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Fourier transform infrared ͑FTIR͒ spectroscopy has found an important analytical niche in the field of condition monitoring ͑CM͒ of lubricants, lubricant quality being a primary determinant of the wear and operational efficiency of engines and machinery. The ability to track a wide range of functional groups associated with chemical changes in lubricants by FTIR spectroscopy allows the overall quality of lubricants to be assessed and informed decisions made as to whether a lubricant needs to be replaced or not. Newer automated FTIR systems in centralized laboratories are now capable of analyzing oil samples at rates of Ͼ120 samples/h, providing trending information on soot, moisture, glycol, oxidative status, anti-wear additives, and nitration, amongst other measures. The current FTIR CM methodology is based on ASTM Standard Practice E2412-10 and is restricted primarily to petroleum or mineral oils; however, the ability to spectrally classify oils could overcome this limitation and broaden the scope of the methodology substantially. Quantitative FTIR methods have come to the fore to carry out more specific measures related to oil condition, specifically the determination of acid content and base content, as well as moisture. These methods have been designed to overcome some key limitations associated with the corresponding ASTM titrimetric procedures and expand the overall utility of FTIR instrumentation in centralized lubricant analysis laboratories. This paper provides an overview of FTIR CM, how it has been and can be further improved, and discusses the recent advances in the newer quantitative FTIR CM methods as well as the issues that need to be addressed to further enhance the utility of FTIR spectroscopy in relation to lubricant analysis.

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Oil filters capture a tremendous amount of tribology information about the operation of a machine. Removal and analysis of the filter debris has proved to be an effective tool for engine health management by determining wear modes and observing failure progression providing long lead times for maintenance remediation. The process of manual debris removal and analysis in a laboratory, however, is tedious. An automated filter debris analysis system provides a repeatable process for at-line or laboratory use. The filters are automatically cleaned; the particles are counted and sized utilizing a quantitative oil debris sensor; and the debris is deposited on a patch for automatic analysis by an integral energy dispersive X-ray fluorescence spectrometer. The XRF analysis procedure provides metallurgical analysis and an expert determination of engine condition. The system has been successfully applied to two operational aircraft fleets, the Canadian Forces S-61 Sea King helicopter fleet and the US Navy EA-6B Prowler aircraft fleet. In both applications, significant benefits have been realized.

Oil condition monitoring is a vital part of integrated asset health management. With an increasing impetus toward real-time decision making, delays incurred in offline laboratory oil analysis are becoming less acceptable. At present, several oil quality parameters can be monitored by commercially available sensors, and active research and development programmes are being pursued by both academic and industrial researchers to develop robust, cost effective sensors for the remaining key parameters. Published (active) ASTM methods or practices do not yet cover the sensor technologies employed or under development, although work is in progress to address this deficit. This paper presents an overview of currently available oil condition sensors and looks at some recent developments, particularly in the following three areas: contamination by metallic wear debris, measurement of total water content, and determination of in-service oil viscosity. In each case, quite different technological solutions have been adopted. Where applicable, alignment and overlap with existing ASTM methods and practices will be reviewed and future directions indicated. Recent improvements in the sensitivity of inductive particle counters have enabled the detection of individual ferrous particles down to the sub-100 μm diameter regime and close to the 100 μm diameter mark for non-ferrous metals. Experiences of particle counters in wind turbine applications have shown the potential for enormous benefits in failure prevention. One standard practice covering the installation, operation, and requirements of such devices is published and a second is currently in draft mode. Online sensors utilising infrared transmission measurements recently have been developed by two independent companies. The systems are targeted primarily at marine diesel engine installations, although the method is not restricted solely to these applications. Maximum water content measurable depends on both the optical path length and the cleanliness of the oil. For marine applications a practical upper measurement limit of 1 % by volume has been adopted. In the system described here, a correction methodology, correlating to an accepted Deutsches Institut fu¨r Normung-Fourier transform infrared standard, has been adopted to cope with oils contaminated by soot. Soot loading increases the opacity of the oil, causing a concomitant reduction in the maximum water content measurable. The correction procedure increases the accuracy of the water content measurement and additionally provides a determination of the soot content. Commercially available viscosity sensors include both the oscillating piston type and high frequency oscillating crystal designs; however, a cost effective device employing a low amplitude, mid-frequency vibrating sensor element has been developed recently. Key features include accurate measurements over a very wide viscosity range and an operating range that covers combustion engine oil temperatures and pressures. Correlation with existing ASTM methods and practices is presently limited to calibration aspects only.