Research On The Optimization Of Intake Port Of A Non-road Gasoline Engine Based On CFD

With increasingly stringent emission regulations,engines are developing towards high thermal efficiency,low pollutant emission and high fuel economy.The combustion quality of the in-cylinder mixture directly affects the thermal efficiency of the engine.As an important part of the engine intake system,the inlet structural parameters of the intake port play an important role in improving the in-cylinder charging coefficient and the mixture uniformity.Therefore,by deeply optimizing the structure of the engine intake port,the air flow in the cylinder can be effectively enhanced,and the combustion quality of the mixture can be improved,so as to provide a certain basis for improving the power,economy and emission performance of the engine.The main contents and conclusions of this paper are as follows:(1)A geometric model for steady flow calculation of non-road gasoline engine intake ports was established,and a grid model was also verified by grid independence.The intake port performance of the original engine was analyzed by using flow coefficient,tumble ratio and flow field distribution characteristics as the evaluation indexes of intake port performance.The results show that there are some problems in the intake port of the original engine,such as small flow coefficient,weak air movement in the cylinder and unreasonable pressure gradient transition,which are not conducive to the combustion of the mixture in the cylinder and lead to the increase of pollutant emissions.(2)The performance parameters of the intake port were improved by optimizing the geometrical structure of the valve guide rod seat ring.Based on the changing rule of the crosssectional area of the intake port,the influencing factors of pressure gradient distribution in the intake port were analyzed.The circular arc design of the vertical wall surface of the valve guide rod seat ring improved the uniformity of the cross-sectional area transition,reduced the throttle effect of the flow resistance.The results show that both the flow coefficient and the tumble ratio of the optimized port structure have been significantly improved,among which the flow coefficient under medium and low valve lift has increased about 3%,and the tumble ratio under high valve lift has increased about 5%.(3)Based on CAESES software,the structural parameters of inlet port offset angle,outlet port offset angle and outlet port boss position were optimized.Sobol sampling was carried out at 20 levels of the three structural parameters,and CAESES software coupling Star CCM+ software was used for steady-state simulation computation.The results show that the flow coefficient increases with the increase of inlet port offset angle ?,and the tumble ratio fluctuates up and down.With the increase of outlet port offset angle ?,the flow coefficient increases slightly within a certain range,and the tumble ratio increases first and then decreases when ? is smaller.The flow coefficient decreases and the tumble ratio increases gradually with the increase of outlet port boss floating distance ?.Based on the above factors,three optimal levels were selected to carried out the orthogonal experiment design.Through the mean and extreme difference analysis,?,?,? are determined as 9.375°,6.875°and 1.375 mm respectively.The flow coefficient and tumble ratio of intake port increased by 7.7% and 17.2% respectively.(4)A grid model applicable to transient computation was established,and the transient simulation of the air movement in the cylinder before and after the optimization was carried out,and the variation rules of the average turbulent kinetic energy and average tumble ratio in the cylinder before and after the optimization were analyzed.The results show that the transient model can reflect the air movement well.The average turbulent kinetic energy increases by 11.2% and the average tumble ratio increases by 13.8%.It can be seen that the optimized intake port enhances the air movement in the cylinder,which is conducive to improving the combustion quality in the cylinder and reducing the emission of pollutants Thus,the research provides a basis for the optimal design of gasoline engine ports.