Descriptionof the O2pressure influence on the oxidation time ofmotor oils

A characteristic index for the oxidation stability this is the oxidation induction time (OIT) which is defined by the time between the start of oxygen exposure and the onset of oxidation. Pressure DSC is required to increase oxygen concentration in order to achieve faster reactions at lower temperatures. OIT measurements of reference engine oils have been used to study the influence of oxygen pressure in the range from 0.1 to 10 MPa. A power law relationship was derived to describe this correlation between OIT and oxygen pressure. From this a quantitation factor is proposed to represent the influence of stabilizer. The exponent describes the sensitivity of the oxidation reaction of the oil towards the oxygen pressure and the term 'inherent stability' is proposed for that.. This relationship characterizes in more details the oxidation behavior. Extrapolation to higher pressures indicates, that the stabilization effects of additives can be overcome by the inherent stability. This signifies, that the ranking of the oils can be affected by the oxygen pressure.