What is the working principle of an IC engine?

Short Answer:

The working principle of an internal combustion (IC) engine is based on the conversion of the chemical energy of fuel into mechanical energy through combustion inside the engine cylinder. When the air-fuel mixture burns, it produces high-pressure gases that push the piston downward, creating motion. This motion is transferred to the crankshaft, which converts it into rotary motion used to drive vehicles or machines.

In an IC engine, this process takes place repeatedly through a series of strokes known as the suction, compression, power, and exhaust strokes. These strokes together form one complete operating cycle of the engine.

Detailed Explanation :

Working Principle of an IC Engine

An internal combustion (IC) engine works on the basic principle of converting the chemical energy of the fuel into mechanical energy through controlled combustion. The combustion of fuel and air mixture occurs inside the engine cylinder, and the expanding gases produced during combustion apply pressure on the piston. This pressure moves the piston downward, and the linear motion of the piston is converted into rotary motion by the crankshaft.

The rotary motion obtained from the crankshaft is then used to drive vehicles, generators, or industrial machines. The IC engine operates on a cyclic process in which different strokes are performed in a sequence. These strokes together complete one working cycle of the engine, allowing continuous power generation.

Four-Stroke Cycle Working Principle

Most internal combustion engines used in automobiles work on the four-stroke principle. The four strokes include Intake (or Suction), Compression, Power (or Expansion), and Exhaust. Each stroke corresponds to one movement of the piston, either upward or downward. The complete cycle takes place in two revolutions of the crankshaft.

Let’s understand each stroke in detail:

  1. Intake Stroke (Suction Stroke):
    During this stroke, the piston moves from the top dead center (TDC) to the bottom dead center (BDC). The inlet valve opens, and the exhaust valve remains closed. As the piston moves downward, a vacuum is created inside the cylinder, allowing the air-fuel mixture (in petrol engines) or air alone (in diesel engines) to enter the cylinder. This fills the combustion chamber with a fresh charge for the next stage.
  2. Compression Stroke:
    After the suction stroke, both the inlet and exhaust valves close. The piston moves upward from BDC to TDC, compressing the charge inside the cylinder. Due to compression, the temperature and pressure of the air-fuel mixture rise significantly. In petrol engines, a spark plug ignites the mixture at the end of this stroke, while in diesel engines, fuel is injected into the hot compressed air, causing it to ignite automatically.
  3. Power Stroke (Expansion Stroke):
    The power stroke is the main working stroke of the IC engine. The combustion of the air-fuel mixture produces high-pressure gases inside the cylinder. These expanding gases push the piston downward with great force. This movement produces useful mechanical work, which is transmitted to the crankshaft through the connecting rod. The crankshaft converts the reciprocating motion of the piston into rotary motion, which is used to move vehicles or run machinery.
  4. Exhaust Stroke:
    After the power stroke, the piston moves upward again from BDC to TDC. The exhaust valve opens, while the inlet valve remains closed. The upward movement of the piston pushes out the burnt gases from the cylinder through the exhaust valve. Once the exhaust gases are expelled, the exhaust valve closes, and the cycle is ready to repeat.

These four strokes continue repeatedly, allowing the engine to produce continuous rotary motion from the combustion of fuel.

Two-Stroke Engine Working Principle

In some engines, the working cycle is completed in two strokes instead of four. These are known as two-stroke engines. In this case, the suction and exhaust processes occur simultaneously, making the engine simpler and lighter but less fuel-efficient compared to a four-stroke engine. Two-stroke engines are commonly used in motorcycles, scooters, and small machinery.

Energy Conversion in IC Engine

The IC engine converts chemical energy stored in the fuel into thermal energy through combustion. This thermal energy increases the temperature and pressure of the gases, which in turn applies force on the piston. The mechanical energy produced by the moving piston is then converted into rotary motion by the crankshaft. This rotary motion is finally used to run the wheels of a vehicle or drive other mechanical devices.

Main Factors Affecting the Working of IC Engine

  1. Proper Air-Fuel Mixture: The correct proportion of fuel and air ensures complete combustion.
  2. Compression Ratio: Higher compression results in greater efficiency.
  3. Ignition Timing: Proper spark timing or fuel injection timing is essential for maximum power output.
  4. Lubrication and Cooling: These systems prevent overheating and reduce wear of moving parts.

Applications Based on Working Principle

The working principle of IC engines is used in various fields, such as:

  • Automobiles like cars, trucks, and bikes
  • Power generators
  • Marine engines in ships
  • Aircraft engines
  • Agricultural and construction equipment

The simple design, high efficiency, and compact structure of IC engines make them the most popular choice in the modern world.

Conclusion:

The working principle of an internal combustion engine is based on the combustion of fuel inside the cylinder, which produces high-pressure gases that move the piston and generate mechanical power. The cycle of suction, compression, power, and exhaust repeats continuously to provide a steady rotary output. This principle allows the IC engine to be efficient, compact, and powerful, making it a key component in transportation and power generation systems worldwide.