The intrinsic relationship between color variation and performances of the deteriorated aviation lubrication oil

https://doi.org/10.1016/j.jiec.2020.08.023Get rights and content

Abstract

Dose the blackened lubrication oil needs to be replaced for flying safety? Since there is very limited room for inaccurate assessment of oil quality due to strict flying safety standards, much aviation lubrication oil is disposed in advance long before their service life. More important, aircrafts still face the fatal challenges from unpredictable lubrication oil deterioration.

Color change is surely a significant signal to diagnose the quality of lubrication oils. Based on the colorimeter, the color numbers of the testing lubrication oils are measured in this paper to identify the color variation degree of the oxidized lubrication oils. Then the molecular structures of the oxidized lubrication oils are investigated to find the intrinsic relationship between the oxidation products and color numbers. Based on key performances of the oxidized oil samples, the oil quality is undoubtfully deteriorated which is coincident with the variation of color number. The color numbers of the used aviation lubrication oils could provide an alternative way to readily and quickly measure the decline degree and residual lifetime.

Graphical abstract

The phenomenon of color change is an important signal to diagnose the quality of lubrication oils.

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Introduction

The color darkening process of lubrication oils has been making sense of consumers and researchers out of confusion when makes decisions that the deteriorated oils should be replaced. Especially in the application of aviation lubrication oils, there is very limited room for the inaccurate assessment of the oil quality due to the strict flying safety standards. Many researches of the oils color number have established many interesting assessment standards about our daily life [1], [2], [3], [4]. In industrial field, the color index of transformer insulating oil has been considering the very critical in ensuring the safety as well as optimal performance of the equipment [5]. The study of oils color could also lead to some important application such as oil separators [6], ginseng [7], pepper [8] and pollen [9] drying strategy which is vital and meaningful towards our living environment.

To be the important component of effective lubrication system, the aviation lubrication oil is facing the challenge of color change which is usually related to the quality deterioration of the oils. Colorimeter has a long history for measuring the quality of the refined petroleum products since 1933 [10], [11], [12], which also suggests the color is an important parameter of aviation lubrication oils. As reported by the previous study [13], [14], [15], the molecular structure change and the properties deterioration of the oxidized oil samples are confirmed, which also result in gradually changing of the oxidized oil samples color. However, the intrinsic relationship between the oil molecules (mainly concentrated on oxidizing products [16] and antioxidants [17]) and the resulting color variation needs to be established which could develop a fast and low-cost strategy to rapidly estimate the oil quality.

On the other hand, the gas chromatography mass spectroscopy (GCMS) is powerful method to be widely applied to determine from the molecular structures [18], exhaust [19] and degradation reactions [20], [21] to oil quality [22] of the lubrication oils. Based on the conjoint analysis of GCMS and color number, the key performances of the oxidized oil samples including fully formulated aviation lubrication oils and base oils are measured to study the relationship between the color, molecular structures and performances of the oxidized oil samples. Towards a fully formulated aviation lubrication oil, the color number could be an easy-acquired oil quality signal to fast evaluate the residual life of the in-service oil after the relationship between the color, molecular structure and performances of the oxidized oil has been established.

In this paper, two base oils (Poly-α-olefin and Di-iso-octyl sebacate) and two fully formulated aviation lubrication oils (928 and 50-1-4Φ aviation lubrication oils) are oxidized in a lab designed aviation lubrication oil comparative oxidation appliance to acquire the deteriorated aviation lubrication oil specimens. The key chemical compounds are identified to predict the consumption level of antioxidants and oxidation degree of base oil. Finally, the performances of the deteriorated aviation lubrication oils are tested to build the relationship between the color number and oil quality.

Section snippets

Materials and methods

Poly-α-olefin (PAO, 3 cSt at 100 °C) and Di-iso-octyl sebacate (DIOS, 3 cSt at 100 °C) base oils are purchased from Shanghai Foxsyn Chemical Science and Technology Co. Ltd. and Shanghai Aladdin Biochemical Technology Co. Ltd., respectively. The 928 and 50-1-4Φ aviation lubrication oils are commercially available in the Henan Hangcai Science and Technology Co. Ltd. Antioxidants, including 2,6-butylated hydroxytoluene (T501), N-phenyl-1-naphthylamine (T531) and 4,4-diisooctanyldiphenylamine

The color number variation of the oxidized oil samples

The fully formulated aviation lubrication oils, 928 and 50-1-4Φ, are applied in the oxidation reactions performs in the appliance shown in Fig. 1. All of the comparative experiments of 928 and 50-1-4Φ aviation lubrication oils carried out in oil bath at the same time and temperature to produce a same oxidation condition in the typical oxidation procedure. After oxidation reaction, the color evolution of the oxidized oil specimens is very clear in Fig. 2.

Based on the SH/T 0168-1992 standard (and

Conclusions

According to the color investigation of the oxidized lubrication oil samples, we found that the color of the oxidized oil samples is mainly determined by the amount and species of antioxidants and oxidation conditions (including catalysts, temperature, time). Based on the incipient oxidation temperature, total acid number and tribological performances tests, the overall performances of the fully formulated aviation lubrication oil (T501 and Tz516 are used as antioxidants) would be remarkably

Declaration of interest statement

We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in, or the review of, the manuscript entitled “The Intrinsic Relationship Between Color Variation and Performances of the Deteriorated Aviation Lubrication Oil”.

Acknowledgments

This work was supported and funded by National Natural Science Foundation of China (Granted No. 51575525), Natural Science Foundation of Jiangsu Province (Granted No. BK20180180) and the Air Force Logistics College Youth Fund (Grant No. KY2018D031C).

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