Terahertz Time-Domain Spectroscopy to Discriminate among Water Contamination Levelsin Diesel Engine Oil

Abstract

Abstract. THz-TDS in the range of 0.5-2.0 THz was evaluated for discriminating among water contamination levels (0%, 0.1%, and 0.2%) in diesel engine oil (SAE 15W-40). Absorption coefficient demonstrated potential to discriminate among the three water contamination levels with significant differences among all three levels across the 1.111-1.332 and 1.669-1.934 THz ranges. At each of these frequency ranges each water contamination level was significantly different from the other two. The 0% water had the lowest absorption coefficient while 0.2% water had the highest absorption coefficient. Refractive index demonstrated greater potential to discriminate among water contamination levels with significant differences among all three water levels across the 0.5-1.5 THz range. The refractive index of 0% water was the lowest and 0.2% water was the highest across the THz range. Linear regression analysis of refractive index as a predictor of water contamination level yielded a highly significant equation (p