Mechanism And Characteristics Research Of Plateau Environment DOC And CDPF

As the internal combustion engine becomes more and more widely used and its number keeps increasing,the impact of it on environmental pollution is becoming more and more serious.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.Considering to the huge plateau area in China,and adding to the diesel engine emission requirement at plateau condition to meet China-six emission regulations,which will brings more challenges to achieve efficient and low-emission diesel engine and its post-processing development.In this paper,based on the plateau environment of the kunming area,the engine platform of the plateau was built,and the the research model is D19 common rail diesel engine.The research shows that with the increasing of engine speed and torque,the engine intake flow and power are also increasing.Compared with the fuel consumption,the oil consumption economic zone is mainly concentrated in medium speed.The supercharger has better efficiency at high speed.The high density of the non-transparent smoke is high at low speed and middle/high load condition.NOx emission increases with increasing speed and torque.The concentration of exhaust oxygen increases with the increase of the rotational speed,while decreases with the increase of the load.The CO₂ change trend is reversed,CO decreases first and then increases with the increase of rotational speed.In the low and middle speed,the exhaust temperature decreases and then increases with the increase of the speed.At medium and high speeds,the trend is reversed.According to the experimental study on the external characteristics of the post-processing system in different modes,the intake flow,torque and power are all decreased using after reprocessing device,especially the DOC+CDPF scheme decresed obviously.Three after reprocessing device to the non-transparent smoke are relatively high,the non-transparent smoke of back-end DOC is higher,NO emissions decresed.While using CDPF and DOC+CDPF could get zero CO emissions at back-end site,and a dramatic rise of CO₂ emissions in low and middle speed.At low RPM,the temperature at the back-end of the CDPF and DOC+CDPF was significantly increased.At the middle and high speed,the back-end temperature began to be lower than the front-end temperature,the front and end temperature of DOC+CDPF becme stablized.With the increase of the rotational speed,the pressure difference between the front and back end of the CDPF was continuously increased,and at the high speed,the end pressure difference of the DOC+CDPF scheme was increased and then gradually decreased.The different number of DOC has little effect on the engine power,economy and emission characteristic.The DOC+CDPF post-processing system stability test research shows that:at 2000 r/min,2500 r/min and 3000 r/min 100%load,along with the stability test cycle condition,the engine air intake flow,torque,power and fuel consumption relative to the original machine hours declined slightly,and began stablized after the third cycle.The air burn ratio is gradually increasing.Engine the non-transparent smoke and CO emissions still tend to be zero.After the stability test,the reprocessing unit still maintains high purification efficiency.In terms of the overall stability test cycle test,the changes of the temperature and pressure difference between the front and back end of the DOC and CDPF are consistent.Compared with the stability test of the original machine,the engine performance has decreased after the stability test.After two stages of the test cycle,DOC and CDPF outside the engine characteristic test of the trend of temperature and pressure difference before and after changes are consistent,capture efficiency and regeneration efficiency still maintained a higher level.In this paper,based on the one dimensional GT-Power model and three dimensional AVL Fire model,to match the VGT D19 high pressure common rail diesel engine as the research model,build the one-dimensional simulation model and the thermodynamic machine DOC+CDPF 3-d simulation model,conduct the DOC+CDPF internal flow field analysis,and numerical simulation study of injection strategy coupling with EGR on diesel engine combustion process and the influence of the CDPF regeneration performance.The fuel injection strategy coupling with EGR on diesel engine combustion process and regeneration performance study shows that:when the CDPF gas passed current stabilizer,distribution of velocity field in the DOC carrier is relatively uniform,the carrier of the velocity vector distribution more uniform.With the main injection timing advancing,BSFC first fall then rise,exhaust temperature reduced,exhaust flow rate and oxygen concentration change is small,NO exhaust increased,CDPF regeneration rate decreases gradually,particles residual volume,pressure drop and the CDPF outlet NO₂ increases at the same time.With the increase of EGR rate,BSFC and exhaust temperature rise,exhaust flow,exhaust oxygen concentration,and NO emission are reduced at the same time.When the main injection timing was late and increasing EGR rate,the regeneration rate of CDPF increased first then decreased,and the residual amount of particulate matter increased slightly after the first drop.When the main injection timing is relatively late,the increase of fuel injection pressure results in a significant reduction in BSFC and exhaust temperature.In the early stage of the main injection timing,BSFC is increased rapidly due to the increase of the injection pressure.In addition,with the injection pressure increased,the exhaust flow rate and oxygen concentration change are small,NO emission increased,CDPF regeneration rate decreased,residual volume,pressure drop and particle CDPF outlet NO₂ emissions increased at the same time.In general,compared with the injection pressure,the main injection timing has more influence on CDPF regeneration process.The intake flow increased,and NO_x was lower than the single injection in a certain range by using post injection.With the spraying time delay or fuel injection amount decreasing,the fuel release heat of the post injection is gradually reduced,the peak heat rate of the main spray is gradually increased,the ignition phase advanced and the heat release duration is prolonged.When the EGR rate was 25%,the post spraying time was delayed and the fuel injection quantity increased,the effective thermal efficiency,heat transfer loss rate and friction loss rate are all decreased,while the exhaust loss rate increased.When the post injection time is relatively early and increase fuel injection,will increase the exhaust temperature,while the NOx and exhaust oxygen concentration will decrease.When the post injection time is relatively late and increase fuel injection will lower the exhaust temperature,while the oxygen concentration in the exhaust will increase.The residual particles of CDPF were increased when post injection time delayed and the post injection fuel amount is relatively small.While the residual particles of CDPF decreased when post injection time delayed and the post injection fuel amount is relatively large.When the post injection time delayed,the CDPF pressure drop and the outlet NO₂ emission increased.The regenerative efficiency of CDPF can be improved effectively by using rational post injection strategy compared with single injection strategy.