Section 2 Basics of Engine Operation
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Summary
A gasoline-fueled engine is a mechanism
designed to transform the chemical energy of
burning fuel into mechanical energy. A gasoline
engine is an internal combustion engine. In an
internal combustion engine, gasoline is combined
with air and burned inside the engine. The more
surface area of gasoline exposed to the air, the
faster a given amount will burn. To produce the
rapid burning required in an engine, gasoline
must be broken up into tiny droplets and mixed
with air. This is called atomizing.
The stroke of a piston is its movement in the
cylinder from one end of its travel to another.
Four-stroke engines need four strokes to complete
the operating cycle: intake, compression, power,
and exhaust. Lubrication of four-stroke engines is
generally provided by a splash system or a pump
system.
In a two-stroke engine, the intake, compression,
power, and exhaust functions take place during
two strokes of the piston. Two-stroke engines have
many advantages over four-cycle units. They do not
have conventional valves, tappets, or a camshaft, so
they are simpler in design. Two-stroke engines are
also smaller and lighter than four-stroke engines
of equivalent horsepower.
The two-stroke engine receives its lubrication
as a fuel-oil mixture is passed through the engine.
Therefore, it will receive adequate lubrication even
when operated at extreme angles.
Review Questions
Answer the following questions on a separate
sheet of paper.
1. In a(n) _____ combustion engine, gasoline
is combined with air and burned inside the
engine.
2. Explain why gasoline is atomized before
being burned in an engine.
3. Name the four strokes of a four-stroke engine
in proper order.
4. Name three important intake valve functions.
5. Why is there a difference in temperature
between the intake and exhaust valves?
6. How does compression increase the force of
combustion?
7. The compression ratio must be limited in
gasoline spark ignition engines, because
_____.
A. there is no power advantage after
compressing the fuel to a certain point
B. the engine becomes too diffi cult to start
C. mechanically it is not possible to increase
the compression ratio
D. the heat of compression will ignite the
air-fuel mixture too soon
8. Time during the four-stroke cycle when both
valves are open is called _____.
9. What are the two methods employed for
lubricating four-stroke engines?
10. What is the main difference between a
four-cycle engine and a two-cycle engine?
Suggested Activities
1. Look up additional information about internal
combustion engine development. Names to look
up include Christian Huygens, Philip Lebon,
Samuel Brown, William Barnett, Pierre Lenoir,
Beau DeRochas, Dr. N. A. Otto, Atkinson,
Gottlieb Daimler, Priestman and Hall, Herbert
Akroyd Stuart, and Rudolph Diesel.
2. Begin a collection of engine repair and service
manuals.
3. Make a bulletin board display that illustrates
the principles of two- and four-stroke engines.
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