Research On In-Cylinder Flow Optimization And Combustion Of EIVC Un-Throttled Gasoline Engine

The fully hydraulic variable valve system(FHVVS)can achieve continuous changes in the maximum lift of the intake valve,the opening duration and the valve phase.Installing the mechanism on the port-injection gasoline engine can cancel the throttle and realize the early closing of the intake valve.Under medium and small loads,the un-throttled gasoline engine can avoid throttle loss,reduce pumping loss,and improve fuel economy.However,the premature closing of the intake valve results in slower combustion rate and lower combustion heat release rate.In order to improve this phenomenon,this paper studies the influence of in-cylinder tumble flow on the combustion performance of un-throttled gasoline engine.(1)Install the FHVVS mechanism on the Chery SQRE4T15B gasoline engine,which can be improved into a non-throttle gasoline engine with early closing of the intake valve,perform bench tests,and build the corresponding one-dimensional and three-dimensional simulation models.Compare the working process of the original engine and the un-throttled gasoline engine with early closing of the intake valve under the working condition of 2000r/min and BMEP of 0.26 MPa.The results show that the combustion rate of the un-throttled gasoline engine is slow,the heat release rate is lower,and the CA50 is delayed.The analysis of the flow field during the compression process of the intake air in the cylinder reveals that the exhaust gas return flow of the non-throttle gasoline engine is reduced,resulting in a slow fuel evaporation rate.At the same time,the tumble motion in the cylinder is greatly weakened due to the early closing of the intake valve.The gas flow rate becomes slower,the turbulent kinetic energy is weaker,and the flame propagation speed is slower,resulting in deterioration of combustion.(2)Study the change of the flow field in the cylinder of a non-throttle gasoline engine with speed and load,select low,medium,and high speeds and three different intake valve lift curves corresponding to different loads,and analyze 9 working conditions.The results show that under the same valve lift curve,the airflow movement in the cylinder increases as the speed increases.The turbulent kinetic energy near the spark plug at the ignition time of 1000 r/min is increased by 543.8%when the lift curve 5 is used at 5000 r/min.At a speed of 1000 r/min,the turbulent kinetic energy in the cylinder at the ignition point of the lift curve 8 is increased by 58.8%compared with the lift curve 5.(3)In order to improve the problem of combustion deterioration in low-and medium-speed and low-load non-throttle gasoline engines,it is necessary to enhance the airflow movement in the cylinder and propose a variable tumble flow mechanism.It achieves the purpose of enhancing the tumble ratio by changing the flow distribution on both sides of the valve.The performance of the mechanism was evaluated through the airway steady-state test,and the steady-state calculation was performed using STAR-CCM+.The results show that as the lift increases,the difference in flow through both sides of the valve is greater,and the tumble flow ratio in the cylinder gradually increases.When the valve lift is increased to 3mm,the tumble ratio is greatly improved,and the throttle loss is also increased to a certain extent.Therefore,when the variable tumble flow mechanism is used under small lift,the flow coefficient decreases and the intensity of tumble flow in the cylinder increases.(4)Further study the influence of the structure size of the variable tumble flow mechanism on the tumble flow movement,including the height of the deflector from the upper side of the intake duct,the length of the deflector,and the angle between the deflector and the axis of the intake valve.The factors are optimized and calculated,and the structural parameters corresponding to the highest turbulent kinetic energy at the moment of ignition are selected.The effect of the optimal scheme of the variable tumble mechanism on the combustion performance is studied.The results show that after the variable tumble mechanism is installed,the turbulent kinetic energy near the spark plug at the moment of ignition is increased by 31.7%,and the maximum explosion pressure and heat release rate are increased by 52.1%and 82.2%,respectively.The flame propagation rate increased significantly,and the after burning period was reduced from 50.5℃A to 14.9℃A.In summary,the variable tumble flow mechanism can improve the combustion of the EIVC un-throttled gasoline engine at small loads at low and medium speeds.