Automotive Systems

Formerly Automotive Systems I

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Internal Combustion Engine

In the internal combustion engine, combustion takes place inside the cylinder and is directly responsible for forcing the piston to move down. With an external combustion engine, such as a steam engine, combustion takes place outside the engine. The external combustion engine requires a boiler to which heat is applied. This combustion causes water to boil to produce steam. The steam passes into the cylinder under pressure and forces the piston to move downward.

The transformation of heat energy to mechanical energy by the engine is based on the fundamental law of physics which states that gas expands when heated. The law also states that when gas is compressed, the temperature of the gas increases. if the gas is confined with no outlet for expansion, then the pressure of the gas increases when heat is applied. In the internal combustion engine, the burning of fuel within an enclosed cylinder results in an expansion of gases. This expansion creates pressure on top of the piston, causing it to move downward. In an internal combustion engine, the piston moves up and down within the cylinder. The relationship between volume, pressure, and temperature within a cylinder of the engine is explained in the chart below and shown in Figure 2-2. Note the changes within the cylinder while the temperature outside remains a constant 70F.

This up-and-down motion is known as reciprocating motion. This motion (straight-line motion) mustbe changed into rotary motion (turning motion) to turn the wheels of a vehicle. A crankshaft and a connecting rod change their reciprocating motion to rotary motion.

All internal combustion engines, whether gasoline or diesel, are basically the same. We can best demonstrate this by saying they all rely on three things—fuel, air, and ignition.

Fuel contains potential energy for operating the engine; air contains the oxygen necessary for combustion; and ignition starts combustion. Each one is fundamental, and an engine cannot operate without them. Any discussion of engines must be based on these three factors and the steps and mechanisms involved in delivering them to the combustion chamber at the proper time.

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Published by SweetHaven Publishing Services
Based upon a text provided by the U.S. Navy

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