Category : Various Text files
Archive   : FUEL.ZIP
Filename : FUELTERM.TXT

ASTM - The "American Society for Testing and Materials" is
widely recognized as the authority on specifications for
petroleum products.

Volatility - The tendency of a fuel to evaporate {to change
from a liquid to a gaseous state}. This quality is of basic
and profound importance in carburated engines because it has a
major influence on the vapor-air ratio in the cylinders at the
time of ignition. The greater (higher) the volatility of a
fuel the greater the tendency to evaporate.
In a normal engine nearly all the fuel needs to be evaporated
before ignition. So for any Engine/Air Temperature combination
there is a minimum volatility that is required for proper
running.

Volatility Curve - Also know as the "Distillation Curve". The
ASTM Distillation test provides a measure, in terms of
volatility, of the relative proportions of all the hydrocarbon
components of a gasoline. The ASTM distillation curve
designates the maximum temperatures at which 10%, 50%, and 90%
of the fuel will be evaporated as well as the maximum end
point temperature. These distillation characteristics, define
and control, starting, warm-up, acceleration, vapor lock, and
crankcase dillution.
The significance of any point on the ASTM volatility curve
depends on the temperature range in question. Under low
temperature conditions as in cold weather starting, when only
a small portion of the fuel is evaporated, the low temperature
end of the curve is of chief importance. While for higher temp
ranges like those in the intake of a hot engine the shape of
the low temp end of the curve is of little importance. Since
all of this part of the fuel is evaporated anyway.
Vapor -
Liquid (V/L) Ratio - The ratio of volume of vapor formed at
atmospheric pressure to the volume of gasoline sampled in ASTM
method D2533. The V/L ratio increases with temperature for any
given gasoline. The temperature at which the maximum V/L ratio
is specified for each ASTM volatility class is based on the
air temperatures and the altitude associated with the use of
the class.

Vapor Lock - A serious restriction of the fuel supply that is
due to excessively rapid formation of vapor in the fuel lines
or carb. Vapor formation begins to occur in fuel lines, pumps,
etc. when the fuel reaches a temperature where the vapor
pressure of the fuel is equal to the pressure in the system.
Gravity feed fuel systems tend to be less prone to vapor lock
than snowmobile type vacuum pump systems where negative
pressures exist.

Reid Vapor Pressure (RVP) - A standard indicator of gasoline
volatility. Oil companies vary RVP seasonally to correspond to
the weather. Gasolines have an RVP range of 5 to 15. High RVP
fuels are used in cold climates for easier climates. A high
RVP fuel can easily vapor lock in hot weather, or under most
racing conditions, regardless of the air temperature. Most
racing fuels have low RVP ratings that are fixed year round,
usally in the 5.5 to 8.0 range.

Air/Fuel Ratio - The ratio of pounds of Air to pounds of Fuel
needed for combustion in an engine. A/F Ratios range from 2:1
to about 16:1 depending on the fuel used and the running
conditions, with 14.7:1 considered the stoichiometric or
chemically correct ratio under perfect conditions with
gasoline. These perfect conditions only seem to exist if you
race on paper.

Specific Gravity - A measure of the density of a liquid
relative to the density of water, with water having a specific
gravity of 1.0. Given the fact that Air/Fuel ratio is based on
pounds of AIR to pounds of FUEL, changing the specific gravity
of your fuel can have a profound affect on the A/F ratio of
your engine. In short you've changed the jetting. Specific
gravity is the basis of the AMA fuel check. (Remember this for
later).

Octane Number - A measure of the anti-knock characteristics of
a given fuel. The octane number you see at the pumps is the
average of two octane numbers; the Research Octane Number
(RON) and the Motor Octane Number (MON). Each of these octane
numbers is determined by ASTM laboratory tests. Low-speed and
low load knock characteristics are determined by the RON test
method. The MON method tests high-speed, high load, high
temperature situations, in practice these conditions exist
during periods of high speed power accelerations, hill
climbing, or any period of high power output(sounds like
racing to me). Obviously the MON number will be lower, but
it's the one racers should concern themselves with.

Hydrocarbons - The building blocks of gasoline. Gasoline is
made up of a combination hydrocarbons with different molecular
weights and structure. The various components that make up
gasoline are classified according to the number of carbon
atoms in the molecules. These components form chemical groups
called Aromatics, Paraffins, and Olefins. Aromatics are the
components that most people are framiliar with. They include
chemicals like Toluene, Benzene, Aniline, Benzene, and Xylene
amoung others. They are commonly used to increase octane and
add to raise BTU content. They can usually be found in
commercial octane boosters. The amount of energy a gallon of
gas will produce is a function of the proper combination
Aromatics, Paraffins, and Olefins. These combinations are
designed to produce a specific distillation curve. They fall
into three basic groups;
Light Fractions - which vaporize from 85 to 130 degrees(F)
Medium Fractions - which vaporize from 130 to 250 degrees(F)
Heavy Fractions - which vaporize from 250 to 400 degrees(F).

Oxygenates - Oxygen bearing chemicals that can be added to
fuel that bring additional oxygen to the combustion process.
Commonly used oxygenates are Methanol, Ethanol, Nitromethane,
Nitropropane #2, Propylene Oxide, Piric Acid, TAME (Tertiary
Amyl Methyl Ether), MTBE (Methyl Tetra Amyl Methyl Ether).
These chemicals vary in the oxygen content from a high of 50%
for methanol to a low of about 15% for TAME. These have
varying degrees of suitability to the task of producing
additional power, not to mention the fact that they are toxic
and can be VERY difficult to handle. EXTREME caution is
advised.

BTU - British Thermal Unit - BTUs are used to measure the
energy content of a fuel, usually in BTU/lb. The higher the
BTU value the greater the potential energy available. Gasoline
is in the range of 20,200 BTUs while Methanol has an energy
content of only 9,700 BTUs.

Flame Front - The advancing of fuel burning from a source of
ignition. During normal combustion there is only one flame
front which advances from the spark plug to the outer edges of
the combustion chamber. During abnormal combustion multiple
flame fronts can start, which leads to detonation.

Pre-Ignition - The starting of ignition by any source other
than the spark plug usually before before normal firing of the
spark plug.

Detonation - The uncontrolled burning of the fuel in the
combustion chamber. This is usually associated with the
pinging sound you here from engines with poor fuel, as
multiple flame fronts collide in the combustion chamber.

Auto Ignition Temperature - The temperature at which a
combustible mixture will ignite on its own. This is sometimes
called the "Spontaneous Coumbustion Point". This is closely
associated with detonation.

Spark Lead Time - The time before TDC needed to fire the spark
plug to ensure complete combustion of the trapped mixture.
Different fuels and engine setups will require different spark
lead times. As a general rule, the more efficient the
combustion the less lead time (timing) the engine will
require. This is especially true of high compression four
cycle engines.

Relative Air Density - RAD - A working number based on
barometric pressure, air temperature, altitude and humidty.
RAD is used by tuners to help determine the jetting changes
required by changes in weather or air temperature. Although
usually measured with a RAD guage, it is possible to calulate
relative air density using a chart or calculator.