Some Thermodynamics
Image taken from Aircraft Gas
Turbine Engine Technology
A pressure - volume diagram (or a P-V diagram)
is a useful tool in thermodynamics. In this case, it relates the
pressure and volume of the gas moving through the engine at different stages.
A P-V diagram can also be helpful in finding the work output of an engine.
Work equals the integral of pressure with respect to volume. Or is
simpler form, work equals the area enclosed in the diagram above.
The above cycle is the Brayton cycle, or the cycle used by aircraft gas
turbine engines.
Explanation of the above cycle:
-
Air enters the inlet at point 1 at atmospheric pressure.
-
As this air passes through the compressor (from point
1 to 2), the pressure rises adiabatically (no heat enters or leaves the
system).
-
Now the air enters the combustion chamber (from point
2 to 3), is mixed with fuel, and burned at a constant pressure.
-
Finally, the air goes through the turbine and out
the exhaust (point 3 to 4) where the gases expand and do work. Thus,
the pressure drops and the volume increases.
