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Figure 1: Engine dynamometer and laboratory bench tests in industry engine oil specifications
Linked to the development of low friction engine oils is the understanding that engine durability cannot be sacrificed, and adequate lubrication should be assured under all operating conditions (e.g. speed, load, oil, and coolant temperatures). This means that fuel economy is not only important as net result over the test cycle, but also in each individual test mode as well. In some engine test phases fuel consumption can show an increase instead of a reduction relative to a proven reference product. This is a clear sign that the lubrication regime moved from hydrodynamic to boundary, which imposes a risk for engine durability. Steady-state tests are better suited than transient tests to evaluate fuel consumption and hence lubrication regime under specific engine operating conditions. Moreover, steady state tests have a better repeatability and are more widely available than transient test rigs.
Development of Next Generation Fuel Economy Lubricants Engine oils are developed against industry and OEM specifications. Figure 1 shows the current ACEA, API and JASO industry laboratory bench and engine dynamometer tests (colour indicates test type). In addition, some OEMs specify in-house and field tests. Figure 1 triggers the following observations: • Number of engine tests increases with engine oil specification upgrades
• The ACEA and API specifications include multiple engine tests for same performance aspects (API CJ-4, CK-4 and FA-4 specify four wear tests)
• Most of the engine tests are based on previous generation engine designs
• Last years, just four new tests have been introduced: Volvo T-13, COAT, and Hino N04C (2x) (encircled).
12 LUBE MAGAZINE NO.153 OCTOBER 2019
New lubricant tests are developed based on current or future needs. Due to the lack of new engine based tests and to assure backward compatibility, old tests remain in new oil categories. The backward compatibility principle was partly dropped with the introduction of the API FA-4 oil category since not all OEMs have approved 2.9-3.2 mPa.s HTHS for their engines.
Engine and lubricant development programs are long lasting programs. Consequently, the OEMs and engine oil developers are currently heavily engaged in development programs for their next generation products. Chevron Oronite is in close contact with all heavy-duty OEMs to make sure we are at the forefront of low HTHS oil development programs. Neither the next generation engines, nor the tests based on these engines, are available to the lubricant industry, and likely will not become available in a timely manner.
To meet the US 2002, Euro IV and JP NLT emission standards, OEMs adopted EGR and retarded injection timing to control NOx emissions. As a consequence, engine oil soot levels raised. The industry responded by developing the Mack T-11 test, which requires adequate handling of soot up to levels of 7%.
Figure 2 shows the end-of-test engine oil soot levels in field tests run by Chevron Oronite in Europe in a variety of trucks of different brands over the last two decades. The increase of soot levels when EGR was introduced is clearly visible around 2005. The plot also shows that modern Euro VI compliant trucks generate oil soot levels much less than 1% at end-of- drain. Lower soot levels in modern engines creates an opportunity to develop engine oils optimised for fuel economy. Moreover, thermal loading of engines and
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