A novel sensor for detection of oil condition and contamination based on a thermal approach

Abstract

Oil condition and contamination can be a major issue in lubrication systems such as aircraft, automobiles etc. Lubricating or cooling oil contamination occurs when metallic or non-metallic particles are produced due to wear of machine components and these are not captured by the filter system. Furthermore, thermal stressing causes oxidation and thereby degradation of the oil. Liquid contamination can occur from water condensation or fuel from heat exchangers. These can cause degradation of the oil and reduce the lubricating properties and clogg oil paths and accelerate the wear of moving parts. On-line oil condition monitoring systems are important for preventive maintenance especially for aircraft engine bearings, aviation gearboxes etc. Current on-line oil condition monitoring sensors are mainly eddy current, optical based. These sensors have a major drawback that they are prone to surface contamination and non-linearity. The gauges are also not sensitive enough to detect extremely small particulates or are prone to false detection such as trapped bubbles. A new sensor has been developed using thin film heat transfer sensors that can detect any form of contamination in oil such as metal, nonmetals, oxidation, liquids etc. The sensor works on the principle of measuring the thermal product of the material, as the composition of the material in contact with the sensor changes the thermal product changes and can be detected. The sensor can be used for both on-line and in-line condition monitoring and has been demonstrated to be robust. Initially, lab based tests were carried out to optimise the system for sensitivity and signal to noise ratio. The sensor has been demonstrated to detect 0:25% of contaminants by mass. Experiments were carried out by seeding metallic and non-metallic particles of various sizes to an engine oil system to validate its performance.