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Written by Terry Shulze
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Saturday, 24 September 2005 |
By Terry Shulze
The lubrication that biodiesel provides to petroleum based diesel is
conceptually known as “lubricity”. Lubricity should not be confused
with viscosity, or the thickness of a lubricant. Viscosity will provide
a fluid wedge to prevent metal on metal contact, lubricity is provided
by components in the fuel that prevent wear on contacting surfaces.
To our knowledge, research on the superior lubrication properties of
Biodiesel has not been conducted down to the molecular level, however,
there are many empirical reports complied from research conducted by
reputable organizations that graphically demonstrate the lubricity
qualities of biodiesel.
There are a number of standard empirical tests used throughout the
fuels and lubrication field. The two most widely used tests are
the “High-Frequency Reciprocating Rig” (HFRR) and the “Scuffing Load
Ball on Cylinder Lubricity Evaluator” (SLBOCLE). These two tests are do
not rely upon theory, but seek to quantify the actual ability of a
lubricant to prevent wear. Both tests are currently balloted by the
American Society for Testing and Materials.
The Engine Manufactures Association has established a specification of
lubricity in diesel fuels. That specification calls for a minimum
loading of 3100grams under the SBOCLE test and a maximum of wear of 450
microns under the HFRR test. When mandated low-sulfur diesel of the
California Air Resources Board was tested it was found that number 2
(#2) diesel can pass the BOCLE test, but number 1 (#1) failed the test.
Significantly, both #1 and #2 failed the HFRR test.
Tests have been performed using biodiesel and other lubricity
additives. Of the additives only “Centex” was able to enhance the
lubricity enough to pass all tests. The other additives “Farmland”,
“Unichem” and “Petrolite” passed the BOCLE test and the #2 HFRR test,
but failed the #1 HFRR test. “Octel” failed both #1 and #2 tests.
Biodiesel was able to meet all tests when blended at 2%.
It should be noted that just .75% biodiesel in #1 or #2 diesel provides
equipment protection superior to the lubricity additives (excepting for
“Centex”). More importantly, just .05% biodiesel will provide the
necessary lubrication for both #2 diesel and JP-8.
The base stock used in making biodiesel, as well as the alcohol used in
production affects the lubricity of the biodiesel. However, all
biodiesel will provide the required lubricity for both #1 and #2 ultra
low sulfur diesel (also Jet A and JP-8) when blended at 2% by volume.
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