By:
Tim Wusz
Aromatics:
This
is a type of chemical compound referred
to as a cyclic organic due to its circular
structure. They are found in nearly all
gasolines, normally as toluene. Xylene is
less common, and benzene are restricted
to very low levels due to toxicity.
Distillation:
A
gasoline contains various hydrocarbons that
boil at different temperatures. As a result,
the gasoline boiling range can extend from
80 °
F to
a maximum of 437 °
F.
This is in contrast to water that boils
only at 212 °
F at
sea level.
Octane
Numbers:
Research
Octane Number (RON) is measured under mild
conditions and is more important in controlling
part throttle knock.
Motor
Octane Number (MON) is measured under more
severe conditions and is most important
for octane satisfaction at wide open throttle.
Anti-Knock
Index (AKI) is the average of the RON and
MON. This is the number posted on the retail
gasoline pumps normally indicating 87, 89,
or 92 octane. Racing gasoline have AKI’s
from 100 to 118.
Oxygenated
Compounds:
These
are required in street gasolines in many
areas of the U.S.
to
help reduce exhaust emissions. The two most
common oxygenated compounds are Methyl Tertiary
Butyl Ether (MTBE) and Ethanol (This is
an alcohol).
Reid
Vapor Pressure:
Normally
measured in psi, RVP is a measure of the
front end volatility of the (RVP)
gasoline. This is important for
getting a carburetor car started in cold
weather. Summer RVP = 7 psi, and winter
RVP = 13.5 psi.
Specific
Gravity:
Measures
the density of gasoline compared to water.
A specific gravity of 0.720 means that the
gasoline weighs 0.72 times as much as water,
or it is 72% of the weight of water. Most
gasolines weigh about 6.2 pounds per gallon.
Volatility:
Used
in referring to the ease with which a gasoline
turns from a liquid to a vapor. Low volatility
refers to low RVP, indicating less light
hydrocarbons in the gasoline front end.
Southern
California
summer grade gasolines have low volatility.
Winter grade gasolines in Michigan
are
high volatility, or high RVP to make the
engine easier to start in sub-zero temperatures.
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