ILMA Compoundings – December 2018 - 18

As fuel efficiency
and emissions
regulations become
more stringent around
the globe, OEMs are
turning to advanced
engine and drivetrain
technologies.
suburban driving at both high and low altitudes. To allow
for high-resolution combustion data, the sample rate was
100,000 hertz, and the amount of data captured over the
trial was nearly 4 terabytes.
Studying this data set showed that LSPI occurred 5,664
times in 65,000 miles. Perhaps most interestingly, the majority
of LSPI occurred above 3,000 rpm. This is a very significant
finding, as the laboratory engine test is conducted at a much
slower 1,750 rpm. This suggests that the term "stochastic
pre-ignition" (SPI) might be more accurate than "LSPI."
In the same testing program, it was observed that LSPI
propensity can increase over an oil drain interval. This is
very significant, as the established ASTM Sequence IX
LSPI test only evaluates fresh oil's LSPI propensity. To
fully mitigate LSPI, it would be necessary to ensure that an
engine oil would protect when new as well as after being
used for some time - a concept known as LSPI durability.
To further evaluate this phenomenon, a new engine testing
methodology was developed.
In this new method, an engine test is first used to evaluate
LSPI propensity on fresh oil, then the engine ages the
oil using a relevant duty cycle for 100 hours, and a test
re-evaluates the aged oil for LSPI propensity. To ensure
real-world relevance, the aging cycle is based on the World
Harmonized Light Vehicle Transient Cycle (WLTC). Using
this three-part testing protocol, researchers evaluated several
different LSPI-mitigating formulations. To ensure a scientific comparison, only one lubricant attribute was changed
at a time. In each case, the performance was compared to
that of a baseline oil. A total of four oils were tested.

3. Formulation 2: an all-calcium detergent with
molybdenum dialkyldithiocarbamate (MoDTC)
4. Formulation 3: an all-calcium detergent with titanium

1. Baseline oil: an all-calcium detergent known to have
poor LSPI performance

The results of the tests found that all three formulation
strategies were successful at mitigating LSPI in fresh oil.
However, the propensity of LSPI was observed to be very
different as the engine oil aged. Results indicated that the
performance of the baseline oil deteriorated over the 100hour aging interval. Further, formulations using high levels
of MoDTC or titanium were observed to offer very low
fresh-oil LSPI, but LSPI propensity rose to an unacceptable
level after 100 hours of aging. Only the first oil formulation,
which used a reduction in calcium and replacement with
magnesium, provided low LSPI as both fresh and aged oil.
From this data, it can be concluded that not all LSPImitigating formulations are the same. Some look very promising when evaluated as fresh oil but rapidly degrade and lose
their ability to mitigate LSPI. The significance of this finding
should not be underestimated. Since the industry-standard
ASTM Sequence IX test only evaluates fresh-oil LSPI
propensity, a large gap is left through which inferior oils may
enter the market. These oils could potentially pass the test but
would not provide LSPI mitigation over the oil drain interval.
By 2025, GDI-equipped vehicles are expected to make up
over two-thirds of light-vehicle production in China, Europe
and the U.S. It is increasingly important for oil marketers to
ensure protection against LSPI by offering a solution tested
to perform in both fresh and aged oil. Protection against
LSPI requires additive solutions with proven performance.
Ensure your consumers are getting the level of protection
they deserve with an API SN PLUS offering that has been
thoroughly tested to go the distance.

2. Formulation 1: a reduced-calcium detergent with the
addition of magnesium detergent

Birze is regional passenger car, engine oils business manager for the
Americas at The Lubrizol Corp.

DECEMBER 2018

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ILMA Compoundings – December 2018

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