At one time, all a gasoline-producing company
to do to produce their product was pump the crude from the ground, run it
through the refinery to separate the fractions, dump in a couple of grams of
lead per gallon, and deliver the finished product to the service station. Of
course, automobiles were much simpler then and what they burned was not very
critical. As long as gasoline vaporized easily and did not cause the lower
compression engines to knock, everything was fine.
Times have changed. Today, refiners are under
constant pressure to ensure that their produce passes a series of rigorous tests
for seasonal volatility, minimum octane, existent gum and oxidation stability,
as well as to add the correct deicers and detergents to make the product
competitive in a price-sensitive marketplace.
Gasoline additives - primarily used in unleaded
gasolines - have different properties and a variety of uses.
Anti-Icing or Deicer
Isopropyl alcohol is added seasonally to
gasoline as an anti-icing agent to prevent gas line freeze-up in cold climates.
Metal Deactivators and Rust Inhibitors
These additives are used to inhibit reactions
between the fuel and the metals in the fuel system that can form abrasive and
Gum or Oxidation Inhibitors
Some gasolines contain aromatic amines and
phenols to prevent formation of gum and varnish. During storage, harmful gum
deposits can form due to the reaction of some gasoline components with each
other and with oxygen. Oxidation inhibitors are added to promote gasoline
stability. They help control gum, deposit formation, and staleness. Stale
gasoline becomes cloudy and smells like paint thinner.
Gum content is influenced by the age of the
gasoline and its exposure to oxygen and certain metals such as copper. If
gasoline is allowed to evaporate, the residue left can form gum and varnish.
Gasoline must have as little gum residue as
possible to prevent gum formation in the intake manifold, carburetor or fuel
injectors, and on intake valve stems.
The use of detergent additives in gasoline has
been the subject of some public confusion. Detergent additives are designed to
do only what their name implies - clean certain critical components inside the
engine. They do not affect octane.
By far the most widely used gasoline additive
today is ethanol, or grain alcohol. Ethanol's value as an octane enhancer
becomes more apparent when considered in the context of the government-mandated
phasedown of tetraethyl lead. Blending 10 percent ethanol into gasoline is seen
as a comparatively inexpensive octane booster that results in an increase of 2.5
to 3 road octane points.
In addition to octane enhancement, ethanol
blending keeps the carburetor or fuel injectors clean due to detergent additive
packages found in most of the ethanol marketed. It also inhibits fuel system and
injection corrosion due to additive packages and decreases carbon monoxide
emissions at the tailpipe due to the higher oxygen content of blended fuel.
Methanol is the lightest and simplest of the
alcohols and is also known as wood alcohol. It can be distilled from coal, but
most of what is used today is derived from natural gas.
In the early 1980s, a few companies begin
selling a blend of 5 percent methanol in gasoline in the Northeast and Midwest.
This showed that methanol plug anticorrosion co-solvents could compete in the
motor fuel market as an octane enhancer. Today, both General Motors and Ford
have working prototypes on the road that can burn any combination of fuel from
nearly neat methanol (85 percent methanol with 15 percent gasoline) to straight
gasoline. They key is a fuel line sensor that detects methanol concentration and
adjusts spark timing and air/fuel mixture accordingly. The federal government is
pushing for methanol acceptance through industry incentives and fleet-sponsored
For now, however, many auto maker continues to
warn motorists about using a fuel that contains more than 10 percent methanol
and co-solvents by volume. Methanol is recognized as being far more corrosive to
fuel system components than ethanol, and it is this corrosion that has auto
Methyl tertiary butyl ether (MTBE) has become
very popular in the past few years as an octane enhancer and supply extender
because of excellent compatibility with gasoline. Current U.S. EPA restrictions
on oxygenates limit MTBE in unleaded gasoline to 11 percent of volume. At that
level, it increases pump octane (RM/2) by 2.5 points. However, it is usually
found in concentrations of 7 to 8 percent of volume.
MTBE has found favor among refiner/suppliers
and independent marketers alike because it is not nearly as sensitive to
moisture as the other oxygenates, has virtually no effect on fuel volatility,
and can be shipped through product pipelines whereas ethanol and methanol blends
MTBE increases octane while reducing carbon
monoxide emissions at the tailpipe and does it at a cost that makes it very
attractive to gasoline marketers across the country.
Some gasoline may contain a small quantity of
alcohol. The percentage of alcohol mixed with the fuel usually does not exceed
10 percent. An excessive quantity of alcohol in gasoline may result in fuel
system corrosion, fuel filter plugging, deterioration of rubber fuel system
components, and a lean air/fuel ratio. These fuel system problems may result in
driver complaints of a lack of power, acceleration stumbles, engine stalling,
and hard or no starts. Some vehicle manufacturers supply test equipment to check
the level of alcohol in gasoline. The following alcohol-in-fuel test procedure
requires only the use of a calibrated cylinder.
1. Obtain a 100-milliliter (100-ml) cylinder
graduated in 1-ml divisions.
2. Fill the cylinder to the 90-ml mark with
3. Add 10 ml of water to the cylinder so the
cylinder is now filled to the 100-ml mark.
4. Install a stopper in the cylinder and shake
it vigorously for 10 to 15 seconds.
5. Carefully loosen the stopper to relieve any
6. Install the stopper and shake the cylinder
vigorously for another 10 to 15 seconds.
7. Carefully loosen the stopper to relieve any
8. Place the cylinder on a level surface for
about 5 minutes to allow the liquids to separate.
9. Any alcohol in the fuel is absorbed by the
water and settles to the bottom. If the water content in the bottom of the
cylinder exceeds 10 ml, there is alcohol in the fuel. For example, if the water
content is not 15 ml, there was 5 percent alcohol in the gasoline.