GPF Capture And Regeneration Characteristics Of GDI Engine Under Typical Working Conditions

With the increasingly stringent emission regulations,how to effectively solve the problem of particulate emissions from GDI engines has become the focus of industry research and a hot spot in recent years.Domestic and international studies have shown that the addition of GPF to engine aftertreatment systems can effectively reduce particulate emissions.However,with the increase in engine operating hours,the soot in the GPF will continue to accumulate resulting in increased back pressure in the exhaust system,increased residual exhaust gas in the engine cylinders,and deterioration in combustion,ultimately leading to lower fuel economy and lower power.Therefore,it is of great guiding significance to study the particle trapping and regeneration characteristics of GPF under typical working conditions,such as steady state and transient state,and to clarify the trigger conditions of regeneration window for subsequent GPF regeneration control strategy.In this paper,the aftertreatment system of a GDI engine that meets the national stage 6motor vehicle emission standards is taken as the research object,the e characteristics of particle trapping and regeneration under typical working conditions such as steady-state and transient WLTC were studied and analyzed by combining bench test and simulation analysis.Firstly,the pressure drop characteristics and trapping characteristics of the unloaded GPF under steady-state conditions were tested by building a GDI engine test rig to clarify the influence of steady-state exhaust flow,temperature and oxygen concentration on the operating characteristics of the GPF and to determine the soot trapping condition point.Then,several soot trapping tests were conducted on the GPF to clarify the carbon soot trapping characteristics of this GPF.After that,the regeneration trigger window test was conducted on the GPF after the trapping was completed to study the influence law of exhaust gas temperature and oxygen content of GPF inlet on the regeneration process.The test results show that under steady-state engine conditions,the exhaust flow increases and the GPF pressure drop gradually increases as the engine speed and engine load gradually increase;at the same engine speed,the GPF pressure drop increases in a quadratic curve as the load increases.The efficiency of GPF for PM capture is mainly above 85%,and the efficiency of PN capture is concentrated in70%～80%.the deep bed filtration stage of GPF soot trapping process,the increase rate of GPF pressure drop gradually decreases;reaching the soot cake trapping stage,the increase rate of pressure drop remains unchanged,and the GPF pressure drop and soot trapping quality increase approximately linearly with time.When the GPF inlet oxygen volume percentage content is 0.15%,the GPF inlet temperature needs to reach above 490℃ to trigger the GPF regeneration.As the oxygen content of GPF inlet increases,the GPF regeneration rate gradually accelerates,but the effect of excessive oxygen content on the regeneration rate is no longer obvious.In order to further clarify the microscopic changes of instantaneous soot mass distribution and local regeneration temperature in the process of GPF soot trapping and soot regeneration,the GPF soot capture and regeneration model was built by GT-Power,and the model was calibrated by experimental data.The error between the calibrated simulation value and the experimental value is less than 10%.Based on the calibrated model,the capture and regeneration characteristics of GPF for soot were simulated and analyzed.The simulation results show that after the GPF trapping of soot is completed,the mass of deep bed soot accounts for only 6.4% of the total mass of soot,but the generated pressure drop accounts for76.8% of the total pressure drop.During GPF trapping,soot mainly accumulates at the back end of GPF.In the early stage of GPF regeneration,the regeneration rate is the fastest,the capture efficiency of GPF for soot and the soot mass in GPF decrease linearly,and the decrease rate of soot thickness in the back end of GPF is higher than that in the front end.At the later stage of GPF regeneration,the soot regeneration rate gradually decreased,the capture efficiency of soot by GPF and the decline rate of soot mass in GPF gradually decreased,and the decline rate of soot in the front end of GPF was higher than that in the back end.Subsequently,the influence of GPF inlet environment on GPF regeneration process was simulated and analyzed.The simulation results show that the exhaust flow has little effect on the regeneration time.The higher the exhaust flow is,the lower the peak temperature of the wall in the regeneration process is,the higher the peak time is,and the regeneration time decreases slightly.The inlet temperature of GPF and the oxygen content at the inlet of GPF have a great influence on the regeneration time.With the increase of the inlet temperature of GPF and the oxygen content at the inlet of GPF,the peak temperature of the wall in the GPF regeneration process gradually increases,and the peak temperature appears in advance,and the regeneration time is gradually shortened.With the increase of initial soot trapping,the peak temperature of wall temperature gradually increases in the GPF regeneration process,and the peak temperature appears almost unchanged,and the regeneration time increases slightly.Finally,based on the GPF inlet test data and the influence of oxygen content and other factors on the regeneration process under steady-state conditions,the representative WLTC cycle conditions in transient conditions were taken as typical conditions to further study the regeneration characteristics of GPF.the capture and regeneration characteristics of GPF under WLTC cycle were studied by combining simulation and experiment,and the exponential function relationship between GPF regeneration time and inlet temperature and inlet oxygen content of GPF was clarified.The results show that the total soot deposition of the GPF without soot trapping is 5.8mg under the WLTC cycle condition,and the amount of soot in the deep bed accounts for 92.9% of the total soot.There is no soot regeneration phenomenon throughout the WLTC cycle.Under the WLTC cycle,the net increase of total soot mass of GPF with initial soot trapping of 4.5g is 1.360 mg,and the soot regeneration occurs during the deceleration of ultra-high speed section,but the regeneration duration is short,and the soot regeneration is only 4.884 mg,and the regeneration effect is not obvious.It is necessary to realize the effective passive regeneration of GPF by frequent deceleration of ultra-high speed section.In the range of engine operating conditions corresponding to the WLTC cycle,the peak wall temperature in the GPF regeneration process will not exceed the limit temperature that GPF can withstand,and the exhaust flow has little effect on the GPF regeneration time.Under the same GPF regeneration time,the inlet temperature and inlet oxygen content of GPF meet a certain exponential function,and the higher the inlet temperature,the lower the inlet oxygen content demand.When the carbon load of GPF reaches the early warning of GPF regeneration,the inlet oxygen content of GPF can be reasonably controlled according to the target regeneration time and the inlet temperature of GPF under the current working condition(the secondary air injection technology of exhaust pipe or the air-fuel ratio control technology of mixed air),so as to realize the continuous,accurate and controllable regeneration of GPF.