Originally Posted by J
Why do turbine engines require a compressor section?
Hi guys,
Can anyone give me an answer on this? Also why is it that both the piston engine and the turbine engine can have their efficiencies increased by increasing the pressure ratio (compression ratio for piston)? Is there some sort of simple thermodynamic explanation for this?
Cheers,
J
First off, I'm just a pilot. My bachelors is in professional aviation. I normally don't do math in public.
I think the answer to the "why" question is simple. It's because they are intended to produce thrust in a specific speed range. (my remarks apply to airplanes only, but could likely be used in other discussions). What is thrust? "Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system."
You can't have an equal and opposite reaction without something to push against. When the exhaust gasses move, they have to push against something in order for there to be an opposite reaction. In a piston type reciprocating engine, the expanding gases push against the piston, which is connected to a crankshaft which converts the linear force to rotating force. In a turbine engine, the expanding gases ultimately have to have something to push against and absorb the energy produced. The compressor blades absorb that push, transfer it to the bearings on their shaft which are connected to the engine cases which are connected to the engine pylon which is connected to the airframe and the entire airframe moves opposite of the exhaust.
I realize that ram/scram jets fly, but they are highly specialized and also work in a specific velocity range. I'm out of my league here, but I think that ramjets also have "something to push against" but that "thing" isn't a structure, it is a pressure wave inside the combustion chamber. Hitler's "buzz bomb" used a pulse jet which was a ramjet with a flapper door at the entrance to the combustion chamber. That flapper provided the expanding exhaust gas with something to push against.