efficiency of the DPF.Under the condition of the same content of soot and ash,the central pressure of the DPF with asymmetric pore structure drops more near the end,the layer ash is thinner,the energy loss is smaller,and the velocity of the airflow in the outlet duct is larger.The results show that:(1)when the pressure drop of the DPF is 25 k Pa,the pressure drop of the diesel engine can be used as a criterion to trigger the active regeneration;when the ash distribution coefficient is 0.2,0.3,0.4 and 0.5,the soot load triggering active regeneration is 7.56 g/L,5.32 g/L,3 g/L and 0.89 g/L respectively.when the ash distribution coefficient is greater than 0.5,even when the DPF is not loaded with soot,it remains in an active regeneration state.(2)the regeneration frequency is defined as 1when the carbon load is 6 g/L and the pressure drop is 25 k Pa,the regeneration frequency is less than 1 when the ash distribution coefficient is 0.2,and the carbon load has exceeded the safe active regeneration soot load(6 g/L),the regeneration frequency with ash distribution coefficient of 0.3 is close to the ideal regeneration frequency.(3)when the aperture ratio of the inlet and outlet of the DPF is 1.3,the ash content has the least influence on the power and economy of the diesel engine.Increasing the number of carriers is beneficial to reducing the pressure drop of the DPF.(4)the power and economy of a turbocharged diesel engine are decreased when a DPF is installed at low altitude,but the power and economy of a turbocharged diesel engine with a DPF are increased as the altitude rises.Under low-speed condition,although the NOx emission of diesel engine decreases with the increase of altitude,the decrease is not big;under middle and high-speed condition,the air-fuel ratio of diesel engine decreases greatly with the increase of altitude,although the temperature of combustion gas in the cylinder increases sharply,however,under the condition of low oxygen concentration,the NOx emission of a turbocharged diesel engine with DPF at high altitude decreases rapidly,although the NOx emission increases slightly.