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Stoichiometry
Stoichiometry means the perfect balance of air
and fuel at a ratio (by weight) of 14.7:1
air to fuel. This can be achieved under most operating conditions
by using computer
control of the fuel system. Older carbureted systems were
operated strictly by vacuum,
and as a result, had wide variations in air/fuel ratios. Because
of the better balance with
computer controls, better performance, fuel economy and reduced
emissions can be
readily obtained.
Fuel System Components
There are several major
components that make up any modern fuel system.
These include:
Fuel Pumps
Today's fuel injection systems require a constant supply of steady
fuel pressure to operate properly. The electric pump is located
in the tank, and the pressure developed by the pump is determined
by the pressure required for the system. Low pressure systems
may run at 15 psi - while higher pressure systems may run at up
40 to 50 psi. Many newer pumps have the filter located on
the
pump inside the tank as well. Older systems used an in-line
filter
between the pump and the fuel injection system in the
engine compartment.
Lines and Filters
Because of the higher pressures
developed in modern fuel systems, special lines and filters
must be used that can withstand the additional
force. Because fuel injectors can be easily
clogged by particles from the tank, the filter
must be of high quality and must be changed
frequently to reduce problems.
Fuel Pressure Regulators
Fuel pressure regulators are designed to maintain a constant fuel
pressure
for electronic fuel injection systems. The spring above the
diapragm is
calibrated so that when the pressure exceeds the spring rating,
excess fuel
pressure will be allowed to return to the tank. Many systems
are also
vacuum controlled as well. These vacuum controlled systems
will allow
lower pressures when there is high vacuum, and higher pressures
when
vacuum decreases (under load or heavy acceleration). Because
of the
extra fuel required when using turbo or super chargers, the regulator
must
allow extra fuel pressure in the system. The vacuum acts on
the upper part
of the diapragm to help reduce spring pressure - allowing lower
pressures
to bypass to the tank. When checking these systems, the vacuum
line
should be checked for the presence of fuel - as this will indicate
a leaking diaphragm.
Fuel Injectors
The type of fuel injector
used will vary with the design of the system - and these are
explained in the next section. Fuel
injectors will spray atomized fuel in a hollow cone-shaped
pattern so that the fuel will mix with the
incoming air to provide a balanced air/fuel mixture.
Fuel can be sprayed into the top of the intake
manifold, or into the intake ports, depending
on the design of the system. Only diesel
fuel injection systems spray fuel directly into
the cylinder.