Open Cycle Gas Turbine is an internal combustion engine that operates on rotary motion instead of reciprocating motion.
This turbine works on the principle of Brayton Cycle.
In this gas turbine, the air is taken from the atmosphere which works as working fluid and after completion of cycle it is released to the atmosphere again.
These turbine are used in a variety of areas like propulsion of jets, marine, etc and are also used in certain industrial processes.
Components Of Open Cycle Gas Turbine:
The compressor is used to compress the air. Most commonly axial flow compressors are used in an open cycle gas turbine.
2 Burner or Combustion Chamber:
After passing the compressor, the air enters the burner or the
Combustion Chamber. In this burner, there will be a constant pressure process. Pressure will be constant but the temperature will increase.
Isentropic process will also be carried out in the turbine.
When the hot gas from the combustion chamber will reach the turbine, it will expand in the turbine. As the gas will expand, some work will be done by the gas and then it will escape from the system.
Working Of Open Cycle Gas Turbine:
From 1-2: Isentropic Compression
From 1 to 2 air enters the compressor. After entering the compressor the air is compressed by the compressor.
As the air is compressed by the compressor, its volume decreases from V1 to V2, and pressure increases from P1 to P2.
It is assumed that the entropy remains constant means no heat is transferred during the process but the temperature will increase due to compression from T1 to T2.
From 2-3: Isobaric expansion
From 2 to 3 the compressed air from the compressor will enter the burner. In the burner, the temperature will increase and the volume will also increase from V2 to V3 due to expansion because of heating.
This process will be a constant pressure process.
Fuel will enter the chamber from the top and will mix with air before burning.
After burning the temperature will increase and expansion will occur.
In the P-V diagram, the pressure (P) will remain constant and the volume will increase from V2 to V3.
In the T-S diagram, the temperature (T) will increase from T2 to T3 and the entropy will also increase from S2 to S3.
From 3-4: Isentropic Expansion:
From 3 to 4, the heated air from the burner or combustion chamber will reach the turbine and the air will expand inside the turbine and some work will be done due to expansion.
This process will be an isentropic process and no heat will be transferred during this process. In this process volume will increase due to expansion and pressure will decrease. This process will be the opposite of the process 1 to 2.
In the P-V diagram, the volume (V) will increase from V3 to V4, and pressure (P) will decrease from P3 to P4.
In the T-S diagram, the temperature (T) will decrease from T3 to T4 and the entropy (S) will remain constant.
From 4-1: Gas released to atmosphere
From 3 to 4, the air from the turbine will be released into the atmosphere. Also, air will be drawn from the atmosphere to the compressor and the whole cycle will repeat again.
In the P-V diagram, the pressure (P) will remain constant and volume (V) will decrease from V3 to V4.
In the T-S diagram, the temperature (T) will decrease from T3 to T4, and entropy (S) will also decrease from S3 to S4.
Advantages Of Open Cycle Gas Turbine:
1) It is low in cost.
2) It is very lightweight.
3) Any type of gas can be used in this turbine. Helium or a combination of helium and carbon dioxide gives high efficiency. So, it is used in nuclear power plants.
4) The regulation of the turbine is very simple.
5) The gas turbine doesn’t depend on the pressure of the atmosphere, so any type of force can be used so that the specific plant output can be improved.
Disadvantages Of Open Cycle Gas Turbine:
1) The part-load efficiency of this turbine is poor.
2) This gas turbine is very sensitive.
Applications Of Open Cycle Gas Turbine:
1) Most commonly these turbines are used in aviation to provide motive power, especially for jet propulsion.
2) Generation of Electric Power.
3) It also used in Certain Industrial Processes.
4) It is also used in the propulsion of marine, automotive, and locomotive.
5) It is also used in the application of mechanical drives.