Short Answer:

Indicated thermal efficiency is the ratio of the indicated power developed inside the engine cylinder to the total heat energy supplied by the fuel. It represents how efficiently the fuel’s chemical energy is converted into work within the combustion chamber before accounting for mechanical losses.

In simple words, indicated thermal efficiency shows how well the combustion process inside the engine converts the heat from fuel into useful pressure energy on the piston. A higher indicated thermal efficiency means the engine has better combustion performance and less energy loss inside the cylinder.

Detailed Explanation :

Indicated Thermal Efficiency

Indicated thermal efficiency (ITE) is an important parameter used to evaluate the performance of an internal combustion (IC) engine. It indicates how efficiently the engine converts the heat energy of the fuel into useful work done on the piston during the power stroke. The word indicated refers to the power developed inside the combustion chamber, which is measured by an instrument called an engine indicator.

The indicated power is the total power produced inside the cylinder due to the pressure of the expanding gases on the piston. However, not all of this power is available at the crankshaft because some part is lost due to friction and mechanical resistance. Hence, indicated thermal efficiency deals with the total power generated before these mechanical losses occur.

Mathematically, indicated thermal efficiency is given by:

Or,

Where,

•  = Indicated thermal efficiency
•  = Indicated Power (kW)
•  = Rate of fuel consumption (kg/s)
•  = Calorific Value of the fuel (kJ/kg)

This ratio shows how much of the total energy supplied by the fuel is effectively converted into pressure energy acting on the piston.

Factors Affecting Indicated Thermal Efficiency

1. Combustion Quality:
   Proper air-fuel mixing and complete combustion lead to higher indicated thermal efficiency. Poor combustion causes unburnt fuel and incomplete burning, reducing efficiency.
2. Compression Ratio:
   Higher compression ratios improve thermal efficiency because they increase the temperature and pressure of the air-fuel mixture before ignition, leading to better energy conversion.
3. Fuel Properties:
   Fuels with higher calorific value and better combustion characteristics enhance indicated thermal efficiency.
4. Ignition Timing:
   Proper timing of ignition ensures that maximum pressure is developed when the piston is at the right position, thus improving the conversion of heat to work.
5. Heat Losses:
   Heat lost to the cooling system and exhaust gases lowers the efficiency. Better insulation and engine design can minimize these losses.
6. Engine Speed and Load:
   Efficiency generally improves at moderate speeds and loads, where combustion is more complete and friction losses are relatively low.

Typical Values of Indicated Thermal Efficiency

For petrol engines, indicated thermal efficiency typically ranges from 30% to 40%, whereas for diesel engines, it ranges between 40% to 50%. Diesel engines usually have higher efficiency because of their higher compression ratios and better fuel utilization.

Importance of Indicated Thermal Efficiency

• Performance Evaluation:
  ITE helps in analyzing the combustion performance of the engine and indicates how effectively the chemical energy of fuel is being used.
• Design Improvement:
  By studying ITE, engineers can identify areas of energy loss within the cylinder and modify combustion chamber design or fuel injection systems to enhance performance.
• Comparison of Fuels:
  It allows comparison between different fuels under identical conditions to determine which one delivers higher efficiency.
• Basis for Other Efficiencies:
  It is used to calculate other efficiencies such as mechanical efficiency and brake thermal efficiency. For instance,

Improving Indicated Thermal Efficiency

1. Optimizing Compression Ratio:
   Increasing the compression ratio improves the combustion process and results in higher thermal efficiency.
2. Better Combustion Chamber Design:
   Modern designs promote better mixing of air and fuel, leading to more complete combustion and higher pressure generation.
3. Efficient Fuel Injection:
   Proper atomization and timing of fuel injection ensure uniform combustion, which increases efficiency.
4. Reducing Heat Loss:
   Using advanced materials and coatings can minimize heat loss to the cylinder walls and cooling system.
5. Use of Turbocharging and EGR (Exhaust Gas Recirculation):
   These techniques improve air intake and reduce harmful heat losses, thus improving overall efficiency.

Relation between Indicated Thermal and Brake Thermal Efficiency

Brake thermal efficiency (BTE) is always less than indicated thermal efficiency (ITE) because mechanical losses reduce the available output power at the crankshaft. The difference between these two efficiencies gives a measure of mechanical losses in the engine.

This relationship helps engineers determine how much energy is lost due to mechanical friction and helps improve engine design.

Conclusion

Indicated thermal efficiency represents how efficiently an internal combustion engine converts the fuel’s chemical energy into indicated power within the cylinder. It reflects the effectiveness of the combustion process before mechanical losses occur. A higher indicated thermal efficiency means more efficient combustion, better fuel utilization, and improved engine performance. Engineers focus on improving ITE by optimizing combustion conditions, enhancing air-fuel mixing, and reducing heat losses, all of which contribute to designing more efficient and eco-friendly engines.