DIY Micro Gas Turbine Engine
A simple demonstration gas turbine engine constructed from an automotive turbocharger
Text reproduced from original “Hobby Gas Turbines”website circa 1993-
I have built a simple gas turbine engine from a Holset diesel engine turbo-
This was built from a steel tube cut from a satellite dish ground stand, the tube is clamped between two plates to form the ends. The bottom plate is bolted to the turbo turbine inlet volute and the top plate originally accepted compressor air through a tube but now air passes into the combustion chamber at the side near the top.
Air is delivered to the combustion chamber through plastic drain pipe, this tends
to blow off if the unit is allowed to go too fast. The flame tube or combustion chamber
liner was made from a camping gaz tin and extended using steel sheet. The gaz tin
gives the right sort of domed top to the liner. Holes are drilled into the liner
to allow air into the combustion zone. The size and positions of the holes were guessed
from looking at various diagrams of commercial engines, no calculations were done.
The engine is fuelled by propane gas, the gas enters the combustion chamber via a
burner ring made from copper pipe drilled with 1mm holes.
A motorcycle spark plug is inserted into the combustion chamber to "light up" the engine. I have tried several different sources of ignition the best being a HT Igniter unit from an early jet aircraft. I have also used a motorcycle ignition coil driven from a home built transistorised inverter. Once ignition has taken place, the combustion chamber seems to hold the flame well, the throttle can be backed right off and the flame does not go out.
Oil is circulated into the turbo-
A complete compressor assembly from another similar turbo-
I have used an optical method for measuring the speed of the gas turbine. An optical fibre illuminates a small portion of the rear face of the compressor wheel, the surface of the wheel is alternately shiny aluminium and matt black, a second optical fibre receives reflected light from the wheel and conveys it to an electronic sensor. As the wheel rotates the reflected light pulses on and off. The sensor converts the light to an electrical signal which operates a homemade rev-
I have fitted a pressure gauge to measure the compressor delivery pressure. The indicated pressure seems to fluctuate so I have inserted a restriction in the gauge feed pipe to dampen oscillation.
The engine is fuelled by propane gas delivered from a portable caravan type cylinder. The regulator is removed and the valve mounted on the cylinder used as the throttle control. The engine has a very healthy appetite for fuel and only lasts about 10 -
This is where the fun starts, to start this home built gas turbine the starter is coupled directly to the turbo inlet and the air turned on gently. The ignition is switched on and the fuel valve opened again gently until the engine lights with a "fut". After the engine has lit up, the air is turned on fully and the throttle opened, initially the rotor spins slowly but as the oil thins and heats up the engine begins to accelerate and at about 35,000 rpm the air supply to the engine is quickly pulled off to allow it to suck in more air and accelerate to a comfortable speed of 50,000 rpm. During starting the oil supply is switched off and only momentarily pulsed to provide some lubrication without causing too much drag, when self sustaining speed is reached the oil is turned on permanently. Once the engine has completed a run and is hot it is much easier to restart, the rotor spins up much faster.
In operation the engine is quite noisy, although with ear defenders the unit sounds
pretty good emitting a delightful "Whistle"from the compressor and a rumble from
the combustion process. Listening with ear defenders helps hear the compressor speed
more clearly which aids throttling the engine which can be tricky. If you close your
eyes you can imagine that you are at the controls of a real jet, I was stood listening
to the Vulcan XH558 the other day and the similarity in the sound o my engine was
uncanny. So far the gas turbine has achieved about 70,000 rpm and at 50,000 rpm the
exhaust gas temperature is only 500 degrees C not bad for a home built engine. The
limit to rpm at the moment is the compressor delivery pipe, it seems to blow off
if the engine runs too fast, flames shoot out of it and the compressor shrieks as
it runs rapidly down. Some of my early attempts suffered from the compressor pipe
blowing off, the original engine would hardly self-
As time allows I hope to develop this demonstration gas turbine further, it can never be used as a propulsion engine as it is far to heavy but with a more secure compressor pipe I think it will spin faster. It exhibits all the characteristics of any other gas turbine and was built at a fraction off the cost of a commercial unit or even a model aircraft turbo-
30/12/1997 The engine is now running very well. I have replaced the compressor delivery pipe with a new stainless steel item and the joints are now fabricated using special turbo-
Developments to Date
In 1999 my brother built me a high energy ignition system to my good friend design. The unit uses a surface discharge plug taken from a racing car engine, light up tests have shown that this arrangement is superior to the high tension systems previously adopted. The igniter works by using an inverter to charge up a 2uf capacitor, a special trigger circuit provides a low energy spark which lionizes the air and causes a high current flash-
High Energy Capacitor Discharge Ignition Exciter