Figure 12-2.-Cylinder, piston, connecting rod, and crankshaft for a one-cylinder engine.combustion engine, the combustion takes place insidethe cylinder and is directly responsible for forcing thepiston to move downward.The change of heat energy to mechanical energy bythe engine is based on a fundamental law of physics. Itstates that gas will expand upon the application of heat.The law also states that the compression of gas willincrease its temperature. If the gas is confined with nooutlet for expansion, the application of heat will increasethe pressure of the gas (as it does in an automotivecylinder). In an engine, this pressure acts against thehead of a piston, causing it to move downward.As you know, the piston moves up and down in thecylinder. The up-and-down motion is known asreciprocating motion. This reciprocating motion(straight line motion) must change to rotary motion(turning motion) to turn the wheels of a vehicle. A crankand a connecting rod change this reciprocating motionto rotary motion.All internal combustion engines, whether gasolineor diesel, are basically the same. They all rely on threeelements: air, fuel, and ignition.Fuel contains potential energy for operating theengine; air contains the oxygen necessary forcombustion; and ignition starts combustion. All arefundamental, and the engine will not operate withoutany one of them. Any discussion of engines must bebased on these three elements and the steps andmechanisms involved in delivering them to thecombustion chamber at the proper time.DEVELOPMENT OF POWERThe power of an internal combustion engine comesfrom the burning of a mixture of fuel and air in a small,enclosed space. When this mixture burns, it expands; thepush or pressure created then moves the piston, therebycranking the engine. This movement is sent back to thewheels to drive the vehicle.12-2
Integrated Publishing, Inc. - A (SDVOSB) Service Disabled Veteran Owned Small Business