A comparison of the total capacitance and total resistance techniques for measuring the thickness of journal bearing oil films in an operating engine

Bearing oil film thickness (BOFT) values were determined for the front main bearing of a four-cylinder engine at different engine speeds, loads, and oil temperatures using two different measurement techniques. The total resistance technique assumes the oil film can be modelled as a simple ohmic resistor. The total capacitance technique assumes the oil film can be described as a simple capacitor. A comparison of results determined using both methods for a set of single-grade oils demonstrated that, although the methods agree quantitatively for certain combinations of engine test conditions and oils, the level of precision with the total capacitance technique is greater than with the total resistance technique