Development of Power

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. 12-2