| According to the working requirements of CC-HP（Compound Combustion-High Power）diesel engine,a new type of high power density diesel engine is proposed.The diesel engine mainly adopts the time-sharing cooperation mode of main and auxiliary double combustion chambers and double injectors.The sequential compression ignition diesel engine realizes time-sharing intervention with the help of the action of the auxiliary combustion chamber in the whole working state,so as to change the compression ratio of CC-HP diesel engine.For this time-sharing intervention mode of secondary combustion chamber,a gas switching device is set between the main and secondary combustion chambers to ensure the flexibility of high and low power density of diesel engine.In this paper,the structural analysis,thermal analysis and switching solution of gas device are studied.In view of the above problems,this paper has done a series of research,and the specific research contents are as follows:Structural design of gas switching device.In this paper,two schemes of gas switching device based on the transformation of traditional valve structure are designed,which are two-stage seal gas switching device and hydraulic auxiliary seal gas switching device.The auxiliary combustion chambers of the two device structures mainly adopt the vortex chamber with the upper hemisphere and the lower cylinder.The valve core mechanism is mainly based on the traditional valve arrangement type and modified.The valve is inverted and closely matched with the valve seat between the main and auxiliary combustion chambers to realize the on-off of gas on both sides of the main and auxiliary combustion chamber.Then the two schemes are compared.Finally,the hydraulic assisted sealing gas switching device is selected as the optimal scheme for subsequent structural optimization and characteristic analysis because of its advantages in sealing mode and driving stability.Thermal simulation calculation of gas switching device.The three-dimensional modeling software Solid Works is used to model the hydraulic auxiliary seal gas switching device,and ANSYS Workbench software is imported to analyze the overall thermodynamic characteristics of the preferred gas switching device under the overall limit working condition.The calculation results show that under the premise of the maximum combustion temperature,the maximum internal temperature of the device in the open state is 2094℃,and the maximum temperature in the closed state is 2061.5℃;Then the cylinder pressure data of CC-HP diesel engine is introduced into the stress field calculation model as the boundary condition.The calculation results show that the maximum stress of the device in the open state occurs at the connection between the valve seat and the auxiliary combustion chamber,and the maximum value is 76.18MPa;When the device is closed,the maximum stress still appears at the connection between the valve seat and the auxiliary combustion chamber,and the maximum value is101.79 MPa.The maximum deformation of the two are 0.0029 mm and 0.0079 mm respectively.The parts with high temperature,large stress and large deformation shall be corrected and parameterized for subsequent optimization.Structural optimization of gas switching device.By consulting relevant literature,the overall material of the device is selected as aluminum alloy A356.The boundary conditions of the device are set based on the de design module under the ANSYS Workbench platform,and the structure of the valve seat,which is a component with large temperature and stress,is optimized.For the valve seat structure,six input variables that can be optimized are selected,which are valve seat channel radius,channel angle,upper valve seat height,upper valve seat diameter,vertical valve seat height and lower valve seat diameter;16 groups of design points were selected by Latin hypercube sampling method.After optimization,the structural parameters correspond to the input variables P3 = 3.503 mm,P4 = 77.502 °,P5 = 9.667 mm,P6 = 54.401 mm,P7 = 15.144 mm,P8 = 66.365 mm.By improving the structural parameters of the valve seat of the device,the parameters of each part of the valve seat optimized under static conditions and the overall model of the device are obtained.Dynamic load characteristic check of gas switching device.Based on LS-Dyna module under ANSYS Workbench platform,this chapter analyzes the two types of collision between valve core and valve seat with 2Cr12 Ni Mo1W1V and 38 Cr Mo Al as the materials of valve core and valve seat at the impact speed of 1m / s.The results show that the laws of elastic rigid collision and elastic elastic collision between valve core and valve seat are roughly the same.The maximum stress at the rigid rigid collision valve core is 77.59 MPa,and the maximum impact stress of eccentric collision is147.63MPa;Under elastic impact,the maximum impact stress of valve core is53.166 MPa,and the maximum impact stress of valve seat is 39.948 MPa.Finally,when the impact speed of the valve core is within the range of 0.5m/s ～ 1m/s,the variation law of the maximum stress of the valve seat and valve core increases with the increase of the impact speed of the valve core is obtained.The dynamic load characteristics of the device are checked,and the dynamic load characteristics of the device meet the design requirements.Verification of fatigue life characteristics of gas switching device.Based on the characteristic analysis of gas switching device under statics and dynamics,the model of gas switching device after structural optimization is imported into ANSYS Workbench software again for thermal calculation and analysis.The obtained simulation data results are imported into the ANSYS life analysis module Fatigue,fitted through the S-N curve of aluminum alloy A356 material,and the fatigue life and safety factor of gas switching device are calculated by using the nominal stress method and based on palmgren miner fatigue cumulative damage theory.The results show that the overall life of the gas switching device is 1e6 times,the minimum life is 5.28e5 times,and the minimum fatigue safety factor of the device is 1.034,which is greater than 1.The verification results of fatigue life characteristics of gas switching device meet the design requirements.The hydraulic auxiliary seal gas switching device based on cc-hp architecture proposed in this paper better solves the controllable problem of gas on-off between two combustion chambers of sequential compression ignition diesel engine,realizes the flexible and variable compression ratio of sequential compression ignition diesel engine,and provides a reference for the project progress and molding of sequential compression ignition high power density diesel engine architecture. |
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