Gas turbines can be classified into two main types based on their operating cycles: constant volume or explosion-type gas turbines. These classifications refer to the gas turbines’ thermodynamic cycles during their operation. In this article, I will discuss the details of constant volume or explosion-type gas turbines.
Constant Volume or Explosion-Type Gas Turbine
In a constant volume or explosion-type gas turbine, fuel combustion occurs at a constant volume. The air drawn from the atmosphere is compressed in the compressor to a pressure of 15- 35 N/cm2 and forced into the combustion chamber through the valves V1 and V2.
The oil is stored in the fuel tank and is pumped into the combustion chamber chamber through valve V3 using a pump when V1 and V2 are closed. After pumping the oil, valve V3 is closed and the oil is ignited in the presence of air by the spark plug.
combustion chamber is a closed vessel, the ignition takes place at constant volume, resulting in an explosion. The pressure rises suddenly to about 100-145 N/cm2. This opens the nozzle valve through which the combustion products pass to the turbine.
As the high-velocity gases flow over the rings of the moving blades of the turbine, their velocity drops imparting the rotary motion to the impulse turbine rotor The nozzle valve remains open until the hot gases are exhausted from the combustion chamber.
The function of Constant Volume or Explosion-Type Gas Turbine
The combustion chamber, nozzles, and rotor blades are cooled by water circulating in the jackets. The exhaust gases from the turbine are passed through a heater, and some of the heat is lost by the exhaust gases to convert the hot water from the jackets into steam.
This steam is supplied to work the steam turbine meant for driving the compressor. Thus, the whole power developed by the rotor of the gas turbine is utilized in driving the generator which is mechanically coupled to the gas turbine. The motor is operated at the time of starting only.
The speed of rotation of the turbine shaft is not constant but fluctuates because the combustion is not continuous. This is the main disadvantage of this type of gas turbine. Also, several valves operating automatically are required for the combustion chamber.
Further, so that enough power for running the compressor may be developed by the steam turbine, the latter must run condensing. Hence, a condenser and cooling water along with other auxiliaries are needed. This involves additional costs. Besides oil, blast furnace gas and pulverized coal may also be used.
This type of turbine works on the Atkinson cycle. It has now become outdated and has been superseded by the constant pressure type gas turbine.
Application of Constant Volume or Explosion-Type Gas Turbine
The choice between constant volume or explosion-type gas turbines is influenced by the specific requirements of various applications. Here are some examples of where each type might be applied:
1. Industrial Power Generation
Gas turbines used for continuous power generation in industrial settings often employ constant volume combustion. This ensures a steady and reliable power output to meet the continuous energy demands of industrial processes.
2. Commercial Aviation
Many commercial aircraft engines use constant volume combustion for their gas turbines. The smooth and continuous power delivery is well-suited for the sustained power requirements of long-haul flights.
3. Power Plants
Gas turbines in power plants, especially those providing baseload power, may use constant volume combustion to contribute to the stable and continuous supply of electricity to the grid.
4. Marine Propulsion
Gas turbines used for marine propulsion, such as in some naval vessels or certain types of ships, might employ constant volume combustion to ensure a continuous and efficient power source for propulsion.
Advantages of Constant Volume or Explosion-Type Gas Turbine
The advantages of Constant Volume or explosion-type gas turbines are-
- Constant volume combustion allows for a steady and continuous power output.
- The combustion process in constant-volume gas turbines is inherently smoother compared to explosion-type combustion.
- Continuous combustion can contribute to better fuel efficiency in certain operating conditions.
- Constant volume combustion can be designed to operate with lower emissions of pollutants.
- Constant-volume gas turbines are suitable for a wide range of applications, including industrial power generation, commercial aviation, and marine propulsion.
- The smoother and more controlled operation of constant volume combustion can contribute to longer component life.
Factors influencing the decision include the desired power output characteristics, efficiency considerations, fuel consumption, and the overall design objectives. In many cases, constant volume combustion is preferred for its smoother power delivery and better fuel efficiency, while explosion-type combustion may be chosen for applications where rapid power changes are critical.
Frequently Asked Questions(FAQ’S)
In which applications are constant-volume gas turbines commonly used?
Constant volume gas turbines find application in industrial power generation, commercial aviation, and marine propulsion, where a consistent and reliable power source is essential.
When is explosion-type combustion preferred in gas turbines?
Explosion-type combustion is often favored in high-performance scenarios, such as military aircraft, high-speed vehicles, and emergency power systems, where rapid power changes are critical.
Are constant-volume gas turbines more environmentally friendly?
Constant volume combustion can be designed to operate with lower emissions, contributing to a more environmentally friendly operation compared to certain explosion-type combustion scenarios.