Lubrication Oxidation Start Temperatures

The results of thermogravimetry in argon of the petroleum based lubrication oils without any additive are listed in Table 4-175 those in air in table 4-176. The thermogravimetry of the synthetic lubricants on samples with and without any additives both in argon and in air is shown in Tables 4-177 and 4-178. The oxidation start temperatures, determined by comparis p of the TGA curves in argon and air, are listed in Table 4-179. The additive-treatment shifted the towards higher temperatures. The values for the synthetics without... 

Dissolved air is not readily drawn out of solution. It becomes a problem when temperatures rise rapidly or pressures drop. Petroleum oils contain as much as 12% dissolved air. When a system starts up or when it overheats, this air changes from a dissolved phase into small bubbles. If the bubbles are very small in diameter, they remain suspended in the liquid phase of the oil, particularly in high viscosity oils. This can cause air entrainment, which is characterized as a small amount of air in the form of extremely small bubbles dispersed throughout the bulk of the oil. Air entrainment is treated differently than foam and is typically a separate problem. Some of the potential effects of air entrainment include pump cavitation, spongy and erratic operation of hydraulics, loss of precision control, vibrations, oil oxidation, component wear due to reduced lubricant viscosity, equipment shutdown when low oil pressure switches trip, microdieseling... 

Another consequence of the suggested chemical interaction between maleated polymers and zinc stearate is that the WPC material starts to decompose at lower temperatures (at about 300°C compared to 350°C) compared to that compounded without the metal-containing lubricant [25]. However, knowing that metal-containing compounds serve as catalysts of oxidation of plastics (see Chapter 15), the earlier plastic degradation could have occurred without any coupling agents, just due to the presence of zinc stearate. A simple test in that case would be to increase an amount of an antioxidant in the system, and the earlier decomposition temperature point would have predictably returned back to normal. Hence, the above experiment... 

Samples of lubricant obtained from the piston ring of a petrol engine under cold start conditions are very different from the sump lubricant condition. Samples from the first operating hour show substantial fuel and water dilution which cause precipitation of additive from the lubrication formulation with multiple phase formation. The physical performance properties of these lubricant samples are drastically changed, e.g.. Base Number drops from 10 to less than 2, anti-oxidancy is reduced and viscometric properties are changed. Implications for short vehicle journeys and temperature distributions within the piston assembly are discussed. 

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