First off this is no "how to guide" no guidelines for yourself. These are simply my notes dictating my ongoing journey of building a small miniature jet engine, which you yourself can read and maybe find useful.
Ive been wanting to construct one of these for a while now. Over the past few years or so Ive been scrounging around for steel, motors, compressors, etc. As you can imagine the hardest things to find were the compressor (in right size and with a good enough efficiency) and the turbine (also in right size etc.)
Seeing how i couldn't begin to construct this, I instead focused mostly on design. Building and constructing this behemoth in my head as well as paper. I started off with a cintrivical compressor, and an axial turbine. I got a hold of my compressor form a vacuum cleaner. I figured if it could hold up to 20,000rpm, maybe it well stay together at hight ones. It also come with a diffuser thats already fitted and computer tested. So going with an already proven device. The turbine i honestly dont remember where i got a hold of it from. The shaft and bearings i got from my local hobby store, its intended to be a tail boom for a helicopter. I assume these will work fine.
The Design
The design I intend to use is very similar to ones used one turbojets incorporating turbochargers (with exclusion to the turbine.)
The Intake
I am going to use the compressor and diffuser which I've already stated, and use the diffuser to sort of shape the rest of the engine. I plan on simply cutting, rolling and welding some thin sheet steel to create the outside lining of the jet engine. This "shell" as i will refer to it, won't see too much heat so i figured i could simply use thinner steel and have thicker steel to support it.This shell should be fine enough to hold the pressures and direct the flow of air into the flame tube/combustion chamber. The bearings for the shaft will be located after the compressor but a few millimeters before the flame tube, hopefully this will keep my bearings in check.
The Combustion Chamber
The combustion chamber and flame tube for this model is one and the same.I'm going to have a single stage flame tube reaching from just after the bearing housing into straight to the NGV (Nozzle Guide Vanes.) It will consist of drilled holes progressively getting larger from compressor to turbine. Im drilling very small holes to start with. I'm hoping these small holes will cause the gas to be 'packed through' creating turbulence. The next set of holes will finish combustion, then the last set will cool the gases so the don't melt my turbine. For fuel im going to burn propane. These jet engines need the fuel to be in a gas state, so a liquid fuel is less forgiving (and i need all the slack i can get with this!) To inject the fuel im going to use a fuel ring. Bending a piece of copper into a ring and drill small holes down the center (again hoping the small holes will aid in turbulence.) To ignite these gases im just going to use a simple ignition coil and spark plug to give a nice hot spark. These, hopefully, hot gases will then expand and push out the exhaust.
Turbine Stage
The hot gases should be traveling in a straight line directly towards the turbine. But gases that push on the turbine in a straight line are not nearly as efficient as diverting the gases in an angle to hit each blade directly. This is where the Nozzle Guide Vanes (NGV) comes in. the NGV impart a force on the gases, giving them rotational energy. These gases then simply hit each blade of the turbine directly and efficiently. The turbine i have will be at the end of the shaft and will transmit power to the compressor, keeping the engine running. If all goes well at least.
