Multi-objective Equivalence Sensitivity Analysis Of Cylinder Cap Structure Parameters Based On Dimensional

As the engine is becoming more and more high-power,the cylinder head as an important part of the engine has seriously hampered power improvement.As the cylinder head structure is more complex,and in the course of work has always been subjected to high temperature,high pressure gas erosion,valve seat breakage,preload tightening bolts,etc.,so optimize the structure of the cylinder head to reduce its highest Temperature and maximum stress become more and more necessary.At present,the optimization of the cylinder head structure with a single reduction in temperature or stress as a goal of optimization,rarely at the same time as the two as the goal of optimization,or even if there is only a simple comparison of a structural changes in temperature or stress,There is no depth to explore the relationship between.Although the measured data can reflect the real situation,but because of the high cost of the experiment,the cycle is longer and difficult to achieve.In view of the above problems,this paper takes the cylinder head of a single cylinder of diesel engine as the research object,and takes the cylinder head,the body,the valve seat ring,the cylinder cylinder,the bolt,the cylinder liner and the cooling water jacket,and uses the direct coupling method to obtain the cylinder Temperature distribution,the temperature of the test point is measured by the comparative test to prove the correctness of the temperature field.Based on the correct temperature field,the stress distribution of the cylinder head under the thermal condition,the preload condition,the burst condition and the coupling condition is calculated,and the working condition and the stress point The The influence of the three factors on the maximum temperature and the maximum stress and the sensitivity of the cooling water flow,the diameter of the pipe under the bridge of the nose and the angle of the pipe were analyzed by orthogonal test.In the multi-objective optimization,each optimization goal can be transformed into a dimensionless value by de-dimensioning.When the optimization goal is not unified,the inverse index is transformed into a positive index,and then the multi-index is transformed into a group of dimensionless Single target value to find the optimal combination.The main contents of this paper are as follows:1.Cylinder head heat-flow-solid coupling analysisThe boundary conditions of each part of the coupling analysis are determined by means of measurement and reference empirical formula or semi empirical formula.The heat transfer is difficult to be determined by the direct coupling method into the internal boundary.The temperature field of each cylinder is obtained by using the CFX software,and the correctness of the analysis is proved compared with the temperature of the experimental point.The maximum temperature of the cylinder head is found.The cylinder head temperature field is analyzed by the fluid-solid coupling analysis as the boundary condition,and the thermal stress of each part of the cylinder head is obtained under the condition of no other constraints.Considering the bolt preload and the valve The load field under the condition of the interference condition of the cylinder head and the stress field of the valve seat are considered.Considering the temperature field of the cylinder head,the bolt preload,the valve The stress of the seat ring and the pressure field under the pressure of the gas,and comprehensively analyze the stress under the above four conditions and find the maximum stress under each condition.2.Three factors on the temperature and stress of the cylinder headThis paper analyzes the influence of the three factors on the maximum temperature and the maximum stress of the cylinder head.In order to explore the influence of these three factors accurately,the five factors are composed of five factors,Three-factor five-level orthogonal test.The maximum temperature and the maximum stress of 25 groups were obtained by the sequence analysis of orthogonal test table.The influence of these three factors on the maximum temperature and maximum stress of cylinder head was obtained by data processing.Then,by means of variance analysis and F test Get the influence of these three factors in the order of magnitude.3.multi-objective dimensionless optimization of the optimal combinationThe maximum temperature and maximum stress of the cylinder head are the inverse(the smaller the value),so do not convert to positive.Assuming that the maximum temperature and the maximum stress are equal weights,the three methods of the maximum value method,the standard difference method and the mean value method are compared by derivation.The formula of the maximum value and the standard difference method is proved by the formula.There is an inequality or data variation in the dimensionality,and the mean method can reflect the law of the data well.Therefore,the mean combination of the three factors is obtained by means of the mean method.