The Simulation Study Of EGR On The Full Load Of Miller-Otto Cycle Gasoline Engine

Miller cycle has become the key technology in the use of gasoline engine for the high thermal efficiency.While the low power density of Miller cycle limits its application.Miller-Otto cycle engine has become one way to extend the application of Miller cycle.In this paper,in order to get the best BSFC(brake specific fuel consumption)of full loads,the external cooler Exhaust Gas Recirculation(EGR)was evaluated with Miller-Otto cycle.The main purpose was to provide references for developing low fuel consumption engine in vehicle widely.In this paper,the studied object was a 2.0-liter gasoline engine with Miller-Otto cycle.Firstly,the engine was tested to get the performance data and combustion data,including combustion pressure,variable valve timing and spark timing.Then the distribution of Miller cycle and Otto cycle were gotten by analyzing the test data.Then,the simulation model of this 2.0-liter gasoline engine was built based on those tested parameters of engine.The external cooler EGR was built in this model to analysis its effects under full loads.The effects of EGR in part load condition showed that EGR decreased the combustion speed and the heat release rate in fixed spark angle.The timing of heat release delayed,resulting in worse combustion.But the pumping loss became less at the same time.Thus,the fuel consumption decreased initially and then increased with the increasing EGR finally.DOE and Genetics Algorithm was adapted to get the best spark and VVT under different EGR.The results showed that EGR can decrease the heat loss and pumping loss,resulting in a higher thermal efficiency.At 2000r/min@0.2MPa,BSFC decreased 6.18 g/(kW·h)with EGR=14%.The effects of EGR in high load showed that EGR decreased the knock tendency efficiently at low speed,and then the spark timing could move forward to a better combustion phase.At high speed of high load,EGR decreased the exhaust temperature and relieved the rich fuel.As a result,the BSFC decreased prominently.At 4000r/min@1.0MPa,with EGR=14%,the BSFC decreased 11.56%.The results showed that the power became less with EGR at WOT(Wide-open throttle)condition.The effects of higher compression ratio(from 13 to 13.98)with EGR were investigated,and the results showed that thermal efficiency increased prominently in part load with the higher compression ratio.At high load,the improvement of BSFC with EGR and higher compression ratio was worse than EGR with original compression ratio.The BSFC of high compression ratio with EGR at 4000r/min@1.0MPa decreased 5%.In conclusion,it demonstrated that external cooler EGR reduced the fuel consumption of Miller-Otto cycle engine.The improvement of BSFC at part load was more prominent with EGR and a higher compression ratio.