Testing the tests
As industry lubricant specifications are revised to meet the needs of the latest vehicles, it is essential that the tests included define lubricants that provide sufficient hardware protection. Joan Evans, Industry Liaison Senior Advisor at petroleum additive organisation Infineum, talks about how test selection and limit setting can impact the ability to assess the real-world performance of a lubricant.
Industry lubricant specifications define the minimum performance level of passenger car and heavy-duty diesel engine oils to ensure they will provide good lubrication for all vehicles when used as recommended. They are recognised globally as the quality stamp for oils that meet the requirements set by international vehicle and engine manufacturers.
OEMs are introducing more sophisticated vehicle hardware to ensure compliance with tightening tailpipe emissions and fuel economy regulations. This new technology requires increasingly sophisticated lubricants that are carefully designed to deliver sufficient performance and protection. To reflect the advances in vehicle technology and to address real-world concerns, industry lubricant specifications must periodically be modified. With the European light and heavy-duty ACEA specifications and the North American, ILSAC GF-6 and PC-11 categories all undergoing revisions, the industry is currently dealing with the largest change to specifications that it has seen in its entire history.
These specification updates should result in lubricants that are not only capable of protecting today’s engines, but also are designed to address field issues. To do that with absolute certainty it would be necessary to test every derivative of every lubricant in the field, which is clearly not possible from either a time or cost standpoint. Instead, specifications use a combination of bench, engine and field tests to define oil quality.
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Bench vs engine tests In an attempt to emulate real-world performance, testing can be carried out in well-controlled, heavily instrumented, static engines in a laboratory. These tests are designed to replicate specific issues, for example: soot handling or engine wear under particular conditions. To be confident that these tests provide the required level of protection, it is absolutely essential that they demonstrate correlation with field performance.
However, engine tests can be expensive and often need to run under extreme duty cycles in order to replicate field effects in a sufficiently short period of time.
These constraints have led industry bodies to develop a variety of bench tests, which are used to measure physical, chemical or performance properties, such as shear stability and oxidation. And, many of these bench tests have been incorporated into industry lubricant specifications.
Their introduction has been well intended, with the key benefits of reduced costs and time required for lubricant evaluation. However, this has led to the scenario where, for some parameters, there are a number of subtly different laboratory tests within the specification all with one common aim. At the very least this scenario is confusing, time consuming, wasteful and can limit the formulation window. But, it is also misleading because oils that pass the bench test do not necessarily protect engines in field conditions.
LUBE MAGAZINE NO.137 FEBRUARY 2017
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