Motor oil degradation during urban cycle road tests

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Friction https://doi.org/10.1007/s40544-020-0386-z

RESEARCH ARTICLE

Motor oil degradation during urban cycle road tests Lei WEI1,2, Haitao DUAN1, Yongliang JIN1, Dan JIA1, Bingxue CHENG1,3, Jianfang LIU1,4, Jian LI1,* 1

State Key Laboratory of Special Surface Protection Materials and Application Technology, Wuhan Research Institute of Materials Protection, Wuhan 430030, China

2

College of Mechanical Engineering, Hunan Institute of Science and Technology, Yueyang 414006, China

3

State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China

4

College of Biological and Pharmaceutical Engineering, Wuhan Polytechnic University, Wuhan 430023, China

Received: 26 November 2018 / Revised: 24 January 2019 / Accepted: 18 March 2020

© The author(s) 2020. Abstract: Several civilian vehicles in China operate in urban traffic conditions and have their motor oil changed every 5,000 km. This study investigates the variations in oil properties after servicing at 5,000 km, based on systematic road tests (including a repeated test, a parallel test, and a new vehicle test). The physicochemical properties, changes in components, oxidation stability, detergent-dispersant performance, and tribological properties of motor oils were analyzed. The results showed that the total acid number (TAN) of oils increased with the operation mileage, by up to 1.41 mgKOH/g. The total base number (TBN) decreased after the road tests were completed, and the decrease was less than 44.6%. The kinematic viscosity (KV) of most oils decreased initially and then stabilized in the middle stage, before starting to increase later in the experiment. The change in KV at 100 ℃ was less than 15.96%. The oxidation onset temperature (OOT) of the oils diminished gradually with the operation mileage. All OOT values of the used oils were higher than 210 ℃. A spot test indicated that the used oils retained their detergentdispersant performance to an appropriate extent. The four-ball wear scar diameters and friction coefficient of the used oils did not increase significantly after the road tests were completed. This study can serve as a reference for end-users when changing motor oils. Keywords: motor oil; urban vehicles; oil degradation; road test; oil analysis

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Introduction

Motor oil provides wear protection, thermal management, and corrosion inhibition functions that are critical to engine performance and longevity [1, 2]. Regardless of the oil type used, the quality declines during use because of degradation and/or contamination [3, 4]. Therefore, motor oil must be changed to counter degradation and contamination, and to maintain the quality necessary to protect the engine [5, 6]. A rapid increase in the number of vehicles has increased the demand for motor oil. There were about 250 million automobiles in China * Corresponding author: Jian LI, E-mail: [email protected]

up to June 2019, and about 200 million of those automobiles were private vehicles. The requirement for gasoline motor oil in China is near one million tons every year [7].

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