Short Answer:

Internal combustion (IC) engines can be classified based on different factors such as the type of fuel used, the number of strokes, the method of ignition, the type of cooling system, and the arrangement of cylinders. The main purpose of classification is to understand the construction, operation, and application of various types of IC engines.

For example, IC engines are divided into petrol and diesel engines based on fuel type, two-stroke and four-stroke based on working cycle, and air-cooled or water-cooled based on cooling method. Each type has its own advantages, applications, and working characteristics.

Detailed Explanation :

Classifications of IC Engines

An internal combustion (IC) engine is a machine that converts the chemical energy of fuel into mechanical energy through combustion inside the engine cylinder. These engines are widely used in vehicles, power plants, and machines. Since IC engines come in many forms and designs, they are classified into different types based on several criteria such as the type of fuel, number of strokes, ignition system, cooling method, and cylinder arrangement.

This classification helps in understanding the working principle, efficiency, and suitable applications of each type of engine. The major classifications of IC engines are explained below in simple form.

1. According to Type of Fuel Used

IC engines are mainly classified into two types based on the type of fuel they use:

• Petrol Engine (Gasoline Engine):
  In a petrol engine, petrol is used as the fuel. The air-fuel mixture is prepared in a carburetor and then supplied to the cylinder. The mixture is ignited by an electric spark using a spark plug. This type of engine is called a spark ignition (SI) engine. Petrol engines are generally used in cars, motorcycles, and light vehicles.
• Diesel Engine:
  In a diesel engine, only air is compressed inside the cylinder, and fuel is injected at high pressure into the hot compressed air. The fuel ignites automatically due to the high temperature of the air. This type of engine is called a compression ignition (CI) engine. Diesel engines are commonly used in buses, trucks, tractors, and heavy machinery.

2. According to Number of Strokes per Cycle

Engines can be classified as:

• Four-Stroke Engine:
  In this engine, one power stroke is obtained for every four strokes of the piston (two revolutions of the crankshaft). The strokes are suction, compression, power, and exhaust. Four-stroke engines are more fuel-efficient, durable, and widely used in automobiles.
• Two-Stroke Engine:
  In this engine, one power stroke is obtained for every two strokes of the piston (one revolution of the crankshaft). The suction and exhaust processes occur simultaneously. Two-stroke engines are simpler, lighter, and commonly used in motorcycles, scooters, and small tools.

3. According to Method of Ignition

• Spark Ignition (SI) Engine:
  The fuel-air mixture is ignited by an electric spark from the spark plug. Petrol engines belong to this category.
• Compression Ignition (CI) Engine:
  The air is compressed to a high temperature, and fuel is injected at high pressure, causing self-ignition. Diesel engines are examples of CI engines.

4. According to Method of Cooling

To remove excess heat generated during combustion, engines are cooled by two methods:

• Air-Cooled Engine:
  Air is used to cool the engine by circulating around the cylinder fins. These engines are simple, lightweight, and mostly used in motorcycles and small vehicles.
• Water-Cooled Engine:
  Water circulates through jackets around the cylinder and absorbs heat. The heated water is then cooled in a radiator. These engines are used in cars, trucks, and large vehicles where better cooling is required.

5. According to Number of Cylinders

• Single-Cylinder Engine:
  It has only one cylinder and one piston. It is simple, compact, and used in small engines like motorcycles and scooters.
• Multi-Cylinder Engine:
  It has more than one cylinder connected to the same crankshaft. Multi-cylinder engines provide more power, smoother operation, and are used in cars, buses, and heavy vehicles.

6. According to Arrangement of Cylinders

• Inline Engine: Cylinders are arranged in a single straight line.
• V-Type Engine: Cylinders are arranged in two separate banks forming a “V” shape.
• Radial Engine: Cylinders are arranged radially around a central crankshaft.
• Opposed Cylinder (Boxer) Engine: Cylinders are placed opposite each other in a horizontal plane.

The arrangement of cylinders helps balance the engine and improve smoothness during operation.

7. According to Type of Fuel Supply System

• Carburetor Engine: Air and fuel are mixed in a carburetor before entering the cylinder.
• Fuel Injection Engine: Fuel is directly injected into the combustion chamber or intake manifold using injectors.

8. According to Type of Cycle Used

• Otto Cycle Engine: Used in petrol engines, works on the constant volume cycle.
• Diesel Cycle Engine: Used in diesel engines, works on the constant pressure cycle.
• Dual Cycle Engine: Works on a combination of constant pressure and constant volume processes.

9. According to Speed of Engine

• Low-Speed Engine: Operates below 350 rpm.
• Medium-Speed Engine: Operates between 350 to 1000 rpm.
• High-Speed Engine: Operates above 1000 rpm, commonly used in automobiles.

Conclusion:

The internal combustion engine can be classified in various ways based on its construction, operation, and working principle. These classifications help engineers choose the right engine for specific purposes. For example, petrol engines are preferred for light vehicles due to smooth operation, while diesel engines are suitable for heavy vehicles due to high efficiency. Understanding these classifications is essential in mechanical engineering for designing, operating, and maintaining engines efficiently.