Analysis of Nonmetallic Constituents of Lubricating Oil Using Indirect Ablation Laser-Induced Breakdown Spectroscopy
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Journal of Applied Spectroscopy, Vol. 87, No. 4, September, 2020 (Russian Original Vol. 87, No. 4, July–August, 2020)
ANALYSIS OF NONMETALLIC CONSTITUENTS OF LUBRICATING OIL USING INDIRECT ABLATION LASER-INDUCED BREAKDOWN SPECTROSCOPY J. Xiu,a* Sh. Liu,a L. Dong,b and H. Qina
UDC 543.42;621.375.826
Indirect ablation laser-induced breakdown spectroscopy (IA-LIBS) was applied to the analysis of the nonmetallic constituents of engine oil and considered as a feasible technique for the evaluation of the consumption and/or combustion of engine oil during routine engine operation. The evolution of CN emission and C2 emission was investigated for different driving time intervals of the motor. The exponentially decaying curve showed that the intensity of CN emission and C2 emission decayed at different driving time intervals. The evolution of total CN emission and C2 emission was analyzed, and the ratio of CN to C2 was calculated, which might be taken as an indicator to evaluate the performance of the used engine oils and/or to diagnose the conditions of the motor engine. Thus, it is shown that IA-LIBS is a potential method for analyzing the metallic and nonmetallic constituents of engine oil. Keywords: indirect ablation laser-induced breakdown spectroscopy, engine oil, emission line. Introduction. Lubricating oil plays an important role in the normal operation of the motor. It is composed of hydrocarbons and nitrile compounds containing one or more cyano groups (–C=N). During engine operation, wear is unavoidable because it has both physical (friction between metallic parts causing high temperature and pressure) and chemical (corrosion) reasons. Chemical wear may produce not only metallic particles but also soluble metallo-organic species, whereas physical wear is generated by metallic particles of varying sizes (up to a few micrometers) [1, 2]. Some metallic elements need to be added to virgin lubricating oil to improve its capacity and achieve antioxidative, anticorrosive, dispersing, antiwear, or other properties. Such compounds involve a large number of elements, such as Mg, Si, Ca, Zn, and Ba [3]. However, the used engine oil may contain gasoline, additives (detergents, dispersants, oxidation inhibitors, rust inhibitors, and viscosity improvers), nitrogen and sulfur compounds, and a broad range of aromatic and aliphatic hydrocarbons with chain lengths ranging from C 15 to C 50, in addition to metals [4]. The used engine oil undergoes heating, friction, oxidation, and combustion when the motor is operating, which may generate higher percentages of polycyclic aromatic hydrocarbons (PAHs) and additives [5, 6]. For example, hydrocarbon molecules will react to incorporate oxygen atoms into their structure over time. This reaction produces acids, sludge, and varnish that foul or damage metallic parts. The compositions of engine oil are always changing with the engine operating, which can affect the performance of engine oil. Therefore, monitoring and determining the composition and concentration of elements in lubricatin
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