mixture enters the engine cylinders on the intake
Q4-2. Which of the following terms best describes
strokes; it is then compressed and ignited. In burning,
the property of a fuel to resist detonation?
the fuel-air mixture expands and high pressure is
1.
Compressibility
produced in the engine cylinders. This pressure forces
2.
Octane rating
the pistons downward on the power strokes. The fuel
3.
Volatility
system must vary the proportions of air and gasoline for
4.
Combustibility
different operating conditions. For normal running with
a warm engine, the proper mixture ratio is about 15
GASOLINE FUEL SYSTEM
parts air to 1 part gasoline. But for initial starting with a
COMPONENTS
cold engine, a much richer mixture is needed; the
mixture does not burn as readily in a cold engine and
LEARNING OBJECTIVES: Identify the
the gasoline does not turn to vapor so readily. Also,
components of a gasoline engine fuel system.
when accelerating, or during high-speed or full-load
Describe engine troubles that can be traced to
operation, a richer mixture is required. Richness means
the carburetor system. Identify two sources
a higher proportion of gasoline; a mixture of 9 parts air
from which emissions originate in the gasoline
to 1 part gasoline is a rich mixture. The opposite of
fuel system and engine.
richness is leanness. A 16 to 1 mixture ratio is a
The primary components of a gasoline fuel sys-
relatively lean mixture.
tem (fig. 4-2) are the fuel tank, fuel pump, fuel
Some gasoline engines use a fuel-injection system.
filter, carburetor, and the fuel lines or tubes that con-
With this system, a pump delivers fuel to a fuel injector.
nect the tank, pump, and carburetor. Other compo-
The injector then injects the proper amount of fuel into
nents, shown in figure 4-2, are added to support the
the cylinder head during the intake stroke.
system.
The fuel system supplies a combustible mixture of
FUEL TANKS
gasoline and air to the engine cylinders. It stores the
gasoline in liquid form in a fuel tank, and then converts
On support equipment, the fuel tank may be
this liquid into a vapor and mixes it with air. The
mounted in a number of places, depending on the
PUMP TO CARBURETOR TUBE
FILTER TO PUMP HOSE
FUEL GAUGE-TANK UNIT
FUEL PUMP
FUEL TANK
CARBURETOR AND GOVENOR
CARBURETOR AIR CLEANER
THROTTLE CONTROL BUTTON
CHOKE CONTROL
BUTTON
ACCELERATOR PEDAL
FUEL GAUGE
WIRE
UNION
ASf04002
FUEL GAUGE-PANEL UNIT
FILTER
FUEL TANK TO FILTER
TO PUMP TUBE
TUBE-FRONT
TANK TO FILTER HOSE
FILTER
FUEL FILTER
TO PUMP HOSE
FUEL TANK TO FILTER TUBE-REAR
FUEL TANK FILLER
CAP
Figure 4-2.--Typical fuel system for a gasoline engine.
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