Study On Improvement Of Numerical Method Of Heat Transfer In Turbocharged Direct Injection Gasoline Engine

As the fuel consumption requirement and emission regulation are becoming stricter over time,downsize、turbocharged & direct injection、high thermal efficiency had became the trends for engine development.The higher power density of the engine increases the thermal load,so the original numerical heat transfer method for naturally aspirated engines is no longer applicable.It is urgent to improve the original calculation method,improve the calculation accuracy,to meet the needs of engine development.In this paper,a 1.5L turbocharged direct injection gasoline engine is taken as the evaluation object.Firstly,the piston and engine body are measured by using the hardness plug and thermocouple.The test results provide the boundary and calibration basis for the subsequent numerical simulation of engine heat transfer.Based on the original calculation method,use Star CCM+ software to completed the fluid-solid coupling analysis.The gas boundary of the combustion chamber and the integrated exhaust manifold wall are coupled at the same time.Through the comparison with the test results,it is found that the maximum relative deviation of temperature calculation is 13.6%,and the relative deviation of heat dissipation is 10%,and the calculation precision cannot meet the engineering application requirements.In order to adapt to the characteristics of the turbocharged direct injection gasoline engine,the calculation method is improved in this paper.The influence of heat transfer between piston and cylinder and boiling heat transfer is further considered.In order to accurately obtain piston-cylinder heat transfer boundary condition,the heat transfer model of piston is established,and a transient cooling model of PCJ(piston cooling jet)is constructed based on VOF multi-phase model.The heat transfer between piston and liner is obtained by coupling the PCJ cooling boundary which is calibrated based on the experimental data of piston temperature field.The heat transfer boundary conditions of piston and combustion are superimposed by Matlab code.Thus,the influence of heat transfer between piston and cylinder is comprehensively considered.For the boiling model,it is integrated into Star CCM+ via User Function of Star CCM+.The customized boiling model contains four sub-models: Hsu model,Chen model,dry-spot model and Bui&Dhir model.The effect of boiling on the temperature field is considered by applying the total boiling heat transfer to the interface of fluid and solid.In this paper,by improving the original numerical heat transfer method,the maximum relative deviation of temperature calculation was improved from 13.6% of the original method to 5.7%.The relative deviation of heat loss calculation was improved from 10% to 6.1%.The calculation accuracy has been improved obviously to meet the needs of engineering application.