Development And Optimization Of High-efficient Turbocharged SI Engine Combustion System Based On Simulation

In order to balance the surplus of gasoline consumption and reduce the increasing cost of medium and heavy-duty diesel engines in the near future,a high thermal efficiency medium-load SI turbocharged gasoline engine is developed based on numerical simulation.In order to improve the engine body strength,making it more responsive to the-increased compression ratio,the combustion system of the high-enhanced gasoline engine is developed.Firstly,model of the original diesel engine based on the GT-Power platform is built and calibrated based on the test data to verify the accuracy of it.Then,with reference to the development goal of the gasoline engine and the relevant competing product data,the key components and combustion system are optimized and re-built.Finally,the non-predictive baseline model of the initial turbocharged gasoline engine is built based on above.According to the goal of external engine characteristics,the key indicators of the turbocharger required for the gasoline engine are back-calculated.Then,the data is embedded in the turbocharger model for the whole machine simulation.The results show that the dynamic performance is lower than the goal at low speed section but meets the dynamic goal.The exhaust temperature before turbine is within the design specifications at all speeds.In order to make full use of the high-enhanced body of the diesel engine,the compression ratio of the developed gasoline engine is optimized considering the peak pressure of the original diesel engine.The compression ratio of the gasoline engine is selected to be 13.8.Subsequently,with the goal of improving the power of low-speed and the goal of improving the thermal efficiency of medium-high-speed,a multi-objective optimization model of the intake and exhaust pipelines is built by the coupling platform of GT-Power and mode FRONTIER.The optimization results show that the thermal efficiency at three speed cases is improved,especially,the improvement of thermal efficiency at the high speed section is the largest（5.24%）,but the middle and low speed sections are less.At the same time,the torques of rated speed and the low speed are improved,while the medium speed is improved less.Further analysis and optimization of the intake and exhaust phases enables the dynamics of low-speed to meet the development goal;and improve the thermal efficiency of medium and high speeds while meeting the dynamic development goals.Based on the work above,the thermal efficiency is chosen as the main optimization goal.The initial ignition advance angle model of the gasoline engine is built based on the experimental rule and the related physical model.Then the ignition advance angle model is coupled with the prediction model in GT-Power and calibrated according to the non-predictive model.Thereby,the initial fuel consumption map of the engine and the minimum fuel consumption condition of the engine(2000r·min^-1,70%load)is obtained.At the best working condition,the effects of the intake valve closing,external intercooled EGR and increasing the opening of the wastegate valve on fuel economy are studied systematically.The results shows that all of three strategies above can decrease the fuel consumption rate;the reduction of the fuel consumption rate is the largest when using intercooled EGR.Finally,a multi-objective optimization-coupling platform is built for the strategy above.And a multi-objective optimization is conducted for each parameter.After optimization,the specific fuel consumption can be reduced up to 9.5 g·（k W·h）^-1.