Procedure for evaluating susceptibility of motor oils to high-temperature oxidation

Abstract

This article proposes a laboratory method for the evaluation of the thickening tendencies (viscosity increase) of motor oils. The high viscosity of used oil results from the accumulation of soluble and insoluble products from oil oxidation and fuel combustion. The influence of oxidative processes on viscosity increase is indicated by the sharp increase in the motor oil's content of sludge, various resins, and acidic products, as indicated by the increase in acid number (large amounts of oxidation products can also be detected in the oil by means of infrared spectroscopy). The proposed lab method is convenient in terms of time required, simple in terms of apparatus, and (when compared with methods using oxygen) it is safe. The test apparatus consists of an air blower, a surge tank, and a system of differential manometers. The motor oil test samples were prepared under lab conditions by blending lube stocks from various sources with the appropriate additives. It is determined that for the oils from the West Siberian crudes, the viscosity increase is far less than for the oils from the Volgograd crudes. The lube stocks from Volgograd crudes, which are low-sulfur and naphthene-paraffin based, respond poorly to many additives and are readilymore » oxidized to form carbenes and carboids. Lube stocks from West Siberian crudes show a good response to most additives. Includes a table.« less