Research On Seal Life Extension Of Piston Rod Cap Seal In Stirling Engine

The performance and service life of piston rod seal directly determine the efficiency and power of Stirling engine.Piston rod sealing device is the core component of Stirling engine.The performance of the device directly affects the efficiency and power of the of Stirling engine.Cap seal is the key part of Sterling engine piston rod sealing device,which working condition involve high pressure,high speed,high temperature and oil-free lubrication,and should achieve low power consumption and long life.Therefore,material selection and structural design of cap seal are particularly important.However,cap seal has problem of low sealing performance and short service life,which seriously affected the reliability,limit and stability of Stirling engine.It has a great significance to the application and development of the Stirling engine to carry out the design of the life extension of the cap seal.The aim of this dissertation is to extend sealing life of Stirling engine piston rod cap seal.According to progressive relation and theoretical studies combined with experiment research,the material of long-life wear-resistant seals was developed firstly.Then,the influence of service conditions on the friction and wear properties of material was studied,and the material friction and wear model was established.Based on the obtained parameters and models,a numerical simulation method of seal under multi-field coupling was established and the change rule of seal performance and life was explored.And then,the influence of structural parameters on performance and service life of seals was studied and structure parameters of cap seal were optimized.Finally,the experimental verification of the conclusions was carried out.The main content of this research are introduced below:?1?The main failure modes of cap seal were analyzed,including excessive wear failure,thermal accumulation failure and breakage failure.Four schemes of polytetrafluoroethylene composites reinforced by PPS,nano-alumina,nano-zirconia and nano-zirconia were prepared.The basic mechanical,thermal and tribological properties of the composites and the reinforcing mechanism of the reinforcing phase were researched.It was found that nanoparticle could effectively improve the hardness,thermal conductivity and tribological properties of materials,and played a mechanical strengthening role in friction transfer film and promoted its chemical adsorption.A fuzzy evaluation method bases on semi-trapezoid subordinate function and analytic hierarchy process for material properties was proposed for evaluated the sealing material.Results show that the best sealing material was PTFE-PPS/nano-ZrO₂composite.?2?A high temperature friction and wear device was developed.The influence of working conditions on the friction coefficient,wear rate,wear mechanism and self-lubrication characteristics of sealing materials was studied.The results show that the increase of load and speed enhanced the self-lubrication of the material,but further increase will destroy the friction transfer of the material,which w ould significantly reduce the friction and wear properties of the material.An improved grey wolf algorithm based was proposed to optimize the parameters of least squares support vector machine,and according to the classical theory and experimental results,the models of friction coefficient and wear rate of materials was obtained.?3?Based on the sealing function and relevant criteria,the structure of cap seal was designed.A numerical simulation method of thermal-stress-wear coupling of cap seal was established based on the finite element technique and the modified Archard wear model,and the material parameters and models were embedded in the calculation process.The operation process of the seal was simulated.Structural stress,contact property,temperature rise and wear marks under different condition during static,reciprocating and wear process were analyzed.It was found that the contact pressure of the seal under static pressure has the same change rule with the structural stress,sealing failure was prone to occur during outward stroke,stress concentration occurs at the bottom of the seal with wear increment.The effect of pressure on sealing performance was obvious than reciprocating speed.?4?The influence of structural parameters of seal on performance and service life during wear was studied.In order to realize the optimization target of getting minimum drop of maximum contact pressure in seal face and maximum seal life,the key structure parameters of cap seal were optimized by applying an optimization strategy based on central composite design response test and non-dominated sorting genetic algorithm-II.Results show that the service life and comprehensive performance of the optimized seal were improved.?5?A test platform for piston rod seal of Stirling engine and wear surface detection instrument was established,and the accuracy of the results of life extension design was verified.The wear of the developed material and designed structure of seal in this paper was significantly lower than the original seal.The measured value of C-ring wear trace was consistent with that of numerical simulation.The sealing pressure drop was significantly lower after optimized.The leakage in the sealing assembly with cap seal was obviously reduced by 30%.This research will provide important experimental basis and theoretical support for the design,application and further research of the piston rod seal of Stirling engine.