Measurements of the cavitation threshold of multigrade engine oils under dynamic stressing by pulses of negative pressure

Abstract

This paper reports the first measurements of the effective tensile strength (or ‘cavitation threshold’) Fc, of degassed samples of a commercial multigrade engine oil over a range of temperatures, T, which are representative of those encountered under normal automotive engine operating conditions (in the range 20° C ≤ T ≤ 140°C). Also reported are the values of Fc obtained for Newtonian silicone oils over a range of shear viscosities. In the experiments reported herein, samples of liquid are subjected to dynamic stressing by a rapid pressure—tension cycle, this being a feature of the conditions experienced by an engine oil within a dynamically loaded journal bearing. The method used herein to estimate Fc avoids reliance upon direct measurements of substantial dynamic negative pressures using transducers which are designed for use in the range of positive pressures.