Clarification of Fuel and Oil Flow Behaviour Around the Piston Rings of Internal Combustion Engines: Visualization of Oil and Fuel Behaviour by Photochromism in Gasoline Engine Under Transient Operating Conditions

Photochromism is a reversible color change phenomenon based on chemical reactions caused by light illumination. In the present study, this technique is applied to visualize the lubricating oil and fuel around the piston rings in the gasoline engine. The oil film was colored with a UV laser and photographed by synchronizing the shutter of a high-speed camera with a flashlight. The color density was evaluated as a value of absorbance, calculated from images taken at two different wavelengths and two different times before and after the coloration. The authors performed photochromism visualization experiments in an engine under motored operation. However, using photochromic dyes that are robust to temperature changes makes it possible to visualize the engine under fired operation. The experiment was conducted mainly by switching to the motored operation for a fixed time between the fired operations. The visualization results showed that during the motored operation, lubricating oil colored on the piston land was transported over the piston ring to the top of the piston. The time variation of the absorbance distribution on the land was quantitatively evaluated. Furthermore, the visualized results by photochromism were compared with the results of oil emission measurement based on mass spectrometry supported by aerosol particle measurement. A time delay was confirmed for the oil in the second land to reach the top of the piston by comparison with experimental results of oil emission measurement. It was also confirmed that photochromism allows visualization of fuel movement in the engine.