Fuel Lubricity and Direct Injection

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Lubricity of Reformulated
& Oxygenated Gasolines
(DAI Informational Document # 970301, March 1997)
In the past few years there have been a number
of compositional changes to gasoline to comply
with the 1990 Clean Air Act Amendments (CAAA).
Such changes have included wintertime oxygenated
fuel programs in carbon monoxide non-attainment
areas and year round reformulated gasolines
in certain ozone non-attainment areas. Reformulated
gasolines also contain oxygenates (MTBE or
ethanol). These compositional changes to gasoline
have prompted some inquiries about any possible
reduction in the lubricity of gasoline.
The lubricity requirements of gasoline are
generally much lower than for diesel fuels. Diesel
fuel pumps operate at much higher pressures than
their gasoline counterparts and rely on the fuel for
part of their lubrication. Gasoline engines inject
fuel upstream of the inlet valves and therefore
operate at lower pressures. Nonetheless, there have
been anecdotal reports of fuel pump failures, in
recent years, which some have attributed to low
lubricity gasoline.
Because fuel lubricity has not technically been
an issue for gasoline applications, little research
work has been done in this area. In fact, there is no
standard industry test for determining gasoline
lubricity. Most researchers use a modified version
of test procedures used to assess diesel fuel lubricity.
Consequently, there is little published technical
work on gasoline lubricity. Among work that
has been published, there are conflicting results.
For instance one technical paper found that both
aromatics and the oxygenate MTBE enhanced lubricity.
In yet another study, gasoline containing
the same additive gave slightly less lubricity. This
would seem to imply that other variables are at play
and may indeed be more important. Work by Ford
Motor Company found that reformulated gasoline
with oxygenates and high aromatic content gave
slightly lower lubricity but concluded, "These data
suggest that the lubricity characteristics of CaRFG
and variations of it are not unusual or markedly
different from other commercially available gasoline."
Still other work exploring the lubricity benefits
of detergents stated, "The incorporation of
oxygenates does not appear to significantly improve
lubricity and may well detract from it", while
yet another study found that oxygenated fuels may
provide better lubricity. Obviously these constantly
conflicting results make thorough assessment difficult.
To further complicate such assessment, fuel
lubricity is affected by a number of other factors
including detergents and other additives as well as
sulfur content of the fuel.
Based on the limited information that is currently
available, only the following conclusions
can be drawn.
• Gasoline lubricity is not currently one of the
characteristics controlled by industry specification.
This is in large part because, at the current
time, fuel lubricity is not thought to have a major
impact on fuel system parts in gasoline engines.
Lubricity requirements may become of more importance
with the introduction of "direct injection"
gasoline engines which will require high pressure
injection pumps.
However as of this date, the
American Automobile Manufacturers Association
(AAMA) has not deemed gasoline lubricity to be of
enough significance to include any type of lubricity
specification in their AAMA Gasoline Specification.
Nor is there any such requirement in ASTM
D 4814 Standard Specification for Automotive
Spark Ignition Engine Fuel.
• There are numerous components in gasoline
that affect its lubricity. Tests conducted to date
have not successfully isolated all these factors and
consequently various test results sometimes con-
tradict each other. This is also in part because wear
characteristics are being measured within such a
small range of variation.
• While tests to date may not be able to totally
define long term wear characteristics resulting
from various fuels, they do indicate that there is no
concern about catastrophic failure related to gasoline
lubricity.
• As noted by Ford's work, the lubricity of
reformulated gasolines and oxygenated fuels is
"Not unusual or markedly different from other
commercially available gasoline."

References
Comparison of the Lubricity of Gasoline and Diesel Fuels,
Wei Dan Ping, et.al., SAE Paper # 962010
CaRFG Performance and Compatibility Test Program, California
Air Resources Board, March 1996
Development of a Benchtop Fuel Lubricity Assessment
Method, J.G. Eleftherakis, et.al., SAE Paper # 941915
Two-Stroke-Cycle Gasoline Engine Fuel Evaluation, Specialized
ASTM TC Sequence II, Valvoline Oil Company,
December 1988
AAMA Gasoline Specification-American Automobile Manufacturers
Association, February 5, 1996
ASTM D 4814 Standard Specification for Automotive Spark
Ignition Engine Fuel
The information contained in this document is based on a limited number of technical papers, test reports,
and information sources. While presented in a condensed form, Downstream Alternatives Inc. has made
every attempt to represent the information as accurately as possible, and it is believed to be accurate as
of the date of printing.
© 1997 All rights reserved. Downstream Alternatives Inc., P.O. Box 190, Bremen, IN 46506.
 
Interesting information. I think based on the limited amount of data that I will continue to add ~ 3.5 Oz of 2C twc oil to ~ 15 gallons of gasoline. Hopefully this will help lubracate the pumping system in my DI Mazda Cx7. I hope this question is more fully investigated in the near future. Comments?
 
Interesting read. I to have been using 2C oil in my Jeep at 4oz per 10gal. Fuel pump definitely operates quieter when the oil is in the fuel. Louder when there is no oil in fuel. It appears to be doing something.
 
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