WORKING CYCLE AND AIRFLOW
CDA –Materiales Aeronáuticos
Ivan Solis A00803014
Introduction
The gas turbine engine is essentially a heat engine using air as a working fluid to provide thrust.
Working cycle
Is similar to that of the four-stroke piston engine.
In the gas turbine engine, combustion occurs at a constant pressure, whereas in the piston engine it occurs at a constant volume.
Each instance there is induction, compression, combustion and exhaust
The relations between pressure,volume and temperature
There are three main conditions in the engine working
cycle during which these changes occur. During
compression, when work is done to increase the pressure
and decrease the volume of the air, there is a
corresponding rise in the temperature. During combustion,
when fuel is added to the air and burnt to increase the
temperature, there is a corresponding increase in volume
whilst the pressure remains almost constant. During
expansion, when work is taken from the gas stream by the
turbine assembly, there is a decrease in temperature and
pressure with a corresponding increase in volume.
Changes in the temperature and pressure of the air can be traced through an engine by using the airflow diagram in fig. 2-5. With the airflow being continuous, volume changes are shown up as changes in velocity.
Changes in velocityand pressure
During the passage of the air through the engine, aerodynamic and energy requirements demand changes in its velocity and pressure.
Where supersonic speeds are encountered, such as in the propelling nozzle of the rocket, athodyd and some jet engines (Part 6), a convergent-divergent nozzle or venturi (fig. 2-4) is used to obtain the maximum conversion of the energy in the combustion gases to kinetic energy.
Airflow
A straight-through flow system is the basic design, as it provides for an engine with a relatively small frontal area and is also suitable for use of the by-pass principle.
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