Introduction to Internal Combustion Engine

Internal combustion Engine

An engine is a device that converts the chemical energy of fuel into mechanical work with the help of a piston connecting rod and crank. For the production of heat, the burning of fuel is a necessary condition. In some of the engines, the burning of fuel takes place inside the engine or outside the engine. if the fuel is burnt inside the engine is called Internal Combustion Engines and if the fuel is burnt outside the engine is known as the external combustion engine. 

The most common applications of I C engines are in automobile engines, lawn cutter engines, diesel generators, boat engines, and many more.

The thermodynamic cycle of an engine consists of four processes like suction, compression, power or expansion, and exhaust. In an engine, this process is completed by the piston movement. The movement of the piston from TDC to BDC is known as a stroke and the process strokes are known as suction stroke, compression stroke, power stroke, and exhaust stroke.

Based on stroke, the engine is defined as 2-Stroke engines and 4-Stroke engines. In 2-stroke engines, all four processes are completed in one revolution of crank whereas in the 4-stroke engine all four processes are completed in 2 revolutions of crank.

Figure: Cross-section of petrol the engine.

The above figure shows the parts of an I C engine. the description of the parts are as follows

• The cylinder is the hollow cylindrical part of an engine in which all the four processes take place, the material of cylinder block is cast iron and aluminum alloy. The aluminum alloy cylinder is light in weight as compared to cast iron piston. 

• The piston is the reciprocating member of the engine, it is also called the heart of an engine, all the four processes are done with the help of piston reciprocating movement. The piston is also made by aluminum alloy.

• Piston rings are mounted near to the top of the piston as shown in the above figure by a yellow color, the first ring is called the compression ring, which prevents the leakage of charge from the combustion chamber to crankcase and second ring is known as the oil ring, which is used to remove the engine oil from the cylinder surface. There are three piston rings are used instead of two rings shown in the figure. The first two top rings of the piston are called compression rings and the third ring is called oil rings. The piston rings are made of cast iron. it also provides safety against wear of the piston from cylinder wall during reciprocation movement.  

• The top dead center is extreme top the position of piston and bottom dead center is the extreme bottom position of the piston.

• Exhaust valve allows the combustible gases to move out of the engine during the exhaust stroke.

• The exhaust manifold is the special design passage in which exhaust gases come from the engines that are collected and sends it to the atmosphere through the pipe consists of the catalytic converter and muffler. 

• A spark plug is a device that helps to ignite the fuel-air mixture inside the cylinder.

• Inlet manifold is a passage in which a fresh mixture of air and fuel comes from carburetor to engine.

• The Inlet valve allows the fresh mixture of air and fuel to come inside the cylinder.

• The carburetor is a device which mixes the fuel and air at a required proportion for the proper working of the engine at different revolutions

• After burning of air-fuel mixture large amount of heat is released, some heat is absorbed by the cylinder wall, this absorbed heat is removed by a water jacket to provide safety against metallurgical failure of the engine cylinder.

• The piston and connecting rod are connected by a pin are called the Gudgeon pin.

• The connecting rod is connecting member and it oscillates between piston and crank. The force acting on the piston is transferred by the connecting rod to the crankshaft. 

• Crankpin is the joint between the crank and the connecting rod.

• The oscillating movement of the connecting rod is converted into rotary motion by the crank. The heat energy of the fuel is converted into the reciprocating movement of the piston then; it converted into the oscillating moment of connecting rod and then converted into rotary motion of crank, which is used for further useful work. 

• The Crankcase the space in which engine oil is filled for cooling purposes.

• The rotation of the crank is transfer to the shaft. On this shaft flywheel of an engine or generator is mounted outside the engine. Here the shaft is used to transmit the mechanical work outside the engine, which is produced inside the engine.

 Figure: Cross-section of diesel engine

In the above figure, the cross-section of the diesel engine is shown, all the parts are the same except the fuel injector which is used to spray the diesel over the hot compressed air instead of spark plug and only air is injected during suction stroke instead of the air-fuel mixture.

The different types of cylinder arrangements are used for a different purpose. Some following arrangements are here

Figure: Cylinder arrangement

from the above figure, we have seen that in the In-line cylinder, the number of the piston is mounted on a single crankshaft. 

In the U-type arrangement, two crankshafts are used for two-piston arranged in a parallel manner. 

In the V-type arrangement, two pistons are mounted on a single crankshaft. the angle between the two pistons is 60 degrees or 90 degrees. 

In the X-type arrangement, four pistons are mounted on a single crankshaft. 

In the radial arrangement, more than four pistons are arranged on the circumference of a circle and all the pistons are mounted on the single crankshaft. Radial engines are found in airplanes. 

In the H-type, on a single crankshaft, two pistons are mounted. Four pistons are mounted on a two crankshaft as shown in the figure. 

In the opposed cylinder arrangement, a single crankshaft is used to connect two pistons as shown in the figure.

In the opposed piston arrangement, two crankshafts is used to connect two pistons as shown in the figure.

In the delta arrangement, three crankshafts are used and six pistons are arranged in such a way to form a delta symbol. 

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