A gas turbine is a heat motor in which air is used as a fluid to provide engine thrust. To achieve this, the air passing through the motor is accelerated; this means that the kinetic energy is increased. In order to achieve this increase, first the pressure energy is increased and then the heat is increased by burning in the combustion chamber before forming the air jet efflux result. The operating cycle of the gas turbine engine is similar to that of the four-stroke piston engine. However, when the combustion of the gas turbine engine occurs at a constant pressure, the piston motors take place at a constant volume.
These cycles are continuous cycling in the reciprocating engine and intermittently in the gas turbine engine. The piston motors allow only one cycle of energy to be generated while others allow the fuel to be sucked, compressed and burned. The turbine engine generates energy in all cycles, producing greater power than a reciprocating motor for a given engine size, although it results in faster fuel consumption.
Because of the continuous energy production of the turbine engine and the fact that the combustion chamber is not a closed area, the air does not rise as the piston motors during pressure burning but the volume increases. This process is known as constant pressure heating. In these conditions, there is no high or fluctuating pressure on the piston motors. Piston motor is high pressure due to constant volume combustion due to the use of durable constructions and high octane fuels compared to lightly manufactured combustion chambers in turbine motors using low octane fuel. The cycle in which the gas turbine engine operates is indicated by the pressure-volume diagram. This cycle is the Brayton Cycle, developed by American engineer George Brayton in 1872 when it was patented for use in a two-stroke kerosene burning piston engine.
Relations Between Pressure, Volume and Temperature
The turbine engine absorbs air during the operating cycle; It changes the pressure, the volume and the temperature. These changes are closely related because they conform to a common primitive formed by a combination of Boyle and Charles’s laws. In short, this means that the volume of the air and the pressure of the various stages of the work cycle is proportional to the absolute temperature of the air in those phases. There are three main conditions in the engine operating cycle in which these changes take place. During compaction, when the pressure is increased and the volume of the air is reduced, there is an equal increase in temperature. When the fuel is added to the air during combustion and burned to increase the temperature, while the pressure remains almost constant, there is an equal increase in volume. When the combustion chamber outlet receives some energy from the existing gas flow with the turbine assembly during expansion, there is a corresponding reduction in temperature and pressure in the volume.
Changes in air temperature and pressure can be monitored with an engine interface using the airflow diagram. As the air flow is constant, volume changes are shown as speed changes.
The efficiency at the end of the cycle will show to what extent the desired ratio between pressure, volume and temperature is reached. The more efficient the compressor is, the higher the pressure produced by a certain temperature rise of a certain amount of air. By using the pressurized high hot gases from the combustion chamber of the turbine more efficiently, the pressure loss at the gas outlet of the gas is low, and the generated thrust is inversely proportional. The air is compressed to 100% efficiency, or when it is expanded, the process is said to be adiabatic 1. Such a change means that there is no loss of energy through the process of friction, transmission or turbulence, so it is absolutely impossible to be realized in practice; 90% is a good adiabatic efficiency for compressor and turbine.
Speed and Pressure Changes
Aerodynamics and energy requirements during the passage of air through the engine vary in speed and pressure. For example: during compression the pressure of the air increases but there is no increase in speed. After the air is heated and the internal energy is increased by combustion, there is an increase in air velocity for turbine drive. At the same time, because of the change in momentum of the air that propels the airplane, we have to catch a high exit velocity from the nozzle. On the other hand, we must also provide local slowdown of the air flow. For example, it is necessary to reduce the speed of the fluid so that the flame does not go down in the combustion chamber and the flame does not move out of the combustion chamber.
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