| In the face of the increasingly stringent requirements of energy conservation and emission reduction,diesel emission control technology has become a research hotspot in domestic and foreign industries.Combined using diesel oxidation catalyst(DOC)and catalyzed diesel particulate filter(CDPF)can not only guarantee the CDPF continuous and reliable work,reduce the PM emissions,but also can effectively reduce the HC and CO emissions so that plays an important role in meeting the increasingly stringent emission regulations.The flow uniformity of DOC+CDPF package structure and CDPF carrier material and structural parameters have a significant impact on the capture and regeneration performance of soot particles.Therefore,optimizing packaging structure and exploring carrier materials and structural parameters have great theoretical significance and engineering value on the impact of capture and regeneration characteristics.Based on a DOC+CDPF package structure,optimizes the front-end rectification device to provide a more uniform flow field distribution for regeneration experiments.The research shows that: the original scheme rectifier has small aperture and small number,resulting in low internal flow velocity,large pressure drop,and speed uniformity to be improved.In the three optimized schemes,the opening ratio and diameter increase,the uniformity is improved,the flow velocity increases,and the pressure drop value decreases.The velocity uniformity of scheme C is 0.962,and the pressure drop value decreases the most than that of the original scheme.The flow field simulation is carried out for the direct and box type of the National VI post-processing technology route(DOC+CDPF+SCR).The simulation results show that: The flow velocity in the channel with a small diameter is large,and the flow field distribution at the rectifier and the mixer is complicated.Due to the different structure,the speed uniformity of the box structure is better than that of the straight structure.The straight system has more complex rectifier mixers,resulting in a pressure drop of 2KPa in the straight system and the turbulence intensity is also greater than that of the box structure.Considering the speed uniformity,pressure drop,turbulent kinetic energy and the space occupied,the box package structure has certain advantages.Based on the DOC+CDPF test bench for the D30 diesel engine installation country VI postprocessing device,,and the equilibrium temperature test of cordierite and silicon carbide CDPF and the pressure drop and regeneration test under different carbon loadings were carried out.The test shows that cordierite and silicon carbide CDPF have almost the same effect on the engine's power and emission under different carbon loadings;the carrier material has no effect on the regeneration equilibrium temperature,and the cordierite and silicon carbide coated with the same catalyst are coated.The regenerative equilibrium temperature of CDPF is 310 °C;as the carbon loading increases,the pressure drop of cordierite and silicon carbide CDPF increases,and the difference between medium and low speed is small,and the difference between high speed and speed is large.Cordierite CDPF has a lower pressure drop than silicon carbide CDPF.At 2400 r/min,100% load and different carbon loads,the pressure drop of CDPF reaches the maximum value.With the increase of carbon load,the pressure drop of cordierite CDPF increases faster than that of silicon carbide CDPF.The regeneration test shows that during the regeneration process,the axial temperature rises continuously from the point of arrival,and the maximum temperature appears near the outlet end;the radial temperature center is high and the circumference is low.The maximum temperature gradient within the carrier during regeneration is at the edge of the carrier near the exit end.In the test,due to the rectification of the rectifier,the temperature distribution of the regeneration inlet is relatively uniform.The maximum temperature gradient of cordierite CDPF is less than that of silicon carbide CDPF,and the larger the carbon load,the larger the maximum temperature gradient.The higher the regeneration inlet temperature,the higher the maximum temperature generated during regeneration and the greater the maximum temperature gradient.The regeneration inlet temperature has a great influence on the regeneration efficiency.The regeneration efficiency is less than 50% at 500 °C,the regeneration efficiency is 100% at 600 °C,the regeneration inlet temperature is 500 °C,and the cordierite CDPF reaches the maximum temperature at 6 g/L.The gradient of 8.8 ° C / cm,the maximum temperature gradient of silicon carbide CDPF is 17.36 ° C / cm;and the regeneration inlet temperature of 600 ° C,the maximum temperature gradient of cordierite CDPF increased to 9.9 ° C / cm.The simulation results show that during the soot capture process,as the exhaust flow increases,the pressure drop of the carrier increases and the capture efficiency decreases.Under the same exhaust flow rate,the smaller the wall aperture,the lower the mesh number and the lower the porosity,the greater the collection efficiency.When the exhaust flow rate is lower than 300Kg/h,the pressure drop value is not much different.After 300Kg/h,the pressure drop value of low mesh and low porosity is higher than that of high mesh and high porosity under the same exhaust flow rate.Big.Under the same exhaust flow rate,the larger the carbon load,the larger the pressure drop value,and the most obvious increase of 200 mesh cordierite CDPF.During the capture of soot,as the exhaust temperature increases,the carrier pressure increases.When there is no carbon load,the pressure value increases uniformly with the discharge temperature.When there is carbon load,the pressure increases at a uniform rate before the exhaust gas temperature is 300 °C.After 300 °C,the pressure accelerates and the cordierite CDPF increases with temperature.The rate is greater than that of silicon carbide CDPF.During the regeneration of soot,the pressure first increases and then decreases,and the pressure value at 300 mesh is the smallest.During the 400 s regeneration time,the higher the mesh number,the more the oxidized soot particles are.The maximum temperature during regeneration does not change with the number of meshes,but the lower the mesh,the shorter the time to reach the highest temperature.During the regeneration process,the wall thickness of the carrier directly affects the pressure value during regeneration.The larger the wall thickness,the greater the pressure and the highest pressure during regeneration,but the time taken to reach the maximum temperature increases.During the 400 s regeneration time,the wall thickness is greatly oxidized.The soot particles are of high quality.The larger the initial carbon load,the larger the pressure value during regeneration,and the more soot particles oxidized during the 400 s regeneration time,the higher the regeneration rate.During the regeneration process,the regeneration of soot does not start at the same time.During the regeneration,the soot is oxidized and burned from the front end to the rear end with the heat release and exhaust direction of the oxidation interface,and the temperature increases from the front end to the rear end of the carrier with time.The axial temperature gradually increases from the inlet end to the outlet end,and the radial temperature gradually decreases from the center to the periphery.The maximum temperature gradient occurs at the edge near the exit end with a maximum temperature gradient of 21 ° C / cm.During the regeneration process,the soot particles are evenly distributed,and the changes in the mesh size and wall thickness do not affect the temperature distribution in the carrier,but have an effect on the time at which the maximum temperature gradient occurs.The larger the mesh and wall thickness,the maximum temperature gradient.The later it appears.The initial carbon loading affects the maximum temperature and maximum temperature gradient.The larger the initial carbon loading,the higher the maximum temperature and the larger the maximum temperature gradient. |
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