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Enginursday: Yeah, I found it on eBay Pt. 2 - Revenge of the turbine

Nearly a year ago I made a terrible mistake. I bought a jet engine.

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Nearly a year ago I made a terrible mistake - I bought a jet engine. So what have I done with it? Well not too much unfortunately. But I do have some progress and a few things learned along the way.

I last left us with a picture of a jet engine sitting on a table and all the excitement and anticipation of great things to come.

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For starters I decided to build a small frame to house the engine and hold all the supporting components. For this build, I first started the design in a CAD program but quickly found myself in a state of "paralysis by analysis." I continued to fiddle with placement of components and tried to characterize how every wire and tube would route. This became tedious enough that I turned to my roots of building.

Starting with some square tube I began to chop, weld, grind, weld, re-grind, come to terms that I am not a welder, then grind some more.

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Using the floor and some masking tape as my template I slowly cut and welded until a frame took shape. It's not pretty but I managed to make something that will work for now.

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Once the frame was built and most of the parts were test fitted, I began to plumb the system. On paper this was easy but in practice it was a tedious affair. The difficulty was in finding the proper connectors that are used on the engine. Luckily I had some help from our resident racing enthusiast, Pearce, who helped me identify that the connectors were AN fittings. And with that piece of the puzzle solved I was off looking on auto parts sites to come up with a myriad of ways to make all the connections I needed.

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Plumbing is complete. Now I just need to get the electronics built up. This is the area I am currently researching. There are a few major components I need to address.

  • Starter - Starts the engine, consumes about 100-150amps
  • Igniter - Starts a small controlled fire in the engine, I'm still afraid of it
  • Fuel pump - Adjusts fuel pressure to the engine
  • Fuel Switch - Safety feature to kill the engine before it kills us
  • Thermocouple - Tells us how hot the engine is
  • Speed sensor - Tells us how fast we are spinning
  • Oil pressure sensor - Tells us that oil is still flowing

So far the only components I have gotten working are the starter and the speed sensor. The starter is very simple - you apply power to the starter solenoid and away it goes. The speed sensor proved to be a bit more challenging. The speed sensor uses a similar technology to electric guitar pickups. It uses a sensor method called a variable reluctance. Instead of a standard pulse output, a sine wave is produced with a voltage of about +/- 10V at peak RPM. I will need to devise a circuit to convert this to a square wave that can be read in by an Arduino.

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While my progress has been slow it will continue. I hope to have a working demo for some of our upcomming events. I have put the build on temporary hold since robot season is in full swing. But that's another post.


Comments 28 comments

  • Have you thought about building one of these for the upcoming AVC? http://www.asciimation.co.nz/beer/

  • Use a MAX9924 for your VR conditioner. It's designed for it and works great.

  • I hate to be the word nazi, but this is not a jet engine. This is a gas turbine, specifically for driving generators or hydraulic pumps. While a jet engine is a gas turbine, a jet engine develops thrust at the exit. Not all gas turbines are jet engines of course.

  • Look into 'zero crossing detector' circuits for your sine wave conversion.

  • The fuel shutoff switch is also important during the start of a turbine engine. No fuel is to be delivered before the turbine is at the start RPM, with ignitors on. Otherwise the engine can start with a bang. (This is bad news when it happens.)

  • Very cool! I literally got into building my own digital electronics about 15 years ago because I needed to build a tachometer for my own jet engine (was building one from a turbocharger). I've since bought many commercial engines myself, including a Boeing 502-6 turboshaft (160shp) and my big one, a T53 out of a Huey helicopter, good for about 860 shp. I've got them on my site... nuclearprojects.com

  • Curious as to the power of this jet engine and/or a part number. Is it from an APU? if so, what is the rating of the generator output? Also curious where the speed sensor is; assuming it is on one of the shafts after some gear reduction and not on the actual turbine rotor shaft that I read can hit 100,000 rpm or more.

    • It's a Tiernay TT10, 10kW power generator, good for around 20-30hp, not real powerful, but does the job it was designed for. I don't know the tach on this one, but most(all?) commercial engines have a tach generator that is mechanically connected to the engine through gearing. It's output is proportional to the % rpm of the engine. I've had several commercial turbine engines myself (T53, Boeing 502-6, etc.)

      • The 20-30hp number comes from the inefficiency of the generator. The engine itself is capable of producing HP in the 80-100 range (when new). There are people using engines similar to this in light aircraft.

  • The thermocouple isn't just there to monitor how hot the engine is. The Exhaust Gas Temperature (EGT) thermocouple can also be used as a shutdown (engine too hot). In most cases the EGT Thermocouple also forms part of the control algorithm (EGT Limiter). It is a relatively simple control loop, let me know if you need more detail.

    • Yes, one of the thermocouple amps I'm looking at has an overtemp setting. This will connect to the fuel shutoff valve to kill the engine if temperatures exceed spec.

  • O and heads up I know your not there yet but once you start using the engine keep an eye out on the welds cause jet engines as you know are powerful and can cause a lot of vibration and we all know vibrations will start cracks in welds.

  • Please tell me this is related to the shortcut. Fight through jet wash to save a little time.

  • Also, on the topic of an oil pressure sensor, I've had luck with Bosch/Sunpro 7577 oil pressure sender unit. They're <$10 and can be interfaced to an Arduino with a simple resistive divider.

    • Any idea how high of a pressure the Bosch/Sunpro 7577 sender can read? Since replacing the 7 HP motor on my air compressor with a 3 phase motor and VFD, I am a bit worried what might happen if the motor fails to turn off, and would like to add some redundant protection circuits...

  • If you would rather have an analog signal to deal with, TI offers the LM2907 for taking VR outputs straight to analog signals.

  • Don't know about this engine, but the aeroderived turbines we use in generators in oil platforms need some care when starting up... you have to obey a ramp regime and also skip some resonance speeds. I'll see if I can find good bibliography on the control and care of gas turbines!

  • I have a feeling next year's AVC is going to be awesome.

  • This might help for picking up the Variable reluctance. I built this for controlling my car's engine timing - which picked up the crank signal from a variable reluctance. Worked really well.

    https://thedeltaecho.wordpress.com/2010/07/02/crank-signal-input-detection-logic/ https://thedeltaecho.wordpress.com/2010/03/14/2jz-ge-cam-crank-signals/ https://thedeltaecho.wordpress.com/2010/03/17/cam-crank-signal-outputs/

    Good luck and keep us posted! I was wondering what would come of this project. :)

  • In order to change the sine wave into a square wave, could you use an op amp comparator that outputs either VCC or 0 based on whether the sine wave is above or below 0?

    • Might be able to force a CMOS device to handle this. I would probably just use a 5V zener and a regular diode to block the negative half. Then feed that to a Schmitt trigger gate.

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