JCL,
In response to your statement a few post ago; "If you are purchasing fuel by volume, and burning it to convert energy, then volumetric energy content is the exact right scale to use. You are simply purchasing less energy in your gallon. There is no magic here. I would be interested in another hypothesis of why the fuel economy is so good, . . . " again the "The Auto Technicians Gasoline Quality Guide - changes in Gasoline III [ http://www.ethanolrfa.org/objects/pd...A/Gasoline.pdf ],
lend some credence to the fuel uage figures I posted below AND, for the record my 'plain jane' '98 F-150 is running on a 98,xxx mile 4.2L V-6 completely stock engine and fuel sustem. The only modifications i've made under the hood are the installation of a home made K & N cold air filter system and the Full Flex Gold FFV conversion kit. Oh, I almost forgot the 4:11 limited slip differential I installed 3-4 years ago before I happened on to the FFV conversion kit on the net.
Exerpts from the aforementioned " . Changes in Gasoline III":
Fuel Economy: There is a great deal of misunderstanding about
the fuel economy (miles per gallon) of various gasolines, especially
those containing oxygenates.
There are a number of variables that confound accurate fuel
economy measurements in anything short of a controlled test or
large well documented fleet study.
Besides fuel related factors, there are a number of vehicle and
climate related issues to consider. Vehicle technology, state of tune,
ambient temperatures, head winds, road grade, tire pressure, use of
air conditioners, and numerous other factors have an impact on fuel
economy.
Some of those that have been documented in testing are covered
In Table 3-2. Even, whether or, not, the car is level each time you
fill it can distort fuel economy readings by several percentage points.
Table3-2
Factors That Influence Fuel Economy of Individual Vehicles
Factor Fuel Economy Impact
Average Maximum
Ambient temperature drop from 77°F to 20°F -5.3% -13.0%
20 mph head wind -2.3% -6.0%
7% road grade -1.9% -25.0%
27 mph vs. 20 mph stop and go driving pattern -10.6% -15.0%
Aggressive versus easy acceleration -11.8% -20.0%
Tire pressure of 15 psi versus 26 psi -3.3% -6.0%
It is easy to see from Table 3-2 why an individual using
one or perhaps a few vehicles cannot make an accurate
determination of the fuel economy impact of various gasolines.
There are simply too many variables.
Through the course of a year, gasoline energy content
can range from 108,500 British thermal units (btu) per gallon
to 117,000 btu/gal. Winter grades are made more volatile
(less dense) to aid in cold start and warm up performance and
typically contain 108,500 to 114,000 btu/gallon. Summer
grades are of much lower volatility to minimize evaporative
emissions and hot start/hot driveability problems. Summer
grades will typically contain 113,000 to 117,000 btu/gallons.
So the energy content, and therefore the fuel economy, can
vary 3.4% to 5.0% just based on the energy content of the fuel.
Furthermore comparing the highest energy content summer
fuels to lowest energy content winter fuels demonstrates that
the variation in energy content is 7.26%. See Table 3-3.
Table 3-3 Gasoline Energy Content
Conventional Content Gasoline - btu
Summer Winter
grade grade
btu btu
Maximum 117,000 114,000
Minimum 113,000 108,500
% 3.4 5.0
Difference between summer maximum and winter minimum-7.26%
The lower energy content of winter fuels and the other wintertime
influences on fuel economy can easily lead to reductions of 10-20%
in miles per gallon during the coldest winter months.
Oxygenated fuel programs, being wintertime only programs, have
therefore been incorrectly blamed for massive fuel economy losses
when, in fact, numerous other variables also contribute to fuel economy
losses during winter months.
The reduction in btu/gallon from the addition of oxygenates is generally
in the 2% to 2.5% range although fuel economy may not be that much
lower.
As an example, ethanol contains 76,100 btu per gallon. A 10 volume
percent ethanol blend would contain about 3.4% less energy per gallon.
However, in controlled tests the fuel economy loss has been far less than
would be indicated by the 3.4% lower energy content.
Table 3-4 lists the btu/gallon (energy content) of each of the four oxygenates
currently in use and also the energy content of resulting fuels when those
oxygenates are blended into a 114,000 btu/gallon base fuel.
The 2.0% oxygen level column is typical of reformulated gasoline while a
2.7% oxygen level is representative of gasoline sold in oxygenated fuel
program areas.
Comparing each of the blends in Table 3-4, you can see that a blend
containing 2.0 wt. % oxygen averages just under 2.0% lower energy
content. A blend containing 2.7 wt. % oxygen will average about 2.5%
lower energy content.
Table 3-4 Energy Content of Oxygenate Blends
(whenblendedwith114,000btu/gallonbasefuel)
Oxygenate Energy Finished Finished
Content blend blend
2.0 wt.% 2.7 wt.%
oxygen oxygen
(btu/gallon) (btu/gal) (btu/gal)
Ethanol 76,100 111,836 111,082
MTBE 93,500 111,745 110,925
ETBE 96,900 111,811 111,059
TAME 100,600 112,215 111,688
These projected fuel economy variations have been validated in numerous
controlled tests and fleet studies. The most recent of these studies, done in
1995, include a fleet test by the State of Wisconsin and a fleet analysis by
Lundberg Survey, Inc.
The Wisconsin Fleet Survey tested eight vehicles, ranging from 1979 to
1994 models, comparing their fuel economy on conventional gasoline to
that achieved on reformulated gasolines containing MTBE, ethanol, and
ETBE.
The average fuel economy loss for the reformulated gasoline was 2.09%.
The Lundberg Survey, analyzing fuel economy complaints in the
Milwaukee area RFG market, analyzed the fuel economy of several large
fleets totaling thousands of vehicles.
The survey compared the fuel economy of these fleets for January 1994
(on conventional gasoline) to January 1995 on reformulated gasoline.
The fuel economy loss for these fleets operating on RFG was 1.63%.
These tests and studies combined with numerous others leaves little doubt
that the fuel economy loss due to oxygen content is approximately 2.0%.
It should be noted that vehicle technology and state of tune also play a role
in fuel economy variations. For instance older vehicles, which operate rich
at specified settings may actually show a fuel economy improvement on
oxygenated gasolines. This is because the chemical enleanment from the
oxygenates results in more complete combustion of the fuel which partially
or totally compensates for the slightly lower btu value.
To aid in responding to questions about fuel oxygenates, a "Quick Rference Guide to Facts About Fuel Oxygenates" follows this chapter.
Oxygen Content and Enleanment: (Non-Feedback Systems)
Oxygenated fuels may contain up to approximately 3.5 weight % oxygen depending on oxygenate type and level.
This level of oxygen should not normally require any adjustments to the air/fuel ratio. However, you may occasionally encounter an auto which has the air/fuel ratio set lean. Since an increase in oxygen further enleans the fuel charge, these autos may display symptoms of enleanment (improper idle, engine dies). This can usually be easily corrected by minor adjustments to enrich the air/fuel mixture.
In those areas where vehicles are subject to Inspection & Maintenance (I/M) programs, care should be exercised to ensure that adjustment will not result in a failed emissions test.
(Feedback Systems) Newer vehicles are equipped with onboard computer control systems. These systems include oxygen sensors, installed in the exhaust manifold, to determine the oxygen content of the exhaust gases. Vehicles equipped with onboard computers will compensate for the oxygen content of the fuel when operating in the closed loop mode. The maximum level of oxygen permitted in gasoline is within the authority range of the sensor.
Q: Have there been any studies on how oxygenates
Affect driveability?
A: Yes, there have been a number of tests and fleet studies on the
effect of fuel oxygenates on vehicle driveability. These studies have
generally indicated that the average consumer will detect no difference
in vehicle performance. In fact, in some fleet studies, drivers have
indicated improved performance from oxygenated fuels. You should
not experience any driveability problems on properly formulated
gasoline/oxygenate blends.
Q: If oxygenates are acceptable fuel components, why do some
auto technicians believe they deteriorate vehicle performance?
A: Auto service technicians do not always have easy access to
information on fuel quality. Such a position may indicate that the
technician is unfamiliar with fuel quality issues or may not have
access to the latest information on the subject.
During the period of time that ethanol and MTBE have grown in use,
there have been a number of other compositional changes in gasoline.
However, many of those changes have not been brought to the attention
of the technician. This results in a perception that the major difference in
today’s gasolines is oxygenate content when, in fact, many other changes
have also taken place.
Q: Have any tests been performed to determine the
compatibility of oxygenates with fuel system parts?
A: Yes, several tests have been performed which indicate
that oxygenates are compatible with the metals and elastomers
in modern vehicle fuel systems.
Q. Will oxygenates result in reduced fuel economy?
A. The addition of oxygenates will result in a fuel economy
loss of about 2%. This has been confirmed through numerous
tests (See Chapter 3, pages 17 & 18). {See above}
Appendix A Fuel System Materials
A number of materials used in vehicle fuel systems have
been tested for use with oxygenated fuel components as part
of the process to secure EPA approval for their use.
Post-1980 vehicle fuel systems typically utilize materials that are
compatible with oxygenates and high aromatic gasolines.
Pre-1980 and especially pre-1975 vehicle fuel systems may
contain materials that are sensitive to high aromatic concentrations,
ethers, or alcohols.
Table A-1 lists typical metals and the fuel system parts where they are
likely to be used. The metals listed in this table were tested with ethanol
blends and other alcohol-blended fuels by immersing metal coupons
(1"x1" metal strips) in both the liquid fuel and the vapor phase of the fuel
for 30 days at 110° F.
Test results indicate that “overall, no oxygenated fuel/metal combination
weight change (in ‘dry’ or ‘wet’ fuels) was significantly different from that
observed for the base unleaded gasoline.”
Table A-2 lists elastomers and non-metal materials along with their most
typical use in the vehicle. These materials have also been tested in oxygen-
ated fuel formulations. Results were generally comparable to that of gasoline not containing oxygenates.
Table A-1 Uses in Vehicles - Metals
Aluminum alloy Carburetor, accelerator pump, fuel pump casing
Magnesium alloy Fuel pump casing, plate on steel, brass component
specialty-purpose two-cycle engine, transmission housings
Copper Brass and bronze
Zinc Brass, air cleaner, carburetor
Carbon steel Fuel line, fuel pump fittings and casings, fuel filter, fuel tank,
carburetor fuel inlet, accelerator pump
Cartridge brass Fuel line fittings, carburetor jets and inlet needle, fuel bowl float,
power valve, valve seats
Aluminum bronze Fuel pumps, fuel distribution system
Stainless steel Carburetor fuel inlet needle, carburetor springs, catalytic converter,
EGR valve
Aluminum alloy Carburetor, accelerator pump, fuel pump casing, fuel tank fill pipe,
(cast) intake manifold
Iron (cast) Carburetor body, iron plates, engine block, intake and exhaust manifolds
Zinc alloy (cast) Carburetor body, plate on steel, carburetor diaphragm
Terne plate Fuel tank, fuel line, air cleaner assemblies
Alloy Typical Use
The materials listed in Table A-1 have been tested with various alcohol blends.
There were no significant differences between the performance of the alcohol blends
compared to a base unleaded gasoline.
An additional reference on
"The Compatibility of Reformulated and
Oxygenated Gasoline with Fuel System Materials (DAI Informational Document # 970201, February 1997)" from
Downstream Alternatives Inc., P.O. Box 190, Bremen, IN 46506-0190.
[ http://www.ethanolrfa.org/objects/pdf/DAI970201.pdf ]
__________________
George in
Santa Fe
'01 BMW X5 3.0i V-6
soon to be Converted to
a FFV capable of burning
E-85 Ethanol.
[ http://www.bmwcca.org/ ]
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