Short Answer:

The working principle of a gas turbine is based on the Brayton cycle (also called the Joule cycle). In this cycle, air is compressed, mixed with fuel, and burned in a combustion chamber to produce high-temperature and high-pressure gases. These gases expand through turbine blades, producing mechanical energy.

In simple words, the gas turbine works by converting the thermal energy of burning fuel into mechanical energy. It involves three main steps — compression of air, combustion of fuel, and expansion of gases — which together generate power efficiently and continuously.

Detailed Explanation :

Working Principle of Gas Turbine

A gas turbine is a rotary engine that converts the energy of burning fuel into mechanical and electrical power. It works on the Brayton cycle, which is a thermodynamic cycle consisting of three main processes — compression, combustion, and expansion. The energy from the expanding gases drives the turbine, which produces power to run a generator or mechanical load.

In a gas turbine, air from the atmosphere is compressed to high pressure, then heated by burning fuel in the combustion chamber. The resulting high-pressure gases expand through turbine blades, producing mechanical work. The turbine drives both the compressor and the output shaft that delivers useful power.

Main Steps in the Working of Gas Turbine

The working of a gas turbine can be divided into the following major stages:

Compression

In the first step, atmospheric air is drawn into the compressor, where it is compressed to a high pressure.
The compressor increases both the pressure and temperature of the air.
This high-pressure air is essential for efficient combustion of fuel in the next stage.
Compression is usually achieved using an axial flow compressor (for large turbines) or a centrifugal compressor (for small turbines).

Purpose of Compression:
The main purpose of compression is to supply high-pressure air to the combustion chamber to ensure efficient mixing and complete combustion of fuel.

Mathematically, the work done on air during compression is represented as:

Where:
= initial and final pressures,
= inlet temperature,
= specific heat ratio of air,
= gas constant.

Combustion (Heat Addition)

The compressed air from the compressor enters the combustion chamber or combustor.
Fuel (such as natural gas, diesel, or kerosene) is injected and mixed with the compressed air.
The mixture is then ignited using an electric spark or pilot flame.
The combustion process occurs at constant pressure, producing high-temperature and high-energy gases.

Purpose of Combustion:
To convert the chemical energy of fuel into heat energy and raise the gas temperature significantly (up to 1000°C – 1500°C).

The heat added during combustion can be expressed as:

Where:
= temperature after compression,
= temperature after combustion.

Expansion (Power Generation)

The high-pressure, high-temperature gases from the combustion chamber enter the turbine.
As the gases expand through the turbine blades, their pressure and temperature drop, and they impart energy to the turbine shaft.
The turbine converts this energy into mechanical power.
Part of this power is used to drive the compressor, while the remaining power is available for external use (like driving an electrical generator).

The expansion process is isentropic, meaning it occurs without heat loss.

The work done by the turbine is given by:

The net work output of the gas turbine plant is:

Exhaust (Heat Rejection)

After expansion, the exhaust gases leave the turbine at high velocity and moderate temperature.
These gases are released into the atmosphere or passed through a heat recovery system (like a regenerator or heat recovery steam generator) to improve efficiency.
In combined-cycle power plants, the exhaust gases are used to produce steam for a steam turbine, further increasing total efficiency.

The heat rejected during this process is expressed as:

Thermodynamic Cycle (Brayton Cycle)

The gas turbine operates on the Brayton cycle, which consists of four thermodynamic processes:

Isentropic Compression: Air is compressed adiabatically in the compressor.
Constant Pressure Heat Addition: Fuel burns and adds heat to the compressed air at constant pressure in the combustion chamber.
Isentropic Expansion: Hot gases expand through the turbine, producing work.
Constant Pressure Heat Rejection: Exhaust gases release heat at constant pressure to the surroundings.

Efficiency of Gas Turbine (η):
The thermal efficiency of an ideal Brayton cycle is given by:

Where is the pressure ratio ().

This means that increasing the pressure ratio and turbine inlet temperature improves the efficiency of the gas turbine.

Energy Flow in Gas Turbine

Chemical Energy (Fuel) → Heat Energy (Combustion)
Heat Energy → Kinetic Energy (Hot Gases)
Kinetic Energy → Mechanical Energy (Turbine Shaft Rotation)
Mechanical Energy → Electrical Energy (Generator Output)

This energy transformation makes gas turbines suitable for power plants, jet engines, and marine propulsion systems.

Key Features of Gas Turbine Working

Continuous combustion process (unlike reciprocating engines).
Produces smooth rotary motion, reducing vibration.
High power-to-weight ratio.
Compact and efficient design suitable for both stationary and mobile applications.

Factors Affecting Gas Turbine Performance

Compressor Pressure Ratio: Higher ratios improve efficiency but increase compressor power consumption.
Turbine Inlet Temperature: Higher temperatures increase output but require advanced materials.
Regeneration: Using exhaust gases to preheat air improves fuel efficiency.
Ambient Conditions: Higher ambient temperature reduces efficiency due to lower air density.
Fuel Type: Cleaner fuels (like natural gas) improve combustion and reduce emissions.

Applications of Gas Turbine Working Principle

Power generation: Used in combined-cycle plants and standalone units.
Aviation: Forms the basis of jet engines and turbofans.
Marine propulsion: Drives naval and commercial vessels.
Industrial use: Operates pumps, compressors, and other machinery.

Conclusion

In conclusion, the working principle of a gas turbine is based on the Brayton cycle, which involves compressing air, burning fuel at constant pressure, and expanding hot gases to produce power. The three main processes — compression, combustion, and expansion — work together continuously to convert fuel energy into mechanical and electrical power. Gas turbines are widely used for their high efficiency, smooth operation, and ability to produce large power in a compact design. With improvements in materials and technology, gas turbines continue to be a key part of modern power and propulsion systems.