Research On Low Pressure Exhaust Gas Recirculation Of Gasoline Engine In Simulation And Experiment

Energy conservation and emission reduction are the essential topics of Auto engineering and have attracted lots of concern in recent years.How to reduce the consumption of petroleum resources and decrease the emission had become an important research direction in the researching of internal combustion engine.The use of the new technologies and methods are the keys to reduce fuel consumption and refine the emission in the process of developing high efficiency and clean exhaust engine.With the development of downsized engine,the compression ratio and power to volume ratio become higher,and the fuel economy becomes better.But there are also some problems brought by downsized engine,such as high combustion temperature,strong knock tendency,high NOx emission,etc.Some methods must be used to avoid the disadvantages in fuel economy and emission when researching and developing downsized engine.Exhaust gas recirculation(EGR)was proposed as a technology in internal combustion engine in last century.After years of mechanism research and experimental verification,EGR has been proved can reduce engine fuel consumption and improve the NOx and particle emission.So far,EGR is widely used in diesel engines in order to decreasing NOx emission,but the examples of EGR used in gasoline engines are rare.This paper is based on practical engineering,has investigated into the apply of Low Pressure Exhaust Gas Recirculation(LP-EGR)in downsized gasoline engine with both simulation and experiment methods.The targets of this research are exploring the LP-EGR system's potential at improving fuel economy and ability of knock suppression when applied on gasoline engine.In this study,a one dimensional model of a 1.5L turbocharged engine with LP-EGR system was established in GT-Power and calibrated with experimental data collected from engine bench test.In order to control the EGR ratio to reach the target value,a control strategy with both EGR valve and mix valve was designed in simulation process.And EGR ratio is precisely controlled to the target value by this strategy.According to the calculate results,LP-EGR is not recommended in low speed low load operating points because of the internal EGR is dominating.In part load operating points,optimum EGR rate increased with the increasing of engine load,and the optimum EGR rate can reach to 20% when engine is working in high load.In the low speed of the wide open throttle(WOT)operating points,the optimum EGR rate is limited to 15% because of the low turbo efficiency.In the high speed of the WOT operating points,the optimum EGR rate can reach to 20%.In the calculated results,the fuel decrease rate of the part load operating points is between 2% to 5%,and the fuel decrease rate of the WOT operating points is between 7% to12%.The results of the one dimensional model are inputted into a vehicle model in order to get the fuel consumption of the vehicle in both New European Driving Cycle(NEDC)and World wide harmonized Light Vehicle Test Procedure(WLTP)applied with LP-EGR system.The results indicate that LP-EGR can decrease vehicle fuel consumption 2%~4% in NEDC test cycle,and 4%~5% in WLTC test cycle.Besides,another one dimensional model is established with the system of air-fuel ratio controlling the exhausted gas temperature at fuel enrichment operating points.Results show that LP-EGR can reduce exhaust gas temperature and eliminate the degree of fuel enrichment.The brake specific fuel consumption(BSFC)of the fuel enrichment operating points can be reduced by 10%~20%.Engine bench test data with LP-EGR system is researched and analyzed in this paper.The methods and operating points of the test is briefly introduced.According to the test data,the LP-EGR system's potential at reducing the fuel consumption is analyzed and the results are approximate with the simulation results.From the test data,LP-EGR system can reduce fuel consumption 2%~5% in part load operating points;10% in high load operating points;15%~20% in WOT operating points.Combustion phase parameter CA50 and Spark Timing in test data are discussed and used to analyze the LP-EGR system's ability of suppression knock.