Fuels and Additives
What is gasoline?
Gasoline
is made up of different hydrocarbon compounds, including aromatics, olefins, and
benzene, all of which contribute to ozone and toxic air pollution. The levels at
which these components are present in reformulated gasoline (RFG) are lower,
resulting in fewer harmful emissions. Gasoline comes from crude oil pumped out
of the ground in the form of a black liquid called petroleum. This oil contains
aliphatic hydrocarbons composed of hydrogen and carbon. The carbons link
together to form different hydrocarbon links of various sizes. The longer the
chain, the heavier and harder the link is to boil. Chain links of C7H16 through
C11H24 are blended together to form gasoline. All of them vaporize at levels
below the boiling point of water. Though gasoline is an aliphatic hydrocarbon,
it does not burn cleanly to form only CO2 and H2O. If gasoline is burned as a
vapor with a hot flame and plenty of oxygen, the products of the reaction would
be CO2 and H2O that are nearly pure. But automobile
exhaust contains a lot more than just carbon dioxide and water, and carbon
monoxide is formed because combustion is incomplete. Oxygen is not available
fast enough to react completely with all of the carbon monoxide present, and
because of the pressure and temperature inside a cylinder, nitrogen and oxygen
combine in various ways to form nitrogen oxide. Not all hydrocarbons participate
in the reaction because of the small amount of time available during the
combustion phase.
What is motor gasoline?
Motor gasoline is a complex mixture of
relatively volatile hydrocarbons that sometimes contains small quantities of
additives to form a fuel suitable for use in spark-ignition engines. As defined
by ASTM Specification D 4814 or Federal Specification VV-G-1690C, motor gasoline
is said to have a boiling range of 122° F to 158º F at the 10 percent recovery point. The recovery point at 90 percent is
365° F to 374º F. Motor gasoline includes conventional gasoline, oxygenated gasoline, including gasohol, and reformulated
gasoline, but it does not include aviation gasoline. To produce finished motor
gasoline, the mechanical mixing of motor gasoline, blending products, and
oxygenates are required. Finished
motor gasoline may be further mixed with other motor gasoline blending
components or oxygenates, which results in increased volumes of finished motor
gasoline and changes in the formulation
of finished motor gasoline.
There are five blends of gasoline marketed in the United States.
Conventional gasoline is
the most widely available gasoline. It is sold where air quality is
satisfactory. Since 1992, it has been formulated to evaporate more slowly in
hot weather to reduce smog, and it now contains detergent additives to
reduce engine deposits.
Winter Oxygenated gasoline
as of 1992, is formulated as conventional gasoline with oxygen-rich
chemicals added, such as MTBE or ethanol. The oxygen promotes cleaner
burning, reduces carbon monoxide, and is generally sold from November to
March because cold engines operate less efficiently and produce more carbon
monoxide.
Reformulated gasoline (RFG) was introduced in 1995 and is mandated in areas where toxins in the air are
a constant problem. It contains oxygen-rich chemicals in lesser
concentrations than conventional and winter oxygenated gasoline. It is also
formulated from certain toxic chemicals found in the gasolines below.
Oxygenated Reformulated Gasoline is a wintertime gasoline exclusive to the New York City area due to the
heavy carbon monoxide pollution.
California Reformulated Gasoline (CaRFG)
was introduced in 1996. It has a different formulation and burns more
cleanly than regular reformulated gasoline. MTBE has been implicated as a
pollutant of groundwater, and in 1999 California ruled that MTBE must be
phased out of CaRFG
by December 31, 2002.
Conventional, oxygenated,
and reformulated gasolines
are classified by three grades:
Regular Gasoline: having an antiknock index (octane rating) greater than or equal to 85
and less than 88.
Mid-grade Gasoline: having an antiknock
index greater than or equal to 88 and less than or equal to 90.
Premium Gasoline: having an antiknock index, i.e., octane rating, greater than 90.
What is octane?
Since 1912 the spark ignition internal combustion engine's
compression ratio has been constrained by the unwanted "knock" that
could rapidly destroy engines. "Knocking" is a very good description
of the sound heard from an engine using fuel of too low octane. The engineers
had blamed the "knock" on the battery ignition system that was added
to cars along with the electric self-starter. The engine developers knew that
they could improve power and efficiency if knock could be overcome. In 1927
Graham Edgar suggested using two hydrocarbons that could be produced in
sufficient purity and quantity. These were "normal heptane" and they
were already obtainable in sufficient purity from the distillation of Jeffrey
pine oil, and " an octane, named 2,4,4-trimethyl pentane " that he
first synthesized. Today we call it " iso-octane " or 2,2,4-trimethyl
pentane. The octane
had a high antiknock value, and he suggested using the ratio of the two as a
reference fuel number. He demonstrated that all the commercially available
gasolines could be bracketed between 60:40 and 40:60 parts by volume heptane:iso-octane.
The reason for using normal heptane and iso-octane was because they both have
similar volatility properties, specifically boiling point, thus the varying
ratios 0:100 to 100:0 should not exhibit large differences in volatility that
could affect the rating test."
What is reformulated gasoline?
The concept of RFG
was originally generated, developed, and endorsed by industry, not by the EPA or
other federal government agencies. Arco Petroleum was the first to successfully
market RFG in California in the 1980's to help reduce motor vehicle emissions. Their formula, "EC-1", was formulated as a replacement for leaded
gasoline. MTBE was an additive.
In 1990 President Bush sent the Clean Air
Act legislation to Congress, which included a number of provisions that would
lead to the introduction of non- petroleum fuels. Petroleum and oxygenate
industries argued that a significant fleet turnover would need to occur if
emission reductions were to be achieved, but RFG, on the other hand, would be
effective immediately on the existing fleet. These industries now offer RFG
programs as a substitute for most of the provisions for alternative fuels. The
final Clean Air Act legislation included a mandate for RFG to contain
oxygenates.
Throughout 1991, the EPA participated in
regulatory negotiation process with industries and organizations representing
the public in order to develop the framework for the RFG rulemaking. Vehicle
manufacturers and the oil companies invested millions of dollars in a research
program called Auto/Oil Air Quality Improvement Research Program. The
results of this program and many other studies conducted by EPA revealed that
large emission benefits of RFG were possible and cost effective. Now as a result
emissions standards for RFG in 2000 surpass the minimum requirements of the
Clean Air Act.
What is in reformulated gasoline?
The ingredients
used to make RFG are not different from the ingredients used to make
conventional gasoline. They only differ in the levels at which the ingredients
are used, thereby reducing the use of ingredients that contribute to air
pollution. Formulations of RFG suit the power requirements of vehicles in which
it is used. Although vehicle performance has always been considered when
choosing fuel formulation, emissions performance in fuel formulation has not.
But because of a mandate in the reduction of vehicle emissions, emissions
performance is now considered in the production of high quality, reformulated
gasoline. Therefore, in terms of RFG's effect on driving, vehicle owners should
notice little change, if any at all, in performance while dramatically reducing
harmful emissions.
What are the differences between reformulated gasoline and
conventional gasoline?
There are three main differences between
reformulated gasoline and conventional gasoline. RFG has lower levels of certain
compounds that contribute to air pollution, will not evaporate as easily as
conventional gasoline, and contains oxygenates. Conventional gasoline is made up
of different hydrocarbon compounds, including aromatics, olefins, and benzene,
all of which contribute to ozone and toxic air pollution. The levels at which
gasoline hydrocarbon components are present in RFG are lower, resulting in fewer
harmful emissions. RFG has lower volatility in the summer months, meaning
that it does not evaporate as easily as conventional gasoline, thereby reducing
the ability of gasoline to evaporate and in turn reducing the amount of
ozone-forming hydrocarbons released into the air. RFG also contains oxygenates
which are added to fuels for purposes of octane enhancement. The EPA claims that
the presence of oxygenates in RFG may result in a 1 to 2 percent reduction in
gas mileage in some vehicles when compared to fuel without oxygenates, although
gas mileage is more effected by the type of engine, driving habits, weather
conditions, and vehicle maintenance. The reformulated gasoline program will
result in a consistently better gasoline that burns more efficiently, has
reduced evaporative tendencies, and contains fewer impurities, which is a
benefit to human health and the environment.
Why choose Ethanol over MTBE?
Ethanol
is the most likely replacement of MTBE in reformulated gasoline. It behaves
better in groundwater and has fewer public health concerns, although ethanol has
encountered issues with its effects on air quality, supply and distribution, and
economics. In respect to protecting water resources, ethanol has several
advantages over MTBE. Like MTBE, ethanol/ gasoline blends are absorbed into the
groundwater, but ethanol is highly biodegradable and transforms into harmless
byproducts before potential receptors are invaded by plumes. It also does
not exhibit a taste or odor when present in water, unlike MTBE. In respect to
air quality, ethanol has several disadvantages when compared to MTBE. One
particular disadvantage is that ethanol may retard biodegradation of benzene, a
known carcinogen, thus allowing benzene plumes to spread further when gasoline
is spilled. Ethanol use can also increase VOC emissions and overall toxic air
emissions when compared to RFG containing MTBE. It also increases emissions of a
toxic air combustion by-product of ethanol, acetaldehyde, in RFG by diluting
lesser quantities of toxic compounds in gasoline. The significant toxic
dilution benefit of oxygenates is decreased with ethanol because only 5.7
percent ethanol, by volume, is necessary as opposed to 11 percent MTBE to meet
minimum oxygen content required for RFG. Production capacity of ethanol does not
currently exist to meet the demand if both California and the Northeast ( two
regions whom are currently thinking of switching to the use of ethanol instead
of MTBE in RFG) were to substitute ethanol for MTBE. The transportation of
ethanol is a problem because it is highly soluble in water, and the typical
transportation of fuel via pipeline is unable to transport ethanol. Therefore,
the current ethanol production would have to be transported from the Midwest (
where it is predominate) to California and the Northeast via truck, rail, or
ship. A possible solution for this supply and distribution problem is to
construct biomass based ethanol production facilities in those areas. Ethanol
will also increase the cost of RFG by 2.5 cents per gallon.