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Oil analysis programs are used to monitor the condition of diesel engines. From the standpoint of engine protection, the size and concentration of oil contaminants are as important as their chemical composition. Wear rates are related to the contaminant size distribution in the oil and degree of filtration. Spectroscopic analysis does not provide particle size information and is incapable of measuring the particularly damaging particles larger than 10 μm. Particle size analysis, when used to complement the spectroscopic analysis, provides a better description of the condition of lubricating and transmission oil. Particle size data can be obtained by particle counters, though in the past it was difficult to obtain reliable data. Recent developments overcome many of these difficulties and permit reliable interpretations of particle size data. This allows better decisions to be made concerning the engine and oil conditions and the filtration requirements of the system.

The gravimetric method is commonly used in engine air filtration technology for air cleaner, filter element and filter media testing. An “absolute” filter is employed in-line to collect any dust particles passing through the test filter. Air filter efficiency is calculated by comparing the mass of dust collected by the test filter with that fed to the filter. This method measures only the mass of dust penetrating the filter. It does not provide information on contaminant particle size. Moreover, this method, in many cases, has inadequate precision to distinguish between filters. Both the dust mass and its particle size are needed to estimate engine wear. Therefore, the SAE J726 Air Cleaner Committee initiated work on a test method to measure engine air cleaner fractional efficiency. This paper discusses problems associated with development of the fractional efficiency method for engine air cleaners.