Farm Power & Machinery

Classification of Internal Combustion Engine (IC engines)

The IC engines can be classified based on number of factors as follows
I. According to Number of Strokes :

Four Stroke Cycle Engine
In this type of engine, one complete combustion cycle is completed in four strokes of the piston or two revolution of the crankshaft. The principle of operation of Four stroke engine is shown in Fig. 2.3.
The four events that take place inside the engine cylinder are:
• Suction of air or air – fuel mixture in to the cylinder
• Compression of the gases
• Ignition of the fuel mixture to produce power
• Exhaust of burnt gases
Fig. 2.3 Principle of operation of Four stroke engine



Two Stroke Cycle Engine

• The two stroke cycle engine completes all the four events i.e. suction, compression, power or expansion and exhaust in two strokes (up stroke & down stroke) of piston or one revolution of crankshaft.
• During each stroke of the piston, two events takes place.
• The Principle of operation of Two stroke engine is shown in Fig. 2.4.


Fig. 2.4 Principle of operation of Two stroke engine


II. According to thermodynamic working cycle:

1. Otto-cycle engine: The heat is taken in at one constant volume and rejected at another constant volume of the cylinder. The combustion of the fuel takes place at constant volume. Petrol engine works on otto cycle.
2. Diesel cycle engine: In this cycle, the heat is taken at constant pressure and rejected at constant volume. The combustion of the fuel takes place at constant pressure. Diesel engine works on this cycle.
3. Dual cycle engine: In this type of engine, some part of the heat is taken at constant volume and the remaining part at constant pressure process. The heat is rejected at constant volume.


III. According to type of fuel used:

Gas engine: In this type of engine, the gaseous fuel like Compressed Natural Gas (CNG), coal gas, Bio gas, Liquid Petroleum Gas (LPG), producer gas is used to operate the engine. The engine is equipped with a special modified manifold system.
Petrol engine: In this type of engine, petrol is used as a fuel. A mixture of petrol and air enters the cylinder in a proper ratio during the suction stroke. The fuel mixture in vapour form is ignited with the help of a electric spark produced in the spark plug. Their method of ignition is called spark ignition ,Most of the two stroke and small engines use this system.
Diesel engine: In this type of engine, diesel is used as a fuel. Here, the air is compressed in the cylinder and atomized diesel is sprayed for ignition. The method of ignition is called compression ignition. All heavy vehicle use this system.


IV. According to number of cylinders:

Single cylinder engine: Here only one cylinder is present as shown in Plate 2.1. The power generated in the power stroke is used for functioning of other strokes of the engine.



Plate : 2.1 Single cylinder engine
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Multi cylinder engine: Here more than one cylinder are present as shown in Plate 2.2. As per the firing order the power suction takes place in the respective cylinders.


Plate : 2.2 Multi cylinder engine
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V. According to cylinder arrangement:

Horizontal cylinder engine: Most of the single cylinder engines are of this type of cylinder arrangement.
Vertical cylinder engine: Most of the present multiple cylinder engines have this type of cylinder arrangement.


VI. According to engine speed:

Low speed engine: The crankshaft speed of the engine is less than 100 rpm.
Medium speed engine: The crankshaft speed of the engine is in between 100 and 250 rpm.
High speed engine: Here the crankshaft speed of the engine is more than 250 rpm.


VII. According to cooling system used:

Air cooled engine: Here the cooling of the engine cylinder is done by air. In this case fins are provided on the cylinder as shown in Plate 2.3.


Plate : 2.3 Air cooled engine


Water cooled engine: Here cooling of the engine cylinder done by water circulated by a radiator and water pump as shown in plate 2.4.

Plate : 2.3 Water cooled engine
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