Research On Bionic Drag Reduction And Swirl Enhancement In Twin-Intake Port Of Diesel Engine

Reducing energy consumption and improving environmental pollution has always been the focus of scientific and technological development.Efficient and clean combustion of internal combustion engine is of great significance to achieve environmental protection.At present,vehicle diesel engines are mainly high-speed direct-injection diesel engine,which rely on compression ignition in high-pressure and high-temperature environment in the cylinder.The mixture formation time is short and the temporal and spatial distribution is extremely uneven.Direct injection combustion chamber is divided into open and semi open.Semi-open combustion chamber is mainly used for small and medium-sized high-speed diesel engines.The semi-open combustion chamber needs strong intake swirl to provide energy for the formation of mixture.It is important to improve intake swirl and improve air flow in cylinder,which can enhance the turbulence intensity of mixture,make oil-gas mixing more uniform,accelerate flame propagation speed and burn more fully.The strength of the intake swirl mainly depends on the design of the intake port.In general,increasing the strength of the intake swirl will cause a decrease in the flow coefficient.The flow coefficient is a parameter for evaluating the perfectness of the engine intake stroke,which is closely related to the resistance of the intake system.Therefore,it is of great significance to improve the combustion efficiency and reduce fuel consumption of the diesel engines by improving the flow characteristics of the intake port to reduce the intake resistance and enhance the intake swirl and the flow coefficient.Due to the extensive and effective application of bionic technology in fluid drag reduction,this study employs the surface morphology of sharkskin,birds and insect as bionic prototype and optimizes the elements morphology and size.Bionic microstructures of spaced straight grooves and pits are designed to construct the efficiency-enhancing functional surfaces of the twin-intake diesel engines.To further enhance the intake swirl,this paper investigated the effect of installing different guide vanes at the front of the intake on the flow characteristics of the intake system.Finally,the more efficient functional surface intake tract is combined with the guide vanes to further enhance the intake vortex.The main research contents and conclusions are as follows:1)According to the bionic prototype,four types bionic functional surfaces with different sizes were extracted and optimized,and the drag reduction characteristics were analyzed by CFD numerical simulation.The results show that the functional surface can increase the thickness of the boundary layer and the velocity of the near wall,and reduce the velocity gradient of the boundary layer to reduce the resistance.The thickness of the boundary layer decreases with the increase of velocity,there are differences in the thickness of the boundary layer of different functional surfaces,and the turbulent pulsation in the boundary layer is large.The size optimization range of spaced straight groove and recess structure is studied,and the results show that the drag reduction rate of spaced straight groove functional surface increases with the increase of groove width and then decreases with the increase of groove depth at the same groove depth;the drag reduction rate of recess functional surface increases with the decrease of groove width at the same depth and decreases with the increase of groove depth at the same width.2)The optimized bionic microstructure of grooves and pits are constructed a synergistic functional surface and applied for the twin-intake diesel engines to study its flow characteristics.A comprehensive test of 2 levels and 3 factors is conducted to determine 9groups of different twin-intake combination schemes.The flow characteristics of twin-intake with different bionic functional surface is analyzed by steady flow bench test.Computational fluid dynamics(CFD)simulation is used to analyze the flow field distribution in the intake process of different combination ports.Taking the visualized optical engine as the test platform,the turbulent motion in the cylinder of diesel engine with optimized twin-intake combined bionic functional surfaces is studied with the help of particle image velocity(PIV),which is verified with CFD.The drag reduction and swirl enhancement effects of intake port on each bionic functional surface are obtained.3)Research on the flow characteristics of the intake port with the guide vanes.The interference research on the intake of the double intake port shows that the installation of the guide device at the front end of the helical intake port has a good comprehensive effect.Nine groups of guide vane schemes with different parameters are determined by uniform design method and added to the front end of helical port to enhance intake swirl.Through the steady flow bench test,the flow characteristics are analyzed and CFD calculation method is used to study the distribution of physical quantities such as velocity,vorticity and turbulence intensity in cylinder under different valve lift.The optimized schemes are compared and analyzed by PIV test technology.The results show that the installation of guide vanes at the front end of the intake tract has a better improvement effect on the flow characteristics of the intake system.When the height of the guide vane is 6mm,the length is65 mm and the angle is 24°,the comprehensive improvement effect is better compared with the base model.After optimizing the guide vane parameters,it is found that the swirl ratio effect is better when the aspect ratio of the guide vane is 6.5?24.5 and the angle is 16.2 ?30.5° at the maximum valve lift.4)Research on the flow characteristics of combination scheme with the addition of guide vanes at the front end of the bionic functional surface intake.Combining bionic functional surface intake with guide vane.Consists of 12 different combinations.Through the steady flow test,the flow characteristics of each combination scheme are studied.And the flow field distribution of each combination scheme is compared with base model.The results show that after adding the guide vanes to the front end of the bionic functional surface intake port,the fluctuation range of the flow coefficient of combination scheme is between-4.3% and 1.7%,and the increase of the swirl ratio is between 16.1% and 38.6%.Among them,when the tangential and helical intake port are both grooved bionic functional surfaces,and the front end is equipped with guide vanes with a height of 6mm,a length of65 mm,and an angle of 24°,the overall effect is better.The swirl ratio increased by 37.438%,and the flow coefficient increased by 0.221%.