The Research On Control Strategy Of Low Pressure EGR System Of GDI Gasoline Engine

The automobile industry occupies a large part of the total global oil consumption,and the emission of automobile exhaust increases the global greenhouse gas rise.Drawing on the laws of the United States,Europe and Japan,China has formulated the fifth stage of fuel consumption regulations with a limit of 4L/100 km,and also formulated the most stringent National Six emission regulations.The above regulations have brought great challenges to the automotive industry.In order to meet the standards of the above regulations,the major automotive companies have proposed different on-board and offboard control strategies for the engine,so as not to be eliminated by the automotive industry,and to reduce fuel consumption.The control strategies are: low-pressure cooling exhaust gas recirculation(EGR)system technology,continuous variable lift technology and turbocharged miniaturization technology.The technologies for reducing emissions are divided into in-machine and out-of-machine technologies.The following are low-pressure cooling EGR technology,Gasoline Direct Injection(GDI),lean nitrogen oxide trappin g technology,and gasoline particulate trapping technology.Considering the cost of each technology and the benefits brought by the technology in the later period,low-pressure cooling EGR technology is the first choice to reduce fuel consumption and emiss ions.The low-pressure cooling EGR system draws gas from the rear of the catalyst while introducing EGR gas to the front of the compressor.To achieve the goal of reducing fuel consumption and emissions by this technology,not only the relationship between hardware such as EGR valve,mixing valve,cooler,etc.needs to be matched,but also a precise control strategy is needed to control the change of EGR rate.The difficulty of low-pressure EGR system control is that due to the long pipeline,the introduction of EGR gas is delayed,the pressure difference across the EGR valve is low,and it is not easy to introduce a large flow of EGR gas.In order to study the control strategy of the low-pressure cooling EGR system,this article is based on the 2.0L turbocharged direct injection gasoline engine provided by a research institute,and the low-pressure cooling EGR system is installed and studied.Under steady-state conditions,change the value of the EGR rate to study changes in engine fuel economy,power,emissions,and combustion performance.Analyze the test results,and then summarize the following control strategies:(1)The EGR function must be disabled under the conditions of engine coolant and intake air temperature that are too high or too low,warm-up enrichment,and parts protection.(2)Under the condition of low and medium load of the engine at low speed,with the increase of EGR rate,the specific fuel consumption is improved,the specific fuel consumption is reduced by 5%,the power performance is not changed much,and the emission performance is well improved.Under load conditions,the ignition advance angle is closer to the top dead center,and the combustion phase is improved.Under partial load,the pressure difference across the EGR valve is small,so a mixing valve needs to be installed to improve the flow ability of the EGR gas.Based on the above performance,under the conditions of small load and large load,the EGR gas introduced does not exceed 14%,and under the condition of medium load,24% EGR gas can be introduced.Under the conditions of medium and small loads,the opening of the mixing valve is basically closed.(3)Under the condition of high speed and large load,as the EGR rate increases,the power of the engine decreases,with a decrease of 23%.Under heavy load conditions,in order to maintain the power of the engine,the EGR rate introduced should be limited to 15%.According to the above test results and control strategy,the Simulink software is used to establish the model of the low-pressure cooling EGR system,and the correction coefficient of the model is calibrated on the bench to optimize the model,and finally the test data on the bench is imported into the model In simulation,the error between the simulation result and the test value is within 5%.