Fuel Glossary
Aromatics:
This is a type of chemical compound referred to
as a cyclic organic due to it's circular structure. They are found in nearly
all gasolines, normally as toluene. Xylene is less common, and benzene
is 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 800F to a maximum of 437F. This is in contrast to water that
bolls only at 212F 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 (RVP):
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.