New visualization technique using photochromism for transport process of lubricating oil around the engine pistol

The internal combustion engine has undergone tremendous revolution since their initial development. The attempts to improve the thermal efficiency of these engines rely on the ability to reduce the friction losses within the engines. Some of the presently used methods in reducing friction include the use of low-tension piston rings and low-viscosity engine oils. However, these methods usually require high oil consumption. To address these issues, several studies have been presented to investigate the oil transport phenomena around the piston based on the visualization of the oil film between the piston surface and the cylinder.

Herein, Tokai University graduate students: Ikkei Kitajima, Kazaki Kuratsuji and led by Professor Akihiko Azetsu from the Department of Mechanical Engineering proposed a new visualization technique for investigating the transport of a lubricating oil film. The technique is based on photochromism, a light-induced reversible color change due to chemical reaction. The researchers wanted to explore the dominant route for oil of oil consumption in internal combustion engines. The paper is published in International Journal of Engine Research.

Briefly, the forward and reverse reactions of photochromism were denoted as coloring and fading reactions respectively. A spiropyran, whose molecular structure and absorption spectrum changes with exposure to ultraviolet light, was used as a photochromic dye owing to is good coloring characteristics. Additionally, ester oil was used as a suitable solvent for spiropyran while the color quantity was quantified based on absorbance calculated from images before and after coloring. Finally, the effects of temperature on fading reactions and ultraviolet light intensity on the coloring reaction were examined.

The oil film thickness was observed to be proportional to the color density. The flow visualization was possible due to slow changes in the color density at room temperature. Consequently, a first-order reaction model was used to quantitatively express the effect of the ultraviolet light intensity on the absorbance. An increase in the energy density of the ultraviolet light increased the absorbance value. On the other hand, Arrhenius plot was used to quantify the temperature dependence of the fading reaction rate of spiropyran and ester oil solution. The concept was validated by successfully being used to visualize the movement of an oil film in the piston land of a single-cylinder 4-stroke optical engine.

In summary, Professor Akihiko Azetsu and colleagues reports a novel visualization technique for oil films based on the photochromism principle. The feasibility of the proposed visualization technique was verified through flow visualization of oil film in optical engines. Based on the findings, the study has been selected by Advances in Engineering selection team as a promising technique with great potential in the investigation of the dominant route and phenomenon involving oil consumption in engines. This is because the approach is suitable for application in a wide variety of engine operating conditions.