Fig. 1. Schematic diagram of the test process

Fig. 2. Infrared spectra of Mobil Jet oil Ⅱ lubricating oil, fuel oil and lubricating oil mixed with 50% fuel oil

Fig. 3. (a) Infrared spectra of lubricating oil samples mixed with different fuel contents; (b) characteristic region area of the sample with 0% fuel content; (c) characteristic region area of the sample with 2% fuel content; (d) characteristic region area of the sample with 3% fuel content; (e) characteristic region area of the sample with 5% fuel content; (f) characteristic region area of the sample with 10% fuel content; (g)characteristic region area of the sample with 25% fuel content

Fig. 4. Working curve fitting using Spectrum Quant software