According to the energy distribution of typical automobiles measured by EPA, the engine friction loss accounts for 4.5% of the total energy loss caused by friction in automobiles, while the fault caused by friction accounts for 47.2% of the total engine faults[2]。It can be seen that lubricating oil plays an important role in the performance of the engine. Therefore, by obtaining lubricating oil film data, we can know the working condition and working life of the engine in some aspects.

In the 1990s, mass spectrometer and gas chromatograph were used to determine the composition of lubricating oil in Western countries. In the 21st century, western developed countries began to apply the quality monitoring technology of lubricating oil on vehicles. Some models have been installed on board as a general configuration, which ensures the quality replacement of vehicle lubricants[3]。In the field of lubricating oil monitoring technology, China started relatively late, but still made remarkable achievements in some areas. In 1977, China began to study ferrography technology, which is currently in the leading position in the world in research results and application fields. However, the application of lubricant testing technology in automobiles in China has not been popularized, and the method of "changing oil on schedule" or "changing oil according to mileage" is still used.

In the research of engine lubricating oil testing, the conventional testing method is to use different monitoring devices and instruments to measure the performance changes of lubricating oil and particle information, and to analyze the quality of lubricating oil. Then the purpose of timely replacement of lubricating oil, the reduction of friction fault, and the service life of engine are achieved, which is on the basis of energy saving.

For example, Zhang Hu, a student of Taiyuan University of Technology, studys that friction lubrication state identification and fault monitoring of internal combustion engine based on acoustic emission (AE) technology [4]. In addition, the lubricant quality analysis system based on multi-sensor information fusion technology designed by Li Xiwu of Jilin University[5], which measured and analyzed the dielectric constant, transmission and scattering value of infrared light of the lubricant, and the iron abrasive content value measured by magnetic permeability method and ultrasonic method. Then analyzing the data to obtain the state parameters of the lubricant.

This graduation thesis accomplish the spectral simulation and film thickness algorithm design by introducing and applying spectral reflection method, and carries out spectral experiments[6-10].Then measuring the thickness and optical constants of lubricating oil film on engine inner wall[11-15]. Furthermore, the wear condition of engine inner wall, the quality and quantity of lubricating oil can be analyzed to judge the working life of engine and the adjustment requirement of lubricating oil, to monitor and analyze of engine operation, improve the working environment of engine. And achieving the purpose of improving the reliability and durability of engine operation. Spectral reflection measurement system has simple structure, convenient measurement, low cost, high efficiency, good seismic performance and strong robustness. The combination of algorithm simulation and sample experiment makes the detection result more reliable.

（1）Understand the working characteristics and state of engine lubricating oil, and the principle and characteristics of thin film measurement by optical method.

（2）Learn the operation of MATLAB, select the appropriate dispersion model and design the algorithm. According to the working characteristics of engine lubricating oil, the range of oil film parameters is selected to carry out spectral simulation. The oil film thickness and optical constants are obtained by image fitting combined with optimization algorith.

（3）Design and manufactured the oil film samples. Carrying out spectral experiments in the laboratory to obtain oil film thickness data, and analyze data to draw relevant conclusion

2.2 The technical scheme and measures

（1）Technical scheme

Fig. 1. flow chart of technical scheme

（2）Measures

After reading and absorbing the information, using MATLAB software and optical knowledge to complete the spectral simulation and film thickness algorithm. Then obtaining the thickness and optical constants of reflected beam and oil film. After that, the oil film samples were prepared for spectral experiments, and the experimental data of the lubricating oil film were obtained. The data is analyzed and processed, and obtaining the relevant conclusions of improving the engine performance. Finally, using AutoCAD to draw engineering drawings.

[11]Seung-Woo Kim, Gee-Hong Kim. Thickness-profile measurement of transparent thin-film layers by white-light scanning interferometry[J]. APPLIED OPTICS, 1999,38(28): 5968-5973.

[12]Ernesto G. Birgin, Ivan E. Chambouleyron, Jos′e Mario Mart′#305;nez, Sergio D. Ventura. Estimation of optical parameters of very thin films[J]. Applied Numerical Mathematics, 2003, 47(2):109-119.

[13]Ricardo Andrade, Ernesto G. Birgin, Ivan Chambouleyron, José Mario Martínez, Sergio D. Ventura5. Estimation of the thickness and the optical parameters of several stacked thin films using optimization[J]. APPLIED OPTICS ,2008,47(28):5208-5220.

[14]Kai Wu, Cheng-Chung Lee, Neal J. Brock, Brad Kimbrough. Multilayer thin-film inspection through measurements of reflection coefficients [J].OPTICS LETTERS, 2011, 36(16): 3269-3271.

[15] Daesuk Kim, Soohyun Kim, Hong Jin Kong et al. Thin-film thickness profile measurement using a Mirau-type low-coherence interferometer[J]. Measurement Science and Technology,2013,24:075002.