I do not recommend anybody to try any of this, but if you are going to try it, this is the way you should do it.
This instructable deals with how to build a gas turbine in 5 steps. Each step deals with an aspect of the project and a suggested design solution, based on what I tried myself that worked.
*Rough* Grabcad model:
Step 1: Turbocharger
Step one involves sourcing a turbocharger. Try to select one with an inlet to outlet diameter ratio of 1:1.5, so the outlet should ideally be 50% bigger in diameter than the inlet.
A turbo from an older petrol car (80's or 90's) is better. All the dimensions used in every turbo are available from the likes of turbomaster.net and a couple of other websites. The closer to the 1:1.5 ratio you can get the easier it will be to get the engine started at the end.
If at all possible, try get a turbo that is large diameter with only an oil gallery to cool the bearings. If you do get one with a coolant gallery also, just blank it off it can run with only oil through the oil gallery as coolant. In preparation the wastegate (bypass) flap should be welded shut. If the turbo you select has an external wastegate, simple remove it. Either way make sure there is no bypassing of the exhaust gas from the combustion chamber.
Pictured above is:
A k14 turbocharger inlet.
The turbine side of the k14 with the waste gate blanked off.
Step 2: Fabricate a Combustion Chamber
The combustion chamber serves to mix fuel into the pressurized air coming from the compressor, ignite it, and feed the hot gasses into the turbine section of the turbo. In other words, cold air goes in, mixes with fuel, ignites, hot air goes out. Simply put the combustion chamber feeds fire to the turbo. It is easiest to position the combustion chamber onto the exhaust flange of the turbo. The combustion chamber is pressurized during combustion up to 2.5 bar of pressure, so it must be air tight and strong enough to withstand such pressures.
Fuel line is copper brake pipe with no valves or regulators hooked up to a propane tank. Ignition is how you please, I used the ignition off a kerosene burner with spark plug leads jammed where the metal prongs usually go. An automotive spark plug will do in this arrangement and works quite well.
Look up the formulae, do the maths. Or just use 1.5mm thick 316L stainless steel pipe, 3" wide like I did, with a flame tube of 0.9mm thick 308 stainless steel 90mm diameter inside.
Which brings us to the flame tube. Online calculators (like jetspecs) will tell you combustion chamber volume, diameters and flame tube hole patterns. You will need to do your research here as a well designed flame tube will make the gas turbine start up very easy and run at a healthy temperature, and a poorly designed flame tube will potentially lead to catastrophic failure of the engine (boom)
Pictured above is:
My combustion chamber from the underside
My combustion chamber from the top showing lpg connection and sparkplug
My combustion chamber disassembled with internal flame tube and copper head gasket
Finally my combustion chamber assembled and mounted on the turbocharger.
Step 3: Oil System
I used a power steering pump from a mk2 golf as an oil pump, with the oil filter and bracket off a mk2 golf engine to smooth out the pulses from the pump (important). To drive this pump i used a vee belt and pulley setup attached to a treadmill motor and controller. This is so i can increase motor speed if needs be and increase oil pressure/flow. Oil should be delivered via a bypass valve so you can tune the oil pressure on the fly.
Failure to adjust the oil pressure to the running conditions of the engine could lead to catastrophic failure (boom)
Try to use parts of the original oil feed for the turbo, 10mm copper pipe and plumbing fittings. Don't skimp here - buy brass and lead solder as many of the connections as possible. I used a gas shutoff (ball) valve as the bypass valve. Oil pressure should be a constant 2 Bar or 30 psi while the gas turbine is running.
Pictured above is:
My oil pump setup with the power steering pump (left) being driven off a pulley from my treadmill motor (right)
My oil filter setup
Step 4: Fuelling
As previously discussed the fuel line should consist of an unrestricted line from tank to combustion chamber. Nearly every gas pipe/ fitting nowadays comes with an inbuilt regulator for safety, so avoid this at all costs as the gas turbine will not run unless the fuel path is completely unrestricted.
The valve on the top of the propane bottle will be used as the throttle of the engine.
This is where it gets a little crazy.
The propane bottle needs to be in a tank of water, 80% submerged, with a large heating element maintaining the water temperature at 30 degrees Celsius. I used a 3 kilowatt immersion heating element from a house. Without this constant heating of the propane bottle the liquid will not turn to gas quickly enough and so pressure in the fuel line will drop, risking catastrophic failure (boom).
Step 5: Instrumentation
Instrumentation is the key to control of the gas turbine. Using only the minimum instruments, you will need:
1 x Air pressure (boost) gauge [0 - 2.5 Bar] or [0 - 35 psi]
1 x Oil pressure gauge [0 - 2.5 bar] or [0 - 35 psi]
1 x Oil temperature gauge [0 - 120 deg Celsius]
1 x Exhaust gas temperature gauge (Use K type thermocouple with gauge) [200 - 1400 deg Celsius]
It is of utmost importance to take the pickup for the oil pressure gauge at the nearest point to the top of the turbine. Failure to do so may result in catastrophic failure (boom). Oil temperature can be taken from the tank. Boost pressure can be taken from the combustion chamber, although it is easier to take it from the turbo where the waste gate was fed. Exhaust gas temperature should be taken inside the turbine housing, approximately 50mm away from the turbine wheel.
Optional is a laser thermometer with the greatest range possible. These are cheap online and allow you to measure the temperature of various surfaces during turbine operation. The outside of my combustion chamber has a normal operating temperature of 70 degrees Celsius.
When the gas turbine is running, you should a have constant 2 Bar on the oil pressure gauge, bearing in mind when the oil heats up the pressure will drop a little so be prepared to adjust for this.
Oil temperature should be 70 - 80 degrees Celsius once engine is warm.
Boost pressure should not exceed 2.2 Bar although this depends greatly on the turbo specifications. See your turbo manufacturers compressor map for details. The Garrett TB0333 compressor map of my gas turbine is pictured above.
Exhaust gas temperature should be 450 degrees Celsius, and should not exceed 550 degrees Celsius. Although I have seen 1100 degrees Celsius momentarily on mine, prolonged exposure of the turbine wheel to high temperatures can result in catastrophic failure (boom).
Pictured above is:
My instrumentation setup (boost pressure, oil pressure, oil temperature, exhaust gas temperature
The compressor map for my Garrett TB0333 turbocharger (Note: the revolutions per minute go up to 153,400..!)
Step 6: Start Up Sequence
I recommend using a petrol powered leaf blower to start the gas turbine as this is the simplest method.
You could also use an airline from a compressor, but this is less reliable / safe.
1. Switch on oil pump, adjust oil bypass valve till oil pressure gauge reads 2 Bar.
2. Start up petrol powered leaf blower, put the outlet of the leaf blower to the inlet of the turbo.
3. Introduce a small amount of propane, and begin ignition sequence immediately.
4. Engine will start with a loud pop, remove leaf blower immediately.
5. Maintain low idle, until oil warms to 80 degrees Celsius. Adjust oil pressure back to 2 Bar once it heats up and the pressure drops. Now you can throttle the engine, keeping an eye on boost pressure and exhaust gas temperature.
There are many ways to construct a gas turbine, so do your research as you could well find a solution that better suits your requirements.
Above is a picture of a pressure tested combustion chamber I made from mild steel.
Build a gas turbine at your own risk, post pictures of it up here.
Ignition starts @ 4 min 46 sec: