What are energy losses in IC engines?

Short Answer:

In an internal combustion (IC) engine, not all the heat energy produced from fuel combustion is converted into useful work. A large part of the energy is lost in different forms such as heat through exhaust gases, cooling water, friction, radiation, and incomplete combustion. These energy losses reduce the overall efficiency of the engine.

The main energy losses in IC engines include exhaust gas loss, cooling loss, frictional loss, pumping loss, and radiation loss. Understanding these losses is very important to improve the performance and efficiency of the engine by applying proper design and maintenance practices.

Detailed Explanation :

Energy losses in IC engines

An internal combustion engine converts the chemical energy of fuel into mechanical energy through combustion inside the engine cylinder. However, this conversion is not 100% efficient because a significant amount of the heat generated is lost in different ways. These energy losses are unavoidable due to physical, mechanical, and thermal limitations of the system. The total input energy (from fuel) is thus divided into useful power output and various losses.

The energy supplied to the engine is in the form of fuel energy, and its total amount can be expressed as:
Total energy = Brake power + Friction loss + Cooling loss + Exhaust loss + Other minor losses.

Let us study the major energy losses in IC engines in detail.

  1. Exhaust gas losses

One of the largest energy losses in IC engines is through exhaust gases. After combustion, the gases expand and exit the cylinder at high temperature. A large part of the heat energy remains in these gases and is carried away through the exhaust pipe. In petrol and diesel engines, about 30% to 35% of total heat energy is lost this way. This heat cannot be fully recovered, but in modern engines, some of it is utilized through turbochargers or exhaust gas recirculation (EGR) systems.

  1. Cooling system losses

The cooling system is necessary to prevent overheating of the engine parts. However, during this process, a considerable portion of the heat is absorbed by the cooling water or air. This heat energy is then rejected to the atmosphere through the radiator or cooling fins. Generally, 20% to 25% of the total heat energy is lost through the cooling system. Although these losses protect the engine, they also reduce the overall efficiency.

  1. Frictional losses

The engine parts such as piston, crankshaft, camshaft, and valves are in constant motion, and friction occurs between them. This friction consumes a portion of the power developed in the cylinder, called friction power. The energy lost due to friction appears in the form of heat and does not contribute to useful output. Regular lubrication and smooth surface finishing help to minimize this loss, which is usually 5% to 10% of the total heat energy.

  1. Pumping losses

During the suction and exhaust strokes, the engine performs work to draw in fresh air-fuel mixture and expel exhaust gases. This work, known as pumping work, is a form of energy loss. It depends on the resistance offered by the intake and exhaust systems. High pumping losses reduce volumetric efficiency and overall power output. Engine design improvements like optimized valve timing and efficient air filters help reduce this type of loss.

  1. Radiation and miscellaneous losses

Some amount of heat is lost through radiation and convection from the outer surface of the engine, such as the cylinder head and block. Though small (around 2% to 3%), this energy loss is unavoidable. Other minor losses include losses due to incomplete combustion, leakage of gases past the piston rings, and mechanical vibrations.

  1. Energy loss summary

In general, the total energy supplied by fuel is distributed approximately as follows:

  • Brake output power (useful work): 25% to 30%
  • Cooling loss: 20% to 25%
  • Exhaust gas loss: 30% to 35%
  • Friction and other losses: 10% to 15%

This distribution shows that only a small part of the total energy is converted into useful work, while the majority is wasted in various forms. Therefore, engineers focus on minimizing these losses through better design, materials, lubrication, and recovery systems.

  1. Methods to reduce energy losses

To improve the efficiency of IC engines, several methods are used:

  • Turbocharging and waste heat recovery: Utilize exhaust heat to increase air intake pressure and recover energy.
  • Improved lubrication: Reduces friction losses.
  • Better cooling control: Maintain optimal temperature to reduce excessive cooling losses.
  • Proper combustion control: Ensure complete combustion to avoid unburnt fuel losses.
  • Aerodynamic design: Minimize pumping losses through smooth flow of gases.

By applying these methods, the thermal efficiency of the engine can be increased, leading to better performance and fuel economy.

Conclusion

Energy losses in IC engines are unavoidable but can be minimized through efficient design and proper operation. The main losses occur through exhaust gases, cooling systems, friction, and radiation. By improving heat recovery systems, lubrication, and combustion efficiency, engineers can reduce these losses and enhance overall engine performance. Understanding the nature and source of these losses is essential for designing more fuel-efficient and environmentally friendly engines.