Figure 2 The color evolution of 928 (Left) and 50-1-4Φ (Right) aviation
lubrication oil oxidized in high purity dry air without metal sheet (the
numbers inset in the square pictures are color numbers measured by
petroleum products chromometer)
According to the color numbers (shown as numbers inset in pictures of
oil samples in Figure 2) measured by the petroleum products chromometer
(model: SYD-0168), the 928 and 50-1-4Φ aviation lubrication oil samples
were significantly darkening after oxidized in high purity dry air. As
mentioned before, the 928 and 50-1-4Φ aviation lubrication oil samples
were treated in same time and temperature to keep every single
experiment in nearly identical circumstances. The oxidized 928 oil
samples are presented in the left side of Figure 2, while the oxidized
50-1-4Φ oil samples are presented in the right side of Figure 2.
Compared with oxidized 50-1-4Φ oil samples, the color of oxidized 928
oil samples is significantly darker, which certainly have higher color
numbers (the color numbers are shown as the inset numbers in the square
pictures of oil samples in Figure 2). The lowest color number of the
oxidized 928 oil sample is 9 which is oxidized at
175 oC for 30 or 60 minutes. However, the color
numbers of the oxidized 928 oil samples increase dramatically with
increasing oxidation time and temperature. Compared with 928 oil
samples, the 50-1-4Φ oil samples have relative higher color stability
under elevated oxidation conditions. Considering the color numbers of
many 928 oil samples exceed the measure range of the petroleum products
chromometer, thus, the results from Figure 2 suggest that 928 aviation
lubrication oil has relative unstable color stability under the same
oxidation condition of 50-1-4Φ aviation lubrication oil.