Section 2 Basics of Engine Operation
88
The previous questions can be categorized into
fi ve basic areas:
1. Mechanical (engine design and construction)
2. Fuel metering (mixing gasoline and air, and
admitting it to the cylinder)
3. Ignition (fi ring the fuel charge)
4. Cooling (heat dissipation)
5. Lubrication (oiling of moving parts)
For purposes of this chapter, we will assume
that the gasoline and air are being mixed correctly,
the fuel charge is being fi red at the right time, and
the engine is properly cooled and lubricated. Each
of these areas will be covered in detail in later
chapters.
Simple Engine in Operation
In its simplest form, an engine consists of a
ported cylinder, piston, connecting rod, and crank-
shaft. See Figure 5-9. The piston is a close fi t inside
Constructing an
Elementary Engine
An elementary engine can be formed by
attaching a crankshaft and a connecting rod to the
setup illustrated in Figure 5-7. The lid will serve
as a piston and the container will act as a cylinder.
See Figure 5-8. When the air-fuel mixture in the
cylinder is ignited, it will drive the piston upward,
causing the crankshaft to turn.
Although it is crude, this elementary engine
illustrates the operating principles of a modern
gasoline engine. Study the names of the various
parts shown in Figure 5-8. Become acquainted with
the parts and their application to engine design.
There are many shortcomings in the engine
pictured in Figure 5-8. These are addressed in the
following questions:
• How will a fresh air-fuel charge be admitted
to the cylinder?
• How will the charge be ignited?
• What holds the various parts in alignment?
• How will the engine be cooled and lubricated?
• What will time the fi ring of the air-fuel mixture
so that the piston will push on the crankshaft
when the journal is in the correct position?
• How will the burned charge be removed
(exhausted) from the cylinder?
• What will keep the crankshaft rotating after
the charge is fi red, and until another charge
can be admitted and fi red?
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Figure 5-7.
A—The lid is placed in a long container. B—Most of the
energy of the burning fuel is absorbed by the lid, imparting
greater speed to the lid when combustion occurs.
A B
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Figure 5-8.
The principles of operation illustrated here are the
same as those used in a modern gasoline engine.
Note how the burning fuel mixture forces the lid
(piston) upward to turn crankshaft and pulley.
Main bearing
Crankshaft
Pulley
Journal
Connecting rod
Cylinder
Piston
Burning
fuel
mixture
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