3.2 The color number influence factors
Since the color of the oxidized 928 aviation lubrication oil samples is darkening very fast while the oxidation temperature exceeds 200 oC, the color numbers go beyond the measuring range after the oil samples were heated more than 4 hours. On the other hand, the highest operating temperature of 50-1-4Φ aviation lubrication oil is 175 oC according to the standard (ГОСТ 13076-86). Therefore, the study prefers the oxidation reactions of the base oils under the condition of 175 oC to investigate the influence of base oils towards the color number of the oxidized oil samples.