Putting tests to the test

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.

Bench vs engine tests

A variety of bench tests have been developed to
measure physical, chemical and performance properties

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.

With these issues in mind, Infineum has taken a close look at the correlation of the bench and engine tests used to measure oxidation.

Oxidation testing

Engine oil oxidation is an important parameter because it is a major oil degradation mechanism. Chassis dynamometer tests can be used to measure oxidation and can stress the oil in a number of ways under a variety of operating conditions to mimic real-world conditions. A variety of bench tests can also be used to measure oxidation, some of which have been incorporated into both OEM and industry lubricant specifications.

Infineum tested oils in both a chassis dynamometer test and the CEC L-109, a severe bench oxidation test, which is used in ACEA specifications.

The results demonstrated that by oversimplifying the variety of complex reactions taking place, the bench test could not predict engine performance.

This means engine oils that pass bench laboratory tests, may not control oxidation in real-world conditions.

We believe that this is something the industry as a whole needs to scrutinise and Infineum looks forward to working with industry stakeholders to improve our processes using a cost benefit analysis approach. Click here to read the full story on oxidation testing.

Stifling innovation

In addition to their inability to mimic real-world conditions, bench tests also have the potential to stifle innovation. Currently, the main drivers for engine oil developments are fuel economy, engine wear protection, cost reduction and more specific issues including low-speed pre-ignition.

While these drivers push oil formulations one way, the proliferation of bench tests creates unnecessary complexity and actively works against the creation of advanced engine oils to meet industry needs.

Future test developments

The best outcome would be to have bench tests that are not redundant to other engine performance parameters and have proven field correlation. As a first step, where there is an engine test that can do the job at a reasonable cost and timescale, the inclusion of bench tests in the specification for the same parameter should be strongly challenged.

In our view, efficient and effective tests should be developed using clear, simple processes that deliver meaningful results in which the industry can have confidence.

All the tests should be judged critically on their relevance to real-world issues and their correlation to field results. Limits should be set that are reasonable in terms of preventing the issue of concern, and that are commensurate with the precision and accuracy of the measurement tool.

To efficiently and effectively deliver lubricants that meet OEMs’ requirements it is essential, where bench and analytical tests are used, to ensure they model field phenomena and are relevant to modern engines. Infineum is looking into the effectiveness of a number of other bench tests and will report on the findings of these investigations as work progresses.

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