Development of an apparatus to evaluate oil deterioration and oil life based on a new principle for environmental conservation

Abstract

From the viewpoint of environmental conservation, a reduction in waste is required. The development of long-life oil has been energetically proposed as a method to reduce waste in lubricants. However, it would be economical and effective for users to be able to know the precise deterioration status of lubricants so that the materials could be completely used up before disposal. The development of super long-life oils has been advanced in automotive engine oils, which hold a large proportion of the lubricant market. Automotive manufacturers recommend that automotive engine oils be changed periodically or at a set mileage because there are a number of engine oils in the market and they are used for individual automobiles. However, the reality is that this oil-change interval depends on the end users’ judgement. Thus, engine oils are often changed needlessly and improperly. Therefore, the authors aimed to simply and precisely evaluate the oil deterioration status with a very small amount of engine oil to ease the burden on users. Generally, in addition to deterioration and decomposition of engine oil itself, there is contamination of substances such as unburned fuel and soot generated from the combustion. In either case, the change of electrical property due to increase of polar substance in engine oil can be predicted. Thus, the relationship between the measured frequency and the dielectric characteristics with a very small amount of oil was examined using a comb-shaped electrode. As a result, it was found that the permittivity was increased as the oil was deteriorated and the frequency characteristics differed between the oils used in a diesel engine and a gasoline engine. In order to investigate the status of basicity component, which is added in engine oil to protect it from a bad influence due to the formation and contamination of acidic compound, the acidity of the engine oils was directly measured with acidic ion sensitivity sensor for pH measurement (pH-ISFET). It was found that the acidity clearly increases as the oil is deteriorated. Also, it is possible to simply and accurately evaluate the engine oil deterioration status using a very small amount of oil by measuring its permittivity frequency characteristics with a comb-shaped electrode and its acidity with pH-ISFET.