Abstract
There continues to be a need for an in-situ sensor system to monitor the engine oil of internal combustion engines. Engine oil needs to be monitored for contaminants and depletion of additives. While various sensor systems have been designed and evaluated, there is still a need to develop and evaluate new sensing technologies. This study evaluated Terahertz time-domain spectroscopy (THz-TDS) for the identification and estimation of the glycol contamination of automotive engine oil. Glycol contamination is a result of a gasket or seal leak allowing coolant to enter an engine and mix with the engine oil. An engine oil intended for use in both diesel and gasoline engines was obtained. Fresh engine oil samples were contaminated with four levels of glycol (0 ppm, 150 ppm, 300 ppm, and 500 ppm). The samples were analyzed with THz-TDS and converted to frequency domain parameters of refractive index and absorption coefficient. While both parameters showed potential, the absorption coefficient had the best potential and was able to statistically discriminate among the four contamination levels.
Highlights
Combustion engine users frequently replace engine oil that is still usable or keep using engine oil that is contaminated and no longer suitable for use
The refractive index decreased with an increase in terahertz frequency, which was similar to previous research with other oils [20,22,25]
The refractive index from Terahertz time-domain spectroscopy (THz-TDS) identified glycol contamination engine oil [7], the 300 ppm contamination level was below the 500 level that was not found to cause levels of 300+ ppm from uncontaminated oil
Summary
Combustion engine users frequently replace engine oil that is still usable or keep using engine oil that is contaminated and no longer suitable for use. Engine oil is exposed to various contaminants and oxidation that affect lubricant efficiency, and the oil has a limited life. Additives for engine oils reduce the effect of contaminants, oxidation, and prevent corrosion [1]. Designers of internal combustion engines recommend changing engine oils after a specified period of operation, even though they know working conditions and failures of identical engines systems are not the same. Two identical engines may even be operating under the same load and external conditions, but the second engine has a gasket failure allowing coolant (containing glycol) to leak into the engine and mix with the engine oil. While the life of the first engine will probably not be reduced by waiting for the designer-specified oil change, the second engine may require a very
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