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measurement accuracy, especially as the size
of the soot particles increases and constitu-
ents like dirt are included.
e maximum detection limit can range
from 1.5 to 5 percent. is is concerning
since the critical limits for engines with
exhaust gas recirculation (EGR) may be
8 percent, and non-EGR systems may be
around 5 percent.
Other alternatives include the pentane
insolubles test, the light extinction method
and thermogravimetric analysis. e pentane
insolubles test consists of separating insolu-
bles from the oil with the aid of a solvent
mixed with the lubricant.
e solvent may commonly be pentane
and toluene. e insolubles are flung out
of the mixture with a centrifuge or filtered
out with a filter membrane. While this is a
preferred method with a lower cost, it poses
concerns when other insolubles are included,
as they will be measured together.
e light extinction method involves light
being casted at specific frequencies through
the oil and then measuring its obstruction
by the drop in voltage. Again, there are some
issues with this method related to other
potential objects obstructing the light, even
water and air bubbles.
ermogravimetric analysis may be the
most accurate measurements of soot load in
an oil sample. It requires heating a sample
through different stages to calculate the soot
concentration by comparing the difference in
weight of the volatile ash components to the
original sample.
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is test may have a much higher cost,
so it is not a viable substitution for routine
tests. Nevertheless, it is perfectly acceptable
for exception testing after a screening test has
been performed.
Soot dispersancy is an important lubricant
property. It is defined as the lubricant's ability
to keep soot particles finely dispersed and
avoid agglomeration into larger soot particles.
This can be measured with a simple
method known as the blotter spot test, which
allows for a visual representation of the soot's
dispersancy.
ML
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