Structural Optimization Design Of Limiting Current Oxygen Sensor

Limiting current oxygen sensor has advantages of wide range and no need for reference gases.It is often used as an oxygen-sensitive component in areas such as aerospace,and automotive industries.Considering the particularity of the high-temperature working environment of this type of sensor,domestic and foreign institutions are devoted to improving its reliability of performance under high-temperature conditions.This thesis combines numerical simulation of the multi-field coupling and optimization methods to conduct research on structural optimization of the oxygen sensor,aims to improve its thermodynamic performance and reduce the response time,and provides design reference for manufacturing highly reliable and sensitive oxygen sensor.Firstly,by analyzing the working principle of the limiting current oxygen sensor,the key factors influencing the oxygen sensor performance are identified.Based on this,for the thermodynamic performance,a mathematical model of the multi-constraint,multi-objective optimization is established with the structural size of the oxygen sensor and the shape of the heating electrode as the optimization objects,for the response time,a mathematical model of the multi-constraint,single-objective optimization is established.Method of the orthogonal experimental sensitivity analysis applicable to the optimization model of the multi-variable and the COBYLA algorithm applicable to the optimization model of the non-linear constraint are further analyzed,which provide support for the subsequent structural optimization of the oxygen sensor.Secondly,according to the actual working conditions of the oxygen sensor,the numerical simulation of the multi-field coupling is applied to performance analysis and lays the foundation for structural optimization.Based on determining the basic form and size of the oxygen sensor structure,the numerical simulation of the electricity-heat-force coupling of the oxygen sensor is carried out with the finite element software COMSOL,the influence of heating voltage on the oxygen sensor’s steady-state temperature and the influence of temperature on the oxygen sensor’s stress distribution are analyzed,It is clear that there is significant stress concentration in the sensitive substrate layer under high-temperature working conditions,and there is some room for optimization.The influence of different methods of the voltage application on the time of cold boot is analyzed,and the conclusion is drawn that the method of the step voltage can significantly reduce the time of cold boot of the oxygen sensor.The response time of the oxygen sensor when the external oxygen concentration changes is analyzed by the simulation of oxygen diffusion,and it is found that the smaller the difference in oxygen concentration between the external environment and the cavity,the shorter the response time.Finally,aiming to address the shortcomings of the oxygen sensor structure revealed in the simulation of the multi-field coupling,with stress reduction as the main optimization objective,structural optimization of the oxygen sensor is carried out.Combined with the established parameterized model of the oxygen sensor,the sensitivity of the thermodynamic performance to structural size parameters is analyzed with the orthogonal experiment.It is clearly identified that the cavity thickness,sensitive substrate thickness,and other structural size parameters should be used as design variables in the optimization model.And then the optimization of the structural size is finished with the COBYLA algorithm.The average temperature of the sensitive substrate is improved and the maximum stress of solid electrolyte and electrode materials is decreased respectively by 43.85 MPa and 35.77 MPa,with a decrease of17.04% and 12.23%,which enhance the thermodynamic performance of the oxygen sensor.According to five heating electrode shapes designed,based on the comparative analysis of heat-force coupling simulation,it is determined that the optimal shape of the heating electrode of the oxygen sensor for the thermodynamic performance is the serpentine shape.By combining the constraint functions related to range and power consumption in the optimization model of the response time,the aperture of the diffusion hole is reasonably increased,and the goal of reducing the response time is achieved.