Research On Pressure Drop And Regeneration Characteristics Of A New Type Of Catalytic Diesel Engine Silicon Carbide DPF

The stringent China VI emission standards,in addition to the extremely low Particulate Matter(PM)limits,also increase the Particulate Number(PN)limit requirements.The combination of Diesel Oxidation Catalyst(DOC)and Catalytic Diesel Particulate Filter(CDPF)not only ensures continuous and reliable operation of CDPF,but also reduces particulate matter emissions by more than 90% and simultaneously changes particle size distribution,which also effectively reduces HC and CO emissions,is recognized as one of the most effective means of reducing diesel PM and PN emissions.With the continuous operation of the diesel engine,CDPF will be blocked due to the continuous trapping of PM in the exhaust gas,resulting in increased engine exhaust back pressure and performance degradation.Therefore,CDPF needs good regenerative capacity and reliability to remove PM.It is important to study the pressure drop and regeneration characteristics of CDPF to evaluate the performance level of the support.Around the low back pressure,high trapping efficiency and regeneration of efficient and reliable technology development goals of the China VI diesel particulate filter,in this paper,the D30 diesel engine equipped with the DOC+CDPF test-bed are built,the effects of different soot loadings of CDPF on engine performance and pressure drop characteristics were tested on three different types of thin walled multi-mesh new national sic CDPF,namely low porosity symmetrical high porosity symmetric and low porosity asymmetric CDPF.The results show that,under the external characteristic conditions,when the fresh support CDPF is installed,the performance of the diesel engine is reduced,the pressure drop of the high porosity CDPF is the lowest,and the pressure drop of the low porosity asymmetric CDPF is the highest.When the low porosity asymmetric and high porosity symmetric CDPF soot loadings are 2g/L,4g/L,6g/L,7g/L,8g/L and 10g/L,the difference in diesel engine performance is small.The pressure drop increases as the speed and airspeed increase.Under different rotational speeds and airspeeds,the CDPF pressure drop increases with the increase of soot loadings.When the soot loading is low,such as 2g/L and 4g/L,the pore pressure drop is dominant,and the low porosity asymmetric pressure drop is high than the high-porosity symmetric CDPF;when the soot loading is higher than 4g/L,the soot layer is dominant,the low porosity asymmetric CDPF pressure drop is lower than the high porosity symmetry CDPF,and the higher the speed,the greater the difference between the two supports and it is more obvious when the soot loading is 8g/L and 10g/L.When the speed is 1000r/min,the low porosity asymmetric and high porosity symmetric CDPF supports have no pressure drop intersection,and the 1200r/min pressure drop intersection corresponds to a soot loading of 3.2g/L,and the corresponding soot loading at the pressure drop intersection points at the rest rotating speeds was within 4.5~5g/L with a small difference.At a rotational speed of 2000r/min,the test found that the regeneration balance temperature of the high porosity symmetric CDPF was 310?.The study of airflow and particle motion for the DPF microscopic channel model shows that,the airflow velocity in the DPF inlet channel increases first and then decreases in the axial direction,decreases to zero at the end of the channel,and the velocity in the outlet channel gradually increases from zero,maximum at the end of the channel.The static pressure in the inlet channel first decreases and then increases in the axial direction,and the static pressure in the outlet channel decreases in the axial direction.The low porosity and high porosity symmetric channel velocity and static pressure change trend and size are basically the same,and the asymmetric channel velocity and pressure drop are higher.The particle velocity gradually decreases to zero along the axial direction of the channel,and the particles show a significant distribution unevenness in the channel before and after.The velocity and concentration of the particles in the asymmetric channel are significantly higher than those in the symmetric channel.For different structures CDPF,the regeneration process of different soot loadings under different inlet temperature conditions was studied by burner regeneration(idle condition)and fuel injection combustion catalytic regeneration(steady state condition).The results show that:(1)Based on the high porosity symmetric CDPF,fuel injection assisted catalytic regeneration was used,when the CDPF inlet temperature is 500?,the CDPF internal temperature distribution trends during the regeneration of soot loadings of 2g/L,4g/L,6g/L and 8g/L are consistent: the axial temperature distribution shows a higher temperature near the rear end of the CDPF.The highest regeneration temperature of different soot loadings appears at the radial middle position of the CDPF rear end;the radial temperature distribution of CDPF shows the highest temperature in the middle ring.The rule of the center temperature is the second and the outer ring temperature is the lowest.The CDPF regeneration peak temperature,maximum temperature gradient,and linear increase with the increase of soot loading,but the values are small.The regenerative pressure drop increases with the increase of soot loading,and the regeneration efficiency decreases with the increase of soot loading,which are 93.3%,45.56%,43.33% and 29.02%,respectively;(2)The method of burner regeneration,the high porosity symmetric CDPF inlet temperature was raised to 600? for regeneration.The CDPF regeneration temperature field is consistent with the inlet temperature of 500?.The regeneration efficiency at 4g/L and 6g/L soot loading is 94% and 48.4% respectively higher than 500? respectively.The highest regeneration temperature,regeneration temperature gradient and the temperature rise rate are high;(3)The low porosity asymmetric CDPF inlet temperature is raised to 600 ? for regeneration by means of fuel assisted combustion catalytic regeneration,the temperature field distributions of 4g/L,6g/L and 8g/L soot loading are consistent and uniform,and the peak temperature of regeneration in the middle of the support is the highest.The highest regeneration temperature gradient is 21.4?/cm,23.5?/cm and 25.3?/cm respectively and appears between the center and the center ring of the medium support.The highest regenerative pressure drop increases with the increase of soot loading,and the regeneration efficiency is 100%,92.78% and 88.25%,respectively,which realizes efficient and reliable regeneration,and the soot loading of safe regeneration can reach 8g/L.This performance of the CDPF support is better.The numerical simulation study of ash deposition on DPF pressure drop and regeneration characteristics shows that:(1)When there is no ash deposition in DPF,the pressure drop of asymmetric structure DPF is higher than that of symmetrical structure only when the soot loading is less than 5g/L.When there is ash deposition,the asymmetric structure DPF pressure is reduced to a symmetrical structure,and the difference is larger as the soot loading increases.When ash-free deposition,the DPF capture efficiency of the three structures is the highest,the symmetrical structure capture efficiency is higher than the asymmetric structure,the low porosity capture efficiency is higher than the high porosity;(2)The larger the proportion of wall ash layer mass to total ash mass is,and the larger DPF pressure drop is.Compared with the three structural DPFs,the ash distribution coefficient has less influence on the asymmetric CDPF pressure drop of the asymmetric structure;(3)The smaller the ash distribution coefficient is,the larger the DPF ash capacity is.Under the same limit back-pressure condition,the DPF ash capacity of asymmetric structure is much higher than that of symmetrical structure.Ash distribution coefficient 0.6 is the stable point of increasing proportion of ash capacity of asymmetric structure;(4)When the soot loading is 6g/L and the ash distribution coefficient is 1,the regeneration pressure drop of the DPF and the maximum temperature of the support increase with the ash component.The low porosity asymmetric DPF pressure drop and the support maximum temperature are the lowest.The soot regeneration rate increases with the increase of ash content,and the residual amount of soot decreases with the increase of ash content.(5)When the soot loading is 6g/L,the ash content distribution coefficient and ash content have little influence on DPF regeneration process.The radial temperature of the support is high in the center and low in the edge.The axial direction is closer to the rear end of the support and the later the peak temperature appears.The temperature distribution in different positions of the support is the highest in the center of the rear segment,followed by the center of the middle segment and the lowest in the outer ring.(6)When the soot loading is 6g/L and the ash content is 40g/L,as the ash distribution coefficient increases,the regeneration pressure drop and the maximum temperature of DPF support with different structures were decreased,the regeneration rate of soot was increased,and the amount of residual soot was reduced.The optimal ash distribution forms of DPF with three kinds of structural supports are all evenly distributed on the channel wall surface.When the ash content and ash distribution coefficient are consistent,the low porositya symmetric DPF has the best regeneration performance.