ASTM D7098 Standard Test Method for Oxidation Stability of Lubricants by Thin-Film Oxygen Uptake (TFOUT) Catalyst B
4. Summary of Test Method
4.1 The test oil is mixed in a glass container with four other liquids used to simulate engine conditions: (1) an oxidized/nitrated fuel component (Annex A3), (2) a mixture of soluble metal naphthenates (lead, iron, manganese, and tin naphthenates (Annex A4), (3) a nitro-paraffinic compound, and (4) Type I reagent water.
4.2 The glass container holding the oil mixture is placed in a pressure vessel equipped with a pressure sensor. The pressure vessel is sealed, charged with oxygen to a pressure of 620 kPa (90 psig), and placed in an oil bath at 160°C at an angle of 30° from the horizontal. The pressure vessel is rotated axially at a speed of 100 r/min forming a thin film of oil within the glass container resulting in a relatively large oil-oxygen contact area.
4.3 The pressure of the pressure vessel is recorded continuously from the beginning of the test and the test is terminated when a rapid decrease of the pressure vessel pressure is observed (Point B, Fig. 1). The period of time that elapses between the time when the pressure vessel is placed in the oil bath and the time at which the pressure begins to decrease rapidly is called the oxidation induction time and is used as a measure of the relative oil oxidation stability.
5. Significance and Use
5.1 This test method was originally developed to evaluate oxidation stability of lubricating base oils combined with additives chemistries similar to those found in gasoline engine oils and service.
5.2 This test method is useful for screening formulated oils before engine tests. Within similar additive chemistries and base oil types, the ranking of oils in this test appears to be predictive of ranking in certain engine tests. When oils having different additive chemistries or base oil type are compared, results may or may not reflect results in engine tests. Only gasoline engine oils were used in generating the precision statements in this test method.
