Thermal Radiation Correlation Imaging Method Of Cylinder Head Inner Wall For Defect Detection

As an important part of the engine,the cylinder head is prone to sag,cracking and other thermal fatigue damage under long-term high temperature and high pressure working environment,which seriously affects the stability of engine operation.Therefore,it is essential to detect the damage on the inner wall of cylinder head.Most of the existing detection techniques are combined with the temperature field simulated by finite element to analyze the fatigue damage of the inner wall stress of cylinder head,but there is a certain gap between the finite element results and the actual situation due to the lack of reasonable basis for the setting of thermal boundary and thermal deformation conditions.Therefore,how to efficiently and intuitively present the image of the inner wall of cylinder head plate is very important to improve the intuitive reliability of the detection scheme.As an indirect imaging method,correlation imaging does not need to directly detect the measured object.It calculates the image information of the object by using two parts of the light field signal and the modulation signal after the interaction between the light field and the object.This imaging method has strong anti-interference and is suitable for high temperature and high pressure and other harsh environments.It can improve the efficiency and reliability of defect detection by applying it to the inner wall detection of cylinder head bottom plate.In this paper,the thermal field detection of the inner wall of the cylinder head and the total thermal energy detection of the outer wall are carried out,and then the image of the inner wall of the cylinder head is obtained by the correlation imaging technology,which provides convenience for the intuitive detection and analysis of the inner wall of the cylinder head when the engine is working.The main research contents are as follows:（1）The thermal field detection of the inner wall of the cylinder head: First,the thermal field change law and characteristics of the inner wall of the cylinder head are analyzed,and the thermocouple test system is determined to be used for detection;Then,the inner wall of the cylinder head is divided into regions,grids and measuring points according to the gradient of thermal field.Finally,the distribution matrix of the heat field in the inner wall of the cylinder head was obtained by interpolation supplement to the detection data of the measuring points.Experimental verification shows that the inner wall thermal field distribution matrix is more accurate under multi-scale region division.（2）The detection of the total heat energy of the outer wall of the cylinder head bottom plate: First,determine the use of patch type thermistor device to detect the heat energy of the outer wall of the cylinder head;Then,the patch type thermistor is distributed in the outer wall area of the bottom plate to collect the total heat energy of the outer wall.Finally,the heat field of the inner wall of the cylinder head and the total heat energy of the outer wall are collected and recorded synchronously through the synchronization system to complete the collection of associated data in the associated imaging.（3）Proposed correlation imaging method of cylinder head inner wall: Based on the heat transfer law and correlation imaging theory of cylinder head bottom plate,the correlation between the heat field distribution of the inner wall of cylinder head bottom plate,the heat transmission function of the inner wall of cylinder head bottom plate and the total energy value of the outer wall of cylinder head bottom plate was studied,the correlation imaging model of the inner wall of cylinder head was established,and the imaging method of the inner wall of cylinder head based on correlation imaging was proposed.Finally,the validity of the correlation imaging method in cylinder head inner wall detection was verified by the objective and visual analysis of reconstructed images.