CHAPTER 4
INTERNAL COMBUSTION ENGINE FUEL SYSTEMS
INTRODUCTION
The question of what is ideal gasoline is more
theoretical than practical. Manufacturers recommend
The fuel system of the internal combustion engine
the octane rating of the gasoline they feel is best for the
is designed to provide the proper quantity of fuel to the
engines they produce. Besides engine design, factors
engine under all normal operating conditions. The type
like the weight of the vehicle, the terrain and highways
of fuel used in either a gasoline or a diesel engine varies
over which it is to be driven, and the climate and
according to the design of the engine and the
altitude of the locality also determine what gasoline is
geographical location in which the engine will operate.
best to use.
Additionally, each application of the engine may
require changes in the type or design of fuel pump,
The function of the gasoline fuel system is to store,
carburetor, or fuel injection components.
transfer and provide gasoline to the engine in varying
Fuels used in modern Navy equipment are man-
quantities to ensure a proper fuel-air mixture at all
ufactured for use in various geographical locations. For
engine operating speeds. To function properly, the
instance, fuels manufactured for use in subzero tem-
gasoline must have the right qualities to burn evenly
peratures must be more volatile than those for use in
regardless of the engine's demands. These qualities
tropical areas. Otherwise, the fuel in cold climates
include volatility, antiknock quality and detonation,
would not vaporize (evaporate) readily enough to allow
and octane rating.
efficient engine operation. The result would be hard
VOLATILITY
starting, excessive fuel consumption, and a marked de-
crease in power developed by the engine. These prob-
The blend of a gasoline determines its volatility;
lems are solved for you by the manufacturer and the
that is, its tendency to change from a liquid to a vapor at
supply department. Your concern with the fuel system
any given temperature. The rate of vaporization
is in the maintenance and repair of the system's
increases as the temperature of the gasoline rises.
components to ensure long life and economical
operation of the engine.
A gasoline of low volatility brings about better fuel
economy and combats vapor lock (the formation of
PROPERTIES OF GASOLINE
vapor in the fuel lines in a quantity sufficient to block
LEARNING OBJECTIVE: Identify the
the flow of gasoline through the system). In the summer
properties of gasoline. Recognize the dif-
and in hot climates, fuels with low volatility lessen the
ferences and uses of various types of fuels.
tendency toward vapor lock.
Gasoline contains carbon and hydrogen in such
proportions that the gasoline burns freely and liberates
ANTIKNOCK QUALITY AND DETONATION
heat energy. If all the potential heat energy contained in
When any substance burns, its molecules and those
a gallon of gasoline could be converted into work, a
of the oxygen in the air around it are set into motion,
motor vehicle could run hundreds of miles on each
producing heat that unites the two groups of molecules
gallon. However, only a small percentage of this heat
in a rapid chemical reaction. In the combustion
energy is converted into mechanical energy by the
chamber of an engine cylinder, the gasoline vapor and
engine. Most authorities consider the power losses
oxygen in the air ignite and burn. They combine, and
within the engine to be as follows:
the molecules begin to move about very rapidly, as the
Engine
Percent of Power Loss
high temperatures of combustion are reached. This
Cooling System
35
rapid movement of molecules provides the push on the
piston to force it downward on the power stroke.
Exhaust Gases
35
In modern, high-compression gasoline engines, the
Engine Friction
5 to 10
fuel-air mixture tends to ignite spontaneously or to
Total
75 to 85
explode instead of burning slowly and uniformly. The
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