Measurement of Oil Film Thickness Using Photochromism Visualization Method and Application to Journal Bearings

In recent years, interest in energy issues has been growing up. In order to reduce friction losses in engines, it is important to understand the lubrication condition of the oil film on sliding parts. Since the conventional methods such as LIF and PIV have limitations, we are researching a visualization method using photochromism that can simultaneously measure oil film thickness and flow. Photochromism is a reversible reaction that occurs when ultraviolet light is irradiated onto a solution containing a dye, causing a change in molecular structure and resulting in a shift in the absorption spectrum. In our laboratory, we quantify the degree of coloration using absorbance. In the calibration experiment using transmitted light, a photochromic solution was filled between a plano-convex lens with a radius of curvature of 184 mm and a glass plate to create an oil film of known thickness. The solution used was 0.05 % mass concentration diarylethene ester oil, and coloring was performed using ultraviolet light with a wavelength of 255 nm every 30 minutes for a total of 180 minutes. For imaging, images of the sample before and after coloring were captured using transmitted light from an LED bar light source installed beneath the sample. The experimental results confirmed that the absorbance at an oil film thickness of 0 μm could be calibrated to a value close to zero, but it was found that the appropriate coloring time varied depending on the oil film thickness. In the future, we plan to adapt this method to a journal bearing test device with an eccentric mechanism and perform oil film thickness measurements using colored oil and uncolored oil.