Jet engines/turbines

[Edont Knoff]

There is a point that makes me wonder since a while about jet engines. The pressure from the combustion should work in both directions, towards the compressor fan(s) as well as the exhaust side turbine.

Why does a jet engine have a definite direction of self-sustained and even excess power rotation if the energy source is symmetric in the first place? The fans on both sides of the combustion area are similar ... is it the geometry of the combustion area and details in the fans? All the explanations that I googled did not explain that detail ...

 

[exchemist]

There is a point that makes me wonder since a while about jet engines. The pressure from the combustion should work in both directions, towards the compressor fan(s) as well as the exhaust side turbine.

Why does a jet engine have a definite direction of self-sustained and even excess power rotation if the energy source is symmetric in the first place? The fans on both sides of the combustion area are similar ... is it the geometry of the combustion area and details in the fans? All the explanations that I googled did not explain that detail ...

Yes. The resistance to the combustion gases exiting via the power turbine is a lot lower than that of pushing back through the compressor. You can get a sense of this by comparing the number of stages and the angles of the blades.

 

[Edont Knoff]

Yes. The resistance to the combustion gases exiting via the power turbine is a lot lower than that of pushing back through the compressor. You can get a sense of this by comparing the number of stages and the angles of the blades.

Thanks, that's good to know. I'll go back to study and look at the fans more closely. I hope I have the brains to make sense of it by myself, otherwise I'll ask again. My tries to build steam engines didn't work too well, guess the jet engine won't be much better But I still want to understand how it need to be done to work.

 

[sideshowbob]

My tries to build steam engines didn't work too well, guess the jet engine won't be much better

I saw plans for building a pulse-jet (like the V-1) once years ago - much simpler than a turbine.

Just googled this: https://www.popularmechanics.com/home/how-to-plans/how-to/a6549/how-to-build-a-pulse-jet/

 

[exchemist]

I saw plans for building a pulse-jet (like the V-1) once years ago - much simpler than a turbine.

Just googled this: https://www.popularmechanics.com/home/how-to-plans/how-to/a6549/how-to-build-a-pulse-jet/

Seems appallingly noisy, impractical and dangerous. What fun!

 

[Edont Knoff]

I saw plans for building a pulse-jet (like the V-1) once years ago - much simpler than a turbine.

I've actually tried to build one as a child, but I couldn't make my fuel explode in the needed way. (94% Ethanol). Maybe I should try again. I'll check that tutorial later. Thanks for the link!

Seems appallingly noisy, impractical and dangerous. What fun!

There have been model airplanes with that sort of engines. Forbidden now because of the noise.