understanding turbojet RPM? Beginner

[steve89]

Hi, I'm new this forum and I'm new to DIY jet engines I have some questions regarding engine RPM.

when building a jet engine I'm aware that there are requirements for RPM speeds like any other engine. What determines the RPM of a turbojet engine, how do I accomplish this task to get the necessary RPM? I want to build a very simple micro turbojet. I'm thinking of using steel soup cans and in future projects I plan on using steel sheet.

I'd very much appreciate any help.

[smithy1]

Hi Steve...and welcome to the forum,

If you're planning on using steel soup cans and/or steel sheet for a turbojet engine....you're wasting your time. Depending on the size of your engine, the rpm's involved will be well over 100,000rpm and temperatures exceeding ~650C+... a soup can and a bit of sheet steel will obviously never stand up to this. You need the proper materials and build techniques before you even start.

What do you plan to use for your shaft, bearings, bearing lubrication, balancing, NGV, combustion chamber, ignition, fueling etc...??

Most of us use turbochargers as a starting point....then we adjust, add to and modify them to suit our requirements. Getting hold of a small turbocharger from a wrecker may help you get started.

Have a look through some of the many forum posts to get an idea of what's required before you do anything. Doing things incorrectly can be dangerous. We're all for DIY, but we also don't wish to see anyone doing damage to themselves or anyone else. Advising you to do anything else would be wrong of us.

There's lots of turbine knowledge here...my best advice is to use it.

Cheers,
Smithy.

[gidge348]

Hi Steve, I don't want to discourage you but soup cans are not he way to go.

I have yet to see one of the "soup can" engines run or be what we call "self sustaining" that is run without the starter or air pushing in. What happens then is it just gets hotter and hotter until it melts everything like this (see from 2.25mins on) www.youtube.com/watch?v=trcnd7qs-S8

The main problem as far as I can see is that, as Smithy points out the smaller the engine the higher the RPM's it needs to run at. A proper turbine the diameter of a soup can would probably run at about 100,000rpm.

So lets say they can seal up all the gaps and bend the blades to be effective and they could get it to that speed.

Well just the centrifugal forces alone are enormous, a turbine weighing 10grams spinning at that speed has over 9 tons (yep 9 tons) of force trying to pull it apart & it would also be way past the melting point of the metal.

That would be something I would not want to be around.

Get a cheap turbo charger and have some fun, picking molten soup cans out of yourself would not fun.

Cheers
Ian