| In order to meet more stringent emission standards,diesel engines must adopt not only advanced interior purification technology,but also complex engine-out purification technology.Diesel particulate filter(DPF)is the most efficient and convenient technology for engine-out purification,and its capture efficiency is over 90%.Precise judgment of DPF regeneration time and dynamic and precise control of regeneration process are the key factors to improve regeneration efficiency.Non-uniformity of flow distribution during the capture stage will lead to excessive wall temperature peak value and temperature gradient during regeneration,resulting in thermal stress and damaging DPF.Therefore,studying the factors affecting DPF capture performance and regeneration efficiency is of great significance for improving the performance and reliability of DPF post-treatment.Taking the post-treatment system of high-pressure common rail diesel engine for road as the research object.A DPF 3D simulation model is established by combining numerical simulation with bench test.The velocity distribution、particle deposition distribution and pressure drop loss law are studied during the DPF capture stage.The combustion effect of particles,wall temperature distribution and pressure drop loss law are studied during the DPF regeneration.Based on the orthogonal experimental design,the influence of many factors on capture and regeneration was analyzed.The results are as follows:(1)Simulation analysis of soot loading.The average velocity in the DPF channels decreases first and then increases along the axial direction,and decreases along the radial direction.With the capture,the average velocity at different locations increases rapidly,then decreases gradually.The deposition of particles showed a trend of "concave" along the axial direction of DPF,with a small change along the radial direction.The pressure drop loss of DPF increases with soot loading.(2)Analysis of factors affecting the capture process.Comparing the effects of expansion tube,CPSI,mass flow rate and exhaust temperature on the trapping characteristics,the average flow velocity increases with the increase of expansion tube,CPSI,mass flow rate and exhaust temperature.The radial distribution uniformity of average velocity and particle deposition deteriorated with the increase of the expansion tube.The axial distribution uniformity of average velocity and particle deposition deteriorated with the increase of the CPSI.The axial and radial distribution uniformity of average velocity and particle deposition decreases with the increase of the mass flow rate.The pressure drop loss of DPF increases with the increase of the mass flow rate and the exhaust temperature.But expansion tube has little effect on the pressure drop loss.When the CPSI is more than 300,the pressure drop increases.When the CPSI is 200 or 300,the difference of pressure drop is not significant.(3)Simulation analysis of regeneration.The soot deposition content decreases sharply in the initial stage and slowly in the later stage of combustion.The soot content decreases rapidly in the initial and later stages of combustion along the axial direction,and larger gradient of soot content decreased in the initial stage of combustion,and later stage was gentle.The soot content decreases at the initial and later stages of combustion along the radial direction,with a larger gradient in the initial stage and a gentle gradient in the later stage.During the preheating stage,the solid temperature rises sharply.At the initial stage of combustion,the solid temperature continues to rise and reaches a peak value then decreases sharply,and decreases gently in the later stage of combustion.The maximum solid temperature increases gradually along the axial direction,but changes slightly along the radial direction.In the later stage of combustion,the solid temperature in both the axial and radial directions tends to be consistent.The pressure drop loss increases sharply during the preheating stage.The pressure drop loss decreases sharply with the combustion of many particles,and eventually tends to be slow.(4)Analysis of factors affecting the regeneration process.Comparing the influence of soot distribution type on regeneration characteristics,the residual particles of "concave distribution" is 0.88g/l,and the regeneration efficiency is higher.The maximum temperature in DPF channels end of gradually decreasing type " is the highest,The maximum temperature difference between the front and end DPF channels of the gradually increasing type" is the largest.the peak pressure drop loss of the "uniform distribution type" is the highest.Comparing the influence of inlet temperature and exhaust oxygen content on regeneration characteristics,the soot combustion rate increases with the increase of inlet temperature and exhaust oxygen content at the initial stage of combustion,and slows down gradually at the later stage of combustion.The maximum solid temperature increases with the increase of inlet temperature and oxygen content.The time of maximum solid temperature arrival is shortened,and the thermal shock is increased.The top pressure drop loss increases with the increase of inlet temperature and decreases with the increase of oxygen content.However,when inlet temperature is higher than 580℃,the top pressure drop loss does not increase.Comparing the influence of initial particle on regeneration process,the soot combustion rate increases with the increase of initial particle during the initial stage of combustion,and soot residues gradually converge during the later stage.The maximum solid temperature at axial different positions increases with the increase of initial particle,and the thermal shock also increases.The peak pressure drop loss increases with the increase of initial particle,and the pressure drop loss tends to be converge during the later stage of combustion.(5)Sensitivity analysis of factors affecting capture and regeneration stage based on orthogonal experimental design.From the orthogonal test results of the expansion tube,CPSI and mass flow rate multi-factors in the DPF capture stage,it is known that exhaust mass flow rate is primary factor affecting the uniformity of axial/radial flow velocity distribution and maximum pressure drop loss.The uniformity of axial soot deposition distribution is most affected by CPSI.The uniformity of radial particle deposition distribution is most affected by expansion tube.From the orthogonal test results of the inlet temperature initial soot load and exhaust oxygen content multi-factors in DPF regeneration stage,it can be seen that the most important factor affecting the residual soot combustion and the peak solid temperature is inlet temperature,while the most important factor affecting the peak pressure drop loss is initial soot load.Therefore,the inlet temperature control is particularly important in DPF regeneration process. |
PDF Full Text Request