Introduction of i c engines
Internal combustion engines are seen every day in automobiles, trucks, and buses. The name internal combustion refers also to gas turbines except that the name is usually applied to reciprocating internal combustion (I.C.) engines like the ones found in everyday automobiles. There are basically two types of I.C. ignition engines, those which need a spark plug, and those that rely on compression of a uid. Spark ignition engines take a mixture of fuel and air, compress it, and ignite it using a spark plug. Figure 1.1 shows a piston and some of its basic components. The name `reciprocating' is given because of the motion that the crank mechanism goes through. The pistoncylinder engine is basically a crank-slider mechanism, where the slider is the piston in this case. The piston is moved up and down by the rotary motion of the two arms or links.
The crankshaft rotates which makes the two links rotate. The piston is encapsulated within a combustion chamber. The bore is the diameter of the chamber. The valves on top represent induction and exhaust valves necessary for the intake of an air-fuel mixture and exhaust of chamber residuals. In a spark ignition engine a spark plug is required to transfer an electrical discharge to ignite the mixture. In compression ignition engines the mixture ignites at high temperatures and pressures. The lowest point where the piston reaches is called bottom dead center. The highest point where the piston reaches is called top dead center. The ratio of bottom dead center to top dead center is called the compression ratio. The compression ratio is very important in many aspects of both compression and spark ignition engines, by de ning the e ciency of engines. Compression ignition engines take atmospheric air, compress it to high pressure and temperature, at which time combustion occurs. These engines are high in power and fuel economy. Engines are also divided into four stroke and two stroke engines. In four stroke engines the piston accomplishes four distinct strokes for every two revolutions of the crankshaft. In a two stroke engine there are two distinct strokes in one revolution. Figure 1.2 shows a p-v diagram for the actual process of a four stroke internal conbustion (IC) engine. When the piston starts at bottom dead center (BDC) the intake valve opens. A mixture of fuel and water then is compressed to top dead center (TDC), where the spark plug is used to ignite the mixture. This is known as the compression stroke. After hitting TDC the air and fuel mixture have ignited and combustion occurs. The expansion stroke, or the power stroke, supplies the force necessary to drive the crankshaft. After the power stroke the piston then moves to BDC where the exhaust valve opens. The exhaust stroke is where the exhaust residuals leave the combustion chamber. In order for the exhaust residuals to leave the combustion chamber the pressure needs to be greater than atmospheric. Then the piston preceeds to TDC where the exhaust valve closes. The next stroke is the intake stroke. During the intake stroke the intake valve opens which permits the air and fuel mixture to enter the combustion chamber and repeat the same process.
Internal combustion engines are seen every day in automobiles, trucks, and buses. The name internal combustion refers also to gas turbines except that the name is usually applied to reciprocating internal combustion (I.C.) engines like the ones found in everyday automobiles. There are basically two types of I.C. ignition engines, those which need a spark plug, and those that rely on compression of a uid. Spark ignition engines take a mixture of fuel and air, compress it, and ignite it using a spark plug. Figure 1.1 shows a piston and some of its basic components. The name `reciprocating' is given because of the motion that the crank mechanism goes through. The pistoncylinder engine is basically a crank-slider mechanism, where the slider is the piston in this case. The piston is moved up and down by the rotary motion of the two arms or links.
The crankshaft rotates which makes the two links rotate. The piston is encapsulated within a combustion chamber. The bore is the diameter of the chamber. The valves on top represent induction and exhaust valves necessary for the intake of an air-fuel mixture and exhaust of chamber residuals. In a spark ignition engine a spark plug is required to transfer an electrical discharge to ignite the mixture. In compression ignition engines the mixture ignites at high temperatures and pressures. The lowest point where the piston reaches is called bottom dead center. The highest point where the piston reaches is called top dead center. The ratio of bottom dead center to top dead center is called the compression ratio. The compression ratio is very important in many aspects of both compression and spark ignition engines, by de ning the e ciency of engines. Compression ignition engines take atmospheric air, compress it to high pressure and temperature, at which time combustion occurs. These engines are high in power and fuel economy. Engines are also divided into four stroke and two stroke engines. In four stroke engines the piston accomplishes four distinct strokes for every two revolutions of the crankshaft. In a two stroke engine there are two distinct strokes in one revolution. Figure 1.2 shows a p-v diagram for the actual process of a four stroke internal conbustion (IC) engine. When the piston starts at bottom dead center (BDC) the intake valve opens. A mixture of fuel and water then is compressed to top dead center (TDC), where the spark plug is used to ignite the mixture. This is known as the compression stroke. After hitting TDC the air and fuel mixture have ignited and combustion occurs. The expansion stroke, or the power stroke, supplies the force necessary to drive the crankshaft. After the power stroke the piston then moves to BDC where the exhaust valve opens. The exhaust stroke is where the exhaust residuals leave the combustion chamber. In order for the exhaust residuals to leave the combustion chamber the pressure needs to be greater than atmospheric. Then the piston preceeds to TDC where the exhaust valve closes. The next stroke is the intake stroke. During the intake stroke the intake valve opens which permits the air and fuel mixture to enter the combustion chamber and repeat the same process.
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