The Study Of Flow Field Characteristics And Mixing Process In A High Tumble GDI Engine

The TKE of the mixture can be increased by elevating tumble level of the GDI engine,which shortens the burning time and improves the thermal efficiency of the engine.It is one of the optimization directions of the GDI engine combustion system.In this paper,the flow field characteristics and the process of oil and gas mixing in a high-tumble GDI engine are studied from the viewpoint of simulation and experiment.The simulations were carried out by means of AVL Fire software.The simulation results were verified by various experiments.Research indicates:(1)Through the Mie scattering test and the PDI test,the penetration distance and the particle size of the constant boom spray can be obtained,and the spray calculation model can be calibrated.And the spray calculation model is applied to the in-cylinder calculation.The calculation result of the in-cylinder spray has good consistency with the in-cylinder spray pattern obtained by the backlight test.(2)The simulation results of the medium and low load conditions(cold condition)are in good agreement with the PIV experimental results,and the flow field change process can be divided into five stages: 1,backflow influence stage 2,two-side intake stage 3,one-side intake stage 4,tumble growing stage 5,tumble breaking stage.The lower intake angle and the sudden change of the throat diameter make the lower inlet passages clogged by the vortices,and the characteristics of air intake only from one side are favorable for tumble formation.(3)In the 4850 rpmWOT conditions fuel and air mixture can be well mixed on TDC,and in the 2000 rpmWOT condition it forms a rich area in the intake side on TDC;(4)There is a significant interaction between the spray and the flow field.The spray field will disturb the tumble flow in the cylinder and reduce the tumble ratio,but increase the average turbulent kinetic energy in the cylinder.Tumble will cause spray deflection,thereby reducing the spray wall impingement and concentrating the mixture on the near side.During compression stroke,the tumble center moves to the exhaust side,while the fuel droplets also to the exhaust side,promoting fuel-air mixing level.