Distinguishing Gasoline Engine Oils of Different Viscosities Using Terahertz Time-Domain Spectroscopy

Abstract

THz-TDS in the range of 0.5-2.0 THz was evaluated for distinguishing among gasoline engine oils of three different grades from the same manufacturer. Absorption coefficient showed limited potential and only distinguished (p < 0.05) the 20W-50 grade from the other two grades in the 1.7-2.0 THz range. Refractive index data demonstrated relatively flat and consistently spaced curves for the three oil grades. ANOVA results confirmed a highly significant difference (p < 0.0001) in refractive index among each of the three oils across the 0.5 -2.0 THz range. Linear regression was applied to refractive index data at 0.25 THz intervals from 0.5 -2.0 THz to predict kinematic viscosity. All seven linear regression models, intercepts, and refractive index coefficients were highly significant (p < 0.0001). All models had a similar fit with R 2 ranging from 0.9773 to 0.9827 and RMSE ranging from 6.33 to 7.75.The refractive indices at 1.25 THz produced the best fit. The refractive indices of these oil samples were promising for identification and distinction of oil grades.

Using Terahertz Time-Domain Spectroscopy to Discriminate among Water Contamination Levels in Diesel Engine Oil

“…The absorption coefficients demonstrated potential for identification and discrimination of water contamination levels of diesel engine oil, particularly at the higher contamination level. The pattern of increasing absorption coefficient with increasing frequency was consistent with studies of other oils, such as transmission fluid (Gorenflo et al, 2006), gasoline engine oil of SF service category (Tian et al, 2009), vegetable oils (Hu et al, 2005) (Li, 2010), and three gasoline engine oil grades (Abdul-Munaim et al, 2015).…”

“…Compared to the refractive index, water contamination level had a lesser effect on THz absorption (Abdul-Munaim et al, 2015;Naftaly et al, 2005). The absorption coefficients demonstrated potential for identification and discrimination of water contamination levels of diesel engine oil, particularly at the higher contamination level.…”

“…Lubricating oil characterization with THz-TDS includes polyglycol oils with water (Gorenflo et al, 2006), mineral oil with additives (Naftaly et al, 2005), six grades of lubricating oil (Tian et al, 2009), oil base stock and additive (Tian et al, 2012), and vegetable oils (Hu et al, 2005;Li, 2010). Our recent study was able to distinguish among three grades of unused gasoline engine oil and predict viscosity (Abdul-Munaim et al, 2015). None of these studies evaluated the potential for THz-TDS to discriminate among unused engine oil samples with levels of water contamination below 0.4%.…”

Terahertz Time Domain Spectroscopy to Detect Different Oxidation Levels of Diesel Engine Oil

“…The same study found noticeable differences in the absorption coefficient of the same engine oil when fresh, after six months of use, and after three years of use with the absorption coefficient increasing with time of use [24]. A THz-TDS study of three grades (SAE 5W20, 10W30, 20W50) of gasoline engine oil found that the refractive index increased with oil viscosity [25]. Hydraulic, diesel engine, gasoline engine, and gear oil were compared with THz-TDS and the refractive index was used to determine the type of oil based on its viscosity and different absorption coefficient peaks were noted for the oils [26].…”

“…A sample (100 mL) from each of the oxidation times of the diesel engine oil and a fresh sample were poured into a separate plastic container provided by a commercial oil analysis lab. Blackstone Laboratories (Fort Wayne, IN, USA) was selected to analyze the oil since it had been used by other studies [25,33]. The laboratory performed a physical and chemical analysis, including TBN and kinematic viscosity at 40 • C using ASTM standards that were modified for production.…”