EPA - Office of Mobile Sources EPA420-F-95-003
Technical Overview August 1995
FUEL ECONOMY IMPACT ANALYSIS OF RFG
• The Environmental Protection Agency (EPA) evaluated fuel economy impacts
of reformulated gasoline (RFG) using a number of reliable studies (including
the $40 million joint research program by the auto and oil industries)
involving approximately 4000 individual observations.
• EPA found that the use of oxygenated fuels and RFG causes a small decrease
(l-3%) in fuel economy.
• EPA determined that a vehicle's fuel economy depends on the energy content
of the gasoline on which it runs. This conclusion matches what would be
expected based on combustion theory.
• This determination is also supported by similar conclusions drawn by
industry through their own studies (both laboratory and on-road testing).
• Therefore, the following points focus on energy content more than fuel
economy. The impact of fuel changes on fuel economy should be very similar
to the impact of fuel changes on the energy content.
Conventional Gasoline
• It is important to note that the energy content of gasolines varies from season
to season. The table below shows that typical summer conventional gasolines
contain 1.7% more energy than typical winter conventional gasolines.
Average Energy Content (btu per gallon)
Summer Winter Difference
114,500 112,500 1.7%
• The energy content of conventional gasolines also varies widely from batch to
batch and station to station. The table below shows this variation within
each season.
Energy Content (btu per gallon)
Minimum Maximum Difference
Summer 113,000 117,000 3.4%
Winter 108,500 114,000 5.0%
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Technical Overview Page 2
Conventional Gasoline vs RFG
• A gallon of RFG contains about 1-3% less energy than a gallon of
conventional gasoline. This difference is considerably smaller than the
differences in energy content among conventional gasolines described above.
• RFG contains oxygenates, which contain less energy per unit volume than
conventional gasoline. The table below outlines the differences in energy
content between RFG and conventional gasoline based on the three most
widely used oxygenates.
Oxygenate
Ethanol
ETBE
MTBE
Energy
Content of
Oxygenate
(btu/gallon)
76,100
96,900
93,500
Volume
of Oxy-
genate
in RFG
5.71%
12.8%
11.0%
Energy
Content
of RFG
(btu/gallon)*
111,836
111,811
111,745
Difference in
Energy Content
(RFG vs
Conventional)
1.9%
1.9%
2.0%
Assumes base gasoline has energy content of 114,000 btu/gallon
Other than oxygenates, there are other minor differences between RFG and
conventional gasoline that also impact the energy content of the fuel. These
impacts are different in summer and winter.
Summer RFGs contain approximately 1.0% less energy than summer
conventional gasolines.
This is expected to reduce fuel economy on average by 1.0% during the
summer.
For example, a car that gets 25 miles per gallon with conventional
gasoline may get 24.75 miles per gallon with RFG.
Winter RFGs contain approximately 3.0% less energy per gallon than winter
conventional gasolines.
This is expected to reduce fuel economy on average by 3.0% during the
winter.
For example, a car that gets 25 miles per gallon with conventional
gasoline may get 24.25 miles per gallon with RFG.
A March 1995 study conducted in Wisconsin confirmed a 2.8% reduction in
average fuel economy with winter RFG. This study used eight private
vehicles of various makes, designs, and ages, four different retail gasolines
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Technical Overview Page 3
(including conventional and reformulated gasolines), and 12,800 miles of driving on
city streets.
Other Fuel Economy Factors
• While all analyses to date show RFG has a minimal direct effect on fuel
economy, there are many other factors that can dramatically affect fuel
economy. The table on page 4 outlines these factors and their potential
impacts on fuel economy. The majority of these factors reduce fuel economy
more than only the use of RFG.
• Drivers experiencing a consistent, drastic change in fuel economy (i.e.,
reductions far greater than the expected 1-3%) that is not the result of the
other mitigating factors described in the table on page 4, should consider
that the reduction may be a maintenance problem or other issue unique to
the vehicle.
Fuel Economy and Pollution
• Common sense suggests that the slight reduction in fuel economy from RFG
would be associated with an increase in pollution. Fuel economy and
pollutants emitted are not always directly related, however, because vehicles
are designed to meet the emission standards on a basis of pollutant per mile.
• Hydrocarbon emissions and other pollutants such as carbon monoxide and
oxides of nitrogen depend mainly on how much the vehicle is driven and how
well the emission controls are functioning. There is little connection between
these emissions and fuel consumption, although it is to some extent
dependent on the circumstances causing the difference in fuel economy. If,
for example, a vehicle suddenly experiences a dramatic change in its fuel
economy due to something going wrong with the vehicle, there is likely to
also be a significant impact on the vehicle's emission performance. But if
that problem does not affect the vehicle's emission control system, then there
may be little or no impact on emissions.
• On the other hand, carbon dioxide (C02) emissions are always linked to fuel
consumption because C02 is the ultimate end product of burning gasoline.
The more fuel a car burns, the more C02 it emits.
• For those situations where fuel economy changes merely as a result of driving
habits, driving conditions, or fuel composition (as is the case with RFG), and
vehicle performance remains unaffected, the emission performance of the
vehicle is also likely to remain unaffected.
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Technical Overview
Page 4
Effect
Temperature*
Head Wind
Hills/Mountains
Poor road
conditions*
Traffic Congestion
Highway speed
Acceleration rate
Wheel Alignment
Tire Type
Tire Pressure*
Air Conditioning
Defroster*
Idling/Warmup*
Windows
Conditions
20oFvs 77oF
20mph
7% road grade
Gravel, curves,
slush, snow, etc.
20 vs 27 mph
average speed
70 vs 55 mph
"Hard" vs "Easy"
1/2 inch
non-radial vs
radial
15 psi vs 26 psi
Extreme Heat
Extreme Use
Winter vs
Summer
Open vs Closed
Average Fuel
Economy
Reduction
5.3%
2.3%
1.9%
4.3%
10.6%
N/A
11.8%
<1%
<1%
3.3%
21%
Analogous to
A/C on some
vehicles
Variable with
Driver
Unknown but
likely small
Maximum Fuel
Economy
Reduction
13%
6%
25%
50%
15%
25%
20%
10%
4%
6%
N/A
20%
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* These factors, with their respective reduction in fuel energy content, can decrease fuel economy in
the winter season relative to summer by 20 percent or more independent of whether the RFG
program is in effect.
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