Optimization Research Of Intake And Combustion Process In Turbocharged Downsizing SI Engine

In order to meet more and more stringent emission regulations,the degree of downsizing and boosting of engines improves,leading to gradual increase of the thermal load and the engine knock tendency in the cylinder,resulting in higher requirements about the performance of the engine combustion system.In this paper,a small downsizing gasoline engine with three cylinders is top-down designed on the basis of 1.3TGDI gasoline engine platform of one native company.Combustion system optimization is a key research in the design,in which structure of intake port and chamber of combustion system are focused to be optimized.With Computational Fluid Dynamics(CFD in short)method,the combustion system of the new generation engine is optimized,saving the cost and the time of development.The main contents are as follows:Firstly,a new case of intake port is optimized based on the original intake port.New optimization case of intake port is finally determined by increasing the radius of the intake port's short turn and the cross section area of the intake short and uplifting the septum location..Based on that intake port,core box is made and test of the box is conducted.Experimental data shows that the average flow coefficient increases by 10.50%,and the tumble ratio reaches 1.658,meeting the expected development requirements.Secondly,3-dimenosional transient simulation is conducted with the foundation case of the combustion system.The foundation case of the combustion system includes the initial intake port and the original chamber.Results show that there is strong tumble movement in the foundation case of the combustion system.The peak transient tumble ratio in cylinder is 2.75,the peak mean turbulence kinetic energy in cylinder is 247.13 m2/s2,and the peak mean turbulence kinetic energy in the spherical area(?6mm)of the spark plug is 311.91m2/s2.The flame front of the foundation combustion system spreads very rapidly.But the center of the turbulence kinetic energy is close to the intake valve,leading to burning close to the intake valve,increasing the tendency of engine knocking.Thirdly,the chamber is optimized by modifying the depth and position of valve masking and removing GDI injector boss in the chamber.Five optimization cases are composed by the optimized chambers and the optimization case of the intake port.Results show that the fifth optimized combustion system is the best among these five cases.The peak transient tumble ratio in cylinder is 2.09 and the peak mean turbulence kinetic energy in cylinder is 189.29 m2/s2,and the peak mean turbulence kinetic energy in the spherical area(?6mm)of the spark plug is 302.85m2/s2.The center of the turbulent kinetic energy is at the cylinder center.The flame front of the fifth optimized case spreads very fast and uniformly and the quality of combustion is good.So,the fifth optimized combustion system is considered to be the final case to be manufactured as the new generation prototype of gasoline engine.Finally,first generation prototype of the original and the optimization case are manufactured and tested.Results show that the prototype of the gasoline engine of the optimization case meets the design requirements of the power and economy performance.The calculated value of accumulated heat release is similar to the experiment,which proves the 3-dimenosional transient simulation used in this paper is accessible.