Figure 12-2.-Cylinder, piston, connecting rod, and crankshaft for a one-cylinder engine.
combustion engine, the combustion takes place inside
the cylinder and is directly responsible for forcing the
piston to move downward.
The change of heat energy to mechanical energy by
the engine is based on a fundamental law of physics. It
states that gas will expand upon the application of heat.
The law also states that the compression of gas will
increase its temperature. If the gas is confined with no
outlet for expansion, the application of heat will increase
the pressure of the gas (as it does in an automotive
cylinder). In an engine, this pressure acts against the
head of a piston, causing it to move downward.
As you know, the piston moves up and down in the
cylinder. The up-and-down motion is known as
reciprocating motion. This reciprocating motion
(straight line motion) must change to rotary motion
(turning motion) to turn the wheels of a vehicle. A crank
and a connecting rod change this reciprocating motion
to rotary motion.
All internal combustion engines, whether gasoline
or diesel, are basically the same. They all rely on three
elements: air, fuel, and ignition.
Fuel contains potential energy for operating the
engine; air contains the oxygen necessary for
combustion; and ignition starts combustion. All are
fundamental, and the engine will not operate without
any one of them. Any discussion of engines must be
based on these three elements and the steps and
mechanisms involved in delivering them to the
combustion chamber at the proper time.
DEVELOPMENT OF POWER
The power of an internal combustion engine comes
from the burning of a mixture of fuel and air in a small,
enclosed space. When this mixture burns, it expands; the
push or pressure created then moves the piston, thereby
cranking the engine. This movement is sent back to the
wheels to drive the vehicle.