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Construction Mechanic Basic Volume 01 - Construction methods and practices | Next
Air-Fuel Ratio |
CHAPTER 4
GASOLINE FUEL SYSTEMS
LEARNING OBJECTIVE: Describe the different types of gasoline fuel systems,
how the components function to provide fuel to the engine in proper quantities, and
servicing of the gasoline fuel system.
The purpose of the fuel system of the internal
combustion engine is to provide a combustible mixture
of fuel and air to the engine cylinders. The ratio of fuel
to air must always be in correct proportions regardless
of the speed and load of the engine.
GASOLINE FUEL SYSTEMS
LEARNING OBJECTIVE: Identify the
properties of gasoline and the components of a
fuel system.
The function of both the carburetor fuel system and
the fuel injection system is to supply a combustible
mixture of air and fuel to the engine. Major elements of
the gasoline fuel supply system include the following:
fuel tank and cap, fuel system emission controls, fuel
lines, fuel pump, fuel filter, carburetor or fuel injection
system, air cleaner, and exhaust system.
Before
discussing the components of a gasoline fuel system,
you should understand the composition and properties
of gasoline.
GASOLINE
Gasoline is a highly volatile flammable liquid
hydrocarbon mixture used as a fuel for internal-
combustion engines. Acomparatively economical fuel,
gasoline is the primary fuel for automobiles worldwide.
Chemicals, called additives, such as lead, detergents,
and anti-oxidants, are mixedinto gasoline to improve its
operating characteristics.
Antiknock additives are used to slow down the
ignition and burning of gasoline. This action helps to
prevent engine ping or knock (knocking sound
produced by abnormal and excessively rapid
combustion). Leaded gasoline has lead antiknock
additives. The lead allows a higher engine compression
ratio to be used without the fuel igniting prematurely.
Leaded gasoline is designed to be. used in older vehicles
that have little or no emission controls.
The fuel used today is unleaded gasoline. Unleaded
gasoline, also called no-lead or lead-free, does NOT
contain lead antiknock additives. Congress has passed
laws requiring that all vehicles meet strict emission
levels. As a result, manufacturers began using catalytic
converters and unleaded fuel.
The properties a good gasoline should have are as
follows:
Proper volatility (how quickly the gasoline
vaporizes)
Resistance to spark knock, or detonation
Oxidation inhibitors to prevent formationof gum
in the fuel system
Antirust agents to prevent rusting of metal parts
in the fuel system
Anti-icers to retard icing and fuel-line freezing
Detergents to help keep the fuel system clean
Dye for identification
PROPERTIES OF GASOLINE
For a gasoline fuel system to function properly, it is
necessary that the fuel have the right qualities to burn
evenly no matter what the demands of the engine are.
To help you recognize the qualities required of gasoline
used for fuel, let’s examine some of the properties of
gasoline and their effects on the operation of the engine.
Volatility
The ease with which gasoline vaporizes is called
VOLATILITY. A high volatility gasoline vaporizes
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